Changing patterns of bacterial substrate decomposition in a eutrophication gradient

Abstract

Bacterial variables are expected to respond differently to eutrophication. This was investigated along the eutrophication gradient in the narrow Schlei fjord (northern Germany). Bacterial extracellular enzyme activities (peptidase, a-and P-glucosidase, chitinase) were measured together with a large number of autotrophic and heterotrophic biological variables. Increases of values measured along the eutrophication gradient were generally higher for bacterial substrate uptake and growth than for bacterial counts and enzyme activities. Annual patterns of activities (per volume of water) obtained from stations with different degrees of eutrophication were clearly different from each other. In contrast, annual patterns of activities per bacterial cell at the stations with different degrees of eutrophication were not clearly different from each other, Indicating that they did not depend on eutrophication. Size fractionation of enzyme activities revealed that most of the peptidase activity was generally associated with free-living bacteria (<0.2 to 3 pm, average 57 % of total). Chitinase (average 54 % of total) and a-/P-glucosidases activities during summer were mainly associated with the > 3 pm particle size class (43 and 5 2 % , respectively). Free enzyme activities (<O 2 pm, % of total) were generally higher in less eutrophic areas than in eutrophic areas. Enzyme activities associated with the bacterial size class were generally higher in eutrophic areas than in less eutrophic areas. It is concl.uded that particle hydrolysis In eutrophic waters is mainly affected by attached bacterial glucosidic and chitinolytic potentials, while peptides are the preferred substrates of free-living bacteria. To cover bacterial C demands for growth, exudation by phytoplankton had to be supplemented by bacterial substrate hydrolysis in eutrophic waters, which was, however, not as high as expected.

Bottom up effects on bacterioplankton growth and composition during summer-autumn transition in the open NW Mediterranean Sea

“…Only a small fraction of dissolved organic matter can be directly taken up by bacteria, therefore, expression (genetic potential) and physiological regulation of ectoenzymatic activity play a major role in heterotrophic bacterial growth. Maximum hydrolysis rates of ectoenzymes, determined by fluorogenic substrates (Hoppe et al, 1998), has been related to a variety of biogeochemical parameters. The presence of ectoenzymes is widespread among marine bacteria (Martinez et al, 1996).…”

Distribution of HNA and LNA bacterial groups in the Southwest Atlantic Ocean

“…Bacteria are players of important roles in the structure and dynamics of food webs and biogeochemical cycles in marine systems (8,21,36,37). Through the microbial loop, dissolved organic carbon (DOC) is transformed into particulated organic carbon (POC) by heterotrophic bacteria and become ready to be incorporated by the next trophic level as these microrganisms are predated.…”

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

“…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). 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).…”

“…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).…”

“…However, statistical relationships between ectoenzyme activities and bacterial parameters are equivocal in many natural environments (e.g. VRBA et al, 1992VRBA et al, , 1996cHOPPE et al, 1998). During the last decade, it has become obvious that other sources may contribute to the extracellular activity of -N-acetylhexosaminidase, chitobiase or lysozyme detected in water samples (GONZÁLES et al, 1993;VRBA et al, 1993VRBA et al, , 1996aVRBA et al, , d, 1997VRBA and MACHÁČ EK, 1994;ESPIE and ROFF, 1995;JENKINS et al, 1998;ZUBKOV and SLEIGH 1998;SHERR and SHERR 1999;OOSTERHUIS et al, 2000;VRBA, 2000).…”