Metagenomic Profiles of Bacterial communities and environmental factors associated with proliferation of malaria vector mosquitoes within the Kenyan Coast

Background: Anopheles mosquitoes are the main malaria vector and as malaria cases decline in Sub Saharan Africa, there is a growing realisation that new interventions need to be added to complement the existing control strategies. To date, vector control is the most effective way to prevent malaria. Since the malaria parasite is maintained by mosquitoes which oviposit, feed and rest in the outdoor environment, there is an urgent need to focus on the control of oviposition sites seeking malaria vectors. In this regard, a detailed understanding of their larval ecology is necessary. In this study, the bacterial community structure and their interactions with physicochemical factors in relation to oviposition site selection in mosquito larval habitats was characterised in Kwale County, where malaria is endemic.

Materials and methods: The physical characteristics of each site with regard to type, permanence, substrate type of the habitat, depth, size and type of vegetation and water physicochemical parameters of the habitats were determined and recorded. Water samples were also collected from the sites for total genomic DNA extraction in order to characterise the bacterial communities in the breeding sites.

Results and Discussion: Physicochemical parameters assessed were not different between the positive and negative sites throughout the dry and rainy seasons (R2 = 0.1180, df = 1, P = 0.106). We found that 63.15% of the positive sites had Anopheles gambiae larvae only, 5.20% had Culex sp. larvae only, and 31.65% had both Anopheles gambiae and Culex sp. larvae. Proteobacteria (48.16 %) was the most common phyla recovered in all samples followed by Bacteroidota (32.91%) and then Actinobacteriota (10.94%). It was also observed that the presence or absence of mosquito larvae in a potential proliferation site was not related to the bacterial community structure in the site (R2 = 0.18157, df = 1, P = 0.353) but was positively correlated with bacterial richness and evenness (F = 2.928, df = 8, P = 0.032). There were 16 most commonly identified bacterial genera that were significantly abundant in the positive sites than in the negative sites. Although bacterial abundance was higher in the positive sites than in the negative sites, these differences were not associated with the physicochemical parameters that were evaluated (Kruskal-Wallis chi-squared = 6, df = 6, P = 0.4232).

Conclusion: Generally, the presence of Anopheles mosquito larvae was found to be positively correlated with bacterial richness and evenness, and negatively correlated with Electrical conductivity, total dissolved solids, salinity and ammonia. Mosquito oviposition and subsequent proliferation are possible in environmental waters with a variety of physicochemical properties and bacterial community compositions but the mosquitoes prefer mostly clean and unpolluted water. The findings of this study may have implications for predicting the potential of environmental water samples to become proliferation sites.