Spiroplasma platyhelix sp. nov., a new mollicute with unusual morphology and genome size from the dragonfly Pachydiplax longipennis

Spiroplasma strain PALS-1T from the gut of the dragonfly Pachydiplax longipennis was shown to be distinct from other species, groups, and subgroups of the genus Spiroplasma as determined by reciprocal serological metabolism inhibition and deformation tests. However, this strain cross-reacted extensively with representatives of other groups when it was used as an antigen. Electron microscopy of cells of strain PALS-1T revealed cells surrounded by a single cytoplasmic membrane. Light microscopy revealed helical cells that exhibited twisting motility rather than rotatory or flexing motility. Variations in the tightness of coiling were transmitted from one end of the helix to the other. The strain was resistant to penicillin, which confirmed that no cell wall was present. The organism grew well in M1D and SP-4 liquid media under either aerobic or anaerobic conditions. Growth also occurred in 1% serum fraction medium and in conventional horse serum medium. The optimum temperature for growth was 30°C, at which the doubling time was 6.4 h. Multiplication occurred at temperatures from 10 to 32°C. Strain PALS-1T catabolized glucose and hydrolyzed arginine but not urea. The guanine-plus-cytosine content of the DNA was 29 ± 1 mol%. The genome size was 780 kbp, the smallest genome size in the genus Spiroplasma. Strain PALS-1 (= ATCC 51748) is designated the type strain of a new species, Spiroplasma platyhelix.