Gut microbiota landscape of <i>Haemaphysalis longicornis</i> under <i>Borrelia burgdorferi</i> infection

This study aimed to explore the reason for Haemaphysalis longicornis restricting Borrelia burgdorferi colonization and transmission from the perspective of gut microbiota, and to investigate the impact of different infection statuses on the Haemaphysalis longicornis microbiota and its potential role in pathogen transmission. Pathogen-free Haemaphysalis longicornis ticks and IFNAR1^-/- mice were used to establish infection models. Ticks fed on pathogen-infected mice, and their midguts were analyzed at day 4 and 10 post-feeding. DNA was extracted from the midguts, and the V3-V4 region of bacterial 16S rRNA gene was amplified and sequenced. Analysis of microbiome data were analyzed using QIIME2 and R. After digesting the bloodmeals, the gut microbiota of ticks that ingested bloodmeal with Borrelia burgdorferi exhibited minimal structural changes, while the ticks with uninfected bloodmeal or bloodmeal with Langat virus showed the dysbiosis. The Borrelia group showed minimal temporal shifts in β-diversity, with stable co-occurrence networks and increased core microbial interactions. Neutral model analysis revealed a hybrid niche in the Borrelia group. Potential biomarkers were identified that may suppress Borrelia burgdorferi transmission. Our findings reveal that Borrelia burgdorferi infection is associated with a stabilized and functionally distinct gut microbiota in Haemaphysalis longicornis. The gut microbiota of Haemaphysalis longicornis functions as a barrier against Borrelia burgdorferi colonization and transmission through microbial regulation and resource limitation, thus providing a potential mechanistic explanation for the observed vector incompetence. These findings highlight the potential of microbiome-targeted strategies to block pathogen transmission and offer new insights into vector-borne disease.