Identifying key players within the plant microbiome involved in enhancing plant defense against pathogens.

Plant-associated microbial communities have been shown to confer multiple beneficial advantages to their host plants, such as nutrient acquisition, growth promotion, pathogen resistance, and environmental stress tolerance. To understand how microbes interact with their host from within the context of the complex community and improve plant tolerance to pathogens, I used a synthetic bacterial community (SynCom) composed of bacterial strains isolated from surface-sterilized Arabidopsis roots. I tested the interaction between SynCom bacteria and the pathogenic bacterium Pseudomonas syringae DC3000 both in vitro and in planta. I found that strains from the genus Bacillus exhibited a high level of inhibition against DC3000. Using a gnotobiotic plant growth system, I applied an iterative community deconstruction approach with the SynCom, starting with a full community and dropping-out taxonomic groups to assess their contribution to plant protection. I found that a complete SynCom provided full protection to the plant from pathogenic attack, but when Bacillus strains were removed from the community, this protection was diminished and the pathogen was able to colonize the leaves. Each one of the Bacillus strains alone was not sufficient to protect the plant, but rather a diverse set of Bacillus strains was needed. Further work is needed to investigate the mechanism of action behind Bacillus-mediated plant protection. This may potentially lead to the identification of novel genes that can be utilized for developing more effective plant protection strategies.