Methanocalculus pumilus sp nov., a heavy-metal-tolerant methanogen isolated from a waste-disposal site

A mesophilic hydrogenotrophic methanogen, strain MHT-1(T), was isolated fro m the leachate of a sea-based site for solid waste disposal (the port of Os aka, Japan). Strain MHT-1(T) was found to be an irregular coccus and was ab le to use H-2/CO2 and formate as energy sources. Acetate was required for g rowth. The optimum temperature and pH for growth were 35 degrees C and 6.5- 7.5, respectively. Strain MHT-1T was resistant to high concentrations of se veral heavy metals such as CdCl2 and CuSO4. The G+C content of the DNA was 51.9 mol%, Analysis of the 16S rRNA gene revealed that the isolate was a me mber of the genus Methanocalculus but distinct from its nearest neighbour, Methanocalculus halotolerans, there being a sequence similarity of 98.9%, D NA-DNA hybridization analysis revealed 51% relatedness with the DNA of M. h alotolerans strain SEBR 4845(T). The optimum NaCl concentration was 1.0%, w hereas the optimum in M, halotolerans was 5.0%, A new species, Methanocalcu lus pumilus, is proposed for strain MHT-1(T). The type strain is MHT-1(T) ( = DSM 12632(T) = JCM 10627(T)).