Bacterial decomposition of recalcitrant dissolved organic matter in estuarine systems

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In this project the decomposition of recalcitrant and humic dissolved organic matter (DOM) by bacterial communities in the salinity gradient of the Weser estuary will be investigated. Three-stage chemostats, fed by natural DOM or specific DOM fractions isolated by tangential flow ultrafiltration and/or adsorption chromatography with XAD resins and inoculated by brackish and marine bacterial communities from the Weser estuary, will be applied. The aim is to enrich, identify and isolate those bacteria of the brackish and marine section of the estuary which decompose the DOM under in situ conditions. The natural and decomposed DOM will be analyzed by high temperature combustion of organic carbon, pyrolysis coupled with gas chromatography and mass spectrometry, and by HPLC. The composition of the bacterial communities and isolated strains will be analyzed by denaturing gradient gel electrophoresis (DGGE) and sequencing of PCR amplified 16S rRNA gene fragments. Bacteria of interest will be quantified in the chemostats and in situ by real time PCR. Decomposition experiments with selected isolates or defined mixed cultures will be carried out in a second step to elucidate the physiological properties of the isolates.