Release of dissolved free amino acids from biofilms in stream water
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We investigated the origin of dissolved free amino acids (DFAA) in stream water focusing on biofilms in the river bed by means of incubation experiments in the laboratory. Stones were placed in the Toyohira River, Hokkaido, Japan, for 3 months, allowing formation of biofilms, and then incubated for 24 h in the laboratory at stream water temperature. After incubation, the composition and concentrations of DFAA in the incubation solution and total hydrolyzed amino acids (THAA) in biofilms were measured by high-performance liquid chromatography. The amount of chlorophyll a (Chl. a) and the number of bacteria were also measured. The DFAA concentration increased greatly in the biofilm incubation solution, but the DFAA composition (mol %) did not change relative to the inception of incubation, where it was similar to stream water. There was no correlation between the increase in DFAA concentration and the THAA concentration, Chl. a amount, or the number of bacteria in biofilms. These results suggest that biofilms are one of the major sources of DFAA in stream water.
KeywordsDissolved free amino acids Biofilm Epilithic algae Salmon homing Toyohira River
We thank Prof. Taizo Motomura, Field Science Center for Northern Biosphere, Hokkaido University, for his help in conducting unialgal incubation experiments. This study was partially supported by a Grant-in-Aid for Scientific Research (A) (18208017) from JSPS, a natural science grant (35-4) from the Mitsubishi Foundation, and an environmental research grant (08-A10) from Mitsui & Co. Ltd to H.U.
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