Molecular characterisation of tsetse-endosymbiont interactions in Kenyan populations of glossina austeni and glossina pallidipes tsetse flies

Abstract

Tsetse flies (Diptera: Glossinidae), which are the major vectors of human and animal trypanosomes, harbour bacterial gut symbionts Wigglesworthia glossinidia, Wolbachia pipientis and Sodalis glossinidius in close association with trypanosomes. The objective of this study was to determine the prevalence, temporal variation and strain diversity of these endosymbionts in G. austeni and G. pallidipes from the Kenyan coast. The co-relation between symbiont and trypanosomes infection was also assessed, in order to provide insight into tsetse-symbionttrypanosome interactions. Fly age was estimated using ovarian ageing and wing fray analysis. Symbiont infection was determined using symbiont-specific assays targeting wsp, 16s rRNA, GPO1 genes. Trypanosome infection was also determined by dissection and generic primers. The diversity of infecting symbiont strains was evaluated by wsp typing, multi-locus strain typing (MLST) and variable number of tandem repeats (VNTRs) methods. Trypanosomesymbiont co-infection was assessed in both natural and experimental populations and in ampicillin-treated flies. The results showed that although Wolbachia infected all G. austeni individuals sampled, no G. pallidipes sampled was Wolbachia-infected. Sodalis infection was found in 3.7% of G. austeni and in 15.9% of G. pallidipes sampled. Wolbachia strains were found to be homogenous based on wsp typing, but slight variations were detected using MLST. In addition, multiple Sodalis strain variations were detected. Age grading revealed that female flies of both species had comparable longevity; but that male G. pallidipes analysis had longer lifespan than G. austeni. Trypanosome infection rates of 12.8% and 9.6% were recorded in G. austeni and G. pallidipes respectively, of which 45.6% were T. congolense infections. In natural populations, Sodalis-trypanosome co-infection was less than 4% in both species, predominantly with T. congolense or T. simiae trypanosomes. The level of significance of the association between trypanosome and Sodalis infection was found to differ depending on fly species and trypanosome species. This study concludes that there is marked heterogeneity in gut microfauna in terms of infection incidence, strain diversity and temporal infection patterns in natural tsetse populations. Additionally, infection with a particular symbiont does not appear to influence either the presence of the other symbionts or trypanosome infection. This study highlights interspecific differences in tsetse-symbiont-trypanosomes tripartite interactions that proposed symbiont-mediated tsetse control interventions should take into account.