A Wolbachia lineage likely representing a new supergroup (Y) dominates the microbiome of the quill mite Syringophilus bipectinatus Heller, 1880 (Acariformes: Syringophilidae).

The microbiome plays a key role in animal biology, including host reproduction. Quill mites (Acariformes: Syringophilidae) are understudied ectoparasites of birds, with many species exhibiting strongly female-biased sex ratios. Previous studies have identified unique strains of Wolbachia and Spiroplasma in quill mites, both known to manipulate host reproduction in other arthropods. To further investigate this association, we analyzed the microbiome of Syringophilus bipectinatus Heller, 1880, a relatively early-diverging quill mite species parasitizing the Red Junglefowl (domestic type) (Galliformes: Phasianidae), using 16S rRNA gene profiling. We categorized mite specimens by sex and developmental stage to test for potential associations between microbiome composition and sex ratios. We report the first detection of Wolbachia in S. bipectinatus with a single amplicon sequence variant (ASV) consistently detected across all analyzed samples, accounting for 56-99% of total bacterial sequence reads. Phylogenetic analysis based on 16S rRNA gene and four protein-coding genes (fbpA, ftsZ, gatB, hcpA) recovered this strain as a deeply divergent Wolbachia lineage that does not cluster with any previously described supergroup. This lineage is therefore interpreted as likely representing a novel Wolbachia supergroup (Y), although its formal status requires further validation using genome-scale data. Its consistent presence across both sexes and all developmental stages suggests a stable and potentially obligate association, although its functional role remains to be determined. In addition, we identified bacterial taxa also reported from avian hosts, including potentially pathogenic genera such as Arcobacter, highlighting the complex microbial ecology of quill mites.