THERMOSIPHO MELANESIENSIS SP. NOV., A NEW THERMOPHILIC ANAEROBIC BACTERIUM BELONGING TO THE ORDER THERMOTOGALES, ISOLATED FROM DEEP-SEA HYDROTHERMAL VENTS IN THE SOUTHWESTERN PACIFIC-OCEAN

A new thermophilic, anaerobic rod-shaped bacterium, strain BI429(T) wa s isolated from the gills of a deep-sea vent hydrothermal mussel, Bath ymodiolus brevior, from the Lau Basin (Southwestern Pacific Ocean). Ph enotypically, this isolate exhibited characteristics similar to those described for members of the order Thermotogales. This organism was id entified as a member of the genus Thermosipho on the basis of the pres ence of the typical outer sheath-like structure (toga), its 16S rRNA s equence, and its ability to grow on carbohydrates (sucrose, starch, gl ucose, maltose, lactose, cellobiose, and galactose). The cells of tilt s organism were gram negative and rod shaped and generally occurred si ngly or in pairs, rarely occurring as chains with a maximum of five ro ds. At the optimum temperature for growth (70 degrees C), optimum pH ( 6.5), and optimum salinity (30 g of NaCl per liter), the doubling time was 100 min. In spite of the high percentage of similarity of its 16S rRNA sequence with that of Thermosipho africanus (98.6%), the weak le vel of DNA-DNA reassociation with this strain (2%) and particular phys iological characteristics allowed us to differentiate this new organis m from the sole species of the genus Thermosipho previously described (T. africanus). On the basis of these observations, we propose that th e new organism should be described as a new species, Thermosipho melan esiensis. The type strain of T. melanesiensis is BI429.