Microbial Diversity in Nankai Trough Sediments Based on 16S rDNA Sequence Analyses
Lina LI*a, Chiaki KATOa, Miki YANAGIBAYASHIa, Jean GUEZENNECb, Pierre HENRYc, and Koki HORIKOSHIa
a The DEEPSTAR Group, Japan Marine Science and Technology Center, 2-15 Natsushima- cho, Yokosuka 237, Japan
b IFREMER, Dept. DRV/VP/BMH, BP70, 29280, Plouzane, France
c ENS, Lab. de Geologie 24, Rue L'Homond, 75231, Paris, Cedex 05, France
The deep-sea is an extreme environment experiencing with low temperature, low nutrient concentrations and high hydrostatic pressure. Defining the diversity and distribution of natural microbial communities from sea sediments has been a long- standing challenge in microbial ecology and evolution. A vast array of chemoautotrophic deep-sea animal communities have been found to exist in cold seep environments as well as hydrothermal vents. The Nankai Trough (33°39'N, 137°56'E) is a typical cold seep environment, with large Calyptogena communities (1).
To study the biological community of a cold seep environment, we have employed molecular phylogenetic techniques to investigate the bacterial diversity in the Nankai Trough sediment cores from different points around Calyptogena beds, obtained by the submersible "Shinkai 6500". Totally, fifty-five 16S rDNA clones from five sediments samples (three from inside the Calyptogena communities at a depth of 0, 7, and 12 cm respectively from the sediment surface, and two from outside of the colonies, at a depth of 5 and 15 cm respectively) were analyzed and sequenced. The results suggested that the fifty-five clones belonged to nineteen different eubacterial 16S rDNAs designated as NK-1-19. From the nineteen sequences, sixteen sequences of 16S rDNA belonged to the group Proteobacteria, and three sequences belonged to the gram- positive bacterial group. Five 16S rDNA sequences (total twenty-one clones) were closely related to the Proteobacteria γ-subdivision, and three of them were closely related to the genus Pseudomonas. Six 16S rDNA sequences (total twenty clones) were closely related to the Proteobacteria ε-subdivision, and three (total eleven clones) to the δ-subdivision. Most of the sequences identified in the Proteobacteriaε- andδ-subdivisions were found inside the Calyptogena colonies at depths of 0-5 cm. Our results demonstrate that there are numbers of bacteria belonging to the δ and ε-subdivisions which include sulfate and sulfur reducing bacteria (2-4), existing mainly in the sediment around Calyptogena colonies. There are also numbers of bacteria belonging to the γ-subdivision existing both outside and inside the colonies. These results indicate a possible metabolic pathway of inorganic
