Sequential secretion of collagenolytic, elastolytic, and keratinolytic proteases in peptide-limited cultures of two Bacillus cereus strains isolated from wool

To characterize the secretion of proteolytic activities against keratin, collagen and elastin in liquid cultures of Bacillus cereus IZ-06b and IZ-06r isolated from wool. Growth of B. cereus IZ-06b and IZ-06r were characterized in batch culture. Both strains needed an organic nitrogen source, were able to grow on wool or peptone as sole carbon and nitrogen sources, and metabolized glucose, maltose and other simple sugars. Proteolytic activities were investigated in batch cultures grown in peptide-restricted, carbon-sufficient medium. Secretion of proteases was induced by peptide limitation while different proteolytic activities appeared sequentially in the growth medium. When the most available components of the peptone were depleted, collagenolytic and elastolytic proteases were produced. These were later replaced by the production of keratinolytic protease. B. cereus can adjust its proteolytic affinity profile in response to the supply of organic nitrogen and sequentially secrete proteases with activities targeted against increasingly inaccessible proteinous substrates as the nutritional availability in the environment deteriorates. Peptide-limited, carbon-sufficient growth media containing no proteinous substrates are well suited for protease production in B. cereus while growth conditions can be adjusted to optimize the proteolytic affinity profiles.