Spiroplasma and Its Interaction with Drosophila: Genome Sequencing and Analysis of Potential Fitness Effects of Naturally Infected Populations
Abstract
Intimate associations of maternally-inherited endosymbiotic bacteria and arthropods are ancient and taxonomically diverse. The nature of such relationships includes reproductive parasitism, as well as nutritional and defensive mutualisms. Spiroplasma are a wall-less bacterium (Class Mollicutes) associated with plants and arthropods. The genus Spiroplasma includes several strains that are heritable endosymbionts of several Drosophila species and other insects. At least four clades of Spiroplasma independently invaded Drosophila: Poulsonii, Citri Tenebrosa and Ixodetis. Spiroplasma frequencies are relatively high in certain populations of several Drosophila species as observed in the defensive strains associated to D. hydei, D. neotestacea D. melanogaster. Several Poulsonii strains act as reproductive manipulators and/or as defensive partners against parasitic wasps and/or nematodes. Herein, we present a draft genome of the defensive symbiont Spiroplasma poulsonii hyd1, a strain that enhances survival of Drosophila hydei flies against parasitism by the wasp Leptopilina heterotoma (Lh14). Additionally, we present a draft genome of the citri clade strain Spiroplasma citri moj, associated to D. hydei and D. mojavensis. Comparison with other available Spiroplasma genomes either associated to other Drosophila species or more distant arthropods allowed us to identify shared and unique genes and reveal interesting aspects about their metabolic capacity and potential factors involved in their phenotypes. Additionally, we performed phylogenomic analyses, which supported some of the previously hypothesized relationships but revealed incongruences regarding the validity of certain clades.
On the other hand, members of the Citri clade of Spiroplasma which are restricted to the repleta species group of Drosophila, can also reach relatively high infection prevalence. No evidence of fitness benefits or reproductive manipulation by members of this clade has been reported to date, although our preliminary work suggests that Spiroplasma from this clade do not confer protection. In the present study, we examined whether two citri-clade strains (moj and ald2) confer protection to their respective natural host species against two parasitic wasps: the cosmopolitan generalist Leptopilina heterotoma (Lh14; Figitidae); and Asobara sp. (Aw35; Braconidae; from Texas). Additionally, we tested whether the citri-clade strains (moj and hyd2; the latter harbored by D. hydei) induce reproductive phenotypes. We assessed oviposition rate in both strains and cytoplasmic incompatibility for moj by examining the outcome of reciprocal crosses of Spiroplasma-infected and Spiroplasma-free individuals. Cytoplasmic incompatibility (CI) was also tested; CI is the embryonic failure of the progeny from crosses between an uninfected female and an infected male, or between a female and male carrying incompatible symbiont strains. Although this reproductive parasitism has been observed in D. simulans and D. melanogaster infected with Wolbachia, we do not find evidence of CI induced by Spiroplasma in Drosophila hosts.
Citation
Martinez Montoya, Humberto (2017). Spiroplasma and Its Interaction with Drosophila: Genome Sequencing and Analysis of Potential Fitness Effects of Naturally Infected Populations. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /200675.