Not so simple, not so subtle: the interspecies competition between Bacillus simplex and Bacillus subtilis and its impact on the evolution of biofilms

Abstract

Bacillus subtilis biofilms have a fundamental role in shaping the soil ecosystem. During this process, they unavoidably interact with neighbour bacterial species. We studied the interspecies interactions between biofilms of the soil-residing bacteria B. subtilis and related Bacillus species. We found that proximity between the biofilms triggered recruitment of motile B. subtilis cells, which engulfed the competing Bacillus simplex colony. Upon interaction, B. subtilis secreted surfactin and cannibalism toxins, at concentrations that were inert to B. subtilis itself, which eliminated the B. simplex colony, as well as colonies of Bacillus toyonensis. Surfactin toxicity was correlated with the presence of short carbon-tail length isomers, and synergistic with the cannibalism toxins. Importantly, during biofilm development and interspecies interactions a subpopulation in B. subtilis biofilm lost its native plasmid, leading to increased virulence against the competing Bacillus species. Overall, these findings indicate that genetic programs and traits that have little effect on biofilm development when each species is grown in isolation have a dramatic impact when different bacterial species interact.

Applying the handicap principle to biofilms: condition‐dependent signalling inBacillus subtilismicrobial communities

“…Surfactin induces potassium‐selective pore formation in the cell membrane (Sheppard et al ., ); moreover, its signalling function is mediated by its toxicity, through the response to potassium leakage (López et al ., ). These properties are also crucial for its non‐signalling roles: surfactin facilitates expansion of the biofilm by lowering surface tension (Angelini et al ., ; van Gestel et al ., ) and may also serve as a means of predation in interspecies competition (Rosenberg et al ., ). It has been suggested that surfactin producers are immune to its effects, as these cells do not differentiate into matrix producers (López et al ., ).…”

“…Cannibalism has been considered a pathway by which cells which have not yet sporulated may defer committing to sporulation by accruing nutrients from lysed neighbouring cells (López et al ., ). The cannibalism toxins have also been proposed to have a role in interspecies competition, along with surfactin (Rosenberg et al ., ). Similarly to surfactin, these toxins can serve to eliminate the most vulnerable cells.…”

“…It has been suggested that surfactin producers are immune to its effects, as these cells do not differentiate into matrix producers (López et al ., ). Interestingly, B. subtilis appears to be more resistant to its effects than other Bacillus species (Rosenberg et al ., ), possibly due to modifications of the cell membrane (Seydlová et al ., ). Similar interactions may occur between neighbouring cells, through the inhibition of surfactin production in cells with lower immunity, in a form of localized competition within the biofilm.…”

“…Similar interactions may occur between neighbouring cells, through the inhibition of surfactin production in cells with lower immunity, in a form of localized competition within the biofilm. As surfactin can be toxic at high concentrations to B. subtilis itself (Rosenberg et al ., ), it is feasible that it also serves as a local selective force in two complementary levels. The first is the induction of lysis of the most vulnerable cells in the culture.…”

From one species to another: A review on the interaction between chemistry and microbiology in relation to cleaning in the built environment

“…108 Bacilli are capable of degrading organic materials, ammonia, sulfides, and more, 109 and some are capable of producing surfactants which can disrupt a variety of biological and synthetic oils. 106,111,112 They may also compete with other common environmental bacteria and fail to persist on a surface, 113 potentially requiring continuous or frequent application. 106,111,112 They may also compete with other common environmental bacteria and fail to persist on a surface, 113 potentially requiring continuous or frequent application.…”