Influence of zooplankton grazing on free dissolved enzymes in the sea

Abstract

In the Northern Adriatic Sea, extracellular enzymatic activity was measured during a Lagrangian study following a drifting buoy for 40 h. Dissolved free enzymatic activity represented 20 to 70% of total activity depending on the type of enzyme. a-and P-glucosidases exhibited a significantly higher free activity than proteolytic enzymes. In subsequent laboratory experiments we investigated the effect of zooplankton on the free enzyme pool. The 4-step approach included: ( l ) determinatlon of the enzymatic activities in copepods (mainly Acartia clausi); (2) enzymat~c activity in fecal pellets; (3) short-and long-term grazing experiments; and (4) degradab~lity of free glucosidase in seawater. a-and P-glucosidases, leu-aminopeptidase, lipase and chitinase were examined. Experiments in which zooplankton were selectively enriched revealed a significant increase in both particle-bound (due to the increase of bacterial density) and dissolved free enzymatic activity. Incubating water enriched in free enzymes released by zooplankton with natural bacterial consortia, we found that 70% of the original a-and P-glucosidase activity remained after 22 h. The presence of microorganisms did not enhance the degradation of these enzymes as compared to autoclaved controls. We found that a considerable amount of free dissolved enzymes is lost by 0.2 pm filtration using Nuclepore filters, thereby leading to an underestimation of dissolved enzymes by -30% in our experiments. Based on our results we conclude that mesozooplankton contribute to the free enzymatic activity in natural waters especially during periods of high grazing activity.

Are Bacteria the Major Producers of Extracellular Glycolytic Enzymes in Aquatic Environments?

“…Previous studies from this lake showed indirect evidence of zooplankton control of phytoplankton (PUG-NETTI and BETTINETTI, 1995;CAMMARANO and MANCA, 1997) and protozoa (CALLIERI et al, 1999;BERTONI et al, 2002) during Daphnia peaks. BOCHDANSKY et al (1995) observed similar increase in both dissolved α-and -glucosidase activities with increase in marine copepods in batch experiments. Small changes in bacterial biomass were not sufficient to explain this strong increase.…”

“…Small changes in bacterial biomass were not sufficient to explain this strong increase. Their results showed, moreover, that dissolved α-and -glucosidases were relatively stable and could therefore accumulate during periods of high zooplankton grazing activity (BOCHDANSKY et al, 1995). We believe that such an accumulation of both glucosidases could also be relevant for in bottom water of LPS.…”

“…Sometimes, change in enzymatic activity did not correspond to variation in bacterial number at all (SALA and GÜDE, 1996;HOPPE et al, 1998). On the other hand, there have been increasing reports of correlations between some fraction of extracellular glycolytic activity and other planktonic organisms like phagotrophic flagellates (VRBA et al, , 1996dKARNER et al, 1994), diatoms (SMUCKER and KIM, 1991;VRBA et al, 1997) or crustacean zooplankton BOCHDANSKY et al, 1995). This study compares large data sets on extracellular -N-acetylhexosaminidase and α-and -glucosidase activity in various freshwater ecosystems.…”

“…Some authors have reported weaker relationships between bacterial variables and ectoenzyme activities in diverse aquatic environments (e.g. VRBA, 1992;VRBA et al, 1992;BOCHDANSKY et al, 1995;HOPPE et al, 1998). Sometimes, change in enzymatic activity did not correspond to variation in bacterial number at all (SALA and GÜDE, 1996;HOPPE et al, 1998).…”

Microbial Parameters as a Practical Tool for the Functional Characterization and Ecological Status Assessment of Transitional Areas

“…Other than bacteria, also zooplankton and eukaryotes (fungi, diatoms, etc.) have shown to be important producers of extracellular glycosidic activities [20][21][22]. AP is an enzyme involved in the mineralization of organic phosphates with regeneration of phosphate; both bacteria and phytoplankton contribute to its synthesis [23].…”