Pectate lyases, amylases and xylanases are examples of probably the most ubiquitous hydrolytic enzymes secreted by Bacillus species (Priest, 1977; Tjalsma et al., 2004). Bacillus subtilis secretes at least seven different exoproteases including two major proteases (subtilisin and neutral metalloprotease E) and five minor proteases (bacillopeptidase F, Mpr, Epr Npr and Vpr) (Pero & Sloma, 1993, Table S1). These exoproteases digest proteins present in the environment, a response that is induced by low levels of available nitrogen (Hata et al., 2001).
Wild-type strains of B. subtilis that are deficient in the production of these extracellular proteolytic activities are also unable to swarm or form biofilms (Pero & Sloma, 1993; Connelly et al., 2004). The other active EPS category includes proteins learn more that interact with substrates of different chemical nature that can be secreted during nutrient deprivation. Bacillus subtilis strains secrete many proteins involved in the degradation of a variety of molecules such as lipids, glutathione, phytic acid and extracellular nucleic acids to cope with conditions of low nitrogen (Priest, 1977; Tjalsma et al., 2004). Among the proteins active in
the formation of the exopolymeric matrix, special attention needs to be drawn to the recently identified selleck kinase inhibitor TasA protein. This protein is encoded by tasA, a gene expressed at the onset of sporulation in B. subtilis (Branda et al., 2006). TasA is required for the structural integrity of the matrix as well as biofilm development: it has been proposed that TasA forms amyloid fibers that bind cells together in the biofilm (Romero et al., 2010). TasA localization within the exopolymeric matrix is dependent on a functional yqxM gene, but the
role of YqxM in biofilm development is still unknown, another area that requires further investigation (Branda et al., 2006). The presence and role of extracellular DNA in B. subtilis strains is another topic that is poorly understood. In the close relative Bacillus cereus, biofilm formation requires DNA as part of the extracellular polymeric matrix (Vilain et al., 2009). DNA in biofilms may be involved in events of recombination that take place in natural environments (Spoering & Gilmore, 2006). Further studies on extracellular Olopatadine DNA in B. subtilis biofilms will help elucidate its role in natural environments. Microorganisms in nature are subject to sudden changes in the environmental conditions such as nutrient deprivation, desiccation, osmotic stress, action of antibiotic molecules released by other microorganisms, UV radiation and temperature variations. Bacillus subtilis can survive these environmental fluctuations, which are typical for soils, through several defense mechanisms (Setlow, 1992). Although spore formation is the main mechanism for long-term survival for B.