Title: Regulatory pathways governing biofilm formation in Bacillus subtilis
Description: Microbes have been traditionally viewed as unicellular organisms that lead a solitary existence. However, social behaviors and multicellular lifestyles have been discovered in numerous microbial species. Currently, it is thought that bacteria in nature primarily exist in surface-attached multicellular communities or biofilms. One of the hallmarks of biofilm formation is the production of an extracellular matrix, which allows cells to adhere to a surface and to one another. Recently, it was discovered that undomesticated strains of B. subtilis are capable of forming architecturally complex biofilms. In this work, I attempted to identify and characterize genes involved in the formation of multicellular communities in B. subtilis . Biofilm formation in B. subtilis requires the production of an extracellular matrix which is composed of polysaccharides and proteins. The epsA-O operon is required for the biosynthesis of the exopolysaccharide component of the biofilm matrix. Here, I present evidence that the major protein component of the B. subtilis extracellular matrix is a secreted protein, TasA. I discovered that the two other members of the tasA operon, yqxM and sipW , are also required for biofilm formation. In keeping with the idea that exopolysaccharide and TasA compose a matrix material that is external to the cell, a mixture of eps operon mutant cells and tasA mutant cells exhibits efficient extracellular complementation.

Biofilm formation in B. subtilis is a highly regulated process involving multiple signaling pathways and numerous transcriptional control proteins. I show that the eps and tasA operons are negatively regulated by two repressors, the master regulator for biofilm formation, SinR, and the transition state regulator AbrB. SinR represses transcription of the eps and tasA operons by binding directly to the promoter regions of both operons. AbrB also inhibits the transcription of both operons but does so in part indirectly. Finally, I describe a regulatory loop governing tasA operon expression. I show that SinR and AbrB negatively regulate the expression of a sinR -like gene called slr , whose product is required for efficient expression of the tasA operon. My investigation has revealed that biofilm formation in B. subtilis is regulated by intricate pathways of gene control.