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Inorganic carbon fixation by sulfate-reducing bacteria in the Black Sea water column

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Neretin Lev N., Abed Raeid M. M., Schippers Axel, Schubert Carsten J., Kohls Katharina, Kuypers Marcel M. M.,
Project R'EQUIP 2002: Anaerobic oxidation of methane in sediments and water column of the Black Sea and in lakes of Switzerland
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Original article (peer-reviewed)

Volume (Issue) 9(12)
Page(s) 3019 - 3024
DOI 10.1111/j.1462-2920.2007.01413.x


The Black Sea is the largest anoxic water basin on Earth and its stratified water column comprises an upper oxic, middle suboxic and a lower permanently anoxic, sulfidic zone. The abundance of sulfatereducing bacteria (SRB) in water samples was determined by quantifying the copy number of the dsrA gene coding for the alpha subunit of the dissimilatory (bi)sulfite reductase using real-time polymerase chain reaction. The dsrA gene was detected throughout the whole suboxic and anoxic zones. The maximum dsrA copy numbers were 5 ¥ 102 and 6.3 ¥ 102 copies ml-1 at 95 m in the suboxic and at 150 m in the upper anoxic zone, respectively. The proportion of SRB to total Bacteria was 0.1% in the oxic, 0.8–1.9% in the suboxic and 1.2–4.7% in the anoxic zone. A phylogenetic analysis of 16S rDNA clones showed that most clones from the anoxic zone formed a coherent cluster within the Desulfonema–Desulfosarcina group. A similar depth profile as for dsrA copy numbers was obtained for the concentration of nonisoprenoidal dialkyl glycerol diethers (DGDs), which are most likely SRB-specific lipid biomarkers. Three different DGDs were found to be major components of the total lipid fractions from the anoxic zone. The DGDs were depleted in 13C relative to the d13C values of dissolved CO2 (d13CCO2) by 14–19‰. Their d13C values [d13CDGD(II–III)] co-varied with depth showing the least 13C-depleted values in the top of the sulfidic, anoxic zone and the most 13C-depleted values in the deep anoxic waters at 1500 m. This co-variation provides evidence for CO2 incorporation by the DGD(II–III)-producing SRB, while the 1:2 relationship between d13CCO2 and d13CDGD(II–III) indicates the use of an additional organic carbon source.