Abstract
Among the complex microbial community living in the mosquito midgut, some bacteria (e.g., Enterobacter spp.) can deliver effector molecules with anti-Plasmodium effects suppressing the development of malaria parasites (Plasmodium falciparum) before the öokinete can penetrate the mosquito midgut epithelium. Despite knowledge of this phenomenon, only a few studies have defined the diversity of microbiota in wild-caught adult Anopheles species. The objective of this study was to analyze and compare the bacterial microbiota in different Anopheles species, including representatives of the primary malaria vectors in western Thailand. Wild female Anopheles species were sampled from malaria-endemic areas in Tak and Mae Hong Son provinces near the Thai-Myanmar border. Midgut/abdominal bacterial diversity was assessed by examining the 16S rRNA gene, V3 hypervariable region, using PCR-Temporal Temperature Gel Electrophoresis (PCR-TTGE) profiling and sequence analysis. A total of 24 bacterial genera were identified from eight Anopheles species. Five bacterial genera were newly reported in Anopheles mosquitoes (Ferrimonas, Megasphaera, Pectobacterium, Shimwellia, and Trabulsiella). Five genera, including Megasphaera, were detected exclusively in a single-malaria (Plasmodium vivax) infected Anopheles minimus and not observed in other non-infected mosquitoes. The use of PCR-TTGE provides the first characterization of the midgut bacterial microbiome present in wild adult Anopheles in Thailand. Evidence that microbiota might impact pathogen development (suppression) in Anopheles and thereby reduce the risk of pathogen transmission deserves more studies to describe the presence and better understand the biological role of bacteria in natural mosquito populations.
Highlights
Despite significant progress in the control of malaria throughout the country, Thailand remains malaria-endemic, along the international borders with Cambodia, Lao PDR, Malaysia, and Myanmar (DDC, 2018)
The analysis of the microbiota detected in the abdomens of eight field-caught Anopheles species from Thailand resulted in 24 bacterial genera, among which five were only detected from one P. vivax-infected An. minimus specimen
A total of five genera were newly reported in Anopheles mosquitoes of which Megasphaera was only found in the malariainfected mosquito
Summary
Despite significant progress in the control of malaria throughout the country, Thailand remains malaria-endemic, along the international borders with Cambodia, Lao PDR, Malaysia, and Myanmar (DDC, 2018). Many Plasmodium gametocytes can be ingested during a single blood-feeding, only a small fraction typically develop to form oocysts (Leroy et al, 2014) The reason for this sharp decrease in potential infection density is multifactorial (genetic and non-genetic) and in large part influenced by the parasite-vector species relationship and individual mosquito susceptibility (competence) to Plasmodium infection allowing successful sporogonic development of the parasite while minimizing significant adverse effects on mosquito fitness (survival, fecundity, etc.) (Black and Severson, 2005; Lefevre et al, 2013). The role of enterobacteria that influences parasite development and transmission has been investigated in Anopheles mosquitoes Additional investigations on this phenomenon may help to develop novel methods involving bacterial symbionts to arrest malaria from vector to host
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