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>

The authors have nothing to disclose.

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

7.0K visualizações.  Tufts University. Usando este protocolo, podemos abordar questões-chave sobre como os micróbios se reúnem e interagem na filosfera. Tem o benefício adicional de que, usando o extrato vegetal estéril, podemos vincular a estrutura das comunidades da esfera phyllo à sua função durante a fermentação vegetal. Essas técnicas permitem que os cientistas testem como micróbios interagem na esfera phyllo e, em seguida, rastreiem como essas comunidades da esfera filo podem impactar a fermentação.Para ...