AwMelWolbachiavariant inAedes aegyptifrom field-collectedDrosophila melanogasterwith increased phenotypic stability under heat stress

Abstract

Mosquito-borne diseases such as dengue, Zika and chikungunya remain a major cause of morbidity and mortality across tropical regions. Population replacement strategies involving the wMel strain of Wolbachia are being used widely to control mosquito-borne diseases transmitted by Aedes aegypti. However, these strategies may be influenced by environmental temperature because wMel is vulnerable to heat stress. wMel infections in their native host Drosophila melanogaster are genetically diverse, but few transinfections of wMel variants have been generated in Ae. aegypti mosquitoes. Here we successfully transferred a wMel variant (termed wMelM) originating from a field-collected D. melanogaster population from Victoria, Australia into Ae. aegypti. The new wMelM variant (clade I) is genetically distinct from the original wMel transinfection (clade III) generated over ten years ago, and there are no genomic differences between wMelM in its original and transinfected host. We compared wMelM with wMel in its effects on host fitness, temperature tolerance, Wolbachia density, vector competence, cytoplasmic incompatibility and maternal transmission under heat stress in a controlled background. wMelM showed a higher heat tolerance than wMel, with stronger cytoplasmic incompatibility and maternal transmission when eggs were exposed to heat stress, likely due to higher overall densities within the mosquito. Both wMel variants had minimal host fitness costs, complete cytoplasmic incompatibility and maternal transmission, and dengue virus blocking under standard laboratory conditions. Our results highlight phenotypic differences between closely related Wolbachia variants. wMelM shows potential as an alternative strain to wMel in dengue control programs in areas with strong seasonal temperature fluctuations.

Genomic and phenotypic comparisons reveal distinct variants of Wolbachia strain wAlbB

“…wspB is pseudogenized in w AlbB-I and this variant maintains higher densities under a high temperature cycle compared to w AlbB-II that carry a full-length version of the gene. This is consistent with two recent studies showing that, among variants of the Wolbachia strain w Mel, pseudogenization of the wspB gene is associated with variation in symbiont density and maternal transmission and that the magnitude of this effect can vary with both temperature and host background (54, 55). Finally, w AlbB variants differed in a number of house-keeping genes involved in essential functions such as DNA replication, RNA processing, translation or cell wall biogenesis that may contribute to the variation in symbiont density, and in heat shock response genes that could potentially control their different degrees of tolerance of heat stress.…”

Complex effects of environment and Wolbachia infections on the life history of Drosophila melanogaster hosts

“…Hague et al (2022), for example, recently described a single SNP in the outer membrane protein (WspB) of w Mel that might be a candidate for thermal sensitivity in bacteria. Another recent work by Gu et al (2022) reported the emergence of a new w MelM strain of Wolbachia in Aedes aegypti that induces increased heat tolerance in comparison to a w Mel variant from an Australian D . melanogaster population which differs in 36 SNPs and small indels.…”

“…Hague et al (2022), for example, recently described a single SNP in the outer membrane protein (WspB) of wMel that might be a candidate for thermal sensitivity in bacteria. Another recent work byGu et al (2022) reported the emergence of a new wMelM strain of Wolbachia in Aedes aegypti that induces increased heat tolerance in comparison to a wMel variant from an Australian D. melanogaster population which differs in 36 SNPs and small indels. Future studies to quantitatively link phenotypic effects and genomic variation of host and symbiont are needed to better understand mechanistically how host-symbiont interactions influence fitness.5 | CON CLUS IONWe observed no influence of bacterial infection on developmental life-history traits.…”

DevelopingWolbachia-based disease interventions for an extreme environment

“…We previously demonstrated that w AlbB and w MelM reduce DENV2 virus titers in Australian Ae. aegypti 64 . Here, we estimated the effects of these Wolbachia strains on DENV2 blocking in Ae.…”

“…Both strains are likely to be suitable for field release due to their strong virus blocking, maternal transmission, incompatibility effects and other characteristics. The w MelM strain in particular exhibited very strong blocking in the Saudi Arabian background, making this strain a good candidate for release given that it does not have severe fitness costs 64 . Note that although we did not test w MelM rigorously for cytoplasmic incompatibility here, it causes complete cytoplasmic incompatibility in an Australian background 64 and preliminary work suggests complete cytoplasmic incompatibility in a Saudi Arabian background (with no eggs hatching from >3000 eggs produced from a cross between a group of w MelM S males and Uninfected S females).…”