Peptides with Antimicrobial Activity in the Saliva of the Malaria Vector Anopheles coluzzii

TL;DR

This study identifies two antimicrobial peptides in the saliva of Anopheles coluzzii mosquitoes that can inhibit the growth of both Gram-positive and Gram-negative bacteria.

Contribution

The discovery of two novel antimicrobial peptides in mosquito saliva that may protect mosquitoes from microbial infections during feeding.

Findings

Hyp6.2 inhibits the growth of Gram-positive and Gram-negative bacteria.

Hyp13 dose-dependently inhibits E. coli and S. marcescens growth and causes membrane disruption.

The peptides may help protect mosquito mouthparts and digestive tracts from microbial infection.

Abstract

Mosquito saliva plays a crucial physiological role in both sugar and blood feeding by helping sugar digestion and exerting antihemostatic functions. During meal acquisition, mosquitoes are exposed to the internalization of external microbes. Since mosquitoes reingest significant amounts of saliva during feeding, we hypothesized that salivary antimicrobial components may participate in the protection of mouthparts, the crop, and the gut by inhibiting bacterial growth. To identify novel potential antimicrobials from mosquito saliva, we selected 11 candidates from Anopheles coluzzii salivary transcriptomic datasets and obtained them either using a cell-free transcription/translation expression system or, when feasible, via chemical synthesis. Hyp6.2 and hyp13, which were predicted to be produced as propeptides and cleaved in shorter mature forms, showed the most interesting results in bacterial growth inhibition assays. Hyp6.2 (putative mature form, 35 amino acid residues) significantly inhibited the growth of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli and Serratia marcescens) bacteria. Hyp13 (short form, 19 amino acid residues) dose-dependently inhibited E. coli and S. marcescens growth, inducing membrane disruption in both Gram-positive and Gram-negative bacteria as indicated with scanning electron microscopy. In conclusion, we identified two A. coluzzii salivary peptides inhibiting Gram-positive and Gram-negative bacteria growth and possibly contributing to the protection of mosquito mouthparts and digestive tracts from microbial infection during and/or after feeding.

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