Articles | Volume 12, issue 10
Biogeosciences, 12, 2847–2860, 2015
Biogeosciences, 12, 2847–2860, 2015

Research article 19 May 2015

Research article | 19 May 2015

Methane-related changes in prokaryotes along geochemical profiles in sediments of Lake Kinneret (Israel)

I. Bar-Or1, E. Ben-Dov2,3, A. Kushmaro2,5,6, W. Eckert4, and O. Sivan1 I. Bar-Or et al.
  • 1Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, Be'er-Sheva, P.O. Box 653, 8410501, Israel
  • 2Avram and Stella Goldstein-Goren Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Be'er-Sheva, P.O. Box 653, 8410501, Israel
  • 3Department of Life Sciences, Achva Academic College, Achva, M.P. Shikmim 79800, Israel
  • 4Israel Oceanographic and Limnological Research, The Yigal Allon Kinneret Limnological Laboratory, P.O. Box 447, 14950 Migdal, Israel
  • 5National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, P.O. Box 653, Be'er-Sheva 8410501, Israel
  • 6School of Materials Science and Engineering, Nanyang Technological University, Singapore

Abstract. Microbial methane oxidation is the primary control on the emission of the greenhouse gas methane into the atmosphere. In terrestrial environments, aerobic methanotrophic bacteria are largely responsible for this process. In marine sediments, a coupling of anaerobic oxidation of methane (AOM) with sulfate reduction, often carried out by a consortium of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria, consumes almost all methane produced within those sediments. Motivated by recent evidence for AOM with iron(III) in Lake Kinneret sediments, the goal of the present study was to link the geochemical gradients in the lake porewater to the microbial community structure. Screening of archaeal 16S rRNA gene sequences revealed a shift from hydrogenotrophic to acetoclastic methanogens with depth. The observed changes in microbial community structure suggest possible direct and indirect mechanisms for the AOM coupled to iron reduction in deep sediments. The percentage of members of the Nitrospirales order increased with depth, suggesting their involvement in iron reduction together with Geobacter genus and "reverse methanogenesis". An indirect mechanism through sulfate and ANME seems less probable due to the absence of ANME sequences. This is despite the abundant sequences related to sulfate-reducing bacteria (Deltaproteobacteria) together with the occurrence of dsrA in the deep sediment that could indicate the production of sulfate (disproportionation) from S0 for sulfate-driven AOM. The presence of the functional gene pmoA in the deep anoxic sediment together with sequences related to Methylococcales suggests the existence of a second unexpected indirect pathway – aerobic methane oxidation pathway in an anaerobic environment.

Short summary
This study attempted to correlate between the performed geochemical and microbial profiles in lake sediments. The geochemical data suggest three main depth related zones of electron acceptor activities in the sediment: sulfate reduction, methanogenesis and a novel, deep iron-driven AOM. The prokaryotic analysis provided clues regarding the microorganisms that may be involved in this novel process and the metabolic paths that occur throughout the microbial assemblage.
Final-revised paper