Bacillus subtilis transcriptional regulators interaction

Bacillus subtilis aprE gene codes for the extracellular protease subtilisin. Its expression is controlled by AbrB, DegU, Hpr, SinI, SinR and Spo0A transition state protein regulators. To determine in vivo the protein-protein interactions among these regulators, we used the LexA-based bacterial genetic two-hybrid system. Our results show homo-dimerization to all the analyzed proteins and hetero-dimerization between SinR-SinI and SinR-Hpr.     

Effects of phosphorelay perturbations on architecture, sporulation, and spore resistance in biofilms of Bacillus subtilis

The spore-forming bacterium Bacillus subtilis is able to form highly organized multicellular communities called biofilms. This coordinated bacterial behavior is often lost in domesticated or laboratory strains as a result of planktonic growth in rich media for many generations. However, we show here that the laboratory strain B. subtilis 168 is still capable of forming spatially organized multicellular communities on minimal medium agar plates, exemplified by colonies with vein-like structures formed by elevated bundles of cells. In line with the current model for biofilm formation, we demonstrate that overproduction of the phosphorelay components KinA and Spo0A stimulates bundle formation, while overproduction of the transition state regulators AbrB and SinR leads to repression of formation of elevated bundles. Time-lapse fluorescence microscopy studies of B. subtilis green fluorescent protein reporter strains show that bundles are preferential sites for spore formation and that flat structures surrounding the bundles contain vegetative cells. The elevated bundle structures are formed prior to sporulation, in agreement with a genetic developmental program in which these processes are sequentially activated. Perturbations of the phosphorelay by disruption and overexpression of genes that lead to an increased tendency to sporulate result in the segregation of sporulation mutations and decreased heat resistance of spores in biofilms. These results stress the importance of a balanced control of the phosphorelay for biofilm and spore development.     

The Biofilm Regulatory Network from Bacillus subtilis: A Structure-Function Analysis

Bacterial biofilms are notorious for their ability to protect bacteria from environmental challenges, most importantly the action of antibiotics. Bacillus subtilis is an extensively studied model organism used to understand the process of biofilm formation. A complex network of principal regulatory proteins including Spo0A, AbrB, AbbA, Abh, SinR, SinI, SlrR, and RemA, work in concert to transition B. subtilis from the free-swimming planktonic state to the biofilm state. In this review, we explore, connect, and summarize decades worth of structural and biochemical studies that have elucidated this protein signaling network. Since structure dictates function, unraveling aspects of protein molecular mechanisms will allow us to devise ways to exploit critical features of the biofilm regulatory pathway, such as possible therapeutic intervention. This review pools our current knowledge base of B. subtilis biofilm regulatory proteins and highlights potential therapeutic intervention points.     

Spo0A positively regulates epr expression by negating the repressive effect of co-repressors, SinR and ScoC, in Bacillus subtilis

Bacillus subtilis under nutritional deprivation exhibits several physiological responses such as synthesis of degradative enzymes, motility, competence, sporulation, etc. At the onset of post-exponential phase the global response regulator, Spo0A, directly or indirectly activates the expression of genes involved in the above processes. These genes are repressed during the exponential phase by a group of proteins called transition state regulators, e.g. AbrB, ScoC and SinR. One such post-exponentially expressed gene is epr, which encodes a minor extracellular serine protease and is involved in the swarming motility of B. subtilis. Deletion studies of the upstream region of epr promoter revealed that epr is co-repressed by transition state regulators, SinR and ScoC. Our study shows that Spo0A positively regulates epr expression by nullifying the repressive effect of co-repressors, SinR and ScoC. We demonstrate via in vitro mobility shift assays that Spo0A binds to the upstream region of epr promoter and in turn occludes the binding site of one of the co-repressor, SinR. This explains the mechanism behind the positive regulatory effect of Spo0A on epr expression.