Methanoculleus chikugoensis sp nov., a novel methanogenic archaeon isolated from paddy field soil in Japan, and DNA-DNA hybridization among Methanoculleus species

A strictly anaerobic, irregularly coccoid, methanogenic archaeon, strain MG62(T) (= JCM 10825(T) = DSM 13459(T) was isolated from paddy field soil in Chikugo, Fukuoka, Japan. The cells stained Gram-negative, were 1.0-2.0 mum in diameter, were lysed by SDS and hypotonic solutions and were flagellated. Motility was not observed. The strain was able to use H-2/CO2, 2-propanol/CO2. formate, 2-butanol/CO2 and cyclopentanol/CO2 as substrates for methanogenesis, but did not utilize acetate, ethanol, methanol or methylamines. The optimum temperature and pH were 25-30 degreesC and 6.7-7.2. Analysis of lipid component parts (core lipids, phospholipid polar head groups and glycolipid sugar moieties) showed the characteristic pattern of members of the family Methanomicrobiaceae except for the absence of glucose as a glycollipid sugar moiety. The G+C content of the DNA was 62.2 mol%. Sequence analysis of the 16S rDNA revealed that the strain belonged to the genus Methanoculleus. The strain had DNA-DNA hybridization values of less than 50% with type strains of Methanoculleus species. On the basis of phenotypic, genotypic and phylogenetic characteristics, the name Methanoculleus chikugoensis sp. nov. is proposed for strain MG62(T) (= JCM 10825(T) = DSM 13459(T)). The DNA hybridization study also revealed the close relationships of three species, Methanoculleus olentangyi, Methanoculleus bourgensis and Methanoculleus oldenburgensis, among Methanoculleus species.