Characterization of functional bacterial groups in a hypersaline microbial mat community (Salins-de-Giraud, Camargue, France)

A photosynthetic microbial mat was investigated in a large pond of a Mediterranean saltern (Salins-de-Giraud. Camargue. France) having water salinity from 70parts per thousand to 150parts per thousand (w/v). Analysis of characteristic biomarkers (e.g., major microbial fatty acids. hydrocarbons, alcohols and alkenones) revealed that cyanobacteria were the major component of the pond. in addition to diatoms and other algae. Functional bacterial groups involved in the sulfur cycle could be correlated to these biomarker's. i.e. sulfate-reducing, sulfur-oxidizing and anoxygenic phototrophic bacteria. In the first 0.5 mm of the mat, a high rate of photosynthesis showed the activity of oxygenic phototrophs in the surface layer. Tell different cyanobacterial populations were detected with confocal laser scanning microscopy: six filamentous species, with Microcoleus chthonoplastes and Halomicronemia excentricum as dominant (73% of total counts); and four unicellular types affiliated to Microcystis, Chroococcus, Gloeocapsa, and Synechocystis (27% of total counts). Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene Fragments confirmed the presence of Microcoleus, Oscillatoria, and Leptolyngbya strains (Halomicronema was not detected here) and revealed additional Pleurocapsa and Calotrix types. Spectral scalar irradiance measurements did not reveal a particular zonation of cyanobacteria, purple or green bacteria in the first millimeter or the mat. Terminal-restriction fragment length polymorphism analysis of PCR-amplified 16S rRNA gene fragments of bacteria depicted the community composition and a fine-scale depth-distribution of at least five different populations of anoxygenic phototrophs and at least three types of sulfate-reducing bacteria along the microgradients of oxygen and light inside the microbial trial. (C) 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.