Sub-seafloor bacterial community structures within massive sulfide deposits at the Southern Mariana Trough

Yet-uncharacterized sub-seafloor bacterial communities within massive sulfide deposits important for ocean elemental flux were investigated by 16S rRNA gene analysis. Shallow sub-seafloor drilling was performed in a deep-sea hydrothermal field (called Pika site) of the Southern Mariana Trough (SMT). The borehole length was 4.252 m and the length of the core sample obtained was 2,920 mm (¬68.7% recovery). The core sample mainly consisted of pyrite (FeS2), sphalerite (ZnS) and chalcopyrite (CuFeS2), and contained barite (BaSO4) as minor components. Three subsamples (upper, middle and lower) of the core sample were picked up from different depth points (0.77, 1.14, 2.37 mbsf). Bacterial 16S rRNA gene analysis was performed for the three subsamples. The community structures based on the detected clones were clearly different from one another. The dominant clone detected in each subsample was related to Gammaproteobacteria, Bacteroidetes and Ignavibacteria, or Nitrospirae, respectively. Many clones detected from the sub-seafloor massive sulfide deposits were similar to those from sulfide chimneys of inactive vents or basaltic lavas on the seafloor including SMT and other areas. Comparative analysis revealed the commonality and difference of the community structures with those in surrounding seafloor environments depending on the sampling depth.