Taxonomy of Microcyclus and Other Nonmotile, Ring-Forming Bacteria

Abstract
The genetic relatedness of some nonmotile, ring-forming bacteria was determined by DNA base composition and base sequence homology experiments. It is proposed that 4 gas vacuolate strains with DNA base compositions of 67.1-68.8 mol% guanine plus cytosine (G + C) be placed in M. aquaticus. Nonmotile vibrioid bacteria of 51% G + C (M. flavus Raj and spirosoma strains 1 and 2) were more closely related to one another than to M. aquaticus and it is suggested that the taxonomic position of M. flavus be reconsidered in relation to the genus Spirosoma. None of the nonmotile ring-forming strains were related to 2 Pseudomonadaceae. A motile variant of a gas vacuolated strain of M. aquaticus was isolated, indicating that immotility is a questionable taxonomic criterion for inclusion in the genus Microcyclus.

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