Name: monitoring bacterial colonization and maintenance on arabidopsis thaliana roots in a floating hydroponic system
Uploaded: 2019-05-28T09:00:00
Description: Watch this Scientific Journal Video about Monitoring Bacterial Colonization and Maintenance on Arabidopsis thaliana Roots in a Floating Hydroponic System at JoVE.com

This work was supported by research funds provided by the Department of Energy Biological and Environmental Research (DOE-BER 0000217519 to E.A.S.), the National Science Foundation (INSPIRE IOS-1343020 to E.A.S). SLH was also supported by the National Science Foundation Graduate Research Fellowship Program. We thank Dr. Jeffery Dangl for providing bacterial strains and invaluable insight. We thank Dr. Andrew Klein and Matthew J. Powers for experimental suggestions. Finally, SLH would like to thank connections on social media for reminding us that disseminating science is a privilege and a responsibility, especially through creative and accessible means.

NOTE: The experimental setup is described for clarity and used to generate the representative results included in this report, but conditions can be modified as desired. All steps should be performed using PPE and following institutional and federal reccomendations for safety, according to the BSL status of the bacteria used.
1. Characterization of bacteria
<ol>
	<li>Determine the morphology of bacteria on the growth medium agar plate. Resuspend cells at an approximate OD600 = 0.5...

<ol>
	<li>Strange, R. N., Scott, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+disease:+a+threat+to+global+food+security.">Plant disease: a threat to global food security.</a> Annual Review of Phytopathology. 43, 83-116 (2005).</li><li>Cook, A. M., Grossenbacher, H., H&#252;tter, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+cultivation+of+microbes+with+biodegradative+potential.">Isolation and cultivation of microbes with biodegradative potential.</a> Experientia. 39 (11), 1191-1198 (1983).</li><li>Vacheron, J., 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=Plant+growth-promoting+rhizobacteria+and+root+system+functioning.">Plant growth-promoting rhizobacteria and root system functioning.</a> Fronteirs in Plant Science. 4, 356 (2013).</li><li>Backer, 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=Plant+Growth-Promoting+Rhizobacteria:+Context,+Mechanisms+of+Action,+and+Roadmap+to+Commercialization+of+Biostimulants+for+Sustainable+Agriculture.">Plant Growth-Promoting Rhizobacteria: Context, Mechanisms of Action, and Roadmap to Commercialization of Biostimulants for Sustainable Agriculture.</a> Fronteirs in Plant Science. 9, 1473 (2018).</li><li>Zamioudis, C., Pieterse, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modulation+of+host+immunity+by+beneficial+microbes.">Modulation of host immunity by beneficial microbes.</a> Molecular Plant-Microbe Interactions. 25 (2), 139-150 (2012).</li><li>Kr&#246;ber, 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=Effect+of+the+strain+Bacillus+amyloliquefaciens+FZB42+on+the+microbial+community+in+the+rhizosphere+of+lettuce+under+field+conditions+analyzed+by+whole+metagenome+sequencing.">Effect of the strain Bacillus amyloliquefaciens FZB42 on the microbial community in the rhizosphere of lettuce under field conditions analyzed by whole metagenome sequencing.</a> Frontiers in Microbiology. 5, 252 (2014).</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>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 USA. 114 (12), E2450-E2459 (2017).</li><li>Richter-Heitmann, T., Eickhorst, T., Knauth, S., Friedrich, M. W., Schmidt, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+Strategies+to+Separate+Root-Associated+Microbial+Communities:+A+Crucial+Choice+in+Rhizobiome+Research.">Evaluation of Strategies to Separate Root-Associated Microbial Communities: A Crucial Choice in Rhizobiome Research.</a> Frontiers in Microbiology. 7, 773 (2016).</li><li>Shank, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+coculture+to+detect+chemically+mediated+interspecies+interactions.">Using coculture to detect chemically mediated interspecies interactions.</a> Journal of Visual Experiments. (80), e50863 (2013).</li><li>Woodward, A. W., Bartel, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biology+in+Bloom:+A+Primer+on+the+Arabidopsis+thaliana+Model+System.">Biology in Bloom: A Primer on the Arabidopsis thaliana Model System.</a> Genetics. 208 (4), 1337-1349 (2018).</li><li>Alatorre-Cobos, F., 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=An+improved,+low-cost,+hydroponic+system+for+growing+Arabidopsis+and+other+plant+species+under+aseptic+conditions.">An improved, low-cost, hydroponic system for growing Arabidopsis and other plant species under aseptic conditions.</a> BMC Plant Biology. 14, 69 (2014).</li><li>Haney, C. H., Samuel, B. S., Bush, J., Ausubel, F. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Associations+with+rhizosphere+bacteria+can+confer+an+adaptive+advantage+to+plants.">Associations with rhizosphere bacteria can confer an adaptive advantage to plants.</a> Nature Plants. 1 (6), (2015).</li><li>Massalha, H., Korenblum, E., Malitsky, S., Shapiro, O. H., Aharoni, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Live+imaging+of+root-bacteria+interactions+in+a+microfluidics+setup.">Live imaging of root-bacteria interactions in a microfluidics setup.</a> Proceedings of the National Academy of Sciences USA. 114 (17), 4549-4554 (2017).</li><li>Townsley, L., Yannarell, S. M., Huynh, T. N., Woodward, J. J., Shank, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclic+di-AMP+Acts+as+an+Extracellular+Signal+That+Impacts.">Cyclic di-AMP Acts as an Extracellular Signal That Impacts.</a> MBio. 9 (2), (2018).</li><li>Beauregard, P. B., Chai, Y., Vlamakis, H., Losick, R., 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=Bacillus+subtilis+biofilm+induction+by+plant+polysaccharides.">Bacillus subtilis biofilm induction by plant polysaccharides.</a> Proceedings of the National Academy of Sciences U S A. 110 (17), E1621-E1630 (2013).</li><li>Matthysse, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adherence+of+Bacteria+to+Plant+Surfaces+Measured+in+the+Laboratory.">Adherence of Bacteria to Plant Surfaces Measured in the Laboratory.</a> Journal of Visual Experiments. 136 (136), (2018).</li><li>Garcia-Betancur, J. C., Yepes, A., Schneider, J., Lopez, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-cell+analysis+of+Bacillus+subtilis+biofilms+using+fluorescence+microscopy+and+flow+cytometry.">Single-cell analysis of Bacillus subtilis biofilms using fluorescence microscopy and flow cytometry.</a> Journal of Visual Experiments. (60), (2012).</li><li>Cole, B. J., 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=Genome-wide+identification+of+bacterial+plant+colonization+genes.">Genome-wide identification of bacterial plant colonization genes.</a> PLoS Biology. 15 (9), e2002860 (2017).</li><li>Lundberg, D. 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=Defining+the+core+Arabidopsis+thaliana+root+microbiome.">Defining the core Arabidopsis thaliana root microbiome.</a> Nature. 488 (7409), 86-90 (2012).</li><li>Grandchamp, G. M., Caro, L., Shank, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pirated+Siderophores+Promote+Sporulation+in+Bacillus+subtilis.">Pirated Siderophores Promote Sporulation in Bacillus subtilis.</a> Applied Environmental Microbiology. 83 (10), (2017).</li><li>Gange, A. C., Gadhave, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+growth-promoting+rhizobacteria+promote+plant+size+inequality.">Plant growth-promoting rhizobacteria promote plant size inequality.</a> Science Reports. 8 (1), 13828 (2018).</li><li>Levy, A., 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=Genomic+features+of+bacterial+adaptation+to+plants.">Genomic features of bacterial adaptation to plants.</a> Nature Genetics. 50 (1), 138-150 (2018).</li><li>Mart&#237;nez-Hidalgo, P., Maymon, M., Pule-Meulenberg, F., Hirsch, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+root+microbiomes+for+healthier+crops+and+soils+using+beneficial,+environmentally+safe+bacteria.">Engineering root microbiomes for healthier crops and soils using beneficial, environmentally safe bacteria.</a> Canada Journal of Microbiology. , 1-14 (2018).</li><li>Niu, B., 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=Quantification+of+the+Composition+Dynamics+of+a+Maize+Root-associated+Simplified+Bacterial+Community+and+Evaluation+of+Its+Biological+Control+Effect.">Quantification of the Composition Dynamics of a Maize Root-associated Simplified Bacterial Community and Evaluation of Its Biological Control Effect.</a> Bio Protocol. 8 (12), (2018).</li></ol>

Plants in all environments interact with thousands to millions of different bacteria and fungi5,7. These interactions can either negatively and positively impact plant health, with potential effects on crop yield and food production. Recent work also suggests that variable colonization of crops by PGPBs may account for unpredictable plant size and crop yield in field trials22. Understanding the mechanisms behind these interactions might al...

Crop destruction by bacterial and fungal diseases results in lowered food production and can severely disrupt global stability1. Based on the discovery that microbes in suppressive soils are responsible for increasing plant health2, scientists have asked whether the plant microbiome can be leveraged to support plant growth by modifying the presence and abundance of particular bacterial species3. Bacteria found to aid in plant growth or development are collectively termed plant growth-promoting bacteria (PGPB). More recently, studies have shifted from simply identifying potential PGPB to understanding how interkingdom interactions in the soil, around roots, or in the rhizosphere (the area directly surrounding and including the root surface) may be impacting PGPB activity4.
Rhizosphere colonization by PGPB can increase the health or the development of host plants in response to diverse stressors relative to uncolonized plants5. However, results are often more variable in native soil conditions compared to those observed in the closely controlled greenhouse and laboratory settings6. One hypothesis for this difference is that the growth or behavior of PGPB may be inhibited by native soil bacteria or fungi in the fields7,8. Beneficial effects by rhizosphere bacteria generally depend on the ability of the bacteria to 1) locate and move towards the root, 2) colonize the root through biofilm formation, and 3) interact with the host plant or pathogens via production of small molecule metabolites7,9. Any of these colonization behaviors may be affected by the presence and activity of neighboring microbes10.
We designed a system to quantify and visualize these distinct bacterial colonization stages of the rhizosphere (Figure 1). This approach will facilitate studies investigating why long-term PGPB maintenance is sometimes not observed following transfer of plants into new environments, such as during the planting of pre-inoculated seedlings. Arabidopsis thaliana as were chosen as a plant model due to its extensive use in laboratory studies as well as the ample data available about its microbial interactions11. There are three stages in the system: 1) A. thaliana growth, 2) bacterial colonization, and 3) bacterial maintenance (see Figure 1). Because A. thaliana is a terrestrial plant, it was important to ensure that it was not suffering undue water stress in the hydroponic system12. Inspired by the methods used by Haney et al.13, the seedlings are grown on plastic mesh to separate the shoot from the liquid growth medium. This system does not appear to compromise the health and development of the plant host, and it improves A. thaliana growth in liquid11. As the plant shoot floats above the surface, the roots are fully exposed to colonization by bacteria inoculated into the liquid bacterial growth medium. This permits bacteria of interest to be examined for colonization in nutrients that are most conducive to growth, while then shifting conditions to allow the plant to continue growing in a nutrient medium designed to support its growth. Both stages include steady shaking to prevent anoxia of the root13. Bacteria can be visualized or quantified from the plant roots following transfer from either the colonization medium or the maintenance medium. This hydroponic system is very flexible, allowing experimental conditions and applied stresses to be easily altered depending on interests of the researchers.
This described method is important in the context of the larger body of literature about plant-microbe interactions because it provides a robust system for studying these interactions at the root surface while also being customizable to the growth preferences of different bacteria. Plant biology labs often perform plant-microbe colonization experiments on solid agar, allowing for only planar movement (if that) of bacteria while also requiring the potentially destructive manipulation of plants during subsequent transfer. In contrast, microbiology labs have frequently prioritized the health of the bacteria within their experiments, to the detriment of the plants14,15. These different priorities of plant- and microbiology-focused labs have historically made it difficult to compare results between these groups, since each typically optimizes experimental conditions to optimize their organism of interest15.&#160;The floating-mesh-plant-growth system described here prevents full plant submersion, a notable advantage to previous microbiology-oriented studies, while also temporarily optimizing the growth and survival of bacteria to facilitate colonization. Thus, the assay we present here may address concerns from both plant biologists (about over-hydration and tactile manipulation of the plant) while satisfying the criteria of microbiologists (allowing for different bacterial growth conditions and multiple species&#8217; interactions)7. This protocol is designed to be adaptable for use with various bacteria, plants, and environmental conditions.

<table>
	<tbody>
		<tr>
			<td>Required Materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL eppendorf tubes</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>24-well plates</td>
			<td>BD Falcon</td>
			<td>1801343</td>
			<td></td>
		</tr>
		<tr>
			<td>Aeraseal</td>
			<td>Excel Scientific</td>
			<td>BE255A2</td>
			<td></td>
		</tr>
		<tr>
			<td>Autoclave</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacteria of Interest</td>
			<td>any</td>
			<td>N/A</td>
			<td>Stored at -80&#730;C in 40% glycerol preferred</td>
		</tr>
		<tr>
			<td>BactoAgar</td>
			<td>BD</td>
			<td>2306428; REF 214010</td>
			<td></td>
		</tr>
		<tr>
			<td>bleach</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Conviron</td>
			<td>any</td>
			<td>N/A</td>
			<td>Short Day Light-Dark Cycles: 460-600 &#181;moles/m&#178;/s set at 9/15 hours light/dark at 18/21&#730;C, with inner power outlet</td>
		</tr>
		<tr>
			<td>Dessicator Jar: glass or heavy plastic</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Flame</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Incubator</td>
			<td>any</td>
			<td>N/A</td>
			<td>At optimal temperature for growth of specified bacteria</td>
		</tr>
		<tr>
			<td>Hydrochloric Acid</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Lennox LB Broth</td>
			<td>RPI</td>
			<td>L24066-1000.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropipetters</td>
			<td>any</td>
			<td>N/A</td>
			<td>Volumes 5 &#181;L to 1000 &#181;L</td>
		</tr>
		<tr>
			<td>Microscope (preferably fluorescence)</td>
			<td>any</td>
			<td>N/A</td>
			<td>Could be light if best definition not important</td>
		</tr>
		<tr>
			<td>MS Salts + MES</td>
			<td>RPI</td>
			<td>M70300-50.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Orbital Plate Shaker</td>
			<td>any</td>
			<td>N/A</td>
			<td>Capable of running at 220 rpm for at least 96 hours</td>
		</tr>
		<tr>
			<td>Petri Dishes</td>
			<td>any</td>
			<td>N/A</td>
			<td>50 mL total volume</td>
		</tr>
		<tr>
			<td>Reservoirs</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Spectrophotometer</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Standard Hole Punch</td>
			<td>any</td>
			<td>N/A</td>
			<td>Approximately 7mm punch diameter</td>
		</tr>
		<tr>
			<td>Sterile water</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical Tape</td>
			<td>3M</td>
			<td>MMM1538-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Teflon Mesh</td>
			<td>McMaster-Carr</td>
			<td>1100t41</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasonicator</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex Mixer</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>X-gal</td>
			<td>GoldBio</td>
			<td>x4281c</td>
			<td>other vendors available</td>
		</tr>
		<tr>
			<td>Suggested Materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>24 Prong Ultrasonicator attachment</td>
			<td>any</td>
			<td>N/A</td>
			<td>For sonicating multiple samples at once. Can be done individually</td>
		</tr>
		<tr>
			<td>Alumaseal II</td>
			<td>Excel Scientific</td>
			<td>FE124F</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass beads</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Multipetter/Repetter</td>
			<td>any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile 96-well plates</td>
			<td>any</td>
			<td>N/A</td>
			<td>For serial dilutions. Can be replaced by eppendorf tubes</td>
		</tr>
		<tr>
			<td>Biological Materials Used</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Arabidopsis thaliana seeds</td>
			<td>any</td>
			<td>N/A</td>
			<td>We recommend Arabidopsis Biological Resource Center for seed stocks</td>
		</tr>
		<tr>
			<td>Arthrobacter nicotinovorans</td>
			<td></td>
			<td></td>
			<td>Levy, et al. 2018</td>
		</tr>
		<tr>
			<td>Curtobacterium oceanosedimentum</td>
			<td></td>
			<td></td>
			<td>Levy, et al. 2018</td>
		</tr>
		<tr>
			<td>Microbacterium oleivorans</td>
			<td></td>
			<td></td>
			<td>Levy, et al. 2018</td>
		</tr>
		<tr>
			<td>Pseudomonas simiae WCS417r</td>
			<td></td>
			<td></td>
			<td>Published in a similar system in Haney, et al. 2015. Strain used developed in Cole, et al. 2017</td>
		</tr>
	</tbody>
</table>

monitoring bacterial colonization and maintenance on arabidopsis thaliana roots in a floating hydroponic system

Bacteria form complex rhizosphere microbiomes shaped by interacting microbes, larger organisms, and the abiotic environment. Under laboratory conditions, rhizosphere colonization by plant growth-promoting bacteria (PGPB) can increase the health or the development of host plants relative to uncolonized plants. However, in field settings, bacterial treatments with PGPB often do not provide substantial benefits to crops. One explanation is that this may be due to loss of the PGPB during interactions with endogenous soil microbes over the lifespan of the plant. This possibility has been difficult to confirm, since most studies focus on the initial colonization rather than maintenance of PGPB within rhizosphere communities. It is hypothesized here that the assembly, coexistence, and maintenance of bacterial communities are shaped by deterministic features of the rhizosphere microenvironment, and that these interactions may impact PGPB survival in native settings. To study these behaviors, a hydroponic plant-growth assay is optimized using Arabidopsis thaliana to quantify and visualize the spatial distribution of bacteria during initial colonization of plant roots and after transfer to different growth environments. This system&#8217;s reproducibility and utility are then validated with the well-studied PGPB Pseudomonas simiae. To investigate how the presence of multiple bacterial species may affect colonization and maintenance dynamics on the plant root, a model community from three bacterial strains (an Arthrobacter, Curtobacterium, and Microbacterium species) originally isolated from the A. thaliana rhizosphere is constructed. It is shown that the presence of these diverse bacterial species can be measured using this hydroponic plant-maintanence assay, which provides an alternative to sequencing-based bacterial community studies. Future studies using this system may improve the understanding of bacterial behavior in multispecies plant microbiomes over time and in changing environmental conditions.

The well-characterized PGPB P. simiae WCS417r is known to colonize the roots of A. thaliana in hydroponic culture. This naturally fluorescent bacterium can easily be visualized using microscopy on the roots of seedlings following colonization (Figure 2). Although it is possible to image the full length of these A. thaliana seedlings&#8217; (4&#8211;6 mm length) roots, doing so for many plants would take a prohibitive amount of time....

Watch this Scientific Journal Video about Monitoring Bacterial Colonization and Maintenance on Arabidopsis thaliana Roots in a Floating Hydroponic System at JoVE.com

Monitoring Bacterial Colonization and Maintenance on Arabidopsis thaliana Roots in a Floating Hydroponic System

Here we describe a hydroponic plant growth assay to quantify species presence and visualize the spatial distribution of bacteria during initial colonization of plant roots and after their transfer into different growth environments.

Monitoring Bacterial Colonization and Maintenance on Arabidopsis thaliana Roots in a Floating Hydroponic System

Bacteria form complex rhizosphere microbiomes shaped by interacting microbes, larger organisms, and the abiotic environment. Under laboratory conditions, ...

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