Mutual exclusion of Asaia and Wolbachia in the reproductive organs of mosquito vectors - PubMed (original) (raw)

doi: 10.1186/s13071-015-0888-0.

Irene Ricci 2, Alessia Cappelli 3, Claudia Damiani 4, Ulisse Ulissi 5, Maria Vittoria Mancini 6, Matteo Valzano 7, Aida Capone 8, Sara Epis 9, Elena Crotti 10, Bessem Chouaia 11, Patrizia Scuppa 12, Deepak Joshi 13, Zhiyong Xi 14, Mauro Mandrioli 15, Luciano Sacchi [ 16](#full-view-affiliation-16 "Dipartimento di Biologia e Biotecnologie "L. Spallanzani", Università di Pavia, Pavia, Italy. luciano.sacchi@unipv.it."), Scott L O'Neill 17, Guido Favia 18

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Mutual exclusion of Asaia and Wolbachia in the reproductive organs of mosquito vectors

Paolo Rossi et al. Parasit Vectors. 2015.

Abstract

Background: Wolbachia is a group of intracellular maternally inherited bacteria infecting a high number of arthropod species. Their presence in different mosquito species has been largely described, but Aedes aegypti, the main vector of Dengue virus, has never been found naturally infected by Wolbachia. Similarly, malaria vectors and other anophelines are normally negative to Wolbachia, with the exception of an African population where these bacteria have recently been detected. Asaia is an acetic acid bacterium stably associated with several mosquito species, found as a dominant microorganism of the mosquito microbiota. Asaia has been described in gut, salivary glands and in reproductive organs of adult mosquitoes in Ae. aegypti and in anophelines. It has recently been shown that Asaia may impede vertical transmission of Wolbachia in Anopheles mosquitoes. Here we present an experimental study, aimed at determining whether there is a negative interference between Asaia and Wolbachia, for the gonad niche in mosquitoes.

Methods: Different methods (PCR and qPCR, monoclonal antibody staining and FISH) have been used to address the question of the co-localization and the relative presence/abundance of the two symbionts. PCR and qPCR were performed to qualitatively and quantitatively verify the distribution of Asaia and Wolbachia in different mosquito species/organs. Monoclonal antibody staining and FISH were performed to localize the symbionts in different mosquito species.

Results: Here we provide evidence that, in Anopheles and in other mosquitoes, there is a reciprocal negative interference between Asaia and Wolbachia symbionts, in terms of the colonization of the gonads. In particular, we have shown that in some mosquito species the presence of one of the symbionts prevented the establishment of the second, while in other systems the symbionts were co-localized, although at reduced densities.

Conclusions: A mutual exclusion or a competition between Asaia and Wolbachia may contribute to explain the inability of Wolbachia to colonize the female reproductive organs of anophelines, inhibiting its vertical transmission and explaining the absence of Wolbachia infection in Ae. aegypti and in the majority of natural populations of Anopheles mosquitoes.

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Figures

Fig. 1

Fig. 1

Quantitative detection of Asaia in organs of three different lab-reared mosquito species obtained by qPCR. The relative amount of the bacteria is expressed as a ratio of bacterial 16S rRNA and mosquito rps7 genes (An. stephensi and Ae. albopictus) or rps3 gene (Cx. quinquefasciatus) copies in a logarithmic scale. Abundance results from the mean±SEM of six pools (10 organs) for each species. Statistically significant differences are represented by asterisks (p<0.01) as determined by multiple comparisons using Mann Whitney test

Fig. 2

Fig. 2

Detection of Asaia sp. on different species of mosquito eggs by IFA with anti-Asaia mAb. Eggs of An. stephensi (a,b), An. gambiae (c,d) and Ae. albopictus (e,f) are shown. a, c and f represent the treatment with secondary antibody only. Red signal shows the presence of Asaia on the surface of the eggs of An. stephensi and An. gambiae (b,d) while no signal was detected on the eggs of Ae. albopictus (e). Phase contrast images are shown in the boxed areas of the panel

Fig. 3

Fig. 3

_Asaia_-GFP colonization in different organs of Cx. quinquefasciatus. Left images show guts of female (top) and male (bottom) Cx. quinquefasciatus mosquitoes analyzed after colonization with _Asaia_-GFP provided with sugar solution. Arrows indicate the localization of main colonization (this area has been magnified in the square). Right images show gonads of female (top) and male (bottom) mosquitoes analyzed after colonization with _Asaia_-GFP. Even in the magnified area no signal of colonization is detected

Fig. 4

Fig. 4

Asaia and Wolbachia detection in gonads of _w_MelPop infected (W+) and uninfected (W−) _Ae. aegypt_i mosquitoes. Detection is shown through interferential contrast microscopy (column 1) and after whole mount in situ hybridization with Asaia (in magenta, column 2) and Wolbachia (in yellow, column 3) specific probes. Bar corresponds to 120 um

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