Caldicellulosiruptor kristjanssonii sp nov., a cellulolytic extremely thermophilic, anaerobic bacterium

A cellulolytic anaerobic bacterium, strain 177R1B(T), was isolated from a biomat sample of an Icelandic, slightly alkaline, hot spring (78 degrees C). Strain 177R1B(T) was rod-shaped, non-spore-forming, non-motile and stained Cram-negative at all stages of growth. It grew at 45-82 degrees C, with an optimum growth temperature around 78 degrees C. At 70 degrees C, growth occurred at ph 5.8-8.0, with an optimum near ph 7.0. At the optimum temperature and ph, with 2 g cellobiose I-1 as substrate, strain 177R1B(T) had a generation time of 2 h. During growth on Avicel, strain 177R1B(T) produced acetate, hydrogen and carbon dioxide as major fermentation products together with small amounts of lactic acid and ethanol. The strain fermented many substrates, including cellulose, xylan, starch and pectin, but did not grow with casein peptone, pyruvate, D-ribose or yeast extract and did not reduce thiosulfate to H2S. The G+C ratio of the cellular DNA was 35 mol%. Comparative 16S rDNA analysis placed strain 177R1B(T) among species of Caldicellulosiruptor. The closest relative was Caldicellulosiruptor lactoaceticus. Hybridization of total DNA showed 42 % hybridization to C. lactoaceticus and 22% hybridization to Caldicellulosiruptor saccharolyticus. A new species, Caldicellulosiruptor kristjanssonii sp. nov. (177R1B(T)) is proposed.