Mycoplasma melaleucae sp. nov., a sterol-requiring mollicute from flowers of several tropical plants

Three sterol-requiring mollicutes from floral surfaces of two tropical plant species (Melaleuca quinquenervia and Melaleuca decora) and a single isolate from a flower of the silk oak (Grevillea robusta) were serologically indistinguishable. Strain M1T (T = type strain), isolated from Melaleuca quinquenervia, was chosen for characterization. Light and electron microscopic observations of strain M1T revealed nonhelical, nonmotile, pleomorphic coccoid cells surrounded by a single cytoplasmic membrane. No evidence of a cell wall was observed. The organism grew well in SP-4 medium, but no sustained growth occurred in conventional mycoplasma media containing horse serum. The optimum temperature for growth was 23 degrees C, but multiplication occurred over a temperature range of 10 to 30 degrees C. Growth was not observed at temperatures above 30 degrees C. Strain M1T and related strains (strains M5, M10, and SO1) catabolized glucose but hydrolyzed neither arginine nor urea. The size of the strain M1T genome was about 561 megadaltons, while the guanine-plus-cytosine content of the DNA was about 27.0 mol%. The organism was serologically unrelated to the type strains of the 80 previously recognized Mycoplasma species or to 18 other unclassified sterol-requiring strains cultivated from animal, plant, or insect sources. Recent sequencing studies of 16S rRNA demonstrated that strain M1T is a member of a clade that contains the type species of the genus Mycoplasma. Strain M1 (= ATCC 49191) is the type strain of Mycoplasma melaleucae sp. nov.