Virus-mediated change in clumping properties ofDrosophila SR spiroplasmas

Transovarially transmitted SR spiroplasmas inDrosophila cause an abnormal sex ratio (SR condition: male-specific killing) in the host fly progenies. A reaction known as clumping takes place between different SR spiroplasma strains in which spiroplasmas instantly form aggregates upon mixing of the two strains. Each strain of SR spiroplasma carries an associated virus that is lytic to certain other strains. When the virus, HIV, from the recently discovered non-male-killingDrosophila hydei spiroplasma (HIS) is injected into host flies carrying the SR spiroplasma ofD. nebulosa (NSR), the latter spiroplasmas either undergo complete lysis and disappear, or survive with decreased numbers and with an abnormal morphology, and are transmissible from generation to generation in host flies. The surviving spiroplasmas possess two viruses, the endogenous virus of thenebulosa spiroplasma, spv-1, and the newly introduced superinfecting virus, HIV. This combination leads to a change in the surface properties of the superinfected spiroplasmas that is manifested in their ability to form clumps with normalnebulosa spiroplasmas, but does not interfere with male killing. This change in spiroplasma phenotype is discussed in terms of host-phenotype modification by infecting viruses.