Noam Eckshtain-Levi, Susanna Leigh Harris, Reizo Quilat Roscios, and Elizabeth Anne Shank

APS Publications; Published Online:20 Oct 2020https://doi.org/10.1094/PBIOMES-02-20-0019-R

Abstract

Plant-growth-promoting bacteria (PGPB) are used to improve plant health and promote crop production. However, because some PGPB (including Bacillus subtilis) do not maintain substantial colonization on plant roots over time, it is unclear how effective PGPB are throughout the plant growing cycle. A better understanding of the dynamics of plant root community assembly is needed to develop and harness the potential of PGPB. Although B. subtilis is often a member of the root microbiome, it does not efficiently monoassociate with plant roots. We hypothesized that B. subtilis may require other primary colonizers to efficiently associate with plant roots. We utilized a previously designed hydroponic system to add bacteria to Arabidopsis thaliana roots and monitor their attachment over time. We inoculated seedlings with B. subtilis and individual bacterial isolates from the native A. thaliana root microbiome either alone or together. We then measured how the coinoculum affected the ability of B. subtilis to colonize and maintain on A. thaliana roots. We screened 96 fully genome-sequenced strains and identified five bacterial strains that were able to significantly improve the maintenance of B. subtilis. Three of these rhizobacteria also increased the maintenance of two strains of B. amyloliquefaciens commonly used in commercially available bioadditives. These results not only illustrate the utility of this model system to address questions about plant–microbe interactions and how other bacteria affect the ability of PGPB to maintain their relationships with plant roots but also may help inform future agricultural interventions to increase crop yields.

See: https://apsjournals.apsnet.org/doi/10.1094/PBIOMES-02-20-0019-R

Figure 4: A, Distributions of Bacillus subtilis on the lower regions of plant roots following colonization (top) and maintenance (bottom) when inoculated either alone or with the indicated strains. Fluorescent cells were false colored yellow in both the DIC-fluorescent image overlays and the fluorescent images. Images from each section were collected from at least two technical replicates of three independent biological replicates of these experiments. Bar = 50 µm. B, Plant root attachment of B. subtilis following colonization (0 days) and maintenance (1 and 3 days) is increased by cocolonization with either ES981, ES1063, or ES1084. Differences in B. subtilis CFU per seedling when coinoculated with another strain are reported as log-fold changes compared with the average B. subtilis CFU per seedling of three replicates in the same biological experiment. Error bars = standard error of the mean; *, **, and *** indicate P < 0.05, 0.01, and 0.001, respectively.