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

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.