AME 22:251-259 (2000)  -  doi:10.3354/ame022251

Variations in the number of active bacteria in the euphotic zone of a recently flooded reservoir

Louis B. Jugnia*, M. Richardot, D. Debroas, T. Sime-Ngando, J. Dévaux

Laboratoire de Biologie des Protistes, UMR-A CNRS 6023, Université Blaise Pascal (Clermont-Ferrand II), 63177 Aubière cedex, France

ABSTRACT: Using the CTC (5-cyano-2,3-ditolyl tetrazolium chloride) method, we estimated the active fraction of bacterioplankton in the euphotic zone of the recently flooded Sep Reservoir, France, with the aim of evaluating its importance and dynamics in relation to temperature and some components of dissolved organic matter (DOM) (i.e. dissolved combined amino acids: DCAA; dissolved free monosaccharides: DFCHO; dissolved combined monosaccharides: DCCHO), and its metabolic significance in conjunction with a bacterial growth indicator: 14C-glucose uptake. From our results, it appears that only a small fraction (0.04 to 3.23%) of total bacterial count in this reservoir was metabolically active. Recorded correlations and multivariate regression analysis suggest that temporal variations in the number of active bacteria are mainly (80%) governed by temperature, together with the high concentrations of those components of DOM, which were present in this ecosystem but which apparently were not always available for bacterial metabolism. We also found a positive relation between the number of active bacteria and the potential heterotrophic activity, which suggest that CTC-positive bacteria are responsible for the bulk of bacterial community metabolism in this recently formed reservoir.

KEY WORDS: Active bacteria · CTC · Dissolved organic matter · Temperature · Bacterial activity · New reservoir

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