Distinct microbial communities of drain flies (Clogmia albipunctata) across sites with differing human influence.

Drain flies (Clogmia albipunctata) are insects that thrive in humid urban environments such as bathrooms drains and sewage systems. While their role in pathogen transmission has been suggested, little is known about their microbiome or ecology in non-clinical contexts. Using 16S rRNA gene metabarcoding, we characterized the bacterial communities of drain flies from three locations in South Korea, public bathrooms from a college in Seoul, a rural port in Ulleungdo island, and a highly frequented public park in Yeouido. In total, we obtained 221 families and 1 474 features. We found significant differences in microbiome composition and diversity as well as a small core microbiome shared among locations, with environmental bacteria such as Pseudomonas and Ralstonia being the dominant taxa across samples. The majority of the detected amplicon sequence variants (ASV) were not shared among locations. These findings suggest drain fly transport a location-specific environmental bacteria. Notably, we also identified ASVs of potential clinical relevance, including Mycobacterium, Acinetobacter baumanii, Providencia, and Nocardia. This is the first metagenomic insight into the microbiome of this species and adds to a renewed interest in the role that non-hematophagous insects play in urban microbial ecology and the spread of microbes.