Components of plant cell walls can induce a bacterium that is used as a plant fertilizer to assemble itself into sticky mats known as biofilms.

Biofilms are often associated with hard-to-treat infections in animals, but those formed by the soil bacterium Bacillus subtilis actually protect plants from pathogens. A team led by Roberto Kolter at Harvard Medical School in Boston, Massachusetts, reports how signals from the roots of the model plant Arabidopsis thaliana prompt bacteria to join up. Pectin and other polysaccharides on the surface of plant cell walls activate bacterial genes known to induce biofilms. The polysaccharides also form the raw materials that bacteria use to synthesize the extracellular matrix that holds the biofilm together. The plant, therefore, provides both the environmental cue and the building blocks to promote beneficial colonization of its roots.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1218984110 (2013)