Denitrifier from the Mariana Trench at 11,000 m Depth
Hideyuki TAMEGAI*+, Lina LI, Noriaki MASUI, Chiaki KATO, and Koki HORIKOSHI
The DEEPSTAR group, Japan Marine Science and Technology Center, 2-15 Natsushima- cho, Yokosuka 237, Japan
+ Present address: Department of Chemistry, Faculty of Science, Tokyo Institute of Technology, 2-12-10-okayama, Meguro-ku, Tokyo 152, Japan
The deep-sea is a world of high pressure and low temperature, and the detailed properties of this remote world are almost unknown because of the difficulty to reach it. Manned- and unmanned-submersibles operated by the Japan Marine Science and Technology Center have been employed to investigate the deep-sea environment and the organisms living there. Recently, mud from the bottom of the Mariana Trench, one of the deepest trenches in the world, was collected in an operation involving the use of KAIKO, an unmanned-submersible operated by the Japan Marine Science and Technology Center. Many kinds of organisms were isolated from this mud (1), and some genetics analyses were performed (2). Among these organisms, we found a bacterium that can grow by means of denitrification. Denitrification is one of a form of anaerobic respiration, and it is thought to represent an ancient form of aerobic respiration (3). Many researchers are interested in the evolution of respiration and the relationship between anaerobic and aerobic respiratory systems.
In the present study, we isolated a denitrifying bacterium, Pseudomonas sp. strain MT- 1 from mud of the Mariana Trench. The optimal temperature and pressure for growth of this bacterium was found to be 30℃ and 0.1 MPa, respectively. However, it showed greater tolerance to low temperature (4℃) and high hydrostatic pressure (50 MPa) as compared to Pseudomonas stutzeri and Paracoccus denitrificans, typical terrestrial denitrifies. From the results, it can be said that this organism is adapted to the environment of deep-sea. The 16S rDNA sequence comparisons showed that strain MT- 1 does not belong to the sub-branch of barophiles, but rather belongs to the genus Pseudomonas, and has an especially close relationship with Ps. stutzeri. Cytochrome content also showed the similarity between strain MT-1 and Ps. stutzeri. Aerobic-grown cells of strain MT- 1 contained c-type cytochrome in the soluble fraction, and b-(o-)type and c-type cytochromes in the membrane fraction. Nitrate-grown cells of the bacterium contained c-type cytochrome in the soluble fraction, and b-(o-)type, c-type and dl-type cytochromes in the membrane fraction. This bacterium, obtained from a remote world, may provide novel insight into the evolution of denitrification.
1. Takami, H., Inoue, A., Fuji, F., and Horikoshi, K. (1997) FEMS Microbiol. Lett., 152, 279-285.
2. Karo, C., Li, L., Tamaoka, J., and Horikoshi, K. (1997) Extremophiles, 1, 117-123.
3. Saraste, M. and Castresana, J. (1994) FEBS Lett., 341, 1-4.
