Microbial Manganese and Sulfate Reduction in Black Sea Shelf ...

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the Panama Basin and the Norwegian Trough, characterized by extremely high ...... ffoor and in sediment cores onboard the ship during the cruise at the same ...
APPLIED AND ENVIRONMENTAL MICROBIOLOGY, July 2000, p. 2888–2897 0099-2240/00/$04.00⫹0 Copyright © 2000, American Society for Microbiology. All Rights Reserved.

Vol. 66, No. 7

Microbial Manganese and Sulfate Reduction in Black Sea Shelf Sediments ´ N ROSSELLO ´ -MORA,1† BO THAMDRUP,1,2* RAMO

AND

RUDOLF AMANN1

1

Max Planck Institute for Marine Microbiology, Bremen, Germany, and Danish Center for Earth System Science, Institute of Biology, SDU—Odense University, Odense, Denmark2 Received 29 February 2000/Accepted 5 May 2000

The microbial ecology of anaerobic carbon oxidation processes was investigated in Black Sea shelf sediments from mid-shelf with well-oxygenated bottom water to the oxic-anoxic chemocline at the shelf-break. At all stations, organic carbon (Corg) oxidation rates were rapidly attenuated with depth in anoxically incubated sediment. Dissimilatory Mn reduction was the most important terminal electron-accepting process in the active surface layer to a depth of ⬃1 cm, while SO42ⴚ reduction accounted for the entire Corg oxidation below. Manganese reduction was supported by moderately high Mn oxide concentrations. A contribution from microbial Fe reduction could not be discerned, and the process was not stimulated by addition of ferrihydrite. Manganese reduction resulted in carbonate precipitation, which complicated the quantification of Corg oxidation rates. The relative contribution of Mn reduction to Corg oxidation in the anaerobic incubations was 25 to 73% at the stations with oxic bottom water. In situ, where Mn reduction must compete with oxygen respiration, the contribution of the process will vary in response to fluctuations in bottom water oxygen concentrations. Total bacterial numbers as well as the detection frequency of bacteria with fluorescent in situ hybridization scaled to the mineralization rates. Most-probable-number enumerations yielded up to 105 cells of acetate-oxidizing Mn-reducing bacteria (MnRB) cmⴚ3, while counts of Fe reducers were