DNA base composition was determined in 73 strains of aerobic, gram negative, methanol-utilizing bacteria, which are divided into nine groups on the basis of chemotaxonomic characteristics and utilization of carbon compounds. Guanine plus cytosine (G+C) contents in their DNAs ranged from 50.0 to 68.8mol% G+C. Group 1 bacteria (obligate methanol -utilizing bacteria) and group 4 bacteria (
Hyphomicrobium strains) showed rather wide distributions in DNA base composition, 50.0 to 56.0 mol% G+C and 59.3 to 65.6mol% G+C, respectively. In contrast, bacteria of group 2 (
Protomonas strains), group 3 (
Microcyclus strains), group 5 (
Xanthobacter strains), group 6, group 7, and group 8 (
Paracoccus denitrificans strains) had narrow ranges in DNA base composition. Group 9 (
Thiobacillus novellus) had 67.7mol% G+C. DNA-DNA homologies among the strains selected from the above-mentioned groups indicated a clear separation of the group 1 from the other groups. Further, group 1 was divided into six subgroups but not enough phenotypic characteristics were found to separate them from each other. Therefore, despite the heterogeneity of group 1 suggested by DNA base composition, DNA-DNA homology relatedness, and other chemotaxonomic characteristics, this group of bacteria are considered to be a single species from the practical point of view.
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