Analysis of Dissimilatory Sulfite Reductase and 16S rRNA Gene Fragments from Deep-Sea Hydrothermal Sites of the Suiyo Seamount, Izu-Bonin Arc, Western Pacific

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Abstract
This study describes the occurrence of unique dissimilatory sulfite reductase (DSR) genes at a depth of 1,380 m from the deep-sea hydrothermal vent field at the Suiyo Seamount, Izu-Bonin Arc, Western Pacific, Japan. The DSR genes were obtained from microbes that grew in a catheter-type in situ growth chamber deployed for 3 days on a vent and from the effluent water of drilled holes at 5°C and natural vent fluids at 7°C. DSR clones SUIYOdsr-A and SUIYOdsr-B were not closely related to cultivated species or environmental clones. Moreover, samples of microbial communities were examined by PCR-denaturing gradient gel electrophoresis (DGGE) analysis of the 16S rRNA gene. The sequence analysis of 16S rRNA gene fragments obtained from the vent catheter after a 3-day incubation revealed the occurrence of bacterial DGGE bands affiliated with theAquificaeand γ- and ε-Proteobacteriaas well as the occurrence of archaeal phylotypes affiliated with theThermococcalesand of a unique archaeon sequence that clustered with “Nanoarchaeota.” The DGGE bands obtained from drilled holes and natural vent fluids from 7 to 300°C were affiliated with the δ-Proteobacteria, genusThiomicrospira, andPelodictyon. The dominant DGGE bands retrieved from the effluent water of casing pipes at 3 and 4°C were closely related to phylotypes obtained from the Arctic Ocean. Our results suggest the presence of microorganisms corresponding to a unique DSR lineage not detected previously from other geothermal environments.

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