Thermophilic anaerobic acetate-utilizing methanogens and their metabolism

Six strains of thermophilic anaerobic acetate-utilizing methanogens were isolated from different full-scale thermophilic biogas plants in China and Denmark. The strain isolated from the Chinese biogas plant was designated KN-6P and the isolates from the Danish full-scale biogas plants were designated HG-1P, LVG-4P R1-1P, SO-2P and V-1P. The isolates were characterized morphologically and physiologically, and their immunological and phylogenetic relatedness to already known isolated strains were established. All isolated strains were identified as organisms belonging to genus Methanosarcina, utilizing the substrates acetate, methanol and methylamines but not hydrogen/carbon dioxide. Strain Methanosarcina sp. SO-2P was able to grow mixotrophically on methanol and hydrogen/carbon dioxide with methane formation from hydrogen and carbon dioxide occurring after methanol depletion. All six Methanosarcina strains required vitamins as growth factor. The isolates differed in cardinal growth pH and temperatures, the kinetic parameters - maximum specific growth rate and half saturation constant - and threshold values during growth on acetate. Analysis of total cell proteins by SDS-page gel electrophoresis revealed patterns of the individual strains distinct from the type strain Methanosarcina thermophila TM-1. Antigenic fingerprints of the isolates were different from that of Methanosarcina thermophila TM-1 and represented new immunotypes. However, the DNA-DNA homology study revealed that the similarity level between strains from the Danish biogas plants and Methanosarcina thermophila TM-1 was higher than 70%, and thus these strains should be considered as organisms belonging to the species Methanosarcina thermophila. DNA of strain KN-6P was only distantly related to the DNA of Methanosarcina thermophila TM-1, with 46% homology, and the strain KN-6P was proposed to be th