engleski

Proportion of metabolically active marine bacteria under different nutrient regimes

Nowadays it is recognized that only a fraction of aquatic bacteria is actively growing but there is little information about the factors constraining their metabolism. Marine bacterioplankton can rapidly modify their metabolic activity level in response to environmental changes. The aim of this study was to determine the importance of highly active ETS (%CTC+) fraction of bacterioplankton following its changes in abundance and activity levels in response to organic matter pools potentionally available for bacterial processing. The natural plankton communities from the northern Adriatic, amended with inorganic nutrinets (P-defficient and nutrient balanced conditions, were incubated in experimental enclosures over two weeks). Indices of bacterial activity included: total and cell-specific incorporation rates of tritiated leucine ([3H]- Leu) and thymidine ([3H]- TdR), ratio of Leu and TdR incorporation and percentage of highly active cells as determined by detectable reduction of fluorogenic dye, 5-cyano-2, 3-ditolyl tetrazolium chloride (CTC). Patterns of change in bacterial metabolic activity were similar for both amandments up to 48 hours of incubation, approaching the maximum proportion of CTC+ bacteria (18-22%) in P-defficient as well as in nutrient balanced conditions. Afterwards, the disproportion of activity started with "unbalanced gorwth" of bacteria, followed by substantial increase of TdR and Leu incorporation and CTC+ bacteria (up to 40%), respectively, in the nutrient balanced conditions. Continouous increase of disproportion in bacterial activity, started before maximum of particulate primary production, indicated differernt structure of organic matter available for bacteria.

Heterotrophic bacteria; CTC; Bacterial production; Nutrient enrichment

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