Halobacillus blutaparonensis Strain M9 as a Source of Extracellular Serine Peptidases with Properties for Biotechnological Purposes

Abstract

In this work, we report on the halophilic bacterium Halobacillus blutaparonensis strain M9, which was isolated from a preserved Brazilian restinga, as a producer of alkaline serine peptidases with potential application as additives for biotechnological purposes. Gelatin-zymography assay revealed the presence of the major peptidase of 70 kDa and two minor ones (50 and 40 kDa) secreted by the living bacterial cells. When a specific chromogenic substrate for chymotrypsin-type serine peptidases was employed by means of an in-solution assay, the bacterial peptidases were completely inhibited by phenylmethylsulphonyl fluoride (PMSF) and slightly inhibited by benzamidine, N-tosyl-L-lysine chloromethyl ketone (TLCK) and 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF), which are classical serine peptidase inhibitors. The proteolytic activity remained extremely stable within a broad pH range (from 5.0 to 9.0) and also displayed moderate thermostability. In addition, the effects of osmolytes/polyols, divalent cations, denaturing agents, and detergents on the enzymatic activity and stability of these serine peptidases were tested. The proteolytic activity increased in the presence of different osmolytes/polyols (e.g., glycerol, glutamate, and mannitol). The enzymatic activity increased to 110% when incubated in the presence of 10 mM Ca2+, while Mg2+ and Mn2+ (both at 10 mM) decreased the proteolytic activity to 95 and 85%, respectively. Interestingly, urea at 1% induced a significant increase (around 160%) in the proteolytic activity. The peptidases showed high stability when incubated with various detergent agents and commercial detergent powders. Collectively, all these properties indicate H. blutaparonensis as a producer of extracellular serine peptidases with possible industrial applications, such as in detergent formulations.