Release of aminoacids and inorganic nutrients by heterotrophic marine micro-flagellates

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Abstract
Heterotrophic microflagellates isolated from the Baltic Sea and grown under laboratory conditions were shown to release dissolved free amino acids (DFAA) when grazing bacteria. Flagellates released 3H-amino acids when fed 3H-leucine-labeled bacteria, and concentrations of amino acids increased in the experimental medium. Serine showed a strong positive correlation with flagellate feeding. Aspartic acid, glutamic acid and ornithine also increased more than other amino acids. During consumption of bacteria, the flagellates released 13% of the ingested N as ammonia, and 30% of the ingested P as PO43-. In a field experiment off Scripps Pier [California, USA], bacterial production, flagellate abundance and concentration of DFAA were measured over a 28 h period. The concentration of DFAA showed a covariation with the flagellate numbers. Results from field and laboratory experiments suggest that flagellates may be a source of DFAA in the sea.