Seasonality and Locality Affect the Diversity of Anopheles gambiae and Anopheles coluzzii Midgut Microbiota from Ghana

Abstract

Symbiotic bacteria can have important implications in the development and competence of disease vectors. In Anopheles mosquitoes, the composition of the midgut microbiota is largely influenced by the larval breeding site, but the exact factors shaping this composition are currently unknown. Here, we examined whether the proximity to urban areas and seasons have an impact on the midgut microbial community of the two major malaria vectors in Africa, An. coluzzii and An. gambiae. Larvae and pupae were collected from selected habitats in two districts of Ghana during the dry and rainy season periods. The midgut microbiota of adults that emerged from these collections was determined by 454-pyrosequencing of the 16S ribosomal DNA. We show that in both mosquito species, Shewanellaceae constituted on average of 54% and 73% of the midgut microbiota from each site in the dry and rainy season, respectively. Enterobacteriaceae was found in comparatively low abundance below 1% in 22/30 samples in the dry season, and in 25/38 samples in the rainy season. Our data indicate that seasonality and locality significantly affect both the diversity of microbiota and the relative abundance of bacterial families with a positive impact of dry season and peri-urban settings.

Fig 1. Map of Ghana showing the studied districts and examples of habitats sampled.

Fig 2

Boxplot comparing OTU (A) and bacterial family (B) abundances for mosquito samples. Plots show distribution of bacteria between mosquito samples categorized under different sampling season, site status, and mosquito species. Black lines indicate medians.

Fig 3. Shannon-Weaver indices compared among samples collected in dry and rainy season.

Crosses in the box indicate the mean, and black lines are medians.

Fig 4

Bacterial family proportions in mosquito midguts sampled from breeding sites in Accra Metropolis (Ac_KBU, Ac_DZW, Ac_OPB) and Kintampo North Municipality (Ki_ATT, Ki_DD1, Ki_DD2, Ki_DD1/2, Ki_KAW, Ki_MAH, Ki_TAH) during the dry (A) and rainy (B) seasons. Families representing ≥0.01 proportions in each site are shown; all families <0.01 are grouped as ‘Others’.

Fig 5. Canonical Correspondence Analysis (CCA) for microbiota composition between breeding sites in the dry and rainy season.

Filled circles represent breeding sites and hollow circles represent samples (taxonomic level = family). Bacterial families with ≥0.01 relative abundance are indicated by name. Filled squares, triangles and stars represent site status (rural, urban), sampling season (dry, rainy), and mosquito species respectively. The length of each arrow indicates the strength of the variable that explains the bacteria dispersion observed. Bottom x-axis and left y-axis are scales for factors plotted, while top x-axis and right y-axis are scales for the biplot (arrows).