A Comparative secretome analysis of four Bacillus clausii strains

Bacillus species are frequently used as bacterial workhorses in industrial microbial cultivation for production of probiotic compounds and antibiotics. Bacterial secretory proteins are known to perform "remote-control" functions, such as the provision of nutrients, detoxification of the environment, and killing of potential competitors. A previous proteomic study carried out in our laboratory examined cell proteins extracted from four closely related isogenic B. Clausii strain, used to produce a commercial probiotic preparation and led to the recognition of a number of proteins differentially expressed in the four strains. Here, we report a proteomic study of the secretome, i.e. the complement of extracellular secreted proteins, of the four B. clausii strains. The main objective of this study was to characterize the proteins actively secreted including secreted enzyme that can be useful in industry and domestic life and metabolic bottlenecks that can contribute to improve process optimization of their production. The electropherogram of the four B. clausii secretomes show more than 400 protein spots separated by two-dimensional gel electrophoresis (2-DE). More pronounced differences were revealed at the expression level of specific proteins, some of which represent the most abundant secreted proteins. The different expression pattern of proteins in the four secretomes demonstrates that the B. clausii strains, which are characterized by a notable low level of intraspecific genome diversity, present distinct pattern of protein secretion.