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

Abstract

A photosynthetic microbial mat was investigated in a large pond of a Mediterranean saltern (Salins-de-Giraud, Camargue, France) having water salinity from 70 per thousand to 150 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 biomarkers, 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. Ten different cyanobacterial populations were detected with confocal laser scanning microscopy: six filamentous species, with Microcoleus chthonoplastes and Halomicronema 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 presence of Phormidium, Pleurocapsa and Calotrix types. Spectral scalar irradiance measurements did not reveal a particular zonation of cyanobacteria, purple or green bacteria in the first millimeter of 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 mat.

Effects of Elevated Carbon Dioxide and Salinity on the Microbial Diversity in Lithifying Microbial Mats

“…Even when individual phyla and subphyla (i.e., Actinobacteria, Bacteroidetes, Cyanobacteria, Deltaproteobacteria) were removed from the Fast UniFrac dataset (data not shown) the overall shift in the community structure in response to salinity was present indicating that salinity imposes a widespread affect on lithifying mat organisms. Of the many taxa to be impacted by the increase in salinity the Alphaproteobacteria showed a change in relative abundance of key taxa including an enrichment of Rhodospirillales (Figure 3), a group of purple-sulfur phototrophs that has been shown to be enriched in many hypersaline habitats [79,80]. Salinity has also been previously shown to significantly impact the metabolic activity of hypersaline mats under gradients and flux conditions [23,77,81].…”

Biogeochemistry of intertidal microbial mats from Qatar: New insights from organic matter characterisation

“…6) and total concentrations ranged from 4 µg/g TOC (1-2 cm) to 16.7 µg/g TOC (0.8-1.0 cm). They were dominated in the surficial layer by n-C 17 (81% of total n-alkanes), a known cyanobacterial biomarker (Han et al, 1968), which has also been identified in hypersaline microbial mats (Grimalt et al, 1992;Fourçans et al, 2004;Rontani and Volkman, 2005;Wieland et al, 2008;Sherf and Rullkötter, 2009). …”

Microbial mat development and dolomite formation under pre-evaporitic conditions during the Atlantic in a temperate area: The Sarliève Lake (French Massif Central)

“…Various fermentative microorganisms (e.g., methanogens, nitrifying or denitrifying bacteria) also are present in the mats but in lower numbers (van Gemerden, 1993;Fourçans, 2004;Fourçans et al, 2004). The growth and metabolic activity of these organisms result in vertical physicochemical gradients of oxygen, sulfide and light Revsbech et al, 1983).…”