SPIROPLASMA-INSOLITUM SP-NOV, A NEW SPECIES OF GROUP-I SPIROPLASMA WITH AN UNUSUAL DNA-BASE COMPOSITION

Spiroplasma strain M55, isolated from a fall flower in Maryland, showed patterns of partial serological cross-reactivity with the other seven group I spiroplasma subgroups but was not serologically related to other spiroplasma groups. Strain M55 had less than 70% DNA-DNA homology with group I subgroups previously assigned binomial names and was unique among the group I subgroups in possessing a higher guanine-plus-cytosine content in its DNA (28 +/- 1 mol%, versus 26 +/- 1 mol% for other group I subgroups). The genome size was 1,850 kb (1,233 MDa). Extensive data on the metabolism of strain M55 and the community ecology of this and similar strains have been reported. These circumstances fulfill criteria proposed by the Subcommittee on the Taxonomy of Mollicutes for elevation of mollicute subgroups to species status. Accordingly, strain M55 was characterized according to proposed minimal standards for species descriptions. Cells of strain M55 were shown by light microscopy to be helical, motile filaments. Electron microscopy showed that the cells possessed no cell wall and were bounded by a single membrane; they were insensitive to penicillin (1,000 U/ml). Strain M55 was culturable in MlD and SP-4 liquid media under aerobic (with or without enhanced carbon dioxide) or anaerobic environments. Optimal growth occurred at 30-degrees-C, with a doubling time of 7.2 h. Growth occurred from 15 to 37-degrees-C but not at 10 or 42-degrees-C. Strain M55 did not utilize urea or hydrolyze arginine but did produce acid from glucose. As a consequence of these studies, strain M55 is designated the type strain (M55T;ATCC 33502T) of a new species, Spiroplasma insolitum.