Bacillus subtilis ensures high spore quality in competition with Salmonella Typhimurium via the SigB-dependent pathway.

The interactions between beneficial bacteria and pathogens are understudied. Here we investigate the interactions between the probiotic strain Bacillus subtilis PS-216 and the pathogen Salmonella Typhimurium SL1344. We show here that the sporulation of B. subtilis is impaired when it competes with S. Typhimurium in a nutrient-depleted medium. The sporulation impairment in B. subtilis is mediated by the sigma factor B (SigB)-dependent general stress response, as the ΔsigB mutant remains blind to manipulative cues from S. Typhimurium. Furthermore, we show that decreased sporulation frequency in B. subtilis depends on cell-cell contact between the two species involving the S. Typhimurium Type VI Secretion System, whereas B. subtilis uses the SigB-dependent response to trade spore quantity for higher spore quality.