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Microbial stratification in deeply buried marine sediment reflects changes in sulfate/methane profiles

Authors

  • J. F. BIDDLE,

    1. Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
    2. Penn State Astrobiology Research Center, The Pennsylvania State University, University Park, Pennsylvania, USA
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  • C. H. HOUSE,

    1. Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania, USA
    2. Penn State Astrobiology Research Center, The Pennsylvania State University, University Park, Pennsylvania, USA
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  • J. E. BRENCHLEY

    1. Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
    2. Penn State Astrobiology Research Center, The Pennsylvania State University, University Park, Pennsylvania, USA
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Corresponding author: C. H. House. Tel.: 814-865-8802; fax: 814 863 7823; e-mail: chouse@geosc.psu.edu

ABSTRACT

We examined sediments collected at Ocean Drilling Program (ODP) Leg 201 Site 1229 on the Peru Margin for microbial populations throughout the sediment column. Heterotrophic cultivation from these sediments yielded numerous colonies from various depths, including 49 bacterial isolates. At ODP Site 1229, there are significant interfaces of sulfate and methane, across which microbial cell numbers increase substantially. At these sulfate/methane transition zones (SMTZs), however, we observed a decrease in the success rate for the cultivation of bacterial colonies. Utilizing both direct plating and enrichment in different media, we cultivated isolates from the upper SMTZ around 30 m below seafloor (mbsf); however, similar attempts yielded no colonies from within the lower zone at 85 mbsf. The phylogenetic relationships of the 16S rRNA gene sequences for the isolates were determined and most were related to other organisms and sequences previously found in the subsurface belonging to the γ-Proteobacteria, cytophagaflavobacteriumbacteroides, high G + C Gram-positives, and Firmicutes groups. The most diverse group of isolates from Site 1229 was found between the SMTZs at 50 mbsf. ODP Leg 201 Site 1228 was examined for comparison and yielded an additional 18 isolates from 16 to 179 mbsf that were similar to those found at Site 1229. Direct plating at Site 1228 also showed decreased colony formation in the area of sulfate/methane transition. Our results suggest that heterotrophic bacterial populations are affected by SMTZs in deeply buried sediment.

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