| Spiroplasmas that kill male progeny of infected female Drosophila by an unknown mechanism are the subject of this dissertation. Each of the four strains of sex-ratio-organisms (SROs), as they are known, harbors an endogenous short-tailed bacteriophage-like virus (spiroplasmavirus type 3, or SpV3), as does a fifth Drosophila spiroplasma that is not male-lethal. These viruses were studied and compared in terms of genome size, and ability of their DNAs to cross hybridize. Drosophila spiroplasma viruses possess genomes of 17, 21.8, or 32.3 kilobase pairs (kbp) of DNA. Two SROs had viruses of two different genome sizes. Hybridization of spiroplasma genomic DNA using a 17 kbp viral genome as a probe showed the 17 kbp viruses to be integrated into host DNA at multiple sites.; Only one of the 5 Drosophila spiroplasmas, D. willistoni strain B{dollar}sb{lcub}rm 3{rcub}{dollar}SR, has been successfully cultivated (triply-cloned, designated strain DW-1). Attempts to cultivate others led to the isolation of a non-fermenting, pink yeast, identified as Rhodotorula rubra, that supported the growth of the D. paulistorum SRO, and also the non-male-lethal strain of the D. willistoni SRO, referred to here as WSR{dollar}sp-{dollar}. Use of the yeast also allowed the reisolation of DW-1 from injected flies, thus satisfying the final condition of Koch's postulates, proving the pathogenicity of the SRO for Drosophila. Having both the male-lethal, and non-male-lethal strain of the D. willistoni SRO in culture should greatly facilitate study of the male-lethal trait.; The mechanics of spiroplasma motility and maintenance of helical morphology are currently unknown. Fundamental to understanding these phenomena is isolation of mutants defective in these properties. S. melliferum was mutagenized with nitrous acid, and subjected to a selective method based on chemotaxis and viscotaxis. Motility mutants, identified on the basis of their abnormal "fried egg" colony morphology on soft agar, were isolated that are non-motile with normal morphology, that have reduced motility and altered morphology, and that are motile within a narrower than normal pH range. These mutants will contribute to understanding the mechanisms of motility and helicity, and the role of spiroplasma motility in pathogenicity. |
