Interspecific Transfer of Bacterial Endosymbionts between Tsetse Fly Species: Infection Establishment and Effect on Host Fitness

Abstract

Tsetse flies (Glossina spp.) can harbor up to three distinct species of endosymbiotic bacteria that exhibit unique modes of transmission and evolutionary histories with their host. Two mutualist enterics, Wigglesworthia and Sodalis, are transmitted maternally to tsetse flies' intrauterine larvae. The third symbiont, from the genus Wolbachia, parasitizes developing oocytes. In this study, we determined that Sodalis isolates from several tsetse fly species are virtually identical based on a phylogenetic analysis of their ftsZ gene sequences. Furthermore, restriction fragment-length polymorphism analysis revealed little variation in the genomes of Sodalis isolates from tsetse fly species within different subgenera (Glossina fuscipes fuscipes and Glossina morsitans morsitans). We also examined the impact on host fitness of transinfecting G. fuscipes fuscipes and G. morsitans morsitans flies with reciprocal Sodalis strains. Tsetse flies cleared of their native Sodalis symbionts were successfully repopulated with the Sodalis species isolated from a different tsetse fly species. These transinfected flies effectively transmitted the novel symbionts to their offspring and experienced no detrimental fitness effects compared to their wild-type counterparts, as measured by longevity and fecundity. Quantitative PCR analysis revealed that transinfected flies maintained their Sodalis populations at densities comparable to those in flies harboring native symbionts. Our ability to transinfect tsetse flies is indicative of Sodalis ' recent evolutionary history with its tsetse fly host and demonstrates that this procedure may be used as a means of streamlining future paratransgenesis experiments.

An insect symbiosis is influenced by bacterium-specific polymorphisms in outer-membrane protein A

“…Based on genome comparison studies and phylogenetic analyses, Sodalis and SOPE form sister taxa (8). Interestingly, our results from multiple PCR-amplification experiments indicate that OmpA SOPE is highly homologous to OmpA Sodalis but has been rendered a nonfunctional pseudogene.…”

“…The symbionts included were Sodalis; CMS, a new lineage from the bloodsucking fly Craterina melbae (4); SOPE, the principle endosymbiont associated with the weevil, Sitophilus oryzae (5); Candidatus Hamiltonella defensa, a facultative symbiont found in many aphid species (20); and Photorhabdus luminescens, which is a mutualistic symbiont of heterorhabditid nematodes (21). Previous phylogenetic analysis indicated that the included symbionts form a distinct lineage related to the enteric pathogens (8). The first 171 aa of OmpA E.coli form eight membrane-traversing ␤-barrels connected by four loops (L1-L4) that are exposed to the external environment (22).…”

“…glossinidius were isolated from surface-sterilized G. m. morsitans pupae and cultured on Aedes albopictus C6/36 cells as described (37). Sodalis, which has a doubling time of Ϸ24 h, were subsequently maintained cell-free in vitro at 25°C in Mitsuhashi-Maramorosch (MM) medium (1 mM CaCl2, 0.2 mM MgCl2, 2.7 mM KCl, 120 mM NaCl, 1.4 mM NaHCO3, 1.3 mM NaH 2PO4, 22 mM D (ϩ) glucose, 6.5 g/liter lactalbumin hydrolysate, and 5.0 g/liter yeast extract) supplemented with 5% heat-inactivated FBS (8). E. coli K12 strains (including mutant and WT MG1655) were grown in LB media.…”

“…Selective elimination of Sodalis results in reduced tsetse longevity (7). Phylogenetic reconstruction analysis using ftsZ indicated that Sodalis from distant tsetse species have undergone minimal coevolution with their hosts, thus signifying the relatively recent establishment of this symbiosis (8). Sodalis can be cultivated in vitro, and a genetic transformation system has been developed to introduce and express foreign gene products both in vitro and in vivo (9).…”

“…Sodalis can be cultivated in vitro, and a genetic transformation system has been developed to introduce and express foreign gene products both in vitro and in vivo (9). Furthermore, distant tsetse species can be reconstituted with different Sodalis strains that subsequently mimic natural infections (8).…”