AME 37:209-217 (2004)  -  doi:10.3354/ame037209

Sulphate reduction, methanogenesis and phylogenetics of the sulphate reducing bacterial communities along an estuarine gradient

D. B. Nedwell1,*, T. M. Embley2, K. J. Purdy1,3

1Department of Biological Sciences, University of Essex, Colchester, Essex CO4 3SQ, UK
2Molecular Biology Unit, Department of Zoology, Natural History Museum, London SW7 5BD, UK
3Present address: School of Animal and Microbial Sciences, University of Reading, Whiteknights, PO Box 228, Reading RG6 6AJ, UK

ABSTRACT: Four sites were investigated along the salinity gradient in the estuary of the River Colne, UK. Sulphate reduction rates at all sites decreased with depth in the sediment, but the annual rate of sulphate reduction over the 0 to 20 cm profile did not decrease significantly, even at a low salinity site up the estuary where sulphate concentrations were much lower than at the estuary mouth. Methane was formed at all of the sites, at rates 2 orders of magnitude lower than sulphate reduction, and was greatest at a site on the marsh top site where organic matter was high. Methane emissions to the atmosphere were substantially lower than sedimentary methanogenesis, suggesting methane oxidation occurred in the sediments before emission, with the proportion oxidized before emission increasing down the estuary. Nucleic acids were extracted from the sediments at each site, slot-blotted onto nylon membranes, and 16S rRNA quantified with radiolabelled oligonucleotide probes against different groups of sulphate reducing bacteria (SRB). Autoradiographs were quantified by laser densitometry compared to known standards of RNA, and expressed as a percentage of the signal from a total bacterial probe. The 4 SRB genera analysed (Desulfovibrio, Desulfobacter, Desulfobulbus and Desulfobacterium) were all detected at all 4 sites. Desulfovibrio was the largest group of SRB at the 3 lower estuary sites, while Desulfobacter, which appeared to be the major acetate utiliser present along the estuary, and Desulfobulbus were detected at lower levels. Signal from the physiologically diverse Desulfobacterium occurred at significantly higher levels in the upper estuary at the Hythe, and it was possible that this was associated with its use of electron acceptors other than sulphate, such as nitrate.

KEY WORDS: Estuarine sediments · Sulphate reduction · Methane formation · Methane oxidation · Sulphate reducing bacteria · Methanogenic archaea · 16S rRNA

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