This study was financed in part by the Coordena&#231;&#227;o de Aperfei&#231;oamento de Pessoal de N&#237;vel Superior - Brasil (CAPES) - Finance Code 001. This study was also supported in part by FAPESP - S&#227;o Paulo Research Foundation. E.C.P.D.M. is grateful for a Researcher Fellowship from National Council for Scientific and Technological Development (CNPq) 306330/2019-9.

1. Production of the probiotic cells
<ol>
	<li>Prepare De Man Rogosa and Sharpe (MRS) broth.</li>
	<li>Reactivate 1% (v/v) of the culture of interest in the MRS broth (here, Lactiplantibacillus paraplantarum FT-259 was used).</li>
	<li>Incubate for 24 h at an adequate temperature (we used 37 &#176;C).</li>
</ol>
2. Separate the bacteria from the culture
<ol>
	<li>Centrifuge the bacterial culture at 7,197 x g for 5 min at 4 &#176;C using 50 mL conical tubes. It is important that the weight of the tubes is balanced before the procedure.</li>
	<li>Using a pipette, remove the supernatant, and discard it in a suitable container. Wash the pellets with a phosphate buffer (pH 7), and homogenize the solution.</li>
	<li>Repeat the centrifugation process as mentioned before.</li>
	<li>To obtain the pellet, use a pipette to remove and discard the supernatant in an appropriate container.</li>
</ol>
3. Addition of drying aids
<ol>
	<li>Select the combination of two drying aid compositions (protectants): inulin:maltodextrin mixture and simulated skim milk (Table 1)22,23.</li>
	<li>Weigh 5 g of inulin and 5 g of maltodextrin to obtain the first combination of protectants.</li>
	<li>Weigh 3 g of inulin, 3 g of lactose, 0.4 g of colloidal SiO2, and 3.6 g of whey protein to obtain the second combination of protectants.</li>
	<li>Add each of the drying aids to ultrapure water (1:10), and submit to magnetic stirring until solubilization.</li>
	<li>Ensure that the protectants and the water are homogeneous, then add the probiotics pellets to the mixture, and stir moderately for 20 min.</li>
</ol>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Drying aids</td>
			<td>Inulin and maltodextrin</td>
			<td>Simulated skim milk</td>
		</tr>
		<tr>
			<td>Maltodextrin</td>
			<td>5%</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Whey protein</td>
			<td>-</td>
			<td>3.60%</td>
		</tr>
		<tr>
			<td>Lactose</td>
			<td>-</td>
			<td>3%</td>
		</tr>
		<tr>
			<td>Inulin</td>
			<td>5%</td>
			<td>3%</td>
		</tr>
		<tr>
			<td>Colloidal SiO2</td>
			<td>-</td>
			<td>0.40%</td>
		</tr>
	</tbody>
</table>
Table 1: Composition of the drying aids.
4. Spray-drying
<ol>
	<li>Turn on the spray dryer (SD), and set the drying gas flow rate, the inlet drying temperature, and the atomizer gas flow rate and pressure as follows: 
	Inlet temperature: 80 &#176;C 
	Air flow: 60 m&#179;/h 
	Feed rate: 4 g/min 
	Atomization flow: 17 L/min 
	Atomization pressure: 1.5 kgf/cm&#178; 
	Diameter of the atomizer nozzle: 1 mm</li>
	<li>Prepare the protectants composition and add the concentrated probiotic pellets.</li>
	<li>Start the feed of the probiotic composition (cells plus protectants) through a peristaltic pump.</li>
	<li>Start the timer, and place the product-collecting vessel when the solution enters the atomizer.</li>
	<li>Register the outlet temperature every 5 min to track possible temperature instabilities.</li>
	<li>Stop the timer when all the probiotic composition has been fed to the SD.</li>
	<li>Weigh the product-collecting vessel to determine the amount of composition fed to the system and the amount of dry product collected, to calculate the drying yield (product recovered) through a mass balance in the dryer.</li>
	<li>Use simulated skim milk to evaluate the effect of temperature on the viability of the probiotic cells, by setting up five different spray-drying temperatures (80 &#176;C, 100 &#176;C, 120 &#176;C, 140 &#176;C, and 160 &#176;C vs.&#160;outlet temperatures of 59 &#176;C, 70 &#176;C, 83 &#176;C, 96 &#176;C, and 108 &#176;C).</li>
</ol>
5. Powder characterization
<ol>
	<li>Product moisture content
	<ol>
		<li>Precisely weigh 100 mg of the dried product, and place it in the titration vessel of the Karl-Fischer equipment.</li>
		<li>Press the initiation button to initiate the bi-amperometric titration of the water present in the sample.</li>
	</ol>
	</li>
	<li>Water activity
	<ol>
		<li>Weigh 0.6 g of the dried product in the sample compartment of the hygrometer at 25 &#176;C.</li>
		<li>Close the equipment cover. 
		&#8203;NOTE: The test will start automatically and stop when the sample reaches the equilibrium vapor pressure within the sample compartment.</li>
	</ol>
	</li>
</ol>
6. Probiotic viability
<ol>
	<li>Dilute the previously prepared bacterial suspensions in 9 mL of peptone water (0.1%, v/v).</li>
	<li>Vortex until complete dispersion.</li>
	<li>Perform serial decimal dilutions (1:10) in 9 mL of saline solution (0.9% NaCl).</li>
	<li>Seed the dilutions onto MRS agar plates, and incubate at 37 &#176;C for 24-48 h.</li>
	<li>Count the colony-forming units (CFU/g) using a colony counter with magnifying lens.</li>
	<li>Calculate the probiotic viability in the dried product according to the following equation: 
	EE (%) = (N&#8725;No) &#215; 100 
	where, N is the number of viable cells after spray drying, and No is the number of bacterial cells before spray drying.</li>
	<li>Express the number of viable cells in CFU/g of product dispersion.</li>
</ol>
7. Data analysis
<ol>
	<li>Tabulate the obtained data in statistical software, and perform the analysis using a multiple comparison test (ANOVA).</li>
</ol>

Optimizing Spray-Dried Probiotic Product Quality Through Process Development

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The authors have no conflicts of interest to declare.

L. paraplantarum FT-259 is a Gram-positive, rod-shaped bacterium, is a producer of bacteriocins with antilisterial activity, and has high probiotic potential20. Son et al.24 previously demonstrated the immunostimulant and antioxidant capacity of L. paraplantarum strains. Besides, they have great probiotic potential, with properties such as stability under artificial gastric and bile conditions, susceptibility to antibiotics, and binding to intestinal cells...

To be defined as probiotics, microorganisms added to foods (or supplements) have to be consumed alive, be able to survive during passage in the gastrointestinal tract of the host, and reach the site of action in adequate amounts to exert beneficial effects1,2,7.
The growing interest in probiotics is due to the several benefits to human health they confer, such as the stimulation of the immune system, the reduction of serum cholesterol levels, and the enhancement of gut barrier function by acting against harmful microbes, as well as their beneficial effects in the treatment of the irritable bowel syndrome, among others2,3. In addition, several studies have demonstrated that probiotics can positively affect other parts of the human body where unbalanced microbial communities can cause infectious diseases3,4,5.
For probiotics to be therapeutically effective, the product should contain between 106-107 CFU/g of bacteria at the time of consumption6. On the other hand, the Italian Ministry of Health and Health Canada have established that the minimum level of probiotics in food should be 109 CFU/g of viable cells per day or per serving, respectively7. Considering high loads of probiotics are needed to guarantee they will have beneficial effects, it is essential to guarantee their survival during processing, shelf storage, and passage through the gastrointestinal (GI) tract. Several studies have demonstrated that microencapsulation is an effective method to improve the overall viability of probiotics8,9,10,11.
In this context, several methods have been developed for the microencapsulation of probiotics, such as spray-drying, freeze-drying, spray-chilling, emulsion, extrusion, coacervation, and, more recently, fluidized beds11,12,13,14. Microencapsulation by spray-drying (SD) is widely used in the food industry because it is a simple, fast, and reproducible process. It is easy to scale up, and it has a high production yield at low energy requirements11,12,13,14. Nonetheless, the exposure to high temperatures and low moisture content can affect the survival and viability of the probiotic cells15. Both parameters can be improved for a given strain by determining the effects of culture age and conditions to pre-adapt the culture and optimize the spray-drying conditions (inlet and outlet temperatures, atomization process) and the encapsulating composition8,14,16,17,18.
The composition of the encapsulating solution is also an important factor during SD as it can define the level of protection against adverse environmental conditions. Inulin, Arabic gum, maltodextrins, and skim milk are widely used as encapsulating agents for probiotic drying5,17,18,19. Inulin is a fructooligosaccharide that presents a strong prebiotic activity and promotes intestinal health19. Skim milk is very effective in maintaining the viability of dried bacterial cells and generates a powder with good reconstitution properties17.
Lactiplantibacillus paraplantarum FT-259 is a lactic acid bacterium that produces bacteriocin and presents antilisterial activity, besides probiotic traits20,21. It is a facultative heterofermentative rod-shaped Gram-positive bacterium that grows from 15 &#176;C to 37 &#176;C20 and is compatible with the homeostatic body temperature. This study aimed to present all the steps involved in the production and physicochemical characterization of a spray-dried probiotic (L. paraplantarum FT-259) and evaluate the influence of the protectants and drying temperatures.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Aqua Lab 4TEV</td>
			<td>Decagon Devices</td>
			<td>-</td>
			<td>Water activity meter</td>
		</tr>
		<tr>
			<td>Centrifuge (mod. 5430 R )</td>
			<td>Eppendorf</td>
			<td>-</td>
			<td>Centrifuge</td>
		</tr>
		<tr>
			<td>Colloidal SiO2 (Aerosil 200)</td>
			<td>Evokik</td>
			<td>7631-86-9</td>
			<td>drying aid</td>
		</tr>
		<tr>
			<td>Fructooligosaccharides from chicory</td>
			<td>Sigma-Aldrich</td>
			<td>9005-80-5</td>
			<td>drying aid</td>
		</tr>
		<tr>
			<td>GraphPad Prism (version 8.0) software</td>
			<td>GraphPad Software</td>
			<td>-</td>
			<td>San Diego, California, USA</td>
		</tr>
		<tr>
			<td>Karl Fischer 870 Titrino Plus</td>
			<td>Metrohm</td>
			<td>-</td>
			<td>Moisture content</td>
		</tr>
		<tr>
			<td>Lactose</td>
			<td>Milkaut</td>
			<td>63-42-3&#160;</td>
			<td>drying aid</td>
		</tr>
		<tr>
			<td>Maltodextrin</td>
			<td>Ingredion</td>
			<td>9050-36-6</td>
			<td>drying aid</td>
		</tr>
		<tr>
			<td>Milli-Q</td>
			<td>Merk</td>
			<td>-</td>
			<td>Ultrapure water system</td>
		</tr>
		<tr>
			<td>MRS Agar</td>
			<td>Oxoid</td>
			<td>-</td>
			<td>Culture medium</td>
		</tr>
		<tr>
			<td>MRS Broth</td>
			<td>Oxoid</td>
			<td>-</td>
			<td>Culture medium</td>
		</tr>
		<tr>
			<td>OriginPro (version 9.0) software</td>
			<td>OriginLab</td>
			<td>-</td>
			<td>Northampton, Massachusetts, USA</td>
		</tr>
		<tr>
			<td>Spray dryer SD-05</td>
			<td>Lab-Plant Ltd</td>
			<td>-</td>
			<td>Spray dryer</td>
		</tr>
		<tr>
			<td>Whey protein</td>
			<td>Arla Foods Ingredients S.A.</td>
			<td>91082-88-1</td>
			<td>drying aid</td>
		</tr>
	</tbody>
</table>

process development for the spray-drying of probiotic bacteria and evaluation of the product quality

Probiotics and prebiotics are of great interest to the food and pharmaceutical industries due to their health benefits. Probiotics are live bacteria that can confer beneficial effects on human and animal wellbeing, while prebiotics are types of nutrients that feed the beneficial gut bacteria. Powder probiotics have gained popularity due to the ease and practicality of their ingestion and incorporation into the diet as a food supplement. However, the drying process interferes with cell viability since high temperatures inactivate probiotic bacteria. In this context, this study aimed to present all the steps involved in the production and physicochemical characterization of a spray-dried probiotic and evaluate the influence of the protectants (simulated skim milk and inulin:maltodextrin association) and drying temperatures in increasing the powder yield and cell viability. The results showed that the simulated skim milk promoted higher probiotic viability at 80 &#176;C. With this protectant, the probiotic viability, moisture content, and water activity (Aw) reduce as long as the inlet temperature increases. The probiotics&#39; viability decreases conversely with the drying temperature.&#160;At temperatures close to 120 &#176;C, the dried probiotic showed viability around 90%, a moisture content of 4.6% w/w, and an Aw of 0.26; values adequate to guarantee product stability. In this context, spray-drying temperatures above 120 &#176;C are required to ensure the microbial cells&#39; viability and shelf-life in the powdered preparation and survival during food processing and storage.

In this study, L. paraplantarum was encapsulated by SD using food-grade encapsulating agents (inulin:maltodextrin and simulated milk powder), showing high product quality and efficacy in preserving the bacterial cell viability17,19.
The results of the SD of probiotics at 80 &#176;C showed that the distinct protectants systems (inulin:maltodextrin and simulated skim milk) promoted efficient protection of the probiotic cells, wi...

Watch this Scientific Journal Video about Process Development for the Spray-Drying of Probiotic Bacteria and Evaluation of the Product Quality at JoVE.com

Author Spotlight: Process Development for the Spray-Drying of Probiotic Bacteria and Evaluation of the Product Quality  

This protocol details the steps involved in the production and physicochemical characterization of a spray-dried probiotic product.

Process Development for the Spray-Drying of Probiotic Bacteria and Evaluation of the Product Quality

Probiotics and prebiotics are of great interest to the food and pharmaceutical industries due to their health benefits. Probiotics are live bacteria that ...

process-development-for-spray-drying-probiotic-bacteria-evaluation

Research

JoVE Journal

Biology

3.1K Views.  Universidade de São Paulo. This protocol details the steps involved in the production and physicochemical characterization of a spray-dried probiotic product.

Video: Author Spotlight: Process Development for the Spray-Drying of Probiotic Bacteria and Evaluation of the Product Quality  

Visualizing the Beating Heart in Drosophila

The Drosophila heart has recently emerged as a good model system for examining the genetic, cellular, and molecular mechanisms underlying function in myogenic hearts. A key step in examining heart function in the fly is finding a way to access the heart in a manner that preserves its myogenic function while still allowing the beating heart organ to be observed and recorded. Two different methods for observing and recording the beating heart in both larva and adult Drosophila are described here. Our semi-intact preparation using adult flies allows clear visualization of the abdominal heart without interference from the pigmented cuticle and overlying fat bodies. To record larval heart beats it is necessary to immobilize the larva, which minimizes body wall movements thereby reducing heart movements that are not associated with myocardial contractions. Our methodologies produce stable adult and larval heart preparations that can beat for hours at rates of 1-3 Hz.

Visualizing the Beating Heart in Drosophila

Technique required for visualizing the beating heart in larval and adult Drosophila are presented. Each life stage requires a different methodology.

The Drosophila heart has recently emerged as a good model system for examining the genetic, cellular, and molecular mechanisms underlying function in ...

Semi-automated Optical Heartbeat Analysis of Small Hearts

We have developed a method for analyzing high speed optical recordings from Drosophila, zebrafish and embryonic mouse hearts (Fink, et. al., 2009). Our Semi-automatic Optical Heartbeat Analysis (SOHA) uses a novel movement detection algorithm that is able to detect cardiac movements associated with individual contractile and relaxation events. The program provides a host of physiologically relevant readouts including systolic and diastolic intervals, heart rate, as well as qualitative and quantitative measures of heartbeat arrhythmicity. The program also calculates heart diameter measurements during both diastole and systole from which fractional shortening and fractional area changes are calculated. Output is provided as a digital file compatible with most spreadsheet programs. Measurements are made for every heartbeat in a record increasing the statistical power of the output. We demonstrate each of the steps where user input is required and show the application of our methodology to the analysis of heart function in all three genetically tractable heart models.

We have developed a Semi-automated Optical Heartbeat Analysis method (SOHA) for analyzing high speed optical recordings from Drosophila, zebrafish and embryonic mouse hearts. We demonstrate the application of our methodology to the analysis of heart function in fruit fly and embryonic mouse hearts.

We have developed a method for analyzing high speed optical recordings from Drosophila, zebrafish and embryonic mouse hearts (Fink, et. al., 2009). Our ...

The use of SC1 (Pluripotin) to Support mESC Self-renewal in the Absence of LIF

Mouse embryonic stem (ES) cells are conventionally cultured with Leukemia Inhibitory Factor (LIF) to maintain self-renewal.1 However, LIF is expensive and activation of the LIF/JAK/STAT3 pathway is not absolutely required to maintain the self-renewal state.2 The SC1 small molecule may be an economical alternative to LIF. SC1 functions through dual inhibition of Ras-GAP and ERK1.3 Illustration of its mechanism of action makes it a useful tool to study the fundamental molecular mechanism of self-renewal. Here we demonstrate the procedure for culturing mouse ES cells in the presence of SC1 and show that they are able to maintain self-renewal in the absence of LIF. Cells cultured with SC1 showed similar morphology compared to cells maintained with LIF. Both exhibited typical mouse ES morphology after five passages. Expression of typical pluripotency markers (Oct4, Sox2, Nanog, and SSEA1) was observed after five passages in the presence of SC1. Furthermore, SC1 caused no overt toxicity on mouse ES cells.

The use of SC1 Pluripotin to Support mESC Self-renewal in the Absence of LIF

SC1 functions through dual inhibition of Ras- GAP and ERK1. We tested the function of SC1 in supporting mouse ES cell self-renewal in the absence of LIF and showed that SC1 is able to maintain self-renewal of mouse ES cell cultures.

Mouse embryonic stem (ES) cells are conventionally cultured with Leukemia Inhibitory Factor (LIF) to maintain self-renewal.1 However, LIF is expensive and ...

Evaluation of the Spatial Distribution of &gamma;H2AX following Ionizing Radiation

An early molecular response to DNA double-strand breaks (DSBs) is phosphorylation of the Ser-139 residue within the terminal SQEY motif of the histone H2AX1,2. This phosphorylation of H2AX is mediated by the phosphatidyl-inosito 3-kinase (PI3K) family of proteins, ataxia telangiectasia mutated (ATM), DNA-protein kinase catalytic subunit and ATM and RAD3-related (ATR)3. The phosphorylated form of H2AX, referred to as &gamma;H2AX, spreads to adjacent regions of chromatin from the site of the DSB, forming discrete foci, which are easily visualized by immunofluorecence microscopy3. Analysis and quantitation of &gamma;H2AX foci has been widely used to evaluate DSB formation and repair, particularly in response to ionizing radiation and for evaluating the efficacy of various radiation modifying compounds and cytotoxic compounds4.
Given the exquisite specificity and sensitivity of this de novo marker of DSBs, it has provided new insights into the processes of DNA damage and repair in the context of chromatin. For example, in radiation biology the central paradigm is that the nuclear DNA is the critical target with respect to radiation sensitivity. Indeed, the general consensus in the field has largely been to view chromatin as a homogeneous template for DNA damage and repair. However, with the use of &gamma;H2AX as molecular marker of DSBs, a disparity in &gamma;-irradiation-induced &gamma;H2AX foci formation in euchromatin and heterochromatin has been observed5-7. Recently, we used a panel of antibodies to either mono-, di- or tri- methylated histone H3 at lysine 9 (H3K9me1, H3K9me2, H3K9me3) which are epigenetic imprints of constitutive heterochromatin and transcriptional silencing and lysine 4 (H3K4me1, H3K4me2, H3K4me3), which are tightly correlated actively transcribing euchromatic regions, to investigate the spatial distribution of &gamma;H2AX following ionizing radiation8. In accordance with the prevailing ideas regarding chromatin biology, our findings indicated a close correlation between &gamma;H2AX formation and active transcription9. Here we demonstrate our immunofluorescence method for detection and quantitation of &gamma;H2AX foci in non-adherent cells, with a particular focus on co-localization with other epigenetic markers, image analysis and 3D-modeling.

Evaluation of the Spatial Distribution of &#947;H2AX following Ionizing Radiation

Microscopic analysis of &gamma;H2AX foci, which form following the phosphorylation of H2AX at Ser-139 in response to DNA double-strand breaks, has become an invaluable tool in radiation biology. Here we used an antibody to mono-methylated histone H3 at lysine 4 as an epigenetic marker of actively transcribing euchromatin, to evaluate the spatial distribution of radiation-induced &gamma;H2AX formation within the nucleus.

An early molecular response to DNA double-strand breaks (DSBs) is phosphorylation of the Ser-139 residue within the terminal SQEY motif of the histone ...

Long-term Lethal Toxicity Test with the Crustacean Artemia franciscana

Our research activities target the use of biological methods for the evaluation of environmental quality, with particular reference to saltwater/brackish water and sediment. The choice of biological indicators must be based on reliable scientific knowledge and, possibly, on the availability of standardized procedures. In this article, we present a standardized protocol that used the marine crustacean Artemia to evaluate the toxicity of chemicals and/or of marine environmental matrices. Scientists propose that the brine shrimp (Artemia) is a suitable candidate for the development of a standard bioassay for worldwide utilization. A number of papers have been published on the toxic effects of various chemicals and toxicants on brine shrimp (Artemia). The major advantage of this crustacean for toxicity studies is the overall availability of the dry cysts; these can be immediately used in testing and difficult cultivation is not demanded1,2. Cyst-based toxicity assays are cheap, continuously available, simple and reliable and are thus an important answer to routine needs of toxicity screening, for industrial monitoring requirements or for regulatory purposes3. The proposed method involves the mortality as an endpoint. The numbers of survivors were counted and percentage of deaths were calculated. Larvae were considered dead if they did not exhibit any internal or external movement during several seconds of observation4. This procedure was standardized testing a reference substance (Sodium Dodecyl Sulfate); some results are reported in this work. This article accompanies a video that describes the performance of procedural toxicity testing, showing all the steps related to the protocol.

Long-term Lethal Toxicity Test with the Crustacean Artemia franciscana

This study concerns the development and standardization of a valuable methodological protocol to determine long-term (14 days) lethal toxicity exerted by chemical substances, industrial wastewater or sewage and liquid environmental samples on the saltwater crustacean, Artemia franciscana.

Our research activities target the use of biological methods for the evaluation of environmental quality, with particular reference to saltwater/brackish ...

The Green Monster Process for the Generation of Yeast Strains Carrying Multiple Gene Deletions

Phenotypes for a gene deletion are often revealed only when the mutation is tested in a particular genetic background or environmental condition1,2. There are examples where many genes need to be deleted to unmask hidden gene functions3,4. Despite the potential for important discoveries, genetic interactions involving three or more genes are largely unexplored. Exhaustive searches of multi-mutant interactions would be impractical due to the sheer number of possible combinations of deletions. However, studies of selected sets of genes, such as sets of paralogs with a greater a priori chance of sharing a common function, would be informative.
In the yeast Saccharomyces cerevisiae, gene knockout is accomplished by replacing a gene with a selectable marker via homologous recombination. Because the number of markers is limited, methods have been developed for removing and reusing the same marker5,6,7,8,9,10. However, sequentially engineering multiple mutations using these methods is time-consuming because the time required scales linearly with the number of deletions to be generated.
Here we describe the Green Monster method for routinely engineering multiple deletions in yeast11. In this method, a green fluorescent protein (GFP) reporter integrated into deletions is used to quantitatively label strains according to the number of deletions contained in each strain (Figure 1). Repeated rounds of assortment of GFP-marked deletions via yeast mating and meiosis coupled with flow-cytometric enrichment of strains carrying more of these deletions lead to the accumulation of deletions in strains (Figure 2). Performing multiple processes in parallel, with each process incorporating one or more deletions per round, reduces the time required for strain construction.
The first step is to prepare haploid single-mutants termed 'ProMonsters,' each of which carries a GFP reporter in a deleted locus and one of the 'toolkit' loci&#x2014;either Green Monster GMToolkit-a or GMToolkit-&alpha; at the can1&Delta; locus (Figure 3). Using strains from the yeast deletion collection12, GFP-marked deletions can be conveniently generated by replacing the common KanMX4 cassette existing in these strains with a universal GFP-URA3 fragment. Each GMToolkit contains: either the a- or &alpha;-mating-type-specific haploid selection marker1 and exactly one of the two markers that, when both GMToolkits are present, collectively allow for selection of diploids.
The second step is to carry out the sexual cycling through which deletion loci can be combined within a single cell by the random assortment and/or meiotic recombination that accompanies each cycle of mating and sporulation.

The Green Monster method enables the rapid assembly of multiple deletions marked with a reporter gene encoding green fluorescent protein. This method is based on driving yeast strains through repeated cycles of sexual assortment of deletions and fluorescence-based enrichment of cells carrying more deletions.

Phenotypes  for a gene deletion are often revealed only when the mutation is tested in a  particular genetic background or environmental condition1,2. ...

Blastomere Explants to Test for Cell Fate Commitment During Embryonic Development

Fate maps, constructed from lineage tracing all of the cells of an embryo, reveal which tissues descend from each cell of the embryo. Although fate maps are very useful for identifying the precursors of an organ and for elucidating the developmental path by which the descendant cells populate that organ in the normal embryo, they do not illustrate the full developmental potential of a precursor cell or identify the mechanisms by which its fate is determined. To test for cell fate commitment, one compares a cell's normal repertoire of descendants in the intact embryo (the fate map) with those expressed after an experimental manipulation. Is the cell's fate fixed (committed) regardless of the surrounding cellular environment, or is it influenced by external factors provided by its neighbors? Using the comprehensive fate maps of the Xenopus embryo, we describe how to identify, isolate and culture single cleavage stage precursors, called blastomeres. This approach allows one to assess whether these early cells are committed to the fate they acquire in their normal environment in the intact embryo, require interactions with their neighboring cells, or can be influenced to express alternate fates if exposed to other types of signals.

The fate of an individual embryonic cell can be influenced by inherited molecules and/or by signals from neighboring cells. Utilizing fate maps of the cleavage stage Xenopus embryo, single blastomeres can be identified for culture in isolation to assess the contributions of inherited molecules versus cell-cell interactions.

Fate maps, constructed from lineage tracing all of the cells of an embryo, reveal  which tissues descend from each cell of the embryo.  Although fate maps ...

Collection, Isolation and Enrichment of Naturally Occurring Magnetotactic Bacteria from the Environment

Magnetotactic bacteria (MTB) are aquatic microorganisms that were first notably described in 19751 from sediment samples collected in salt marshes of Massachusetts (USA). Since then MTB have been discovered in stratified water- and sediment-columns from all over the world2. One feature common to all MTB is that they contain magnetosomes, which are intracellular, membrane-bound magnetic nanocrystals of magnetite (Fe3O4) and/or greigite (Fe3S4) or both3, 4. In the Northern hemisphere, MTB are typically attracted to the south end of a bar magnet, while in the Southern hemisphere they are usually attracted to the north end of a magnet3,5. This property can be exploited when trying to isolate MTB from environmental samples.
One of the most common ways to enrich MTB is to use a clear plastic container to collect sediment and water from a natural source, such as a freshwater pond. In the Northern hemisphere, the south end of a bar magnet is placed against the outside of the container just above the sediment at the sediment-water interface. After some time, the bacteria can be removed from the inside of the container near the magnet with a pipette and then enriched further by using a capillary racetrack6 and a magnet. Once enriched, the bacteria can be placed on a microscope slide using a hanging drop method and observed in a light microscope or deposited onto a copper grid and observed using transmission electron microscopy (TEM).
Using this method, isolated MTB may be studied microscopically to determine characteristics such as swimming behavior, type and number of flagella, cell morphology of the cells, shape of the magnetic crystals, number of magnetosomes, number of magnetosome chains in each cell, composition of the nanomineral crystals, and presence of intracellular vacuoles.

We demonstrate a method to collect magnetotactic bacteria (MTB) that can be applied to natural waters. MTB can be isolated and enriched from sediment samples using a relatively simple setup that takes advantage of the bacteria's natural magnetism. Isolated MTB can then be examined in detail using both light and electron microscopy.

Magnetotactic bacteria (MTB) are aquatic microorganisms that were first notably described in 19751 from sediment samples collected in salt marshes of ...

Gap Junctional Intercellular Communication: A Functional Biomarker to Assess Adverse Effects of Toxicants and Toxins, and Health Benefits of Natural Products

This protocol describes a scalpel loading-fluorescent dye transfer (SL-DT) technique that measures intercellular communication through gap junction channels, which is a major intercellular process by which tissue homeostasis is maintained. Interruption of gap junctional intercellular communication (GJIC) by toxicants, toxins, drugs, etc. has been linked to numerous adverse health effects. Many genetic-based human diseases have been linked to mutations in gap junction genes. The SL-DT technique is a simple functional assay for the simultaneous assessment of GJIC in a large population of cells. The assay involves pre-loading cells with a fluorescent dye by briefly perturbing the cell membrane with a scalpel blade through a population of cells. The fluorescent dye is then allowed to traverse through gap junction channels to neighboring cells for a designated time. The assay is then terminated by the addition of formalin to the cells. The spread of the fluorescent dye through a population of cells is assessed with an epifluorescence microscope and the images are analyzed with any number of morphometric software packages that are available, including free software packages found on the public domain. This assay has also been adapted for in vivo studies using tissue slices from various organs from treated animals. Overall, the SL-DT assay can serve a broad range of in vitro pharmacological and toxicological needs, and can be potentially adapted for high throughput set-up systems with automated fluorescence microscopy imaging and analysis to elucidate more samples in a shorter time.

This protocol describes a scalpel loading-fluorescent dye transfer technique that measures intercellular communication through gap junction channels. Gap junctional intercellular communication is a major cellular process by which tissue homeostasis is maintained and disruption of this cell signaling has adverse health effects.

This protocol describes a scalpel loading-fluorescent dye transfer (SL-DT) technique that measures intercellular communication through gap junction ...

Adipo-Clear: A Tissue Clearing Method for Three-Dimensional Imaging of Adipose Tissue

Adipose tissue plays a central role in energy homeostasis and thermoregulation. It is composed of different types of adipocytes, as well as adipocyte precursors, immune cells, fibroblasts, blood vessels, and nerve projections. Although the molecular control of cell type specification and how these cells interact have been increasingly delineated, a more comprehensive understanding of these adipose-resident cells can be achieved by visualizing their distribution and architecture throughout the whole tissue. Existing immunohistochemistry and immunofluorescence approaches to analyze adipose histology rely on thin paraffin-embedded sections. However, thin sections capture only a small portion of tissue; as a result, the conclusions can be biased by what portion of tissue is analyzed. We have therefore developed an adipose tissue clearing technique, Adipo-Clear, to permit comprehensive three-dimensional visualization of molecular and cellular patterns in whole adipose tissues. Adipo-Clear was adapted from iDISCO/iDISCO+, with specific modifications made to completely remove the lipid stored in the tissue while preserving native tissue morphology. In combination with light-sheet fluorescence microscopy, we demonstrate here the use of the Adipo-Clear method to obtain high-resolution volumetric images&#160;of an entire adipose tissue.

Due to the high lipid content, adipose tissue has been challenging to visualize using traditional histological methods. Adipo-Clear is a tissue clearing technique that allows robust labeling and high-resolution volumetric fluorescent imaging of adipose tissue. Here, we describe the methods for sample preparation, pretreatment, staining, clearing, and mounting for imaging.

Adipose tissue plays a central role in energy homeostasis and thermoregulation. It is composed of different types of adipocytes, as well as adipocyte ...