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Investigation of the methanogen population structure and activity in a brackish lake sediment

Authors

  • Natasha Banning,

    1. Cardiff School of Biosciences, Cardiff University, Main Building, Park Place, PO Box 915, Cardiff CF10 3TL, Wales, UK.
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  • Fiona Brock,

    1. School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, PO Box 914, Cardiff CF10 3YE, Wales, UK.
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  • John C. Fry,

    1. Cardiff School of Biosciences, Cardiff University, Main Building, Park Place, PO Box 915, Cardiff CF10 3TL, Wales, UK.
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  • R. John Parkes,

    1. School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, PO Box 914, Cardiff CF10 3YE, Wales, UK.
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  • Edward R. C. Hornibrook,

    1. Bristol Biogeochemistry Research Centre, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 IRJ, UK.
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  • Andrew J. Weightman

    Corresponding author
    1. Cardiff School of Biosciences, Cardiff University, Main Building, Park Place, PO Box 915, Cardiff CF10 3TL, Wales, UK.
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*E-mail weightman@cf.ac.uk; Tel. (+44) 029 2087 5877; Fax (+44) 029 2087 4305.

Summary

The methanogen community in sediment from the edge of a small brackish lake connected to the Beaulieu Estuary (Hampshire, UK) was investigated by analysis of 16S rRNA gene diversity using new methanogen-specific primers plus Archaea-specific primers. 16S rRNA gene primers previously used for polymerase chain reaction (PCR) detection of methanogenic Archaea from a variety of environments were evaluated by in silico testing. The primers displayed variable coverage of the four main orders of methanogens, highlighting the importance of this type of primer evaluation. Three PCR primer sets were designed using novel reverse primers to facilitate specific amplification of the orders Methanomicrobiales/Methanosarcinales, Methanobacteriales and Methanococcales. Diversity of the methanogen functional gene, methyl coenzyme M reductase (mcrA), was also studied. All gene libraries constructed from this sediment indicated that Methanomicrobiales and Methanosarcinales were the only methanogens detected. There was good agreement between the relative sequence abundances in the methanogen-specific 16S rRNA gene library and terminal restriction fragment length polymorphism (T-RFLP) profiling, suggesting that the population was dominated by putative H2/CO2 utilizing Methanomicrobiales, although acetate-utilizing methanogens were also present. The methanogen population analyses were in agreement with methanogenic activity measurements, which indicated that bicarbonate methanogenesis was higher than acetate methanogenesis at all depths measured and overall there was a significant difference (P = 0.001) between the rates of the two pathways. This study demonstrates the utility of new 16S rRNA gene PCR primers targeting specific methanogenic orders, and the combined results suggest that the CO2 reduction pathway dominates methanogenesis in the brackish sediment investigated.

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