Abstract
Asaia bacteria commonly comprise part of the microbiome of many mosquito species in the genera Anopheles and Aedes, including important vectors of infectious agents. Their close association with multiple organs and tissues of their mosquito hosts enhances the potential for paratransgenesis for the delivery of antimalaria or antivirus effectors. The molecular mechanisms involved in the interactions between Asaia and mosquito hosts, as well as Asaia and other bacterial members of the mosquito microbiome, remain underexplored. Here, we determined the genome sequence of Asaia strain W12 isolated from Anopheles stephensi mosquitoes, compared it to other Asaia species associated with plants or insects, and investigated the properties of the bacteria relevant to their symbiosis with mosquitoes. The assembled genome of strain W12 had a size of 3.94 MB, the largest among Asaia spp. studied so far. At least 3585 coding sequences were predicted. Insect-associated Asaia carried more glycoside hydrolase (GH)-encoding genes than those isolated from plants, showing their high plant biomass-degrading capacity in the insect gut. W12 had the most predicted regulatory protein components comparatively among the selected Asaia, indicating its capacity to adapt to frequent environmental changes in the mosquito gut. Two complete operons encoding cytochrome bo3-type ubiquinol terminal oxidases (cyoABCD-1 and cyoABCD-2) were found in most Asaia genomes, possibly offering alternative terminal oxidases and allowing the flexible transition of respiratory pathways. Genes involved in the production of 2,3-butandiol and inositol have been found in Asaia sp. W12, possibly contributing to biofilm formation and stress tolerance.
Highlights
Bacteria of the genus Asaia are classified as acetic acid bacteria (AAB) in the classAlphaproteobacteria, family Acetobacteraceae; they are Gram-negative aerobic rods [1].These bacteria are frequently isolated from tropical plants such as Bauhinia purpurea and Plumbago, where they metabolize plant sugars and alcohol for growth [2]
Asaia species live in the mosquito midgut lumen and actively colonize other tissues and organs, including the salivary glands and reproductive organs, indicating that, if ingested in a sugar meal from a plant, Asaia bacteria pass through the tissue body barriers, such as midgut epithelium and basal lamina, reaching and infecting other tissues and organs [1]
W12 formed a clade with mosquito-associated A. bogorensis SF2.1 and A. bogorensis GD01, as well as ant-associated Asaia As-1742 (Figure 1); it departed from the cluster formed by plant-associated A. prunellae JCM25354, A. platycodi JCM25414, and A. astilbis
Summary
Alphaproteobacteria, family Acetobacteraceae; they are Gram-negative aerobic rods [1]. These bacteria are frequently isolated from tropical plants such as Bauhinia purpurea and Plumbago, where they metabolize plant sugars and alcohol for growth [2]. Asaia was one of the most predominant bacterial members found in samples of male and female mosquito midguts [4,5]. They persist in host mosquitoes without variations due to sex, blood and sugar meals, and age [5,6]. The infection of Asaia among mosquitoes occurs by horizontal transmission through mating (venereal transmission from adult male to adult female), as well as by vertical transmission from mother to progeny via ovarian infection to eggs [7,8]
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