Identification of novel halotolerant bacillopeptidase F-like proteinases from a moderately halophilic bacterium, Virgibacillus sp. SK37

Abstract

Virgibacillus sp. SK37 isolated from Thai fish sauce produced numerous NaCl-activated subtilisin-like proteinases. Our objectives were to purify, characterize and identify these extracellular proteinases. Three major subtilisin-like enzymes including 19, 34 and 44 kDa were partially purified and showed maximum activity at pH 8, 55-60°C, 25-30% NaCl and 70-100 mmol l(-1) CaCl(2) . Enzymes showed stability at 0-30% NaCl and <20 mmol l(-1) CaCl(2) and were completely inhibited by phenylmethanesulphonyl fluoride but not by ethylenediaminetetraacetic acid. The isoelectric points of 19-, 34- and 44-kDa proteinases were at 3·6, 5·2 and 3·8, respectively, based on 2D electrophoresis. Peptide mass fingerprint and de novo peptide homology analysis of tryptic peptides using MALDI-TOF and LC-MS/MS, respectively, suggested that all three enzymes were novel and homologous to bacillopeptidase F. The three major proteinases are a member of bacillopeptidase F-like enzymes exhibiting thermophilic and halotolerant characteristics with high stability at 30% NaCl. This is the first report on bacillopeptidase F-like proteinases in genus Virgibacillus with a distinct halotolerant feature. They showed potential to be a processing aid for food and biotechnological applications, particularly in high salt condition.