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One hundred and fifty pink-pigmented facultatively methylotrophic bacteria (PPFMs) of the ‘Pseudomonas extorquens’ type, 28 other facultative methylotrophs and 16 non-methylo-trophic marker strains of the genera Pseudomonas, Alcaligenes, Mycoplana and Microcyclus were compared in a numerical phenetic study using 140 unit characters. Data were analysed using the simple matching (SSM ) and Jaccard (SJ ) coefficients and single, complete and average linkage algorithms. Cluster composition was largely the same with each similarity coefficient and linkage method. Four major and seven minor clusters containing 187 of the 194 strains were defined above the 80% similarity level. The non-pink methylotrophs were recovered in two major, four minor and two single-membered clusters. One of the major clusters could be equated with Microcyclus aquaticus but strains in the other were not identified. Strains in two of the minor clusters were identified as Pseudomonas species but members of the other two minor and one of the single-strain clusters were not positively identified. They had pseudomonad properties but were not closely associated with any marker strains. The other single-membered methylotroph cluster was thought to be a cytophaga or flexibacter. The remaining minor and single-membered clusters contained only marker strains. All the PPFMs were recovered in the two remaining major clusters which were closely related to each other but not to the rest of the organisms studied. The generic assignment of the PPFMs is discussed and the suggestion is made that the genus Methylobacterium may be the most appropriate place for them, despite their apparent inability to utilize methane.
Green et al. (Mon,) studied this question.