Microbial communities in a Wadden Sea sediment core—clues from analyses of intact glyceride lipids, and released fatty acids

In this study microbial communities were investigated in a 55 cm sediment core from a tidal flat close to Neuharlingersiel, NW Germany, using bulk and molecular geochemical parameters. We focussed on the analysis of various types of glyceride lipids. In particular, we concentrated on the analysis of intact phospholipids by HPLC-MS(MS) as biomarkers for “viable” microorganisms. Highest abundances of intact microbial lipids were found in the surface layer of the sediment, where phospholipid types and their fatty acid patterns indicated a strong contribution of eukaryotic algae. Microbial lipids appeared to be recycled or degraded rapidly within the uppermost 10 cm of the sediment because abundances of intact phospholipids and triglycerides rapidly decreased with depth. Also, the sedimentary contents of their degradation products (e.g. di- and monoglycerides, free fatty acids) showed a strong decline in the top layers. In the depth interval of 10-20 cm, phospholipid contents and species indicated a high abundance of bacterial biomass. In the deepest samples, intact phospholipids still were detected suggesting the presence of “viable” bacteria at a sediment depth of 50 cm.