THERMOANAEROBIUM-ACETIGENUM SPEC-NOV, A NEW ANAEROBIC, EXTREMELY THERMOPHILIC, XYLANOLYTIC NON-SPORE-FORMING BACTERIUM ISOLATED FROM AN ICELANDIC HOT-SPRING

An anaerobic, extremely thermophilic, xylanolytic nonspore-forming bac terium, strain X6B, was isolated from a 70-degrees-C Icelandic hot spr ing sediment. The bacterium was rod-shaped, 3.6-5.9 mum long and 0.7 t o 1.0 mum wide, and cells grew singly, in pairs, and occasionally form ed chains. The bacterium was nonmotile with no flagella. Cells from mi d-to late exponential gowth-phase cultures stained gram-negative but h ad a gram-positive like cell wall structure in transmission electron p hotomicrographs. The bacterium grew between 50-degrees-C and 78-degree s-C with an optimum temperature at about 65-degrees-C to 68-degrees-C. Growth occurred between pH 5.2 and 8.5 with an optimum pH close to 7. During growth on beech wood xylan, glucose and D-xylose, the isolate produced CO2, acetate and H-2 as major fermentation products, and a sm all amounts of ethanol; lactate was not produced. X6B did not reduce a cetone to isopropanol or sulphate or thiosulfate to sulfide. The base composition of X6B's cellular DNA was 35.7 mol% guanine + cytosine. Th e properties of this strain do not fit any previously described specie s. The name proposed for the isolated bacterium was Thermoanaerobium a cetigenum, spec. nov.