PHAGOTROPHIC NANOFLAGELLATES CONTRIBUTE TO OCCURRENCE OF ALPHA-GLUCOSIDASE AND AMINOPEPTIDASE IN MARINE ENVIRONMENTS

Using fluorogenic substrate analogs, the dynamics of extracellular enz yme activities (EEA) of free and particle-bound alpha-glucosidase and aminopeptidase were investigated in mixed cultures of marine phagotrop hic nanoflagellates and bacteria. Flagellate growth on either live or heat-killed bacteria led to an expression of free aminopeptidase activ ity with up to 94 % of total EEA found in the dissolved phase. No sign ificant release of free alpha-glucosidase or free aminopeptidase was f ound in flagellate-free bacterial cultures. Fed with heat-killed bacte ria, flagellates seemed to exhibit both cell wall bound alpha-glucosid ase and aminopeptidase activities. Flagellate biovolume-specific EEA i n flagellate assemblages grown on heat-killed bacteria was similar in magnitude to bacterial biovolume-specific EEA in flagellate-free bacte rial cultures. The significance of these results is further discussed according to current theories on enzyme-catalyzed organic matter cycli ng.