Thermococcus barophilus sp. nov., a new barophilic and hyperthermophilic archaeon isolated under high hydrostatic pressure from a deep-sea hydrothermal vent

A novel barophilic, hyperthermophilic, anaerobic sulfur-metabolizing archae on, strain MPT (T = type strain), was isolated from a hydrothermal vent sit e (Snakepit) on the Mid-Atlantic Ridge (depth, 3550 m). Enrichments and iso lation were done under 40 MPa hydrostatic pressure at 95 degrees C. Strain MPT was barophilic at 75, 80, 85, 90, 95 and 98 degrees C, and was an oblig ate barophile between 95 and 100 degrees C (T-max). For growth above 95 deg rees C, a pressure of 15.0-17.5 MPa was required. The strain grew at 48-95 degrees C under atmospheric pressure. The optimal temperature for growth wa s 85 degrees C at both high (40 MPa) and low (0.3 MPa) pressures. The growt h rate was twofold higher at 85 degrees C under in situ hydrostatic pressur e compared to at low pressure. Strain MPT cells were motile, coccoid, 0.8-2 .0 mu m in diameter and covered by a hexagonal S-layer lattice. The optimum pH and NaCl concentration for growth at low pressure were 7.0 and 20-30 g l(-1), respectively. The new isolate was an obligate heterotroph and utiliz ed yeast extract, beef extract and peptone for growth. Growth was optimal i n the presence of elemental sulfur. Rifampicin and chloramphenicol inhibite d growth. The core lipids consisted of a major archaeol and a complex lipid pattern consisting of a major phospholipid. The DNA G+C content was 37.1 m ol%. Sequencing of the 16S rRNA gene revealed that strain MPT belonged to t he genus Thermococcus and it is proposed that this isolate should be design ated as a new species, Thermococcus barophilus.