SpV3 viruses of Drosophila spiroplasmas.

The presence of spiroplasmas in the hemolymph of four Drosophila willistoni group species has been shown to cause elimination of males from the progeny of infected females. These spiroplasmas, known as sex-ratio organisms (SROs), are found in D. equinoxialis (ESRO), D. nebulosa (NSRO), D. paulistorum (PSRO), and D. willistoni (WSRO). In addition, a nonmale-lethal spiroplasma (HIS) has been found in the hemolymph of D. hydei. Only the WSRO has been cultivated. Each of the Drosophila spiroplasmas sheds at least one endogenous virus into the hemolymph by a budding process. These viruses are short-tailed polyhedrons resembling the SpV3 virus of Spiroplasma citri, and all have been shown to lyse at least one other strain of SRO. The Drosophila spiroplasma viruses have been extracted from infected flies and purified by metrizamide gradient centrifugation. The viruses, thus purified, maintained infectivity and lysed indicator strains of SROs. Electrophoresis of viral DNA produced bands indicating genomes of three different sizes: 17, 21.8, and greater than 30 kbp. Some SRO strains have more than one SpV3 virus. Restriction endonuclease digestion of DNA of the spiroplasma viruses HSV and NSV (both 21.8 kbp) produce patterns on agarose gels that indicate linear, circularly permuted genomes. The fragments generated by cleavage of NSV with EcoRI have been cloned into pBR325 and amplified in Escherichia coli. Restriction endonuclease digestion of NSV DNA hybridized with these clones indicates that there are two different 21.8-kbp SpV3 viruses in NSRO.