# Characterization of the Bacteriome of Culicoides reevesi from Chihuahua, Northern Mexico: Symbiotic and Pathogenic Associations

## TL;DR

This study explores the bacteria living inside Culicoides reevesi midges from northern Mexico, revealing both helpful and harmful microbes that could impact disease transmission.

## Contribution

This is the first characterization of the bacteriome of Culicoides reevesi, revealing symbiotic and pathogenic associations.

## Key findings

- The bacteriome is dominated by Pseudomonadota, with symbiotic taxa like Asaia and Cardinium and pathogenic bacteria such as Escherichia coli.
- Functional analysis shows pathways related to energy use, amino acid biosynthesis, and microbial communication.
- Bacterial composition varied between midge groups, suggesting host or environmental variability.

## Abstract

Biting midges are very small insects that can transmit diseases to animals and humans, yet we know little about the bacteria that live inside them. In this study, we examined the bacteria associated with Culicoides reevesi, a species found in northern Mexico that has not been well studied. We collected groups of adult midges and analyzed their bacteria using genomic and bioinformatic methods. We found that some of the bacteria may help in the metabolic process of insects, while others are known to cause disease in animals or humans. The bacteria also showed signs of being involved in important processes such as energy use, production of essential nutrients, and communication between microbes. Interestingly, even though all insects were collected from the same place and time, the types of bacteria varied between groups, suggesting that local conditions or differences among the insects themselves may play a role. This is the first study to describe the bacteria of C. reevesi. These findings can support better understandings of disease risks and may help to future strategies for controlling biting midges.

Culicoides biting midges are vectors of veterinary and zoonotic pathogens, yet the bacteriome of several species remains unexplored. Culicoides reevesi, a poorly studied species in northern Mexico, represents an opportunity to investigate microbial associations that may influence vector biology. Adults of C. reevesi were analyzed using 16S rRNA amplicon sequencing, followed by functional prediction with PICRUSt2. Heatmaps and pathway summaries were generated to highlight dominant taxa and functions. The bacteriome was dominated by Pseudomonadota, followed by Actinomycetota, Bacillota, and Bacteroidota. Symbiotic taxa such as Asaia and Cardinium were identified alongside potentially pathogenic bacteria, including Escherichia coli, Mycobacterium avium, Vibrio parahaemolyticus, and Enterococcus faecalis. Functional predictions indicated metabolic versatility, with abundant pathways related to aerobic respiration, the TCA cycle, amino acid biosynthesis, and quorum sensing. Despite all samples being collected from the same site and date, apparent differences in bacterial composition were observed across pools, suggesting microhabitat or host-related variability. This study provides the first taxonomic and functional baseline of the C. reevesi bacteriome. The detection of both symbiotic and pathogenic bacteria highlights the dual ecological role of the microbiome in host fitness and pathogen transmission potential. In conclusion, we suggest that these microbial associations influence vector physiology and competence, providing a basis for future microbiome-based control strategies. These findings emphasize the importance of integrating microbiome analyses into entomological surveillance and vector control strategies in endemic regions.