Transcriptome of Coxiella-like endosymbionts in Haemaphysalis longicornis during blood feeding

Coxiella-like endosymbionts (CLEs) are obligate nutritional mutualists of ticks that are thought to supplement B vitamins and other essential metabolites that are deficient in the tick's blood meal. Extensive colonization of CLEs has been observed in the ovaries and Malpighian tubules of several tick species, including Haemaphysalis longicornis. Despite experimental evidence linking symbionts to host fitness, their roles in blood feeding remain poorly understood. Here, we conducted a comparative transcriptomic analysis of CLE genes in adult female H. longicornis ticks before and two days after feeding. CLE genes were identified by mapping RNA-seq data onto the putative CLE genomes derived from the draft genome assembly of H. longicornis. Our analysis explored the potential function of CLEs during the early stage of blood feeding. The results revealed abundant expression of genes involved in B vitamin biosynthesis and enrichment of Gene Ontology terms associated with biotin and ubiquinone biosynthesis. Although most expressed CLE genes were shared between the two organs, gene expression patterns in response to blood feeding differed between the Malpighian tubules and ovaries. These findings suggest that CLEs in the Malpighian tubules and ovaries exhibit distinct functions during the early stage of blood feeding. Overall, this study provides a fundamental basis for identifying potential targets in anti-tick control strategies and enhances our understanding of how blood feeding impacts tick physiology.