RELEASE OF DISSOLVED AMINO-ACIDS BY FLAGELLATES AND CILIATES GRAZING ON BACTERIA

Release of amino acids was examined in the laboratory in the form of d issolved primary amine (DPA) by two marine planktonic protozoa (the ol igotrichous ciliate, Strombidium sulcatum and the aplastidic flagellat e Pseudobodo sp.) grazing on bacteria. DPA release rates were high (19 -25 x 10(-6) and 1.8-2.3 x 10(-6) mu mol DPA cell(-1) h(-1) for flagel lates and ciliates, respectively) during the exponential phase, when t he ingestion rates were maximum. Release rates were lower during the o ther growth phases. The release of DPA accounted for 10 % (flagellates ) and 16 % (ciliates) of the total nitrogen ingested. Our data suggest that the release of DPA by protozoa could play an important role in s upporting bacterial and consequently autotrophic pico- and nanoplankto n growth, especially in oligotrophic waters, where the release of phyt oplanktonic dissolved organic matter is low. (C) Elsevier, Paris.