1Center for Marine Environmental Studies, Ehime University, Matsuyama, Ehime, Japan, 2Faculty of Engineering, Yokohama National University, Yokohama, Japan, 3Faculty of Life and Environmental Sciences (Bioindustrial Sciences), University of Tsukuba, Ibaraki, Japan
The biodegradation of proteins in the sea is thought to be mainly driven by bacteria. We here show that not only bacteria but also eukaryotic microbes are required for an efficient and rapid degradation of bacterial proteins in marine environments. Kinetic analysis of protein degradation was examined by microcosm experiment with addition of heat-killed Pseudomonas aeruginosa as proteinaceous substrates. Protease activities, protein concentrations, particulate and dissolved organic carbon concentrations, and protein composition profiles were monitored simultaneously in 7 microcosms subjected to different compositions of microbes. There was only an increase in protease activity in microcosms containing protists, suggesting that these protists were the source of the enzymes. Bacterial proteins were retained for 30 days in the presence of bacteria but protists, whereas the substrate proteins were completely disappeared in the presence of both bacteria and protists. This result suggests that the protein degradation requires bacteria and protists enzymes. In the process of the protein degradation, co-existence of bacteria and protists should accelerate the reminalization of organic matters in the marine ecosystem.
keywords:protein degradation,protease,protist,Pseudomonas aeruginosa,ciliate