Screening and characterization for cold-active protease-producing bacteria from Bikal Lake

Abstract

The Korea Polar Research Institute (KOPRI) had collected heterotrophic bacterial strains from water and ice of Baikal Lake. To identify excellent protease-producers among the bacterial collection (50 strains), 43 strains were examined for their extracellular protease activity on R2A plates supplemented with 1% skim milk at various temperatures (4-20 C). This rapid and direct screening method permitted the selection of a small group of 3 cold-adapted bacterial strains that showed proteolytic activities even at low temperature of 4oC. The cold-active proteases from these strains exhibited relative activities of 32%, 19%, and 15% at 5 C, respectively, compared to 100% activity at an optimal temperature of 40oC, and the molecular weights of the proteases were all estimated to be 75,000 Da by zymography. The proteases were classified into four categories (serine protease, aspartic protease, cysteine protease, and metalloprotease) according to the extent of enzymatic inhibition by a class-specific protease inhibitor. Since highly active and/or cold-adapted proteases have a potential for industrial or commercial enzymes, the protease-producing bacteria selected in this work will be studied as a valuable natural source for new proteases. This work was supported by a grant to KOPRI (PE11060).