Characterisation of the dynamic gut microbiota of members of the Anopheles gambiae complex

Abstract

The gut microbiota of mosquitoes plays a pivotal role in their life history. This includes insecticide resistance and immune responses, which makes it a potential target for vector control interventions. Although a growing body of research characterises the gut microbiota of various mosquito species, there is limited information on most members of the Anopheles gambiae complex. This study characterised the gut microbiota of four laboratory reared strains, namely SENN (Anopheles arabiensis- an insecticide susceptible major vector), SENN DDT (Anopheles arabiensis- an insecticide resistant major vector), MAFUS (Anopheles merus- minor vector) and SANGWE (Anopheles quadriannulatus- non-vector). The gut microbiota of fourth instar larvae, three-day old, fifteen-day old non-blood fed and fifteen-day old blood fed females was characterised and compared, bacterial identification was performed using Next-Generation Sequencing (NGS) of the bacterial 16S ribosomal RNA (rRNA) gene. The larval environment plays a role in acquiring gut microbes. This study characterised the gut microbiota of laboratory reared and wild F1 population An. arabiensis adult females and how changes in the larval environment affect the dynamics of the adult gut microbiota. Additionally, the effects of heavy metals on the gut microbiota of laboratory reared and F1 population of An. arabiensis adult females post-exposure to heavy metals in the larval breeding site were assessed. Furthermore, the effect of changes in the salt concentration in the larval environment on the gut microbiota of An. merus larvae and adults were examined. All bacterial identification of the gut microbiota was performed using NGS of the bacterial 16S rRNA. The dynamic gut mycobiota of SENN, SENN DDT and fourth instar larvae, three-day old, fifteen-day old non-blood fed and fifteen-day old blood fed laboratory reared and wild F1 population An. arabiensis females were characterised. Fungal identification was performed using NGS of the fungal internal (ITS) transcribed spacer of the rRNA cistron. Distinct differences were observed between the diversity and abundance of the gut microbiota of major malaria vectors and the minor and non-vectors, with the minor and non-vector harbouring more Plasmodium-protective bacterial genera. Pesticide-degrading bacteria were found in insecticide susceptible and insecticide resistant strains of An. arabiensis, suggesting that the gut microbiota does not contribute to insecticide resistance. However, differences between these strains indicate that the diversity of the gut microbiota is affected by the insecticide resistant phenotype. The F1 population and wild population of An. arabiensis had a greater gut microbiota diversity than laboratory reared An. arabiensis strains. Exposure to heavy metals as larvae significantly changed the abundance of gut bacteria in adults. The F1 population and SENN DDT adults had more heavy metal degrading bacterial genera present viii than SENN. Changes in the salinity of the larval environment of An. merus significantly affected larval development time, adult longevity, fecundity and deltamethrin tolerance. Additionally, An. merus adults exposed to the highest salt concentration at the larval stage had more Plasmodium-protective bacterial genera than the lower concentrations. The insecticide resistant phenotype of laboratory reared An. arabiensis affected the diversity and the differential abundance of fungi observed in the gut mycobiota. Furthermore, the gut mycobiota of the F1 population of An. arabiensis was similar to that of the laboratory reared insecticide resistant strain. In conclusion, these findings have implications for using gut bacteria as a vector control intervention in South Africa. The gut microbiota of the An. gambiae complex is a dynamic network consisting of what seems to be a core microbiota crucial to its function. The gut microbiota of the selected members of the An. gambiae complex corresponds to their capacity to transmit Plasmodium. Furthermore, the larval environment strongly influences the dynamics of the gut microbiota of members from the An. gambiae complex. Therefore, the impact of the larval environment on the adult microbiota must be considered for the development and implementation of future microbial-based strategies.