Screening for Cold-Active Protease-Producing Bacteria from the Culture Collection of Polar Microorganisms and Characterization of Proteolytic Activities

Abstract

The Korea Polar Research Institute (KOPRI) has assembled a culture collection of cold-adapted bacterial strains from both the Arctic and Antarctic. To identify excellent protease-producers among the proteolytic bacterial collection (874 strains), 78 strains were selected in advance according to their relative activities and were subsequently re-examined for their extracellular protease activity on 0.1×ZoBell plates supplemented with 1% skim milk at various temperatures. This rapid and direct screening method permitted the selection of a small group of 15 cold-adapted bacterial strains,belonging to either the genus Pseudoalteromonas (13 strains) or Flavobacterium (2 strains), that showed proteolytic activities at temperatures ranging between 5-15？°C. The cold-active proteases from these strains 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 the potential for industrial or commercial enzyme development, the protease-producing bacteria selected in this work will be studied as a valuable natural source of new proteases. Our results also highlight the relevance of the Antarctic for the isolation of protease-producing bacteria active at low temperatures.