10:45 AM - 11:00 AM
[AOS20-01] Extracellular protease activities in the subarctic and subtropical western North Pacific
Keywords:Extracellular hydrolases activities, Microbial loop, Nutrient regeneration
Heterotrophic prokaryotes play important roles in marine ecosystem in terms of the main player in “microbial loop” and nutrient regeneration. Fresh bio-organic molecules, usually high-molecular weight molecules, could be good food for heterotrophic prokaryotes, however, those must be downsized extracellularly to smaller molecules prior to microbial uptake. For this purpose, extracellular hydrolytic enzymes were used. Proteases are the major extracellular hydrolytic enzymes detected in aquatic environment.
Although the subarctic and subtropical regions of the western North Pacific are known to differ in their characteristics of distribution of nutrients, main primary producers and primary production, there is not much information on the differences in organic matter metabolism by heterotrophic microorganisms.
During KH-23-3 Hakuho-maru cruise (July, 2023), extracellular protease activities (aminopeptidase and trypsin-type activity) in seawater were measured at subarctic (K2) and subtropical (KEO, S1, KEOS) stations in the western North Pacific. Aminopeptidase is an exo-type enzyme that cleaves amino acids from the N-terminus of a peptide chain, while trypsin is an endo-type enzyme that cleaves the inside of the peptide chain.
At the subarctic station K2, both extracellular protease activities were highest in the 0-10 m surface layer and decreased with depth. There was a positive correlation between protease activity and chlorophyll-a concentration, suggesting that organic matter decomposition activity is also higher in layers with higher primary production. At the subtropical stations KEO, S1, and KEOS, the activity in the surface layer was much lower than that in the subarctic layer, but increased with depth, reaching a maximum at subsurface (around 60 to 80 m), and decreasing with depth below that depth. The ratio of trypsin-type activity to aminopeptidase activity (T/A ratio) was higher in the subtropical than in the subarctic, and the T/A ratio was particularly high in the subtropical sub-surface layer. Moreover, the T/A ratio tended to be higher in the layer depleted of major nutrients. These results implied that efficient microbial metabolism using extracellular endo-type hydrolases by heterotrophic prokaryotes may support regenerative production under oligotrophic conditions.
Although the subarctic and subtropical regions of the western North Pacific are known to differ in their characteristics of distribution of nutrients, main primary producers and primary production, there is not much information on the differences in organic matter metabolism by heterotrophic microorganisms.
During KH-23-3 Hakuho-maru cruise (July, 2023), extracellular protease activities (aminopeptidase and trypsin-type activity) in seawater were measured at subarctic (K2) and subtropical (KEO, S1, KEOS) stations in the western North Pacific. Aminopeptidase is an exo-type enzyme that cleaves amino acids from the N-terminus of a peptide chain, while trypsin is an endo-type enzyme that cleaves the inside of the peptide chain.
At the subarctic station K2, both extracellular protease activities were highest in the 0-10 m surface layer and decreased with depth. There was a positive correlation between protease activity and chlorophyll-a concentration, suggesting that organic matter decomposition activity is also higher in layers with higher primary production. At the subtropical stations KEO, S1, and KEOS, the activity in the surface layer was much lower than that in the subarctic layer, but increased with depth, reaching a maximum at subsurface (around 60 to 80 m), and decreasing with depth below that depth. The ratio of trypsin-type activity to aminopeptidase activity (T/A ratio) was higher in the subtropical than in the subarctic, and the T/A ratio was particularly high in the subtropical sub-surface layer. Moreover, the T/A ratio tended to be higher in the layer depleted of major nutrients. These results implied that efficient microbial metabolism using extracellular endo-type hydrolases by heterotrophic prokaryotes may support regenerative production under oligotrophic conditions.