Use of data on the DNA G+C content in studies of molecular phylogeny of methanogenic archaebacteria

A new method for theoretical analysis of the molecular phylogeny of bacteri a, successfully applied earlier to nitrifying bacteria, was used to study t he molecular phylogeny of methanogenic archaebacteria. The group studied in cluded Methanococcus igneus, Methanococcus vannielii, Methanothermus fervid us, Methanolobus tindarius, Methanobacterium formicicum, Methanosarcina bar keri, Methanobacterium thermoformicicum, Methanoplanus limicola, Methanospi rillum hungatei, and Methanobacterium thermoautotrophicum. Based on the hyp othesis that direct linear regression always exists between evolutionary ch anges in the DNA G+C content and the primary structure of rRNA, the branchi ng order of the phylogenetic tree of methanogenic archaebacteria was determ ined. For this tree, the values of the evolutionary distance between 16S rR NA primary structures E-i and the values of the G+C evolutionary distance P -i exhibited a correlation coefficient of 0.78. Thus, the DNA G+C content i s not only an important taxonomic characteristic but also provides informat ion helpful for the determination of the branching order of phylogenetic tr ees constructed based on 16S rRNA primary structures.