Aminopeptidase Activity of Haloalkalophilic Bacteria of the Genus Halomonas Isolated from the Soda-Saline Lakes in the Badain Jaran Desert

Abstract

Three strains of haloalkaliphilic bacteria were isolated from microbial mats of soda-saline lakes of the Badain Jaran Desert, Inner Mongolia (China). Based on the data on ribosomal phylogeny, they were identified as members of the genus Halomonas. These bacteria were moderate alkaliphiles and extreme halophiles. The peptidases secreted by these bacteria were shown to have narrow substrate specificity. They hydrolyzed proteins and para-nitroanilide substrates and showed maximal activity in the hydrolysis of L-leucyl-p-nitroanilides (LpNA). The maximum activity of the peptidases occurred at alkaline pH values (8–10) and elevated salinity (50–100 g/L); the enzymes were thermostable (up to 50°С). The results of inhibitor analysis and substrate specificity examination of extracellular enzymes indicated them to belong to the class of aminopeptidase-like metallopeptidases.