BIOFILMS COMPETE FOR ROOT SURFACE BY COORDINATING GLIDING MOTILITY AND POLYKETIDE SYNTHESIS

Plant roots harbor many bacterial species that are in constant competition over space and nutrients, and are frequently found to exist as micro-colonies or biofilms. Both the Gram-positive Bacillus subtilis and the Gram-negative Serratia plymuthica can form biofilms on plant roots, presenting an intriguing model system to explore interspecies interaction between biofilms. During the interaction, B. subtilis asymmetrically advances towards S. plymuthica, while activating non-ribosomal antibiotic synthesis and mining dead cell debris from the competing colony. Following this asymmetric expansion, cell-contact on the solid surface promoted engulfment and killing of the entire Serratia plymuthica population. Surprisingly, the movement towards and engulfment of Serratia colonies relied on the production of exopolysaccharides, which had been primarily described as a structural component of Bacillus biofilms. This unique multifactorial capacity of established B. subtilis biofilms to consume competing colonies was also apparent upon interaction with P. chlororaphis. Our results indicate a mechanism that allows biofilms of B. subtilis to overcome biofilms formed by Gram-negative bacteria during colonization of plants. Strikingly, the plant host produces a secondary metabolite that influences the efficiency of the killing by affecting the polyketides synthesis. These results suggest that the plant microbiome can be highly influenced by host dependent effects on bacterial antibiotic production.