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Bioreactor Janssand

Fermentation processes in tidal flat sediments
of the German Wadden Sea

Background

Tidal flat sediments are microbially active systems characterized by a high turnover of organic matter under anoxic conditions. A representative sampling site is the backbarrier area of "Spiekeroog", which is intensively studied within the frame of the research group "BioGeoChemistry of tidal flats". Until now investigations predominantly focused on sulfate reduction and methanogenesis, the terminal degradation steps. However, the initial fermentation processes remain poorly understood. The open questions are: What are the main pathways of the stepwise organic matter degradation? Which are the intermediate substances? Who are the microbial key-players involved?


First experiments

To get deeper insights into the course of fermentation, we have performed growth experiments that were monitored by microcalorimetry. This technique allows a highly sensitive detection of the heat production resulting from metabolic activities. Two peaks of activity were found in sediment-slurries amended with 10 mM glucose indicating at least two subsequent degradation steps. During the experiment, the active bacterial community compositions were analyzed by PCR-DGGE of 16S rRNA. The stimulated members were identified by combining microcalorimetry and RNA-based stable-isotope probing using 13C-glucose as sole carbon source. In addition, complex substrates such as intact cells of spirulina instead of glucose will be used to simulate natural conditions.

Team

Publications

Graue J, Kleindienst S, Lueders T, Cypionka H, Engelen B (2012) Identifying fermenting bacteria in anoxic tidal-flat sediments by a combination of microcalorimetry and ribosome-based stable-isotope probing. FEMS Microbiol Ecol 81:7887

Graue J, Engelen B, Cypionka H (2012) Degradation of cyanobacterial biomass in anoxic tidal-flat sediments: a microcosm study of metabolic processes and community changes. ISME J 6:660-669

Logemann J, Graue J, Köster J, Engelen B, Rullkötter J, Cypionka H (2011) A laboratory experiment of intact polar lipid degradation in sandy sediments. Biogeosciences 8:2547-2560

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