Microbial communities and exopolysaccharides from Polynesian mats

Area of Science:

• Microbiology
• Biogeochemistry
• Marine Ecology

Background:

• Microbial mats are complex microbial communities found in diverse environments.
• Exopolysaccharides (EPS) play crucial roles in microbial mat structure and function.
• Cyanobacteria are often primary producers in shallow marine ecosystems.

Purpose of the Study:

• To characterize the microbial composition and exopolysaccharide content of microbial mats from French Polynesian atolls.
• To investigate the distribution of cyanobacteria and sulfate-reducing bacteria within the mat structure.
• To partially characterize the extracted exopolysaccharides.

Main Methods:

• Sampling of microbial mats from two shallow atolls.
• Microbial community analysis using specific biomarkers for sulfate-reducing bacteria.
• Extraction and partial characterization of exopolysaccharides.
• Monosaccharide composition analysis of EPS fractions.

Main Results:

• Microbial mats were rich in exopolysaccharides, with cyanobacteria dominating the surface layers.
• Deeper mat layers contained sulfate-reducing bacteria, including Desulfovibrio and Desulfobacter species.
• Extracted exopolysaccharides contained both neutral sugars and uronic acids, with neutral sugars predominating.
• A diverse range of monosaccharides suggests biosynthesis by multiple or unidentified cyanobacterial species.

Conclusions:

• Cyanobacteria are key producers of exopolysaccharides in these French Polynesian microbial mats.
• The vertical stratification of microbial life, from cyanobacteria to sulfate reducers, is evident.
• The complex exopolysaccharide composition highlights the diverse biosynthetic capabilities within the cyanobacterial populations.