The authors gratefully acknowledge financial support provided by the German Research Foundation (DFG) through the collaborative research center SFB 578 "From Gene to Product" at the Technische Universit&auml;t Braunschweig, Germany.

1. Reactor Setup and Start of Cultivation
4 bioreactor cultivations in total are conducted.
<ol>
 <li>Use a 3 L stirred tank bioreactor with a working volume of 2.2 L for the cultivation of A. niger SKAn1015.</li>
 <li>Pour 72.6 g glucose monohydrate into the reactor and fill it up with 1.9 L deionized water.</li>
 <li>Install the reactor equipment such as 3 baffles, a two six-bladed disk turbine impeller, a pH electrode, a gas inlet with air filter, a cooling finger, an exhaust air cooler with air filter, an immersion tube for sterile sampling with air filter and inlet hoses for medium, inoculum, acid and base.</li>
 <li>Autoclave the reactor at 121 &deg;C for 20 min.</li>
 <li>Connect the reactor with the acid-base reservoir (2 M HCl, 2 M NaOH) and the corresponding pumps and set up a pH-value of 5.0 &plusmn; 0.05 with the pH control unit.</li>
 <li>Link the reactor with the cooling-water system and put the heating jacket around the reactor vessel.</li>
 <li>Install the temperature sensor with corresponding control unit and set up a temperature of 37 &plusmn; 0.1 &deg;C at the temperature control unit.</li>
 <li>Fit the agitation motor atop of the reactor and bring it into service with an agitation speed of 200 min-1.</li>
 <li>Add the sterile minimal growth medium11 trough one of the sterile inlet hoses (250 mL). For medium preparation all components were autoclaved at 121 &deg;C for 20 min and mixed together. For three cultivations the components include talc powder (3MgO&bull;4SiO2&bull;H2O) in the concentrations of 1 g/L (reactor 2), 3 g/L (reactor 3) and 10 g/L (reactor 4). Prior to use, re-suspend the micro particles in 50 mM sodium acetate buffer (pH 6.5) and add it to the sterile medium. In control cultures (without particles) replace the micro particle suspension by 50 mM sodium acetate buffer (pH 6.5).</li>
 <li>Add the spore suspension (inoculum) as prepared in Wucherpfennig et. al (2011)11 trough one of the sterile inlet hoses (50 mL) so that the concentration of spores amounts to 1X106 mL-1. The inoculation marks the start of cultivation (h = 0 h).</li>
 <li>Start the aeration with a rate of 1.0 L min-1.</li>
</ol>
2. Sterile Sampling after 24, 48 and 72 h of Cultivation
<ol>
 <li>Take 50 mL of sterile culture broth into a flacon tube.</li>
 <li>Use sample for determination of biomass dry weight, &beta;-fructofuranosidase activity and microscopic analysis.</li>
</ol>
3. Determination of the Biomass Dry Weight after 24, 48 and 72 h of Cultivation
<ol>
 <li>Biomass samples are to be taken at least in duplicate.</li>
 <li>Weight a cellulose filter with a micro scales after drying in the desiccator and place the filter in a B&uuml;chner funnel with connected water-jet vacuum pump.</li>
 <li>Filter a defined sample volume (e. g. 10 mL) and rinse the filter with 10 mL deionized water to remove medium compounds from the biomass.</li>
 <li>Wrinkle the filter once in the middle, place it in a glass Petri dish and put it into a compartment dryer until weight constancy (at least 24 h).</li>
 <li>Cool the filter in a desiccator and measure the weight.</li>
 <li>Calculate the biomass dry weight as the difference between the weight of the filter with and without dried biomass divided by the used sample volume.</li>
</ol>
4. Determination of the Extracellular Enzymatic Activity of &beta;-fructofuranosidase by GOD/POD-essay after 24, 48 and 72 h of Cultivation
Store the samples on ice constantly while working with them.
<ol>
 <li>Filter 1.5 mL culture suspension trough a cellulose acetate filter by pressing the culture suspension with a syringe through the filter into a reaction tube. Store the reaction tube at -20 &deg;C until usage.</li>
 <li>For the reaction mixture use 20 &mu;L sample and add 200 &mu;L of 1.65 M sucrose dissolved in 0.05 M phosphate buffer (pH 5.4) to initiate the reaction from sucrose to glucose. Cary out the reaction at least in duplicate.</li>
 <li>Incubate the reaction mixture at 40 &deg;C for 20 min in a heating block. Stop the reaction by incubating at 95 &deg;C for 10 min in a heating block. Cool the reaction mixture by storing it on ice and spin down the condensed water by centrifuge at 13.000 g for 10 min at 4 &deg;C.</li>
 <li>To account the pH and temperature dependent cleavage of sucrose to glucose, carry out a blank value by using 20 &mu;L deionized water instead of 20 &mu;L sample.</li>
 <li>To account for residual glucose in the culture broth, carry out a negative control for each sample. To that end use 20 &mu;L of the sample and inactivate &beta;-fructofuranosidase by heating at 95 &deg;C for 10 min prior to add the sucrose and incubate as described in step 4.3.</li>
 <li>Dilute the samples such that the following measured adsorption is in the calibrated value range.</li>
 <li>Carry out all enzymatic assays in triplicate. Apply 2 &mu;L diluted sample in a micro titer plate well. Apply a standard range for calibration on the micro titer plate by each using 2 &mu;L of ten glucose solutions with ten different know concentrations (from 1 mM to 15 mM) instead of 2 &mu;L sample. For zero point calibration use 2 &mu;L deionized water instead of 2 &mu;L sample.</li>
 <li>Add 200 &mu;L of the reagent solution to each well by using a multi pipette.</li>
 <li>Incubate the mixture for 10 min at room temperature.</li>
 <li>Store the micro titer plate at 6 &deg;C until measurement (a few hours at most).</li>
 <li>Measure the absorption at 450 nm using a 96-well Sunrise micro plate reader and the Magellan data retrieval software. Set the mixing time up to 5 sec. and the rest period up to 1 sec.</li>
 <li>Open the result chart with a spreadsheet and construct a calibration line by using the standard range: 
 glucose concentration = a X absorption + b </li>
 <li>Calculate the activity: 
 activity = (absorption X dilution factor-blank value ) X a+b </li>
 <li>Figure out the &beta;-fructofuranosidase activity by calculating the difference between the activities of the sample and the appropriate negative control.</li>
 <li>Calculate the specific productivity for following use by taking into account biomass dry weight and &beta;-fructofuranosidase activity 11.</li>
</ol>
5. Microscopy and Automated Image Analysis after 72 h of Cultivation
<ol>
 <li>Place around 3 mL culture suspension in a plastic Petri dish and dilute them with physiological sodium chloride solution until the morphological structures are separated.</li>
 <li>Situate the Petri dish under a microscope, which features an integrated or connected camera. Acquire and save about 100 images (Figure 2) of morphological structures per sample. Pay attention that on each image at least one object is completely pictured.</li>
 <li>Open all images of the same sample with the image processing program ImageJ12. Convert the images to black and white by using the process tool "Make Binary" (Figure 2). For applying the command to the whole series of images use a macro code as follows. run(,,Make Binary") 
 </li>
 <li>Open the processed binary images with ImageJ again. Calculate the shape factors Feret's diameter, projected area, perimeter, circularity, aspect ratio, roundness und solidity for every image with the analyze tool "Set Measurement". For applying the command to a series of images use a macro code as follows. 
 run("8-bit"); 
 run("Make Binary"); 
 run("Set Scale...", "distance=X known=1000 pixel=1 unit=&mu;m global"); 
 run("Set Measurements...", "area perimeter shape feret's limit display redirect=None decimal=3"); 
 run("Analyze Particles...", "size=10000-Infinity circularity=0.00-1.00 show=Outlines display"); 
 Determine X as the number of pixels which correlates to 1000 &mu;m by constructing a straight line across a scale bar. Correlate the number of pixels of the straight line with the length of the scale bar in &mu;m.</li>
 <li>Open the result chart containing shape factor values for each image with a spreadsheet. Calculate a Morphology number as follows for each image. 
 <img alt="Equation 1" src="/files/ftp_upload/4023/4023eq1.jpg" /></li>
 <li>Calculate mean value and standard deviation for the Morphology number taking into account all images of one sample.</li>
 <li>Use a graphing and data analysis program for graphical correlation of the Morphology number with the specific productivity and determine the mathematical relation by mathematical regression.</li>
</ol>
6. Representative Results
Through addition of talc micro particles A. niger SKAn 1015 morphology is changed from a true pellet morphology to a dispersed or even mycelial morphology. Whereas pellet morphology is exhibited at standard conditions a mycelial morphology is created by supplementation of medium with 10 g/L of talc micro particles (Figure 4.). Concurrently the activity of &beta;-fructofuranosidase increases around 3 fold 3-5. A supplementation of 1 or 3 g/L of talc powder leads to a dispersed morphology, with a doubled fructofuranosidase activity (Figure 4.).
The micro particle dependent morphology can be comprehensively described by the Morphology number which can be calculated using parameters determined by automatic image analysis. Perfectly round and smooth pellets will in microscopic images appear as perfect circles. For such particles the Morphology number has a value of 1. The smallest fragment of mycelial morphology can be simplified as a one-dimensional line yielding a Morphology number of 0. All intermediate morphological forms like elongated irregular pellets or clumps will therefore have values between 0 and 1. Fairly large particles will result in a high, fungal particles with a large surface or elongated particles, in a rather low Morphology number 11.
At standard conditions the morphology in reactor 1 exhibits a Morphology number around 0.8. The morphology in reactor 4 with 10 g/L talc powder features a Mn around 0.1. The Morphology number for reactors 2 and 3, with talc powder concentrations of 1 and 3 g/L, lies between these extremes, demonstrating a dispersed morphology. Since micro particle dependent morphology is closely related with the &beta;-fructofuranosidase productivity, a mathematical correlation of Morphology number and productivity similar to Figure 5 is obtained.
<img alt="Figure 1" src="/files/ftp_upload/4023/4023fig1.jpg" /> 
Figure 1. Overall scheme of the experimental design and the analytic procedure. A. niger is cultivated (with or without micro particles) in an 3 L stirred tank bioreactor for 72 h. After 24, 48 and 72 h a sample is taken for determination of biomass dry weight and &beta;-fructofuranosidase activity, which again are used for calculation of the specific productivity. After 48 h the fungal morphology is examined by microscope and characterized by digital image analysis. Relevant parameters of image analysis are combined to a Morphology number, which is mathematical correlated with the specific productivity.
<img alt="Figure 2" src="/files/ftp_upload/4023/4023fig2.jpg" /> 
Figure 2. Steps of image processing for microscopic-generated images of morphological structures from A. niger. Step 1: image acquisition by microscope. Step 2: image improvement if necessary. Step 3: image binarization, black-and-white (binary) image generated in ImageJ. Step 4: the binary image is processed by and unwanted object are cleared. Step 5: morphological analysis is conducted with the "Analyze particles" function of the open source program ImageJ.
<img alt="Figure 3" src="/files/ftp_upload/4023/4023fig3.jpg" /> 
Figure 3. Different morphological forms of A. niger dependent on the concentration of added micro particles. With increasing concentration of micro particles added the pellet size can be precisely decreased down to small core-shell pellets, small flocks and even freely dispersed mycelium. Morphology engineering of Aspergillus niger SKAn1015 by micro particle supplementation in submerged culture. Without microparticles (A), 10 mg/L (B), 0.1 g/L (C), 0.2 g/L (D), 0.3 g/L (E), 0.6 g/L (F), 1.0 g/L (G), 1.5 g/L (H), 2.0 g/L (I), 2.5 g/L (J), 3.0 g/L (K), 3.5 g/L (L), 4.0 g/L (M), 4.5 g/L (N), 5.0 g/L (O), 10 g/L (P), 15 g/L (Q), 20 g/L (R), 30 g/L (S) and 40-50 g/L (T). Images were taken by light microscopy after 72 h of cultivation.
<img alt="Figure 4" src="/files/ftp_upload/4023/4023fig4.jpg" /> 
Figure 4. Fructofuranosidase activity in dependence of talc micro particle concentration 1 g/L (reactor 2), 3 g/L (reactor 3) and 10 g/L (reactor 4). Reactor 1 is not supplemented with micro particles; here the cultivation is conducted under standard conditions.
<img alt="Figure 5" src="/files/ftp_upload/4023/4023fig5.jpg" /> 
Figure 5. Representative good correlation (R2 = 0.91) of the Morphology number and the specific productivity. The Morphology number is plotted (abscissa) against the specific productivity (ordinate). Nonlinear regression yields the exponential correlation.

<ol>
	<li>Wucherpfennig, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Advances in Applied Microbiology. 72, 89-136 (2010).</li><li>Driouch, H., H&#228;nsch, R., Wucherpfennig, T., Krull, R., Wittmann, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+enzyme+production+by+bio-pellets+of+Aspergillus+niger:+Targeted+morphology+engineering+using+titanate+microparticles.">Improved enzyme production by bio-pellets of Aspergillus niger: Targeted morphology engineering using titanate microparticles.</a> Biotechnology and Bioengineering. 109, 462-471 (2012).</li><li>Driouch, H., Roth, A., Dersch, P., Wittmann, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimized+bioprocess+for+production+of+fructofuranosidase+by+recombinant+Aspergillus+niger.">Optimized bioprocess for production of fructofuranosidase by recombinant Aspergillus niger.</a> Applied Microbiology and Biotechnology. 87, 2011-2024 (2010).</li><li>Driouch, H., Roth, A., Dersch, P., Wittmann, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Filamentous+fungi+in+good+shape:+Microparticles+for+tailor-made+fungal+morphology+and+enhanced+enzyme+production.">Filamentous fungi in good shape: Microparticles for tailor-made fungal morphology and enhanced enzyme production.</a> Bioengineered Bugs. 2, 100-104 (2011).</li><li>Driouch, H., Sommer, B., Wittmann, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphology+engineering+of+Aspergillus+niger+for+improved+enzyme+production.">Morphology engineering of Aspergillus niger for improved enzyme production.</a> Biotechnology and Bioengineering. 105, 1058-1068 (2010).</li><li>Kaup, B. -. A., Ehrich, K., Pescheck, M., Schrader, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microparticle-enhanced+cultivation+of+filamentous+microorganisms:+Increased+chloroperoxidase+formation+by+Caldariomyces+fumago+as+an+example.">Microparticle-enhanced cultivation of filamentous microorganisms: Increased chloroperoxidase formation by Caldariomyces fumago as an example.</a> Biotechnology and Bioengineering. 99, 491-498 (2008).</li><li>Hirayama, M., Sumi, N., Hidaka, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+and+characterization+of+a+fructooligosaccharide-producing+beta-fructofuranosidase+from+Aspergillus+niger+ATCC+20611.">Purification and characterization of a fructooligosaccharide-producing beta-fructofuranosidase from Aspergillus niger ATCC 20611.</a> Agricultural and Biological Chemistry. 53, 667-673 (2006).</li><li>Rajoka, M. I., Yasmeen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+productivity+of+beta-fructofuranosidase+by+a+derepressed+mutant+of+Aspergillus+niger+form+conventional+and+non-conventional+substrates.">Improved productivity of beta-fructofuranosidase by a derepressed mutant of Aspergillus niger form conventional and non-conventional substrates.</a> World Journal of Microbiology and Biotechnology. 21, 471-478 (2005).</li><li>Zuccaro, A., G&#195;&#182;tze, S., Kneip, S., Dersch, P., Seibel, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tailor-made+fructooligosaccharides+by+a+combination+of+substrate+and+genetic+engineering.">Tailor-made fructooligosaccharides by a combination of substrate and genetic engineering.</a> ChemBioChem. 9, 143-149 (2008).</li><li>Huggett, A. S. G., Nixon, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+glucose+oxidase,+peroxidase,+and+o-dianisidin+in+determination+of+blood+and+urinary+glucose.">Use of glucose oxidase, peroxidase, and o-dianisidin in determination of blood and urinary glucose.</a> The Lancet. , 270-368 (1957).</li><li>Wucherpfenning, T., Hestler, T., Krull, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphology+engineering+-+Osmolality+and+its+effect+on+Aspergillus+niger+morphology+and+productivity.">Morphology engineering - Osmolality and its effect on Aspergillus niger morphology and productivity.</a> Microb. Cell Fact. 10, (2011).</li><li>Rasband, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ImageJ. , (1997).</li><li>Papagianni, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+the+fractal+nature+of+mycelial+aggregation+in+Aspergillus+niger+submerged+cultures.">Quantification of the fractal nature of mycelial aggregation in Aspergillus niger submerged cultures.</a> Microbial Cell Factories. 5, 5 (2006).</li></ol>

I have nothing to disclose.

The modification of fungal morphology has been of interest in biotechnology since many decades. Different studies have tried to vary selected process parameters such as pH value, power input, temperature, medium nutrients or inoculum concentration 1, but suffer from rather imprecise and incomplete control of morphology, high energy costs, inhibition effects or product instability, In contrast, the supplementation of micro particles allows a precise engineering of fungal morphology through fine-tuned variation of particle size and concentration. This opens new possibilities to use micro particles for optimization and for tailor-made design of high producing morphology in biotechnological production with A. niger and other filamentous microorganisms.
The digital image analysis is an easy reproducible method to characterize fungal macro morphology. However, the variety of parameters for size, shape and surface character of morphological structures described in literature makes quick assessment of fungal morphology complicated. The presented Morphology number as a combination of relevant parameters, avoids this deficiency and can be used not only for comprehensive characterization of morphological structures but also for direct mathematical correlation with productivity. This again renders an estimation of productivity by given morphology and therefore a customization of morphology for process needs possible.
Using the Morphology number, it is possible to distinguish between various pellet and clump morphologies 4,5. For further development of the Morphology number the consideration of the fractal dimension seems to be promising. A fractal dimension gives a measurement of the complexity and mass filling properties of an object 13 and is therefore predestinated for holistic characterization of mycelial morphology.
The creation of a high producing mycelial morphology, however, might lead to problems with process performance especially in large scale cultivation, because the mycelial growth form has been previously shown to exhibit much greater culture broth viscosities 2. This leads to problems with heat and mass transfer and formation of stagnant non mixed zones, which require a higher power input and make the cultivation more expensive to operate1. Therefore the relationship between fungal morphology and culture broth viscosity should be considered when changing the morphology and be incorporated in further models.

Table of Equipment:
<table border="1">
	<tbody>
		<tr>
			<td>
			Equipment</td>
			<td>
			Company</td>
			<td>
			Catalogue Number/model</td>
		</tr>
		<tr>
			<td>
			autoclave</td>
			<td>
			Systec</td>
			<td>
			V150</td>
		</tr>
		<tr>
			<td>
			B&uuml;chner funnel (plastic)</td>
			<td>
			VWR</td>
			<td>
			-</td>
		</tr>
		<tr>
			<td>
			cellulose filter (for biomass dry weight)</td>
			<td>
			Sartorius Stedim Biotech</td>
			<td>
			Filter Discs Grade 389</td>
		</tr>
		<tr>
			<td>
			cellulose acetate filter (for air filtration at reactor)</td>
			<td>
			Sartorius stedim biotech</td>
			<td>
			Midisart 200 PTFE</td>
		</tr>
		<tr>
			<td>
			cellulose acetate filter (for enzyme activity)</td>
			<td>
			Sartorius Stedim Biotech</td>
			<td>
			Midisart NML</td>
		</tr>
		<tr>
			<td>
			centrifuge</td>
			<td>
			Eppendorf</td>
			<td>
			Centrifuge 5415R</td>
		</tr>
		<tr>
			<td>
			centrifuge</td>
			<td>
			Heraeus</td>
			<td>
			Biofuge fresco</td>
		</tr>
		<tr>
			<td>
			centrifuge</td>
			<td>
			Heraeus sepatech</td>
			<td>
			Varifuge 3.0R</td>
		</tr>
		<tr>
			<td>
			compartment dryer (105 &deg;C)</td>
			<td>
			Heraeus</td>
			<td>
			Kelvitran t</td>
		</tr>
		<tr>
			<td>
			control unit (temperature)</td>
			<td>
			Jumo</td>
			<td>
			Jumo iTron 08</td>
		</tr>
		<tr>
			<td>
			control unit (pH-value)</td>
			<td>
			meredos</td>
			<td>
			pH Control 2</td>
		</tr>
		<tr>
			<td>
			desiccator</td>
			<td>
			Duran</td>
			<td>
			Vacuum stable</td>
		</tr>
		<tr>
			<td>
			Falcon tubes</td>
			<td>
			Omnilab</td>
			<td>
			FALC352070</td>
		</tr>
		<tr>
			<td>
			heating block 40 &deg;C</td>
			<td>
			Biometra</td>
			<td>
			TB1 Thermoblock</td>
		</tr>
		<tr>
			<td>
			heating block 95 &deg;C</td>
			<td>
			HLC</td>
			<td>
			HBT 130</td>
		</tr>
		<tr>
			<td>
			micro plate reader</td>
			<td>
			Tecan</td>
			<td>
			Sunrise-Microplate-Reader</td>
		</tr>
		<tr>
			<td>
			micro scales</td>
			<td>
			Sartorius</td>
			<td>
			CP 225</td>
		</tr>
		<tr>
			<td>
			microscope (digital inverted)</td>
			<td>
			AMG</td>
			<td>
			EVOS xl</td>
		</tr>
		<tr>
			<td>
			micro pipettes and tips (different sizes)</td>
			<td>
			Omnilab</td>
			<td>
			5283303
			5283298 
			5283299 
			5283300</td>
		</tr>
		<tr>
			<td>
			micro titer plate</td>
			<td>
			Nunc</td>
			<td>
			MaxiSorp</td>
		</tr>
		<tr>
			<td>
			multi pipette and tips</td>
			<td>
			Eppendorf/ Omnilab</td>
			<td>
			5283611/ 5283611</td>
		</tr>
		<tr>
			<td>
			pH-electrode</td>
			<td>
			Schott</td>
			<td>
			pH-Meter CG840</td>
		</tr>
		<tr>
			<td>
			reaction tubes</td>
			<td>
			Roth</td>
			<td>
			E518.1</td>
		</tr>
		<tr>
			<td>
			scale</td>
			<td>
			Sartorius</td>
			<td>
			CP 3202 S</td>
		</tr>
		<tr>
			<td>
			stirred tank bioreactor with equipment</td>
			<td>
			Applikon Biotechnology</td>
			<td>
			2L Bioreactor set</td>
		</tr>
		<tr>
			<td>
			syringe</td>
			<td>
			Eppendorf</td>
			<td>
			Combitips Plus 5 mL</td>
		</tr>
	</tbody>
</table>
Table of Reagents:
<table border="1">
	<tbody>
		<tr>
			<td>
			Name of the reagent</td>
			<td>
			Company </td>
		</tr>
		<tr>
			<td>
			Acetic acid</td>
			<td>
			Roth</td>
		</tr>
		<tr>
			<td>
			Disodium hydrogen phosphate</td>
			<td>
			Merck</td>
		</tr>
		<tr>
			<td>
			Ethanol (95%)</td>
			<td>
			Roth</td>
		</tr>
		<tr>
			<td>
			Glucose monohydrate, (&alpha;-D-)</td>
			<td>
			Roth</td>
		</tr>
		<tr>
			<td>
			Glucose oxidase (Typ II from Aspergillus niger)</td>
			<td>
			Sigma</td>
		</tr>
		<tr>
			<td>
			Hydrochloride acid (37 % w/v)</td>
			<td>
			Fiedel-de Ha&euml;n</td>
		</tr>
		<tr>
			<td>
			Hydrous magnesium silicate</td>
			<td>
			Roth</td>
		</tr>
		<tr>
			<td>
			Monopotassium phosphate</td>
			<td>
			Merck</td>
		</tr>
		<tr>
			<td>
			o-dianoisidine dihydrochloride</td>
			<td>
			Sigma</td>
		</tr>
		<tr>
			<td>
			Peroxidase (Typ II from horseradish)</td>
			<td>
			Sigma</td>
		</tr>
		<tr>
			<td>
			Sodium acetate</td>
			<td>
			Roth</td>
		</tr>
		<tr>
			<td>
			Sodium hydroxide</td>
			<td>
			Merck</td>
		</tr>
		<tr>
			<td>
			Sucrose, D-(+)</td>
			<td>
			Fluka</td>
		</tr>
		<tr>
			<td>
			Water (deionized)</td>
			<td>
			-</td>
		</tr>
	</tbody>
</table>
Table of Solutions and Medium Composition:
<table border="1">
	<tbody>
		<tr>
			<td>
			Solution</td>
			<td>
			Components</td>
			<td>
			Amount</td>
		</tr>
		<tr>
			<td>
			50 mM sodium acetate buffer (pH 6.5)</td>
			<td>
			Sodium acetate
			Bring to volume with deionized water
			Adjust at pH 6.5 with acetic acid</td>
			<td>
			4.1 g L-1</td>
		</tr>
		<tr>
			<td>
			0.05 M monopotassium phosphate solution</td>
			<td>
			Monopotassium phosphate
			Bring to volume with deionized water</td>
			<td>
			6.805 g L-1</td>
		</tr>
		<tr>
			<td>
			0.05 M disodium hydrogen phosphate solution</td>
			<td>
			Disodium hydrogen phosphate
			Bring to volume with deionized water</td>
			<td>
			7.1 g L-1</td>
		</tr>
		<tr>
			<td>
			0.05 M phosphate buffer (pH 7.0)</td>
			<td>
			0.05 M disodium hydrogen phosphate solution
			Bring to volume with 0.05 M monopotassium phosphate solution</td>
			<td>
			61.2 mL</td>
		</tr>
		<tr>
			<td>
			0.05 M phosphate buffer (pH 5.4)</td>
			<td>
			0.05M disodium hydrogen phosphate solution
			Bring to volume with 0.05 M monopotassium phosphate solution</td>
			<td>
			3 mL</td>
		</tr>
		<tr>
			<td>
			1.65 M sucrose solution</td>
			<td>
			D-(+)-sucrose
			Bring to volume with phosphate buffer (pH 5.4)</td>
			<td>
			564.8 g L-1</td>
		</tr>
		<tr>
			<td>
			reagent solution</td>
			<td>
			o-Dianisidin-Dihydrochlorid
			Ethanol (95%)</td>
			<td>
			25 mg
			10 mL</td>
		</tr>
		<tr>
			<td>
			Glucose reagent solution</td>
			<td>
			Glucose oxidase
			Peroxidase
			Phosphate buffer (pH 7.0)
			reagent solution</td>
			<td>
			10.5 mg
			3 mg
			90 mL
			10 mL</td>
		</tr>
	</tbody>
</table>

customization of aspergillus niger morphology through addition of talc micro particles

The filamentous fungus A. niger is a widely used strain in a broad range of industrial processes from food to pharmaceutical industry. One of the most intriguing and often uncontrollable characteristics of this filamentous organism is its complex morphology. It ranges from dense spherical pellets to viscous mycelia (Figure 1). Various process parameters and ingredients are known to influence fungal morphology 1. Since optimal productivity correlates strongly with a specific morphological form, the fungal morphology often represents the bottleneck of productivity in industrial production.
A straight forward and elegant approach to precisely control morphological shape is the addition of inorganic insoluble micro particles (like hydrous magnesium silicate, aluminum oxide or titanium silicate oxide) to the culture medium contributing to increased enzyme production 2-6. Since there is an obvious correlation between micro particle dependent morphology and enzyme production it is desirable to mathematically link productivity and morphological appearance. Therefore a quantitative precise and holistic morphological description is targeted.
Thus, we present a method to generate and characterize micro particle dependent morphological structures and to correlate fungal morphology with productivity (Figure 1) which possibly contributes to a better understanding of the morphogenesis of filamentous microorganisms.
The recombinant strain A. niger SKAn1015 is cultivated for 72 h in a 3 L stirred tank bioreactor. By addition of talc micro particles in concentrations of 1 g/L, 3 g/L and 10 g/L prior to inoculation a variety of morphological structures is reproducibly generated. Sterile samples are taken after 24, 48 and 72 hours for determination of growth progress and activity of the produced enzyme. The formed product is the high-value enzyme &beta;-fructofuranosidase, an important biocatalyst for neo-sugar formation in food or pharmaceutical industry, which catalyzes among others the reaction of sucrose to glucose 7-9. Therefore, the quantification of glucose after adding sucrose implies the amount of produced &beta;-fructofuranosidase. Glucose quantification is made by a GOD/POD-Assay 10, which is modified for high-throughput analysis in 96-well micro titer plates.
Fungal morphology after 72 hours is examined by microscope and characterized by digital image analysis. In doing so, particle shape factors for fungal macro morphology like Feret's diameter, projected area, perimeter, circularity, aspect ratio, roundness und solidity are calculated with the open source image processing program ImageJ. Relevant parameters are combined to a dimensionless Morphology number (Mn) 11, which enables a comprehensive characterization of fungal morphology. The close correlation of the Morphology number and productivity are highlighted by mathematical regression.

Watch this Scientific Journal Video about Customization of Aspergillus niger Morphology Through Addition of Talc Micro Particles at JoVE.com

Customization of Aspergillus niger Morphology Through Addition of Talc Micro Particles

A method to precisely generate and to comprehensively characterize morphology of filamentous fungus Aspergillus niger is described, which allows the mathematical correlation of morphological appearance and productivity.

Customization of Aspergillus niger Morphology Through Addition of Talc Micro Particles

The filamentous fungus A. niger is a widely used strain in a broad range of industrial processes from food to pharmaceutical industry. One of the most ...

customization-aspergillus-niger-morphology-through-addition-talc

Research

JoVE Journal

Immunology and Infection

18.9K Views.  Technische Universität Braunschweig. A method to precisely generate and to comprehensively characterize morphology of filamentous fungus Aspergillus niger is described, which allows the mathematical correlation of morphological appearance and productivity.

Video: Customization of Aspergillus niger Morphology Through Addition of Talc Micro Particles

Packaging HIV- or FIV-based Lentivector Expression Constructs &amp; Transduction of VSV-G Pseudotyped Viral Particles

As with standard plasmid vectors, it is possible to transfect lentivectors in plasmid form into cells with low-to-medium efficiency to obtain transient expression of effectors. Packaging lentiviral expression constructs into pseudoviral particles, however, enables up to 100% transduction, even with difficult-to-transfect cells, such as primary, stem, and differentiated cells. Moreover, the lentiviral delivery does not produce the specific cellular responses typically associated with chemical transfections, such as cell death resulting from toxicity of the transfection reagent 1, 2. When transduced into target cells, the lentiviral construct integrates into genomic DNA and provides stable expression of the small hairpin RNA (shRNA), cDNA, microRNA or reporter gene 3, 4. Target cells stably expressing the effector molecule can be isolated using a selectable marker contained in the expression vector construct such as puromycin or GFP. After pseudoviral particles infect target cells, they cannot replicate within target cells because the viral structural genes are absent and the long terminal repeats (LTRs) are designed to be self-inactivating upon transduction 5, 6.
There are three main components necessary for efficient lentiviral packaging 1, 5, 6, 7. 
1. The lentiviral expression vector that contains some of the genetic elements required for packaging, stable integration of the viral expression construct into genomic DNA, and expression of the effector or reporter. 
2. The lentiviral packaging plasmids that provide the proteins essential for transcription and packaging of an RNA copy of the expression construct into recombinant pseudoviral particles. This protocol uses the pPACK plasmids (SBI) that encode for gag, pol, and rev from the HIV or FIV genome and Vesicular Stomatitis Virus g protein (VSV-G) for the viral coat protein. 
3. 293TN producer cells (derived from HEK293 cells) that express the SV40 large T antigen, which is required for high-titer lentiviral production and a neomycin resistance gene, useful for reselecting the cells for maintenance.
An overview of the viral production protocol can be seen in Figure 1. Viral production starts by co-transfecting 293TN producer cells with the lentiviral expression vector and the packaging plasmids. Viral particles are secreted into the media. After 48-72 hours the cell culture media is harvested. Cellular debris is removed from the cell culture media, and the viral particles are precipitated by centrifugation with PEG-it for concentration. Produced lentiviral particles are then titered and can be used to transduce target cells. Details of viral titering are not included in this protocol, but can be found at:
<a href="http://www.systembio.com/downloads/global_titer_kit_web_090710.pdf" target="_blank">http://www.systembio.com/downloads/global_titer_kit_web_090710.pdf</a> 8.
This protocol has been optimized using the specific products indicated. Other reagents may be substituted, but the same results cannot be guaranteed.

Lentiviral expression vectors are the most effective vehicles for stably expressing different effector molecules or reporter constructs in dividing and non-dividing mammalian cells and whole organisms. Here we provide a protocol on how to package lentivector expression constructs in pseudoviral particles and to transduce target cells using the pseudoviral particles.

As with standard plasmid vectors, it is possible to transfect lentivectors in plasmid form into cells with low-to-medium efficiency to obtain transient ...

Detection of Fluorescent Nanoparticle Interactions with Primary Immune Cell Subpopulations by Flow Cytometry

Engineered nanoparticles are endowed with very promising properties for therapeutic and diagnostic purposes. This work describes a fast and reliable method of analysis by flow cytometry to study nanoparticle interaction with immune cells. Primary immune cells can be easily purified from human or mouse tissues by antibody-mediated magnetic isolation. In the first instance, the different cell populations running in a flow cytometer can be distinguished by the forward-scattered light (FSC), which is proportional to cell size, and the side-scattered light (SSC), related to cell internal complexity. Furthermore, fluorescently labeled antibodies against specific cell surface receptors permit the identification of several subpopulations within the same sample. Often, all these features vary when cells are boosted by external stimuli that change their physiological and morphological state. Here, 50 nm FITC-SiO2 nanoparticles are used as a model to identify the internalization of nanostructured materials in human blood immune cells. The cell fluorescence and side-scattered light increase after incubation with nanoparticles allowed us to define time and concentration dependence of nanoparticle-cell interaction. Moreover, such protocol can be extended to investigate Rhodamine-SiO2 nanoparticle interaction with primary microglia, the central nervous system resident immune cells, isolated from mutant mice that specifically express the Green Fluorescent Protein (GFP) in the monocyte/macrophage lineage. Finally, flow cytometry data related to nanoparticle internalization into the cells have been confirmed by confocal microscopy.

Analysis of nanoparticle interaction with defined subpopulations of immune cells by flow cytometry.

Engineered nanoparticles are endowed with very promising properties for therapeutic and diagnostic purposes. This work describes a fast and reliable ...

Optimization of a Quantitative Micro-neutralization Assay

The micro-neutralization (MN) assay is a standard technique for measuring the infectivity of the influenza virus and the inhibition of virus replication. In this study, we present the protocol of an imaging-based MN assay to quantify the true antigenic relationships between viruses. Unlike typical plaque reduction assays that rely on visible plaques, this assay quantitates the entire infected cell population of each well. The protocol matches the virus type or subtype with the selection of cell lines to achieve maximum infectivity, which enhances sample contrast during imaging and image processing. The introduction of quantitative titration defines the amount of input viruses of neutralization and enables the results from different experiments to be comparable. The imaging setup with a flatbed scanner and free downloadable software makes the approach high throughput, cost effective, user friendly, and easy to deploy in most laboratories. Our study demonstrates that the improved MN assay works well with the current circulating influenza A(H1N1)pdm09, A(H3N2), and B viruses, without being significantly influenced by amino acid substitutions in the neuraminidase (NA) of A(H3N2) viruses. It is particularly useful for the characterization of viruses that either grow to low HA titer and/or undergo an abortive infection resulting in an inability to form plaques in cultured cells.

This study describes an imaging-based micro-neutralization assay to analyze the antigenic relationships between viruses. The protocol employs a flatbed scanner and has four steps, including titration, titration quantitation, neutralization, and neutralization quantitation. The assay works well with current circulating influenza A(H1N1)pdm09, A(H3N2), and B viruses.

The micro-neutralization (MN) assay is a standard technique for measuring the infectivity of the influenza virus and the inhibition of virus replication. ...

Production of Pseudotyped Particles to Study Highly Pathogenic Coronaviruses in a Biosafety Level 2 Setting

The protocol aims to generate coronavirus (CoV) spike (S) fusion protein pseudotyped particles with a murine leukemia virus (MLV) core and luciferase reporter, using a simple transfection procedure of the widely available HEK-293T cell line. Once formed and released from producer cells, these pseudovirions incorporate a luciferase reporter gene. Since they only contain the heterologous coronavirus spike protein on their surface, the particles behave like their native coronavirus counterparts for entry steps. As such, they are the excellent surrogates of native virions for studying viral entry into host cells. Upon successful entry and infection into target cells, the luciferase reporter gets integrated into the host cell genome and is expressed. Using a simple luciferase assay, transduced cells can be easily quantified. An important advantage of the procedure is that it can be performed in biosafety level 2 (BSL-2) facilities instead of BSL-3 facilities required for work with highly pathogenic coronaviruses such as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus (SARS-CoV). Another benefit comes from its versatility as it can be applied to envelope proteins belonging to all three classes of viral fusion proteins, such as the class I influenza hemagglutinin (HA) and Ebola virus glycoprotein (GP), the class II Semliki forest virus E1 protein, or the class III vesicular stomatitis virus G glycoprotein. A limitation of the methodology is that it can only recapitulate virus entry steps mediated by the envelope protein being investigated. For studying other viral life cycle steps, other methods are required. Examples of the many applications these pseudotype particles can be used in include investigation of host cell susceptibility and tropism and testing the effects of virus entry inhibitors to dissect viral entry pathways used.

Here, we present a protocol to generate pseudotyped particles in a BSL-2 setting incorporating the spike protein of the highly pathogenic viruses Middle East respiratory syndrome and severe acute respiratory syndrome coronaviruses. These pseudotyped particles contain a luciferase reporter gene allowing quantification of virus entry into target host cells.

The protocol aims to generate coronavirus (CoV) spike (S) fusion protein pseudotyped particles with a murine leukemia virus (MLV) core and luciferase ...

Measuring Phagocytosis of Aspergillus fumigatus Conidia by Human Leukocytes using Flow Cytometry

Invasive pulmonary infection by the mold Aspergillus fumigatus poses a great threat to immunocompromised patients. Inhaled fungal conidia (spores) are cleared from the human lung alveoli by being phagocytosed by innate monocytes and/or neutrophils. This protocol offers a fast and reliable measurement of phagocytosis by flow cytometry using fluorescein isothiocyanate (FITC)-labeled conidia for co-incubation with human leukocytes and subsequent counterstaining with an anti-FITC antibody to allow discrimination of internalized and cell-adherent conidia. Major advantages of this protocol are its rapidness, the possibility to combine the assay with cytometric analysis of other cell markers of interest, the simultaneous analysis of monocytes and neutrophils from a single sample and its applicability to other cell wall-bearing fungi or bacteria. Determination of percentages of phagocytosing leukocytes provides a means to microbiologists for evaluating virulence of a pathogen or for comparing pathogen wildtypes and mutants as well as to immunologists for investigating human leukocyte capabilities to combat pathogens.

Measuring Phagocytosis of Aspergillus fumigatus Conidia by Human Leukocytes using Flow Cytometry

This protocol provides a fast and reliable method to quantitatively measure phagocytosis of Aspergillus fumigatus conidia by human primary phagocytes using flow cytometry and to discriminate phagocytosis of conidia from mere adhesion to leukocytes.

Invasive pulmonary infection by the mold Aspergillus fumigatus poses a great threat to immunocompromised patients. Inhaled fungal conidia (spores) are ...

Infection of Zebrafish Larvae with Aspergillus Spores for Analysis of Host-Pathogen Interactions

Invasive aspergillosis (IA) is one of&#160;the most common fungal infections among immunocompromised individuals. Despite the availability of antifungal drugs, IA can cause &#62;50% mortality in infected immunocompromised patients. It is crucial to determine both host and pathogen factors that contribute to infection susceptibility and low survival rates in infected patients in order to develop novel therapeutics. Innate immune responses play a pivotal role in recognition and clearance of Aspergillus spores, though little is known about the exact cellular and molecular mechanisms. Reliable models are required to investigate detailed mechanistic interactions between the host and pathogen. The optical clarity and genetic tractability of zebrafish larvae make them an intriguing model&#160;to study host-pathogen interactions of multiple human bacterial and fungal infections in a live and intact host. This protocol describes a larval zebrafish Aspergillus infection model. First, Aspergillus spores are isolated and injected into the zebrafish hindbrain ventricle via microinjection. Then, chemical inhibitors such as immunosuppressive drugs are added directly to the larval water. Two methods to monitor the infection in injected larvae are described, including the 1) homogenization of larvae for colony forming unit (CFU) enumeration and 2) a repeated, daily live imaging setup. Overall, these techniques can be used to mechanistically analyze the progression of Aspergillus infection in vivo and can be applied to different host backgrounds and Aspergillus strains to interrogate host-pathogen interactions.

Infection of Zebrafish Larvae with Aspergillus Spores for Analysis of Host-Pathogen Interactions

This protocol describes an Aspergillus infection model in zebrafish larvae. Aspergillus spores are microinjected into the hindbrain of larvae, and chemical treatment is used to induce immunosuppression. Infection progression is monitored via a daily imaging setup to monitor fungal growth and immune responses as well as enumeration of live spores by colony forming unit plating.

Invasive aspergillosis (IA) is one of&#160;the most common fungal infections among immunocompromised individuals. Despite the availability of antifungal ...

Supervised Machine Learning for Semi-Quantification of Extracellular DNA in Glomerulonephritis

Glomerular cell death is a pathological feature of myeloperoxidase anti neutrophil cytoplasmic antibody associated vasculitis (MPO-AAV). Extracellular deoxyribonucleic acid (ecDNA) is released during different forms of cell death including apoptosis, necrosis, necroptosis, neutrophil extracellular traps (NETs) and pyroptosis. Measurement of this cell death is time consuming with several different biomarkers required to identify the different biochemical forms of cell death. Measurement of ecDNA is generally conducted in serum and urine as a surrogate for renal damage, not in the actual target organ where the pathological injury occurs. The current difficulty in investigating ecDNA in the kidney is the lack of methods for formalin fixed paraffin embedded tissue (FFPE) both experimentally and in archived human kidney biopsies. This protocol provides a summary of the steps required to stain for ecDNA in FFPE tissue (both human and murine), quench autofluorescence and measure the ecDNA in the resulting images using a machine learning tool from the publicly available open source ImageJ plugin trainable Weka segmentation. Trainable Weka segmentation is applied to ecDNA within the glomeruli where the program learns to classify ecDNA. This classifier is applied to subsequent acquired kidney images, reducing the need for manual annotations of each individual image. The adaptability of the trainable Weka segmentation is demonstrated further in kidney tissue from experimental murine anti-MPO glomerulonephritis (GN), to identify NETs and ecMPO, common pathological contributors to anti-MPO GN. This method provides objective analysis of ecDNA in kidney tissue that demonstrates clearly the efficacy in which the trainable Weka segmentation program can distinguish ecDNA between healthy normal kidney tissue and diseased kidney tissue. This protocol can easily be adapted to identify ecDNA, NETs and ecMPO in other organs.

Extracellular DNA (ecDNA) released during cell death is proinflammatory and contributes to inflammation. Measurement of ecDNA at the site of injury can determine the efficacy of therapeutic treatment in the target organ. This protocol describes the use of a machine learning tool to automate measurement of ecDNA in kidney tissue.

Glomerular cell death is a pathological feature of myeloperoxidase anti neutrophil cytoplasmic antibody associated vasculitis (MPO-AAV). Extracellular ...

Fecal (micro) RNA Isolation

It is becoming clear that RNA exists in the gut lumen and feces in animals and humans. The protocol described below isolates total RNA including microRNAs from fecal samples of animal and human subjects. The aim is to isolate total RNA with high purity and quantity for downstream analyses such as RNA sequencing, RT-PCR, and micro-array. The advantages of this optimized protocol in the miRNA isolation are capabilities of isolating highly purified RNA products with additional washing steps described, increased quantity of RNA obtained with an improved method in the resuspension of sample, and important tips of decontamination. One limitation is the inability to process and purify larger sample of more than 200 mg as these sample sizes would cause a difficulty in the clear formation of the interphase. Consequently, the large sample size may contaminate the aqueous phase to be extracted as described in the protocol with organic matters that affect the quality of RNA isolated in the end. However, RNA isolates from a sample of up to 200 mg are sufficient for most of downstream analyses.

Fecal micro RNA Isolation

This protocol isolates high quality total RNA from fecal samples of animal and human subjects. A commercial miRNA isolation kit is used with significant adaption to isolate pure RNA with optimized quantity and quality. The RNA isolates are good for most downstream RNA assays such as sequencing, micro-array, and RT-PCR.

It is becoming clear that RNA exists in the gut lumen and feces in animals and humans. The protocol described below isolates total RNA including microRNAs ...

Confocal Laser Scanning Microscopy-Based Quantitative Analysis of Aspergillus fumigatus Conidia Distribution in Whole-Mount Optically Cleared Mouse Lung

Aspergillus fumigatus conidia are airborne pathogens that can penetrate human airways. Immunocompetent people without allergies exhibit resistance and immunological tolerance, while in immunocompromised patients, conidia can colonize airways and cause severe invasive respiratory disorders. Various cells in different airway compartments are involved in the immune response that prevents fungal invasion; however, the spatio-temporal aspects of pathogen elimination are still not completely understood. Three-dimensional (3D) imaging of optically cleared whole-mount organs, particularly the lungs of experimental mice, permits detection of fluorescently labeled pathogens in the airways at different time points after infection. In the present study, we describe an experimental setup to perform a quantitative analysis of A. fumigatus conidia distribution in the airways. Using fluorescent confocal laser scanning microscopy (CLSM), we traced the location of fluorescently labeled&#160;conidia in the bronchial branches and the alveolar compartment 6 hours after oropharyngeal application to mice. The approach described here was previously used for detection of the precise pathogen location and identification of the pathogen-interacting cells at different phases of the immune response. The experimental setup can be used to estimate the kinetics of the pathogen elimination in different pathological conditions.

Confocal Laser Scanning Microscopy-Based Quantitative Analysis of Aspergillus fumigatus Conidia Distribution in Whole-Mount Optically Cleared Mouse Lung

We describe the method for quantitative analysis of the distribution of Aspergillus fumigatus conidia (3 &#181;m in size) in the airways of mice. The method also can be used for the analysis of microparticles and nanoparticle agglomerate distribution in the airways in various pathological condition models.

Aspergillus fumigatus conidia are airborne pathogens that can penetrate human airways. Immunocompetent people without allergies exhibit resistance and ...

Analysis of SARS-CoV-2 Using Dual-Reporter and Multiplex Technology

Profiling of Surface Protein Epitopes on Viral Particles by Multiplex Dual-Reporter Strategy

Membrane proteins on enveloped viruses play an important role in many biological functions involving virus attachment to target cell receptors, fusion of viral particles to host cells, host-virus interactions, and disease pathogenesis. Furthermore, viral membrane proteins on virus particles and presented on host cell surfaces have proven to be excellent targets for antivirals and vaccines. Here, we describe a protocol to investigate surface proteins on intact severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) particles using the dual-reporter flow cytometric system. The assay exploits multiplex technology to obtain a triple detection of viral particles by three independent affinity reactions. Magnetic beads conjugated to recombinant human angiotensin-converting enzyme-2 (ACE2) were used to capture viral particles from the supernatant of cells infected with SARS-CoV-2. Then, two detection reagents labeled with R-phycoerythrin (PE) or Brilliant Violet 421 (BV421) were applied simultaneously. As a proof-of-concept, antibody fragments targeting different epitopes of the SARS-CoV-2 surface protein Spike (S1) were used. The detection of viral particles by three independent affinity reactions provides strong specificity and confirms the capture of intact virus particles. Dose-dependency curves of SARS-CoV-2 infected cell supernatant were generated with replicate coefficient variances (mean/SD) &#706;14%. Good assay performance in both channels confirmed that two virus surface target protein epitopes are detectable in parallel. The protocol described here could be applied for (i) high-multiplex, high-throughput profiling of surface proteins expressed on enveloped viruses; ii) detection of active intact viral particles; and (iii) assessment of specificity and affinity of antibodies and antiviral drugs for surface epitopes of viral antigens.The application can be potentially extended to any type of extracellular vesicles and bioparticles, exposing surface antigens in body fluids or other liquid matrices.

Author Spotlight: Advancing Antiviral Strategies Through Novel Immunocapture and Mass Spectrometry Techniques

Here, we describe a newly developed multiplex fluorescent immunoassay that uses a dual-reporter flow cytometric system to concurrently detect two unique spike protein epitopes on intact severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral particles that had been captured by angiotensin-converting enzyme-2-coupled magnetic microspheres.

Membrane proteins on enveloped viruses play an important role in many biological functions involving virus attachment to target cell receptors, fusion of ...