Bacillus subtilis is a Gram positive rhizobacterium, ubiquitous in soil and is known to form root-associated biofilms that protects plants against fungal and microbial infections. This bacterium is able to form endospores and produce different broad spectrum antibiotics.[1] It also has the capacity to promote plant growth. However, plant-bacteria signaling modules are still poorly characterized. B. subtilis is used as the model organism in this study, as it can differentiate into a large number of distinct cell types, (motile cells, rafts of swarmer cells, chains of non-motile cells, genetically competent cells, matrix-producing cells etc.)[2] This variability of different cell types and the availability of powerful methods of molecular genetics have made B. subtilis a highly informative model-system for determining how cells specialize, form a community, and switch back and forth between an individual lifestyle and a cooperative lifestyle. However, very little information is available regarding to how these behaviors are regulated when associated with the root.
Plants are able to biosynthesize and secrete various secondary metabolites, among them root derived indoles. Those indoles have a major role in plants development. In addition, they share high resemblance with known quorum sensing molecules. We used B. subtilis as a model to test whether these indoles are regulators of bacterial social behaviors. Using both synthetic chemistry and classic biology approaches, we found that B. subtilis social behaviors such as swarming, biofilm formation and resistance to antibiotics were all transcriptionally regulated by unique cluster of indole derived metabolites.
[1] I. Moszer, FEBS Lett. 1998, 430, 28.
[2] C. Aguilar, H. Vlamakis, R. Losick, R. Kolter, Curr. Opin. Microbiol. 2007, 10, 638.
