Gluconate acts as a signal to induce biofilm in Bacillus subtilis.

Bacillus subtilis is the best-studied Gram-positive microorganism, but little is known about how the presence and utilization of diverse carbon sources impacts its production of biofilm. Here, we have identified gluconate as a carbon source that induces biofilm wrinkling in B. subtilis colony biofilms. Targeted phenotypic analysis revealed that the genes encoding the canonical structural biofilm components ( tasA , epsA-O , and bslA ) are required for this response. Import and metabolism of gluconate, however, are not required to induce these phenotypic changes. We show that the effect of gluconate on B. subtilis is linked to iron availability: production of the siderophore bacillibactin is decreased by gluconate and B. subtilis mutants unable to import bacillibactin grow better and wrinkle more in the presence of gluconate. In addition, supplementation of single-carbon media with iron dramatically increased growth and wrinkling of a B. subtilis bacillibactin mutant grown on gluconate but did not impact B. subtilis grown on glucose. We conclude that gluconate acts as a signal to increase biofilm in B. subtilis and increases iron availability in a bacillibactin-independent manner.