Spiroplasma montanense sp. nov., from Hybomitra horseflies at northern latitudes in North America

Spiroplasma strain HYOS-1T was isolated from the gut of H. opaca collected in Montana, USA. The organism was serologically distinct from other spiroplasma species, groups and subgroups and was recently designated the representative of spiroplasma Group XXXI. The cells of strain HYOS-1T, as determined by light microscopy, were long motile helices. Electron microscopy revealed wall-less cells delimited by a single membrane. The cells passed through 450- and 300-nm filter pores with a 10-fold reduction in titre, but failed to pass through 100-nm pores. Strain HYOS-1T grew very well in most conventional medium formulations for spiroplasmas or other mollicutes. The organism grew at temperatures ranging from 5 to 41°C, and the optimum temperature was 32°C. The doubling time at the optimum temperature was 0.7 h, one of the shortest values obtained for members of the genus Spiroplasma. The strain catabolized glucose and hydrolysed arginine but not urea. Growth of the organism was stimulated by cholesterol and serum, but the strain was nevertheless able to grow in the absence of sterols or serum. The guanine-plus-cytosine content of the DNA was about 28±1 mol%, and the genome size was 1225 kbp. On the basis of the experimental results reported here and previously reported data, Group XXXI strain HYOS-1 (= ATCC 51745) is designated the type strain of a new species, S. montanense sp. nov.