A NEW THERMOPHILIC ANAEROBIC CARBOXYDOTROPHIC BACTERIUM CARBOXYDOTHERMUS-RESTRICTUS SP-NOV

A new thermophilic, anaerobic, obligately carboxydotrophic bacterium, strain Z-RI, was isolated from a freshwater thermal vent of Raoul Isla nd. The cells of the isolate are Gram-positive non-sporeforming short rods with peritrichous flagella. The bacterium grows on CO (100% in th e gas phase) as the sole source of carbon and energy with the producti on of an equimolar amount of H-2 according to the equation CO + H2O = CO2 + H-2. NO other products are formed; no other substrates are used. Growth occurs at temperatures between 45 and 82 degrees C, with an op timum at 70 degrees C and within a pH range of 6.6 - 8.0 with an optim um at 7.0. Under optimal growth conditions with 100% CO in the gas pha se and without agitation the generation time is 8.3 h. At a concentrat ion of 100 mu g/ml, penicillin, vancomycin, erythromycin, and chloramp henicol completely inhibit growth and CO utilization. The isolate is n ot sensitive to streptomycin, rifampicin, and tetracycline (100 mu g/m l). The DNA GC content is 39 +/- 1 mole%. DNA - DNA hybridization with Carboxydothermus hydrogenoformans Z-2901(T) showed 7% homology. Based on the GC content in DNA, the data on DNA - DNA hybridization, and mo rphological and physiological features the isolate was assigned to a n ew species: Carboxydothermus restrictus (type strain Z-RI).