Name: a gnotobiotic system for studying microbiome assembly in the phyllosphere and in vegetable fermentation
Uploaded: 2020-06-03T14:00:00
Description: Watch this Scientific Journal Video about A Gnotobiotic System for Studying Microbiome Assembly in the Phyllosphere and in Vegetable Fermentation at JoVE.com

This work was supported by the USDA-NIFA grant: 2017-67013-26520. Tracy Debenport and Claire Fogan provided technical support and Ruby Ye and Casey Cosetta provide helpful comments on early versions of this manuscript.

1. Growing germ-free cabbages
<ol>
	<li>Preparing equipment for growing germ-free cabbages
	<ol>
		<li>Cleaning the calcined clay to remove fine dust particles
		<ol>
			<li>Rinse calcined clay (Table of Materials) at least 3x with tap water; drain off water. 
			CAUTION: Calcined clay produces very fine dust and it is recommended to wear a protective mask (Table of Materials) when washing.</li>
			<li>Spread calcined clay out as a thin layer (~4 cm) into an autoclave tray and aut...

<ol>
	<li>Grady, K. L., Sorensen, J. W., Stopnisek, N., Guittar, J., Shade, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assembly+and+seasonality+of+core+phyllosphere+microbiota+on+perennial+biofuel+crops.">Assembly and seasonality of core phyllosphere microbiota on perennial biofuel crops.</a> Nature Communications. 10 (1), 4135 (2019).</li><li>Pii, Y., 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=Microbial+interactions+in+the+rhizosphere:+beneficial+influences+of+plant+growth-promoting+rhizobacteria+on+nutrient+acquisition+process.+A+review.">Microbial interactions in the rhizosphere: beneficial influences of plant growth-promoting rhizobacteria on nutrient acquisition process. A review.</a> Biology and Fertility of Soils. 51 (4), 403-415 (2015).</li><li>Berendsen, R. L., Pieterse, C. M. J., Bakker, P. A. H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+rhizosphere+microbiome+and+plant+health.">The rhizosphere microbiome and plant health.</a> Trends in Plant Science. 17 (8), 478-486 (2012).</li><li>Bai, Y., 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=Functional+overlap+of+the+Arabidopsis+leaf+and+root+microbiota.">Functional overlap of the Arabidopsis leaf and root microbiota.</a> Nature. 528 (7582), 364-369 (2015).</li><li>Bulgarelli, D., Schlaeppi, K., Spaepen, S., Ver Loren van Themaat, E., Schulze-Lefert, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+and+functions+of+the+bacterial+microbiota+of+plants.">Structure and functions of the bacterial microbiota of plants.</a> Annual Review of Plant Biology. 64, 807-838 (2013).</li><li>Dinu, L. D., Bach, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Induction+of+viable+but+nonculturable+Escherichia+coli+O157:H7+in+the+phyllosphere+of+lettuce:+a+food+safety+risk+factor.">Induction of viable but nonculturable Escherichia coli O157:H7 in the phyllosphere of lettuce: a food safety risk factor.</a> Applied and Environmental Microbiology. 77 (23), 8295-8302 (2011).</li><li>Heaton, J. C., Jones, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbial+contamination+of+fruit+and+vegetables+and+the+behaviour+of+enteropathogens+in+the+phyllosphere:+a+review.">Microbial contamination of fruit and vegetables and the behaviour of enteropathogens in the phyllosphere: a review.</a> Journal of Applied Microbiology. 104 (3), 613-626 (2008).</li><li>Bringel, F., Cou&#233;e, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pivotal+roles+of+phyllosphere+microorganisms+at+the+interface+between+plant+functioning+and+atmospheric+trace+gas+dynamics.">Pivotal roles of phyllosphere microorganisms at the interface between plant functioning and atmospheric trace gas dynamics.</a> Frontiers in Microbiology. 6, 486 (2015).</li><li>Maignien, L., DeForce, E. A., Chafee, M. E., Eren, A. M., Simmons, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ecological+succession+and+stochastic+variation+in+the+assembly+of+Arabidopsis+thaliana+phyllosphere+communities.">Ecological succession and stochastic variation in the assembly of Arabidopsis thaliana phyllosphere communities.</a> mBio. 5 (1), e00682 (2014).</li><li>Carlstr&#246;m, C. I., 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=Synthetic+microbiota+reveal+priority+effects+and+keystone+strains+in+the+Arabidopsis+phyllosphere.">Synthetic microbiota reveal priority effects and keystone strains in the Arabidopsis phyllosphere.</a> Nature Ecology &amp; Evolution. 3 (10), 1445-1454 (2019).</li><li>Meyer, K. M., Leveau, J. H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbiology+of+the+phyllosphere:+a+playground+for+testing+ecological+concepts.">Microbiology of the phyllosphere: a playground for testing ecological concepts.</a> Oecologia. 168 (3), 621-629 (2012).</li><li>Humphrey, P. T., Nguyen, T. T., Villalobos, M. M., Whiteman, N. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diversity+and+abundance+of+phyllosphere+bacteria+are+linked+to+insect+herbivory.">Diversity and abundance of phyllosphere bacteria are linked to insect herbivory.</a> Molecular Ecology. 23 (6), 1497-1515 (2014).</li><li>Williams, T. R., Marco, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phyllosphere+microbiota+composition+and+microbial+community+transplantation+on+lettuce+plants+grown+indoors.">Phyllosphere microbiota composition and microbial community transplantation on lettuce plants grown indoors.</a> mBio. 5 (4), e01564 (2014).</li><li>Di Cagno, R., Coda, R., De Angelis, M., Gobbetti, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exploitation+of+vegetables+and+fruits+through+lactic+acid+fermentation.">Exploitation of vegetables and fruits through lactic acid fermentation.</a> Food Microbiology. 33 (1), 1-10 (2013).</li><li>K&#246;berl, M., 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=Deciphering+the+microbiome+shift+during+fermentation+of+medicinal+plants.">Deciphering the microbiome shift during fermentation of medicinal plants.</a> Scientific Reports. 9 (1), 13461 (2019).</li><li>Yu, A. O., Leveau, J. H. J., Marco, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Abundance,+diversity+and+plant-specific+adaptations+of+plant-associated+lactic+acid+bacteria.">Abundance, diversity and plant-specific adaptations of plant-associated lactic acid bacteria.</a> Environmental Microbiology Reports. 12 (1), 16-29 (2020).</li><li>Miller, E. R., 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=Establishment+limitation+constrains+the+abundance+of+lactic+acid+bacteria+in+the+Napa+cabbage+phyllosphere.">Establishment limitation constrains the abundance of lactic acid bacteria in the Napa cabbage phyllosphere.</a> Applied and Environmental Microbiology. 85 (13), e00269 (2019).</li><li>Stamer, J. R., Stoyla, B. O., Dunckel, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+rates+and+fermentation+patterns+of+lactic+acid+bacteria+associated+with+sauerkraut+fermentation.">Growth rates and fermentation patterns of lactic acid bacteria associated with sauerkraut fermentation.</a> Journal of Milk and Food Technology. 34 (11), 521-525 (1971).</li><li>Yildiz, F., Westhoff, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Associative+growth+of+lactic+acid+bacteria+in+cabbage+juice.">Associative growth of lactic acid bacteria in cabbage juice.</a> Journal of Food Science. 46 (3), 962-963 (1981).</li><li>Zabat, M. A., Sano, W. H., Wurster, J. I., Cabral, D. J., Belenky, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbial+community+analysis+of+sauerkraut+fermentation+reveals+a+stable+and+rapidly+established+community.">Microbial community analysis of sauerkraut fermentation reveals a stable and rapidly established community.</a> Foods. 7 (5), 77 (2018).</li><li>Lee, S. H., Jung, J. Y., Jeon, C. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Source+tracking+and+succession+of+kimchi+lactic+acid+bacteria+during+fermentation.">Source tracking and succession of kimchi lactic acid bacteria during fermentation.</a> Journal of Food Science. 80 (8), M1871 (2015).</li><li>Trivedi, P., Schenk, P. M., Wallenstein, M. D., Singh, B. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tiny+Microbes,+Big+Yields:+enhancing+food+crop+production+with+biological+solutions.">Tiny Microbes, Big Yields: enhancing food crop production with biological solutions.</a> Microbial Biotechnology. 10 (5), 999-1003 (2017).</li><li>Knief, C., 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=Metaproteogenomic+analysis+of+microbial+communities+in+the+phyllosphere+and+rhizosphere+of+rice.">Metaproteogenomic analysis of microbial communities in the phyllosphere and rhizosphere of rice.</a> The ISME Journal. 6 (7), 1378-1390 (2012).</li><li>Wuyts, S., 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=Carrot+Juice+Fermentations+as+Man-Made+Microbial+Ecosystems+Dominated+by+Lactic+Acid+Bacteria.">Carrot Juice Fermentations as Man-Made Microbial Ecosystems Dominated by Lactic Acid Bacteria.</a> Applied and Environmental Microbiology. 84 (12), AEM.00134 (2018).</li><li>Niu, B., Paulson, J. N., Zheng, X., Kolter, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simplified+and+representative+bacterial+community+of+maize+roots.">Simplified and representative bacterial community of maize roots.</a> Proceedings of the National Academy of Sciences of the United States of America. 114 (12), E2450-E2459 (2017).</li><li>Steinkraus, K. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lactic+acid+fermentation+in+the+production+of+foods+from+vegetables,+cereals+and+legumes.">Lactic acid fermentation in the production of foods from vegetables, cereals and legumes.</a> Antonie van Leeuwenhoek. 49 (3), 337-348 (1983).</li></ol>

Germ-free Napa cabbage plants have been used to study dispersal limitation of lactic acid bacteria in the Napa cabbage phyllosphere17. Germ-free Napa cabbages can also be used to test individual or pair-wise growth in the phyllosphere (Figure 1). Methods for making sterile vegetable extract has been tested for three different varieties of cabbage: red, green and Napa. Each of these SVEs act as a reliable growth media; inoculated microbes grow consistently across the d...

Microbial diversity of the phyllosphere plays an important role in maintaining plant health and can also influence the ability of plants to withstand environmental stress1,2,3,4,5. In turn, the health of crops directly impacts food safety and quality6,7. Plants play a role in ecosystem functioning and their associated microbiomes both affect the ability of plants to carry out these activities as well as directly influencing the environment themselves8. While scientists have begun to decipher the function and composition of the phyllosphere, the ecological processes that influence phyllosphere microbial community assembly are not fully understood9,10. The phyllosphere microbiome is an excellent experimental system for studying the ecology of microbiomes11. These communities are relatively simple and many of the community members can be grown on standard lab media10,12,13.
Fermented vegetables are one system where the community structure of the phyllosphere has important consequences. In both sauerkraut and kimchi, the microbes that naturally occur on vegetable leaves (the phyllosphere of Brassica species) serves as the inoculum for fermentation14,15. Lactic acid bacteria (LAB) are considered ubiquitous members of vegetable microbiomes, however they can be in low abundance in the phyllosphere16. Strong abiotic selection during fermentation drives a shift in microbial community composition enabling lactic acid bacteria to increase in abundance. As LAB grow, they produce lactic acid which creates the acidic environment of fermented vegetable products17. The link between the phyllosphere and the ferment provides an opportunity to use vegetables as a model to understand how microbiomes are structured.
We have developed methods to grow germ-free Napa cabbages and to inoculate them with specific microbial communities using spray bottles. This is an inexpensive and reliable method of evenly inoculating the cabbage with either individual microbes or mixed communities. A sterile vegetable extract (SVE) has also been developed from three different cabbage types/varieties: red and green cabbage (Brassica oleracea) and Napa cabbage (B. rapa). The addition of salt to these SVEs replicates the fermentation environment and allows for small-scale and relatively high-throughput experimental studies of fermentation microbiome assembly. These methods can be used to study microbial community assembly in the phyllosphere and how microbial community dynamics in the phyllosphere can be linked to the success of vegetable fermentation.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1.5 mL microcentrifuge tubes</td>
			<td>VWR</td>
			<td>20170-650</td>
			<td></td>
		</tr>
		<tr>
			<td>15 mL conical tubes</td>
			<td>Falcon</td>
			<td>352096</td>
			<td></td>
		</tr>
		<tr>
			<td>7-way tray tray</td>
			<td>Sigma Magenta</td>
			<td>T8654</td>
			<td></td>
		</tr>
		<tr>
			<td>Amber Round Boston Glass Bottle</td>
			<td></td>
			<td>GPS 712OZSPPK12BR</td>
			<td>Ordered on Amazon.com from various suppliers</td>
		</tr>
		<tr>
			<td>Basket coffee filters</td>
			<td>If you care</td>
			<td></td>
			<td>(unbleached paper) Purchased from Wholefoods</td>
		</tr>
		<tr>
			<td>Bleach (mercury-free)</td>
			<td>Austin&#39;s</td>
			<td>50-010-45</td>
			<td></td>
		</tr>
		<tr>
			<td>Borosilicate Glass tubes</td>
			<td>VWR</td>
			<td>47729-586</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcined clay</td>
			<td>Turface</td>
			<td>MVP</td>
			<td>Ordered on Amazon.com from Root Naturally 6 Quart Bags. Particle size approximately 3-5 mm</td>
		</tr>
		<tr>
			<td>Cuisinart blender</td>
			<td>Cuisinart</td>
			<td></td>
			<td>Cuisinart Mini-Prep Plus Food Processor, 3-Cup</td>
		</tr>
		<tr>
			<td>Dissection scissors</td>
			<td>7-389-A</td>
			<td>American Educational Products</td>
			<td>Ordered on Amazon.com</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>VWR</td>
			<td>89125-172</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Aven</td>
			<td>18434</td>
			<td>Ordered on Amazon.com</td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Fisher Scientific</td>
			<td>56-81-5</td>
			<td></td>
		</tr>
		<tr>
			<td>KleenGuard M10</td>
			<td>Kimberley-Clark</td>
			<td>64240</td>
			<td></td>
		</tr>
		<tr>
			<td>Large plastic container</td>
			<td>Rubbermaid</td>
			<td></td>
			<td>Ordered on Amazon.com</td>
		</tr>
		<tr>
			<td>Light racks</td>
			<td>Gardner&#39;s Supply</td>
			<td>39-357</td>
			<td>full-spectrum T5 fluorescent bulbs</td>
		</tr>
		<tr>
			<td>Magenta tm 2-way caps</td>
			<td>Millipore Sigma</td>
			<td>C1934</td>
			<td></td>
		</tr>
		<tr>
			<td>Man, Rogosa, and Sharpe</td>
			<td>Fisher Scientific</td>
			<td>DF0881-17-5</td>
			<td>This media is for broth and 15 g of agar is added to make plates</td>
		</tr>
		<tr>
			<td>Micro pH probe</td>
			<td>Thermo Scientific</td>
			<td>8220BNWP</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropestle</td>
			<td>Carolina</td>
			<td>215828</td>
			<td>Also called Pellet Pestle</td>
		</tr>
		<tr>
			<td>MS nutrient broth</td>
			<td>Millipore Sigma</td>
			<td>M5519</td>
			<td>Murashige and Skoog Basal Medium</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma Aldrich</td>
			<td>S9888</td>
			<td></td>
		</tr>
		<tr>
			<td>Napa cabbage seeds</td>
			<td>Johnny&#39;s Select Seeds</td>
			<td>2814G</td>
			<td>B. rapa var pekinensis (Bilko)</td>
		</tr>
		<tr>
			<td>Petri dish 100 mm x 15 mm</td>
			<td>Fisher</td>
			<td>FB0875712</td>
			<td>Used to make agar plates</td>
		</tr>
		<tr>
			<td>Phosphate buffer saline</td>
			<td>Fisher Scientific</td>
			<td>50-842-941</td>
			<td>Teknova</td>
		</tr>
		<tr>
			<td>Plant tissue culture box</td>
			<td>Sigma</td>
			<td>Magenta GA-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Serologial pipettes</td>
			<td>VWR</td>
			<td>89130-900</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile dowel</td>
			<td>Puritan</td>
			<td>10805-018</td>
			<td>Autoclave before use to sterilize</td>
		</tr>
		<tr>
			<td>Sterilizing 0.2 &#181;m filter</td>
			<td>Nalgene</td>
			<td>974103</td>
			<td></td>
		</tr>
		<tr>
			<td>Tryptic soy agar</td>
			<td>Fisher Scientific</td>
			<td>DF0370-17-3</td>
			<td>This media is for broth and 15 g of agar is added to make plates</td>
		</tr>
		<tr>
			<td>Wide orifice pipette tips</td>
			<td>Rainin</td>
			<td>17007102</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast, peptone and dextrose</td>
			<td>Fisher Scientific</td>
			<td>DF0428-17-5</td>
			<td>This media is suitable but media can also be made using yeast, peptone and dextrose, add 15 g of agar when making plates</td>
		</tr>
	</tbody>
</table>

a gnotobiotic system for studying microbiome assembly in the phyllosphere and in vegetable fermentation

The phyllosphere, the above ground portion of the plant that can be colonized by microbes, is a useful model system to identify processes of microbial community assembly. This protocol outlines a system for studying microbial community dynamics in the phyllosphere of Napa cabbage plants. It describes how to grow germ-free plants in test tubes with a calcined clay and nutrient broth substrate. Inoculation of germ-free plants with specific microbial cultures provides opportunities to measure microbial growth and community dynamics in the phyllosphere. Through the use of sterile vegetable extract produced from cabbages shifts in microbial communities that occur during fermentation can also be assessed. This system is relatively simple and inexpensive to set up in the lab and can be used to address key ecological questions in microbial community assembly. It also provides opportunities to understand how phyllosphere community composition can impact the microbial diversity and quality of vegetable fermentations. This approach for developing gnotobiotic cabbage phyllosphere communities could be applied to other wild and agricultural plant species.

Growth rates of Napa cabbages 
The seed sterilization method was tested with several different Napa cabbages (B. rapa var pekinese; Supplemental Figure 1) from a number of different suppliers and all grew consistently with similar growth rates. However, testing the methods with different species of Brassica (B. rapa: Turnip Purple Top; B. oleracea: Cairo Hybrid, Tropic Giant Hybrid; B. campestris: Pak Choi...

Watch this Scientific Journal Video about A Gnotobiotic System for Studying Microbiome Assembly in the Phyllosphere and in Vegetable Fermentation at JoVE.com

A Gnotobiotic System for Studying Microbiome Assembly in the Phyllosphere and in Vegetable Fermentation

A method of growing germ-free Napa cabbages has been developed which enables researchers to evaluate how single microbial species or multispecies microbial communities interact on cabbage leaf surfaces. A sterile vegetable extract is also presented which can be used to measure shifts in community composition during vegetable fermentation.

The phyllosphere, the above ground portion of the plant that can be colonized by microbes, is a useful model system to identify processes of microbial ...

Using this protocol, we can address key questions regarding how microbes assemble and interact in the phyllosphere. It has the added benefit that by using the sterile vegetable extract, we can link the structure of phyllo sphere communities to their function during vegetable fermentation. These techniques enable scientists to test how microbes interact in the phyllo sphere and then track how these phyllo sphere communities can impact fermentation.To surface sterilize the cabbage seeds, start by placing 100 seeds in a 1.5 milliliter micro centrifuge tube. Add one milliliter of 70%ethanol to the tube and vortex it for five minutes. Then use a pipette to discard the ethanol.Add one milliliter of 50%bleach and vortex the tube for five minutes, then discard the bleach. Rinse the seeds four times, by adding one milliliter of autoclaved deionized water vortexing the tube, then discarding the water. After the last rinse, soak the seeds in sterilized deionized water for two to eight hours to soften the seed coat before planting.Weigh 10 grams of clean calcium clay into a 15 by 2.5 centimeter glass tube. Add approximately nine milliliters of prepared MS Broth to each tube to cover the calciumed clay. Loosely cap the glass tubes with 22 millimeter two way test tube caps.Autoclave the tubes at 121 degrees Celsius for 60 minutes. When removing the tubes from the autoclave, push the caps onto the glass tubes to seal them, then cool the tubes to room temperature before use. When the tubes have cooled, used extra long forceps to gently place one sterile cabbage seed into the center of each tube.Lace the tubes in a seven way tray and place the tray under light racks with a 16 hour light cycle at 24 degrees Celsius. The seeds will develop their first true leaf after five days, which is the first vascular leaf after the cotyledons have formed. It has a wrinkled edge and is covered in tricombs.To test the germ-free cabbage for sterility, gently grip the base of the plant with sterilized forceps and pull it out. Before fully removing the cabbage from the tube, carefully cut off the roots with sterilized dissection scissors. Then, compact the cabbage leaves into a 1.5 milliliter micro centrifuge tube.Add 400 microliters of PBS to each micro centrifuge tube and use a sterile micro pestle to homogenize the cabbage. Blade 100 microliters of the cabbage homogenate onto agar plates, making sure to use a wide orifice pipette tip. To make glycerol stocks of inoculating strains, gently streak out individual colonies onto two or three new plates of the same media.Row the colonies for two to five days, then scrape them from the plates into a 15 milliliter conical tube with 15 milliliters of 15%glycerol. Vortex the tube thoroughly to mix. Aliquot one milliliter of the mixed glycerol stock into a micro centrifuge tube and store it 80 degrees Celsius until ready to use along with the remaining 14 milliliters of glycerol stock.One week prior to use, thaw the one milliliter aliquot on ice and place it at several different dilutions to determine the concentration of the inoculation stock. When ready to inoculate the cabbage, thaw the glycerol stock on ice and dilute it to the desired concentration. Add 10 milliliters of the diluted stock to the sterile pump bottle and pump five sprays into a large waste collection beaker.Remove the lid from the cabbage tube and tilt the cabbage towards the spray bottle. Spray each cabbage with three pumps of the inoculation solution, then harvest a subset of the cabbages to assess the actual input inoculation concentration. To harvest the cabbage, remove it from the tube with sterilized forceps.Cut off the roots with sterile dissection scissors and carefully place it in a pre weighed sterile micro centrifuge tube. Record the weight of the cabbage for future calculations. Add 400 microliters of PBS to each tube with the cabbage and grind it 30 times with a micro pestle, then plate the cabbage homogenate using wide orifice pipette tips.Remove and discard the outermost leaves of the cabbage and chop all remaining cabbage to fit into a blender. Blend it to a fine pulp and weigh the cabbage homogenate. Add two milliliters of distilled water per gram of cabbage.Then filter the cabbage slurry through two layers of basket coffee filters. Dispense the slurry into centrifuge tubes and centrifuge it at 20, 000 times G for 20 minutes or until large particles settle out of solution. Remove the supernatant, taking care to not disturb the pelleted cabbage debris.To recreate the fermentation conditions with standard salt concentrations, add 2%weight to volume sodium chloride to the extract. Bilder the vegetable extract with a 0.2 micrometer filter attached to a vacuum, dispense it into sterile tubes and freeze it at minus 80 degrees Celsius. The seed sterilization method was tested with several Napa cabbages and they all demonstrated similar growth rates.However, other species of brassica gave limited success because the plants either had low germination rates after sterilizing or the stem elongated rapidly to make a spindly unhealthy plant. Microbial isolates were inoculated either as single strain isolates or in combination with another isolate. A total of 15 germ-free cabbages were tested for each treatment and harvested either immediately, at four days or at 10 days after inoculation.The isolates demonstrated rapid growth in the Napa cabbage Phyllosphere. Two yeasts and three bacteria were inoculated into three different types of sterile vegetable extract or SVE made from red, green and Napa cabbage. Growth of the inoculates was recorded over 14 days by spot plating five microliters of each treatment onto either MRS or YPD agar plates.Measurements of pH throughout the fermentation showed that the lactic acid bacteria were capable of acidifying the SVE to levels below pH four, indicating a ferment that is safe for consumption. These methods have specifically applied to the cabbage microbiome but could be useful in other plant systems. It can be challenging to keep the system sterile, our outline protocols are detailed, but we found each step to be important.

a-gnotobiotic-system-for-studying-microbiome-assembly-phyllosphere

Research

JoVE Journal

Environment

Methods for Performing Crosses in Setaria viridis, a New Model System for the Grasses

Setaria viridis is an emerging model system for C4 grasses. It is closely related to the bioenergy feed stock switchgrass and the grain crop foxtail millet. Recently, the 510 Mb genome of foxtail millet, S. italica, has been sequenced 1,2 and a 25x coverage genome sequence of the weedy relative S. viridis is in progress. S. viridis has a number of characteristics that make it a potentially excellent model genetic system including a rapid generation time, small stature, simple growth requirements, prolific seed production 3 and developed systems for both transient and stable transformation 4. However, the genetics of S. viridis is largely unexplored, in part, due to the lack of detailed methods for performing crosses. To date, no standard protocol has been adopted that will permit rapid production of seeds from controlled crosses.
The protocol presented here is optimized for performing genetic crosses in S. viridis, accession A10.1. We have employed a simple heat treatment with warm water for emasculation after pruning the panicle to retain 20-30 florets and labeling of flowers to eliminate seeds resulting from newly developed flowers after emasculation. After testing a series of heat treatments at permissive temperatures and varying the duration of dipping, we have established an optimum temperature and time range of 48 &deg;C for 3-6 min. By using this method, a minimum of 15 crosses can be performed by a single worker per day and an average of 3-5 outcross progeny per panicle can be recovered. Therefore, an average of 45-75 outcross progeny can be produced by one person in a single day. Broad implementation of this technique will facilitate the development of recombinant inbred line populations of S. viridis X S. viridis or S. viridis X S. italica, mapping mutations through bulk segregant analysis and creating higher order mutants for genetic analysis.

Methods for Performing Crosses in Setaria viridis, a New Model System for the Grasses

We have developed a methodology for performing crosses in Setaria viridis (S. viridis). The method involves pruning the panicle prior to a hot water treatment to kill viable pollen. Crosses are performed following a well-controlled growth regime and typically result in the recovery of 1 to 7 cross-pollinated seed/s per panicle.

Setaria viridis is an emerging model system for C4 grasses. It is closely related to the bioenergy feed stock switchgrass and the grain crop foxtail ...

Technique for Studying Arthropod and Microbial Communities within Tree Tissues

Phloem tissues of pine are habitats for many thousands of organisms. Arthropods and microbes use phloem and cambium tissues to seek mates, lay eggs, rear young, feed, or hide from natural enemies or harsh environmental conditions outside of the tree. Organisms that persist within the phloem habitat are difficult to observe given their location under bark. We provide a technique to preserve intact phloem and prepare it for experimentation with invertebrates and microorganisms. The apparatus is called a &#8216;phloem sandwich&#8217; and allows for the introduction and observation of arthropods, microbes, and other organisms. This technique has resulted in a better understanding of the feeding behaviors, life-history traits, reproduction, development, and interactions of organisms within tree phloem. The strengths of this technique include the use of inexpensive materials, variability in sandwich size, flexibility to re-open the sandwich or introduce multiple organisms through drilled holes, and the preservation and maintenance of phloem integrity. The phloem sandwich is an excellent educational tool for scientific discovery in both K-12 science courses and university research laboratories.

We provide a technique to preserve intact tree phloem and prepare it for observation. We create an apparatus called a phloem sandwich that allows for the introduction and observation of arthropods, microbes, and other organisms that inhabit phloem tissues.

Phloem tissues of pine are habitats for many thousands of organisms.  Arthropods and microbes use phloem and cambium tissues to seek mates, lay eggs, rear ...

Transient Gene Expression in Tobacco using Gibson Assembly and the Gene Gun

In order to target a single protein to multiple subcellular organelles, plants typically duplicate the relevant genes, and express each gene separately using complex regulatory strategies including differential promoters and/or signal sequences. Metabolic engineers and synthetic biologists interested in targeting enzymes to a particular organelle are faced with a challenge: For a protein that is to be localized to more than one organelle, the engineer must clone the same gene multiple times. This work presents a solution to this strategy: harnessing alternative splicing of mRNA. This technology takes advantage of established chloroplast and peroxisome targeting sequences and combines them into a single mRNA that is alternatively spliced. Some splice variants are sent to the chloroplast, some to the peroxisome, and some to the cytosol. Here the system is designed for multiple-organelle targeting with alternative splicing. In this work, GFP was expected to be expressed in the chloroplast, cytosol, and peroxisome by a series of rationally designed 5&#8217; mRNA tags. These tags have the potential to reduce the amount of cloning required when heterologous genes need to be expressed in multiple subcellular organelles. The constructs were designed in previous work11, and were cloned using Gibson assembly, a ligation independent cloning method that does not require restriction enzymes. The resultant plasmids were introduced into Nicotiana benthamiana epidermal leaf cells with a modified Gene Gun protocol. Finally, transformed leaves were observed with confocal microscopy.

This work describes a novel method for selectively targeting subcellular organelles in plants, assayed using the BioRad Gene Gun.

In order to target a single protein to multiple subcellular organelles, plants typically duplicate the relevant genes, and express each gene separately ...

LC-MS Analysis of Human Platelets as a Platform for Studying Mitochondrial Metabolism

Perturbed mitochondrial metabolism has received renewed interest as playing a causative role in a range of diseases. Probing alterations to metabolic pathways requires a model in which external factors can be well controlled, allowing for reproducible and meaningful results. Many studies employ transformed cellular models for these purposes; however, metabolic reprogramming that occurs in many cancer cell lines may introduce confounding variables. For this reason primary cells are desirable, though attaining adequate biomass for metabolic studies can be challenging. Here we show that human platelets can be utilized as a platform to carry out metabolic studies in combination with liquid chromatography-tandem mass spectrometry analysis. This approach is amenable to relative quantification and isotopic labeling to probe the activity of specific metabolic pathways. Availability of platelets from individual donors or from blood banks makes this model system applicable to clinical studies and feasible to scale up. Here we utilize isolated platelets to confirm previously identified compensatory metabolic shifts in response to the complex I inhibitor rotenone. More specifically, a decrease in glycolysis is accompanied by an increase in fatty acid oxidation to maintain acetyl-CoA levels. Our results show that platelets can be used as an easily accessible and medically relevant model to probe the effects of xenobiotics on cellular metabolism.

Here we show isolated human platelets can be used as an accessible ex vivo model to study metabolic adaptations in response to the complex I inhibitor rotenone. This approach employs isotopic tracing and relative quantification by liquid chromatography-mass spectrometry and can be applied to a variety of study designs.

Perturbed mitochondrial metabolism has received renewed interest as playing a causative role in a range of diseases. Probing alterations to metabolic ...

Empirical, Metagenomic, and Computational Techniques Illuminate the Mechanisms by which Fungicides Compromise Bee Health

Growers often use fungicide sprays during bloom to protect crops against disease, which exposes bees to fungicide residues. Although considered &#34;bee-safe,&#34; there is mounting evidence that fungicide residues in pollen are associated with bee declines (for both honey and bumble bee species). While the mechanisms remain relatively unknown, researchers have speculated that bee-microbe symbioses are involved. Microbes play a pivotal role in the preservation and/or processing of pollen, which serves as nutrition for larval bees. By altering the microbial community, it is likely that fungicides disrupt these microbe-mediated services, and thereby compromise bee health. This manuscript describes the protocols used to investigate the indirect mechanism(s) by which fungicides may be causing colony decline. Cage experiments exposing bees to fungicide-treated flowers have already provided the first evidence that fungicides cause profound colony losses in a native bumble bee (Bombus impatiens). Using field-relevant doses of fungicides, a series of experiments have been developed to provide a finer description of microbial community dynamics of fungicide-exposed pollen. Shifts in the structural composition of fungal and bacterial assemblages within the pollen microbiome are investigated by next-generation sequencing and metagenomic analysis. Experiments developed herein have been designed to provide a mechanistic understanding of how fungicides affect the microbiome of pollen-provisions. Ultimately, these findings should shed light on the indirect pathway through which fungicides may be causing colony declines.

Microbial consortia within bumble bee hives enrich and preserve pollen for bee larvae. Using next generation sequencing, along with laboratory and field-based experiments, this manuscript describes protocols used to test the hypothesis that fungicide residues alter the pollen microbiome, and colony demographics, ultimately leading to colony loss.

Growers often use fungicide sprays during bloom to protect crops against disease, which exposes bees to fungicide residues. Although considered ...

Comparison of Scale in a Photosynthetic Reactor System for Algal Remediation of Wastewater

An experimental methodology is presented to compare the performance of two different sized reactors designed for wastewater treatment. In this study, ammonia removal, nitrogen removal and algal growth are compared over an 8-week period in paired sets of small (100 L) and large (1,000 L) reactors designed for algal remediation of landfill wastewater. Contents of the small and large scale reactors were mixed before the beginning of each weekly testing interval to maintain equivalent initial conditions across the two scales. System characteristics, including surface area to volume ratio, retention time, biomass density, and wastewater feed concentrations, can be adjusted to better equalize conditions occurring at both scales. During the short 8-week representative time period, starting ammonia and total nitrogen concentrations ranged from 3.1-14 mg NH3-N/L, and 8.1-20.1 mg N/L, respectively. The performance of the treatment system was evaluated based on its ability to remove ammonia and total nitrogen and to produce algal biomass. Mean &#177; standard deviation of ammonia removal, total nitrogen removal and biomass growth rates were 0.95&#177;0.3 mg NH3-N/L/day, 0.89&#177;0.3 mg N/L/day, and 0.02&#177;0.03 g biomass/L/day, respectively. All vessels showed a positive relationship between the initial ammonia concentration and ammonia removal rate (R2=0.76). Comparison of process efficiencies and production values measured in reactors of different scale may be useful in determining if lab-scale experimental data is appropriate for prediction of commercial-scale production values.

An experimental methodology is presented to compare the performance of small (100 L) and large (1,000 L) scale reactors designed for algae remediation of landfill wastewater. System characteristics, including surface area to volume ratio, retention time, biomass density, and wastewater feed concentrations, can be adjusted based on application.

An experimental methodology is presented to compare the performance of two different sized reactors designed for wastewater treatment. In this study, ...

Measuring and Mapping Patterns of Soil Erosion and Deposition Related to Soil Carbonate Concentrations Under Agricultural Management

Spatial patterns of soil erosion and deposition can be inferred from differences in ground elevation mapped at appropriate time increments. Such changes in elevation are related to changes in near-surface soil carbonate (CaCO3) profiles. The objective is to describe a simple conceptual model and detailed protocol for repeatable field and laboratory measurements of these quantities. Here, accurate elevation is measured using a ground-based differential global positioning system (GPS); other data acquisition methods could be applied to the same basic method. Soil samples are collected from prescribed depth intervals and analyzed in the lab using an efficient and precise modified pressure-calcimeter method for quantitative analysis of inorganic carbon concentration. Standard statistical methods are applied to point data, and representative results show significant correlations between changes in soil surface layer CaCO3 and changes in elevation consistent with the conceptual model; CaCO3 generally decreased in depositional areas and increased in erosional areas. Maps are derived from point measurements of elevation and soil CaCO3 to aid analyses. A map of erosional and depositional patterns at the study site, a rain-fed winter wheat field cropped in alternating wheat-fallow strips, shows the interacting effects of water and wind erosion affected by management and topography. Alternative sampling methods and depth intervals are discussed and recommended for future work relating soil erosion and deposition to soil CaCO3.

Spatial patterns of soil erosion and deposition can be inferred from differences in ground elevation mapped at appropriate time increments. Such changes in elevation are related to changes in near-surface soil carbonates. Repeatable methods for field and laboratory measurements of these quantities and data analysis methods are described here.

Spatial patterns of soil erosion and deposition can be inferred from differences in ground elevation mapped at appropriate time increments. Such changes ...

Methodology for Developing Life Tables for Sessile Insects in the Field Using the Whitefly, Bemisia tabaci, in Cotton As a Model System

Life tables provide a means of measuring the schedules of birth and death from populations over time. They also can be used to quantify the sources and rates of mortality in populations, which has a variety of applications in ecology, including agricultural ecosystems. Horizontal, or cohort-based, life tables provide for the most direct and accurate method of quantifying vital population rates because they follow a group of individuals in a population from birth to death. Here, protocols are presented for conducting and analyzing cohort-based life tables in the field that takes advantage of the sessile nature of the immature life stages of a global insect pest, Bemisia tabaci. Individual insects are located on the underside of cotton leaves and are marked by drawing a small circle around the insect with a non-toxic pen. This insect can then be observed repeatedly over time with the aid of hand lenses to measure development from one stage to the next and to identify stage-specific causes of death associated with natural and introduced mortality forces. Analyses explain how to correctly measure multiple mortality forces that act contemporaneously within each stage and how to use such data to provide meaningful population dynamic metrics. The method does not directly account for adult survival and reproduction, which limits inference to dynamics of immature stages. An example is presented that focused on measuring the impact of bottom-up (plant quality) and top-down (natural enemies) effects on the mortality dynamics of B. tabaci in the cotton system.

Methodology for Developing Life Tables for Sessile Insects in the Field Using the Whitefly, Bemisia tabaci, in Cotton As a Model System

Life tables allow quantification of the sources and rates of mortality in insect populations and contribute to understanding, predicting and manipulating population dynamics in agroecosystems. Methods for conducting and analyzing cohort-based life tables in the field for an insect with sessile immature life stages are presented.

Life tables provide a means of measuring the schedules of birth and death from populations over time. They also can be used to quantify the sources and ...

Techniques for Investigating the Anatomy of the Ant Visual System

This article outlines a suite of techniques in light microscopy (LM) and electron microscopy (EM) which can be used to study the internal and external eye anatomy of insects. These include traditional histological techniques optimized for work on ant eyes and adapted to work in concert with other techniques such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM). These techniques, although vastly useful, can be difficult for the novice microscopist, so great emphasis has been placed in this article on troubleshooting and optimization for different specimens. We provide information on imaging techniques for the entire specimen (photo-microscopy and SEM) and discuss their advantages and disadvantages. We highlight the technique used in determining lens diameters for the entire eye and discuss new techniques for improvement. Lastly, we discuss techniques involved in preparing samples for LM and TEM, sectioning, staining, and imaging these samples. We discuss the hurdles that one might come across when preparing samples and how best to navigate around them.

This article outlines a suite of techniques in light and electron microscopy to study the internal and external eye anatomy of insects. These include several traditional techniques optimized for work on ant eyes, detailed troubleshooting, and suggestions for optimization for different specimens and regions of interest.

This article outlines a suite of techniques in light microscopy (LM) and electron microscopy (EM) which can be used to study the internal and external eye ...

A Flexible Low Cost Hydroponic System for Assessing Plant Responses to Small Molecules in Sterile Conditions

A wide range of studies in plant biology are performed using hydroponic cultures. In this work, an in vitro hydroponic growth system designed for assessing plant responses to chemicals and other substances of interest is presented. This system is highly efficient in obtaining homogeneous and healthy seedlings of the C3 and C4 model species Arabidopsis thaliana and Setaria viridis, respectively. The sterile cultivation avoids algae and microorganism contamination, which are known limiting factors for plant normal growth and development in hydroponics. In addition, this system is scalable, enabling the harvest of plant material on a large scale with minor mechanical damage, as well as the harvest of individual parts of a plant if desired. A detailed protocol demonstrating that this system has an easy and low-cost assembly, as it uses pipette racks as the main platform for growing plants, is provided. The feasibility of this system was validated using Arabidopsis seedlings to assess the effect of the drug AZD-8055, a chemical inhibitor of the target of rapamycin (TOR) kinase. TOR inhibition was efficiently detected as early as 30 min after an AZD-8055 treatment in roots and shoots. Furthermore, AZD-8055-treated plants displayed the expected starch-excess phenotype. We proposed this hydroponic system as an ideal method for plant researchers aiming to monitor the action of plant inducers or inhibitors, as well as to assess metabolic fluxes using isotope-labeling compounds which, in general, requires the use of expensive reagents.

A simple, versatile, and low-cost in vitro hydroponic system was successfully optimized, enabling large-scale experiments under sterile conditions. This system facilitates the application of chemicals in a solution and their efficient absorption by roots for molecular, biochemical, and physiological studies.