Resumen de Microbial Population Dynamics in the Sediments of a Eutrophic Lake (Aydat, France) and Characterization of Some Heterotrophic Bacterial Isolates

C. Mallet, M. Basset, Gérard Fonty, C. Desvilettes, Gilles Bourdier, Didier Debroas

• The bacterial populations of anoxic sediments in a eutrophic lake (Aydat, Puy-de-Dôme-France) were studied by phospholipid fatty acid analysis (PLFA) and also by culturing heterotrophic bacteria under strictly anaerobic conditions. The mean PLFA concentrations of prokaryotes and microeukaryotes were 5.7 ± 2.9 mgC g−1 DS and 9.6 ± 6.7 mgC g−1 DS, respectively. The analysis of bacterial PLFA markers was used to determine the dynamics of the Gram-positive and Gram-negative species of anaerobic bacteria, Clostridiae, and sulfate-reducing bacteria. Throughout the sampling period the concentrations of i15:0 (from 20 nmol g−1 DS to 130 nmol g−1 DS), markers of Gram-positive bacteria, were higher than those for Gram-negative bacteria. The dynamics of Clostridiae (Cy15:0) paralleled those of sulfate-reducing bacteria that were marked by i17:1ω7. Partial 16S rDNA sequencing and the physiological study of the various fermenting strains, whose abundance in the superficial sediment layer was 1.1 ± 0.4 × 106 cells mL−1, showed that all the isolates belonged to the Clostridiae and related taxa (Lactosphaera pasteurii, Clostridium vincentii, C. butyricum, C. algidixylanolyticum, C. puniceum, C. lituseburense, and C. gasigenes). All the isolates were capable of metabolizing a wide range of organic substrates.