Abstract
A mesophilic hydrogenotrophic methanogen, strain MHT-1(T), was isolated from the leachate of a sea-based site for solid waste disposal (the port of Osaka, Japan). Strain MHT-1(T) was found to be an irregular coccus and was able to use H(2)/CO(2) and formate as energy sources. Acetate was required for growth. The optimum temperature and pH for growth were 35 degrees C and 6.5--7.5, respectively. Strain MHT-1(T) was resistant to high concentrations of several heavy metals such as CdCl(2) and CuSO(4). The G+C content of the DNA was 51.9 mol%. Analysis of the 16S rRNA gene revealed that the isolate was a member of the genus Methanocalculus but distinct from its nearest neighbour, Methanocalculus halotolerans, there being a sequence similarity of 98.9%. DNA--DNA hybridization analysis revealed 51% relatedness with the DNA of M. halotolerans strain SEBR 4845(T). The optimum NaCl concentration was 1.0%, whereas the optimum in M. halotolerans was 5.0%. A new species, Methanocalculus pumilus, is proposed for strain MHT-1(T). The type strain isMHT-1(T) (=DSM 12632(T)=JCM 10627(T)).