Exploration of the diversity of Blackflies gut bacteriome and Onchocerca volvulus infection

Background: Studies of arthropods involved in vectors borne diseases (tsetse flies, mosquitoes, and Drosophila) demonstrated the role of insect native bacteria in their host's physiology and metabolism with significant outcomes either to improve vector competence or on the contrary to induce host protective effects against these parasites infections. Their potential as biological tool for vector control strategies has also been successfully experienced and offer new perspectives to fight vector-borne diseases. However, such bacteria have never been described on blackfly, an arthropod transmitting Onchocerca volvulus, a parasite responsible of onchocerciasis a debilitating disease, endemic in many sub-Saharan Africa countries. This study aimed to fill this gap by providing an overview of the blackfly bacteriome diversity, highlighting significant associations of gut bacterial communities with the infections status of the blackflies to O. volvulus infection. Methodology: Entomological survey was conducted in three communities of Bafia health district in Cameroon. Transmission levels was assessed by measuring infectivity and infection rates through the O. volvulus detection on captured blackflies using quantitative PCR. Bacterial communities were screened from blackflies gut samples through high throughput sequencing of V3-V4 variable regions of the 16S ribosomal DNA gene and bioinformatics analysis allowed the taxonomic classification of bacterial species. Principal findings: From 1,496 dissected blackflies, a total of 207 parous flies was obtained, with a parity rate of 13.84%. The infestation rate of 10%, was indicative of ongoing onchocerciasis transmission in surveyed communities; Biatsota was the most active focus as per its close proximity with Mbam River (first line community) with 10.1% and 4.0% infection and infectivity rates, respectively. Sequencing process revealed 23 phyla and 210 genera. This result, highlighting the diversity of gut blackflies bacterial communities, which seems significantly larger than those of other arthropods of medical importance e.g. tsetse flies and mosquitoes. Besides, a diversity within the collected blackfly samples was also evidenced which is not associated to bacterial diversity. Wolbachia was the predominant genus with 70% of relative abundance of blackflies gut bacterial communities. Serratia sp and Acidomonas genera were significantly abundant among infected blackflies (p=0.043 and p=0.027 respectively), whereas other genera as Brevibacterium were associated with the absence of infection (p=0.008). Conclusion/Significance: This study revealed that whereas some bacteria genera are potentially involved in blackfly infection by O. volvulus, other genera could prevent the parasite infestation of blackfly and thus presents an interesting potential as a biological tool for a novel approach of vector control for fighting onchocerciasis. Keywords: onchocerciasis, black flies, Onchocerca volvulus, bacteriome, next generation sequencing