Changes in Proteolytic Activities in Stored Seawater and Bacterial Isolates

Organic matter in the ocean water column is produced predominantly as high molecular weight matter that cannot be directly assimilated by bacteria. Consequently, bacterial extracellular ectoenzymes act in the processing of the polymer in the sea. Proteins are important substrates for bacterial growth and sources of organic carbon and nitrogen. However, little is known about the protein degradation process and the distribution of the proteolytic enzymes among the bacterial species in natural assemblages. In this study, we evaluated the potential activities of proteolytic enzymes in seawater and the isolated bacteria from seawater. Results on seawater showed that trypsin, chymotrypsin and aminopeptidase were most active whereas the elastase activity was weak. Enzyme activities during 112 days experiment showed that microbial activity acting in proteolysis process varies in many ways in seawater. Gammaproteobacteria, Alphaproteobacteria, Cytophaga-FlexibacterBacteroides and Betaproteobacteria were isolated from the stored seawater. Among the 52 isolates, Alpha-, Betaproteobacteria and Cytophaga-FlexibacterBacteroides showed highest activities in aminopeptidase whereas Gammaproteobacteria showed aminopeptidase and chymotrypsin activities, suggesting that different bacterial species produce different types of proteases. This study suggests different enzymes produced by diverse natural bacterial communities are acting in different reactions in the protein processing in sea.