Microbial diversity in deep sediments of the Benguela Upwelling System

Abstract

The microbial diversity of sulfate-reducing and methanogenic subsurface sediments of the Benguela Upwelling System was analyzed using 16S rRNA gene-directed molecular methods. Communities mediating anaerobic oxidation of methane (AOM) in the sulfate-methane transition zone (SMTZ) were also targeted. Denaturing gradient gel electrophoresis (DGGE) of DNA extracted from sediment samples showed the presence of complex bacterial communities in the sediment zones above and below the SMTZ, whereas only 3 DGGE-defined populations were detected in the SMTZ. Sequencing of excised DNA fragments revealed the presence of bacterial populations related to sulfate-reducing bacteria (SRB) and those distantly related to the Haloanaerobium phylum. One of the populations detected at the SMTZ was closely related to SRB and to bacterial populations detected at mud volcanoes in the Black Sea. Comparative analysis of sequences from a clone library made with genomic DNA from the SMTZ and primers specific for archaeal 16S rRNA genes revealed members of 5 different lineages, including unusual crenarchaeal ribosomal RNA sequences. None of the archaeal sequences, however, was related to groups previously implicated in anaerobic methane oxidation. © Inter-Research 2007.