TAXONOMIC ANALYSIS OF THERMOPHILIC STRAINS OF THE GENUS METHANOBACTERIUM - RECLASSIFICATION OF METHANOBACTERIUM-THERMOALCALIPHILUM AS A SYNONYM OF METHANOBACTERIUM-THERMOAUTOTROPHICUM

DNA reassociation, a comparative analysis of whole-cell protein patter ns, and indirect immunofluorescence methods were used to determine the taxonomic relationships of thermophilic Methanobacterium strains. On the basis of the results dendrograms showing degrees of similarity amo ng the organisms were constructed. The organisms studied are members o f three different groups. One group, whose members exhibit 10 to 40% c ross-hybridization, includes Methanobacterium wolfeii, ''Methanobacter ium defluvium'' ADZ, and ''Methanobacterium thermooflexum'' IDZ. The s econd group contains Methanobacterium thermophilum M(T) (T = type stra in) and Methanobacterium thermoaggregans (levels of DNA relatedness, 3 0 to 45%). The third group, whose members exhibit 65 to 99% cross-hybr idization, includes Methanobacterium thermoautotrophicum DELTAH(T), F- 1, and DV; Methanobacterium thermoformicicum Z-245T; and Methanobacter ium thermoalcaliphilum AC60T. The combination of three independent tax onomic methods showed that the group of strains studied is phenotypica lly, genotypically, and antigenically diverse. The most distinct organ isms are M. wolfeii, M. thermoaggregans, M. thermophilum, ''M. defluvi um,'' ''M. thermoflexum,'' and M. thermoautotrophicum. These species n ames should be adopted. The results of a DNA-DNA hybridization study ( level of hybridization, 99%), an immunological analysis (+3 reaction), and a protein similarity study (level of similarity, 75%) indicate th at M. thermoakaliphilum should be reclassified as a synonym of M. ther moautotrophicum.