Comparative study of the role of surfactin-triggered signalling in biofilm formation among different Bacillus species.

The signal molecule surfactin in biofilm formation has been extensively studied in B. subtilis, but there is rare reports in other Bacillus species. In this study, we compared the surfactin-Spo0A-SinI-SinR/SlrR signalling in regulating biofilm formation amongst four Bacillus species including B. subtilis, B. amyloliquefaciens, B. velezensis, and B. licheniformis. The role of surfactin in biofilm formation was dependent on Bacillus species and strains, and the importance of surfactin was as following: B. velezensis R9 = B. amyloliquefaciens WH1 > B. licheniformis 285-3 > B. subtilis CYY. The global regulator Spo0A was essential and very conservative for biofilm formation in all four Bacillus species. The regulators SinI and SinR played different roles to regulate biofilm formation in different Bacillus species. SinI had no obvious roles in B. velezensis, B. amyloliquefaciens and B. subtilis but had a positive role in B. licheniformis. SinR had no obvious roles in B. subtilis, but played a positive role in B. velezensis, B. amyloliquefaciens and B. licheniformis. The regulator SlrR played a positive role in the biofilm formation of all four Bacillus species. Collectively, surfactin, Spo0A and SlrR are essential for the biofilm formation in all four Bacillus species, and SinR and SinI plays different roles in different Bacillus species.