Abstract
Organic-rich subsurface marine sediments were taken by gravity coring up to a depth of 10 m below seafloor at six stations from the anoxic Black Sea and the Benguela upwelling system off Namibia during the research cruises Meteor 72-5 and 76-1, respectively. The quantitative microbial community composition at various sediment depths was analyzed using total cell counting, catalyzed reporter deposition – fluorescence in situ hybridization (CARD–FISH) and quantitative real-time PCR (Q-PCR). Total cell counts decreased with depths from 109 to 1010 cells/mL at the sediment surface to 107–109 cells/mL below one meter depth. Based on CARD–FISH and Q-PCR analyses overall similar proportions of Bacteria and Archaea were found. The down-core distribution of prokaryotic and eukaryotic small subunit ribosomal RNA genes (16S and 18S rRNA) as well as functional genes involved in different biogeochemical processes was quantified using Q-PCR. Crenarchaeota and the bacterial candidate division JS-1 as well as the classes Anaerolineae and Caldilineae of the phylum Chloroflexi were highly abundant. Less abundant but detectable in most of the samples were Eukarya as well as the metal and sulfate-reducing Geobacteraceae (only in the Benguela upwelling influenced sediments). The functional genes cbbL, encoding for the large subunit of RuBisCO, the genes dsrA and aprA, indicative of sulfate-reducers as well as the mcrA gene of methanogens were detected in the Benguela upwelling and Black Sea sediments. Overall, the high organic carbon content of the sediments goes along with high cell counts and high gene copy numbers, as well as an equal abundance of Bacteria and Archaea.
Highlights
The Black Sea and the Benguela upwelling system off the Atlantic coast of Namibia are both represent organic carbon-rich marine environments
The functional genes cbbL, encoding for the large subunit of ribulose1.5-bisphosphate carboxylase/oxygenase (RuBisCO), the genes dissimilatory sulfite reductase (dsrA) and adenosine -phosphosulfate reductase subunit A (aprA), indicative of sulfate-reducers as well as the mcrA gene of methanogens were detected in the Benguela upwelling and Black Sea sediments
Results of the quantitative microbial community composition in subsurface marine sediments of the Black Sea and the Benguela upwelling area off Namibia are shown in Figures 3 and 4, respectively
Summary
The Black Sea and the Benguela upwelling system off the Atlantic coast of Namibia are both represent organic carbon-rich marine environments. The Black Sea is the largest anoxic seawater basin on earth It is characterized by high biological productivity in the oxygenated surface waters (Yilmaz et al, 2006). On the continental slope and rise the organic carbon flux to the underlying sediments is relatively high The sediments of these two marine areas have been well-studied for their biogeochemical processes (Niewöhner et al, 1998; Ferdelman et al, 1999; Brüchert et al, 2000, 2003, 2006; Fossing et al, 2000; Jørgensen et al, 2001, 2004; Emeis et al, 2004; Neretin et al, 2004; Knab et al, 2008; Dale et al, 2009; Goldhammer et al, 2010, 2011; Riedinger et al, 2010; Holmkvist et al, 2011) but microbiological data are available for surface sediments mainly (Schulz et al, 1999; Thamdrup et al, 2000; Schulz and Schulz, 2005; Coolen et al, 2006a; Neretin et al, 2007; Coolen and Shtereva, 2009; Schubotz et al, 2009; Julies et al, 2010). Few microbiological data are published for subsurface sediments of the Black Sea and the Benguela upwelling system (Leloup et al, 2007; Schäfer et al, 2007; Blazejak and Schippers, 2010, 2011)
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