RESUMO
Two species of Spiroplasma (Mollicutes) bacteria were isolated from and described as pathogens of the European honey bee, Apis mellifera, ~30 years ago but recent information on them is lacking despite global concern to understand bee population declines. Here we provide a comprehensive survey for the prevalence of these two Spiroplasma species in current populations of honey bees using improved molecular diagnostic techniques to assay multiyear colony samples from North America (U.S.A.) and South America (Brazil). Significant annual and seasonal fluctuations of Spiroplasma apis and Spiroplasma melliferum prevalence in colonies from the U.S.A. (n = 616) and Brazil (n = 139) occurred during surveys from 2011 through 2013. Overall, 33% of U.S.A. colonies and 54% of Brazil colonies were infected by Spiroplasma spp., where S. melliferum predominated over S. apis in both countries (25% vs. 14% and 44% vs. 38% frequency, respectively). Colonies were co-infected by both species more frequently than expected in both countries and at a much higher rate in Brazil (52%) compared to the U.S.A. (16.5%). U.S.A. samples showed that both species were prevalent not only during spring, as expected from prior research, but also during other seasons. These findings demonstrate that the model of honey bee spiroplasmas as springtime-restricted pathogens needs to be broadened and their role as occasional pathogens considered in current contexts.
Assuntos
Abelhas/microbiologia , Spiroplasma/isolamento & purificação , Animais , Carga Bacteriana , Brasil , Estações do Ano , Spiroplasma/classificação , Spiroplasma/genética , Estados UnidosRESUMO
Spiroplasma endosymbionts are maternally transmitted bacteria that may kill infected sons resulting in the production of female-biased broods. The prevalence of male killers varies considerably both between and within species. Here, we evaluate the spatial and temporal status of male-killing and non-male-killing Spiroplasma infection in three Brazilian populations of Drosophila melanogaster, nearly a decade after the first occurrence report for this species. The incidence of the male-killing Spiroplasma ranged from close to 0 to 17.7 % (so far the highest estimate for a Drosophila species) with a suggestion of temporal decline in a population. We also found non-male-killing Spiroplasma coexisting in one population at lower prevalence (3-5 %), and we did not detect it in the other two. This may be taken as a suggestion of a spreading advantage conferred by the male-killing strategy. Sequencing two loci, we identified the phylogenetic position of Spiroplasma strains from the three localities, showing that all strains group closely in the poulsonii clade. Due to intensive sampling effort, we were able to test the association between Spiroplasma infections and another widespread endosymbiont, Wolbachia, whose prevalence ranged from 81.8 to 100 %. The prevalence of Wolbachia did not differ between Spiroplasma-infected and uninfected strains in our largest sample nor were the prevalences of the two endosymbionts associated across localities.
Assuntos
Drosophila melanogaster/microbiologia , Spiroplasma/genética , Spiroplasma/fisiologia , Wolbachia/fisiologia , Animais , Brasil , DNA Bacteriano/genética , DNA Bacteriano/isolamento & purificação , Feminino , Masculino , Filogenia , Reação em Cadeia da Polimerase , Prevalência , Fatores Sexuais , Razão de Masculinidade , Especificidade da Espécie , Spiroplasma/classificação , Spiroplasma/isolamento & purificação , Simbiose , Wolbachia/genética , Wolbachia/isolamento & purificaçãoRESUMO
Elucidation of the mechanism of action of selfish genetic elements is difficult outside species with well-defined genetics. Male-killing, the phenomenon whereby inherited bacteria kill male hosts during embryogenesis, is thus uncharacterized in mechanistic terms despite being common and important in insects. We characterized the prevalence, identity and source of the male-killing infection recently discovered in Drosophila melanogaster in Brazil. Male-killing was found to be present in 2.3% of flies from Recife, Brazil, and was uniquely associated with the presence of Spiroplasma infection. The identity of sequences across part of the 16S and across the 16S-23S ITS region indicated that the male-killing infection of D. melanogaster was very closely related to S. poulsonii, the source of the male-killing infection in willistoni group flies also found in South America. The sequences of two further protein-coding genes indicated the D. melanogaster infection to be most closely related to that found in D. nebulosa, from the willistoni group. Our data suggest that the establishment of D. melanogaster in South America was associated with the movement of male-killing bacteria between species.