Carboxydobrachium pacificum gen. nov., sp nov., a new anaerobic, thermophilic, CO-utilizing marine bacterium from Okinawa Trough

A new anaerobic, thermophilic, CO-utilizing marine bacterium, strain JM(T), was isolated from a submarine hot vent in Okinawa Trough. Cells of strain JM(T) were non-motile thin straight rods, sometimes branching, with a cell wall of the Gram-positive type, surrounded with an S-layer. Chains of three to five cells were often observed. The isolate grew chemolithotrophically on CO, producing equimolar quantities of H-2 and CO2 (according to the equa tion CO+H2O --> CO2+H-2) and organotrophically on peptone, yeast extract, s tarch, cellobiose, glucose, galactose, fructose and pyruvate, producing H-2 , acetate and CO2. Growth was observed from 50 to 80 degreesC with an optim um at 70 degreesC. The optimum pH was 6.8-7.1. The optimum concentration of sea salts in the medium was 20.5-25.5 g l(-1). The generation time under o ptimal conditions was 7.1 h. The DNA G+C content was 33 mol%. Growth of iso late JM(T) was not inhibited by penicillin, but ampicillin, streptomycin, k anamycin and neomycin completely inhibited growth. The results of 16S rDNA sequence analysis revealed that strain JM(T) belongs to the Thermoanaerobac ter phylogenetic group within the Bacillus-Clostridium subphylum of Gram-po sitive bacteria but represents a separate branch of this group. On the basi s of morphological and physiological features and phylogenetic data, this i solate should be assigned to a new genus, for which the name Carboxydobrach ium is proposed. The type species is Carboxydobrachium pacificum; the type strain is JM(T) (= DSM 12653(T)).