Identification of microbiota associated with Polypedilum sp. (Diptera; Chironomidae), a midge adapted to extremely acidic environment

Chironomids (Diptera; Chironomidae), or non-biting midges, constitute a diverse family of holometabolous insects. Larvae of many species tolerate extreme conditions such as pollution, low pH, desiccation, heavy metals, salinity, low temperatures, and extreme depths. Recent studies suggest that their association with specific microorganisms can contribute to their tolerance. This study focused on bacteria associated to chironomids, an undescribed species of Polypedilum sp., present in Yukawa River of extremely acidic environments with complex stresses, hydrogen ions, heavy metal ions, and oligotrophic nutrition. Using 16S rRNA amplified sequencing, the microflora associated with Polypedilum sp. was investigated and compared to the microbial community of the Yukawa River, revealing lower larval alpha diversity and enrichment of specific strains of bacteria. To annotate those bacteria at the species level, we identified full-length 16S rRNAs, which showed at least three presumed new species, Acidithiobacillus sp., Oikeobacillus sp., and Anaeropeptidivorans sp., of bacteria in the body of the Polypedilum sp., possessing about 1×10^5 bacterial cells per specimen. Studying the microbes enriched in these larvae can provide insight into the mechanism of acid-tolerant chironomids.