Seasonal changes in peptidase activities and their properties in the surface water of Lake Shinryu

Abstract

Serial monthly peptidase activities were assayed in the surface water of Lake Shinryu, located in the Chugoku district of Japan, using artificial fluorescent peptidase substrates. The results indicated that the lake water had higher aminopeptidase activities than endopeptidase activities except in November and December, whereas lake water filtrated using membranes with a pore size of 0.2 lm showed higher endopeptidase activities than aminopeptidase activities from June to December, with peaks in June and November. The serial aminopeptidase activity profile was relatively similar to that of the chlorophyll-a concentration. The size distribution of aminopeptidase activities indicated that half of the total activity was retained in the fraction between 5 and 100 lm. These results suggest that phytoplankton participate in the digestion of peptides with aminopeptidase activities. Electrophoretic analysis detected the presence of three peptidase bands (1, 2, and 3) in the lake water that passed through the 0.2-lm membranes. Samples from June, September, and November dominantly contained these active bands in different electrophoretic profiles.

Different diversity-functioning relationship in lake and stream bacterial communities

“…The much higher rates of cellobiohydrolase and the cbh/phox and β‐xyl/β‐gluc ratios in stream communities indicate a preferential use of large polymeric carbon compounds (cellulose and hemicellulose decomposed respectively by the enzymes cellobiohydrolase and β‐xylosidase) probably derived from plant material (Artigas et al ., ; Sinsabaugh & Follstad Shah, ). In contrast, the rates of peptide degradation (leu‐aminopeptidase) were higher in lakes, suggesting a greater availability of high‐quality organic matter (providing C and N) probably derived from phytoplankton exudates or decaying cells (Debroas, ; Naito et al ., ). Lake bacteria in the water column communities showed an elevated phenol oxidase activity indicating the use of lignin compounds, such as those derived from decaying woody and plant material (Sinsabaugh, ).…”