Glycine-rich antimicrobial peptides in Anopheles gambiae

Antimicrobial peptides (AMPs) are an important group of immune effectors that play a role in fighting microbial infections. However, while AMPs have been described in mosquitoes, their contribution to host antimicrobial defense is still not completely understood.

In this study, we used transcriptional profiling to identify AMP genes differentially expressed in Anopheles gambiae adult female mosquitoes after challenge with three Gram-positive bacteria, four Gram-negative bacteria, and two yeast species, respectively. Our analyses identified nine out of the eleven annotated AMP genes to be differentially expressed at 12h post infection in at least one of the nine challenges. Using this approach, we also identified two genes encoding glycine-rich peptides (35 and 52% glycine content, respectively) that are differentially expressed upon microbial challenge. By exploring the genome annotation of these potential glycine-rich AMPs, we identified at least five paralogs, several of which have orthologs across the Culicidae.

To evaluate their antimicrobial activity, we used RNAi in adult female mosquitoes to silence a number of annotated AMP genes as well as two of the candidate AMPs and performed zone of inhibition assays with their hemolymph after bacterial challenge. Our results show that one of our candidates has antimicrobial activity comparable to known mosquito AMPs, reducing the growth of Micrococcus luteus by at least 50%.

In summary, our study provides information that increases our understanding of the role of AMPs in response to microbial infections in mosquitoes and expands the known spectrum of antimicrobial peptides in An. gambiae.