Molecular detection and maternal transmission of a bacterial symbiont Asaia species in field-caught Anopheles mosquitoes from Cameroon

Abstract

Background Malaria control relies mainlyon insecticide-based tools. However, the effectiveness of these tools is threatened by widespread insecticide resistance in malaria vectors, highlighting the need for alternative control approaches. The endosymbiont Asaia has emerged as a promising candidate for paratransgenic control of malaria, but its biology and genetics still need to be further analyzed across Africa. Here, we investigated the prevalence of Asaia and its maternal transmission in the natural population of Anopheles mosquitoes in Cameroon. Methods Indoor-resting adult mosquitoes belonging to four species (An. coluzzii, An. arabiensis, An. funestus and An. gambiae) were collected from eight localities across Cameroon from July 2016 to February 2020. PCR was performed on the Asaia-specific 16S ribosomal RNA gene, and samples positive by PCR for Asaia were confirmed by Sanger sequencing and phylogenetic analysis. The vertical transmission of Asaia was investigated by screening F1 mosquitoes belonging to F0Asaia-positive females. Results A total of 895 mosquitoes were screened. We found 43% (384) Asaia infection prevalence in four mosquito species. Phylogenetic analysis revealed that Asaia from Cameroon clustered together with the strains of Asaia isolated from other parts of the world. In addition, seven nucleotide sequence variants were found with low genetic diversity (π = 0.00241) and nucleotide sequence variant diversity (Hd = 0.481). Asaia was vertically transmitted with high frequency (range from 42.5 to 100%). Conclusions This study provides field-based evidence of the presence of Asaia in Anopheles mosquitoes in Cameroon for exploitation as a symbiont in the control of malaria in sub-Saharan Africa. Graphical abstract

Contrasting patterns ofAsaiasp association withPlasmodium falciparumbetween field collectedAnopheles gambiaeandAnopheles coluzziifrom Cameroon

“…coluzzii suggesting that both species are susceptible to the infection by Asaia sp. This infection rate of Asaia is higher than the one obtained in the previous study in Anopheles species in Cameroon [18]. This difference in prevalence could be due to seasonal and geographical heterogeneities variation in microbiota composition in Anopheles mosquitoes from the various studies sites [31][32][33].…”

“…It utilizes the genetically manipulated native microbiota of the insect vector to inhibit or kill the pathogen within the insect vector. Among the several candidates of paratransgenic control of malaria, Asaia is the focus of consideration due to its specific features such as stable association with Anopheles mosquitoes, genetic tractability, and horizontal and vertical transmission modes [18]. This study assessed the infection rate and density of Asaia sp.…”

“…Asaia has been shown to be a promising candidate for paratransgenic control of malaria. This is as a result of its negative effect on the development of Plasmodium at different stages [41] and its ability to transmit and persist in field Anopheles species [18]. In this study, we focused on the interaction Asaia - Plasmodium in natural Anopheles gambiae s.l populations by quantifying the amount of Asaia in Plasmodium infected and non-infected mosquitoes.…”

“…To confirm the bacterial isolates, amplified bacterial isolates products were sent for Sanger sequencing. In addition, in order to investigate whether the strains of Asaia infecting field mosquitoes differ from one season to another in both localities, samples from Bankeng and Gounougou were subjected to PCR as previously described [18] and also send for sequencing. Overall, four colonies of isolates and 57 individuals field samples were analysed using 16S rRNA gene.…”

Seasonal variation of microbiota composition in Anopheles gambiae and Anopheles coluzzii in two different eco‐geographical localities in Cameroon

“…gambiae by paratrangenesis. Bacteria from the genus Asaia have been evaluated as paratransgenic agents to control malaria transmission (Damiani et al, 2010 ; Favia et al, 2007 ; Maffo et al, 2021 ). Bacteria from this genus are considered viable candidates due to their stable association with anopheline mosquitoes throughout the body and different life stages; they can also be easily cultivated and transformed.…”