Abstract

A moderately halophilic bacterium, TKNR13-3, isolated from fermented shrimp paste (ka-pi) in Thailand was identified as Virgibacillus halodenitrificans based on its phenotypic and chemotaxonomic characteristics, 16S ribosomal ribonucleic acid (Rrna) gene sequence and deoxyribonucleic-deoxyribonucleic (DNA-DNA) relatedness. The strain TKNR13-3 produced substantial amount of extracellular protease.  Its protease production was maximum when grown in JCM No.377 medium without casamino acids but containing 2% (w/v) yeast extract and 5% (w/v) NaCl at 37°C, pH 6.5 for 3 days. The optimum pH, salt concentration and temperature for the protease activity were pH 8, 15% (w/v) NaCl and 60°C, respectively. Thus, the enzyme was salt-tolerant and slightly thermoalkaliphilic. The protease activity was strongly inhibited (77.62%) by chymostatin. Therefore, the protease of strain TKNR13-3 was serine protease type chymotrypsin. Activity stained-substrate gel of the crude protease indicated the presence of several proteases with the estimated molecular mass of 12, 21, 29, 39 and 49 kDa. 

Key words: Halophilic bacteria, Virgibacillus halodenitrificans, protease, fermented shrimp paste.