title: Inorganic carbon fixation by sulfate-reducing bacteria in the Black Sea water column.
abstract: 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 sulfate-reducing 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 x 10(2) and 6.3 x 10(2) 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 non-isoprenoidal 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 (13)C relative to the delta(13)C values of dissolved CO(2) (delta(13)C(CO2)) by 14-19 per thousand. Their delta(13)C values [delta(13)C(DGD(II-III))] co-varied with depth showing the least (13)C-depleted values in the top of the sulfidic, anoxic zone and the most (13)C-depleted values in the deep anoxic waters at 1500 m. This co-variation provides evidence for CO(2) incorporation by the DGD(II-III)-producing SRB, while the 1:2 relationship between delta(13)C(CO2) and delta(13)C(DGD(II-III)) indicates the use of an additional organic carbon source.
authors.affiliation: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany.
authors.forename: Lev N
authors.initials: LN
authors.lastname: Neretin
authors.forename: Raeid M M
authors.initials: RM
authors.lastname: Abed
authors.forename: Axel
authors.initials: A
authors.lastname: Schippers
authors.forename: Carsten J
authors.initials: CJ
authors.lastname: Schubert
authors.forename: Katharina
authors.initials: K
authors.lastname: Kohls
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
mesh_terms: D017554:Carbon Compounds, Inorganic / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D004269:DNA, Bacterial / Q000032:analysis / Q000302:isolation & purification; D020564:Deltaproteobacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism; D005995:Glyceryl Ethers / Q000737:chemistry / Q000378:metabolism; D050885:Hydrogensulfite Reductase / Q000235:genetics; D007287:Inorganic Chemicals / Q000378:metabolism*; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012426:Russia; D012623:Seawater / Q000382:microbiology*; D013431:Sulfates / Q000378:metabolism*; D016999:Sulfur-Reducing Bacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism*
chemical_list: D017554:Carbon Compounds, Inorganic; D004269:DNA, Bacterial; D005995:Glyceryl Ethers; D007287:Inorganic Chemicals; D012336:RNA, Ribosomal, 16S; D013431:Sulfates; D002245:Carbon Dioxide; D050885:Hydrogensulfite Reductase