Organ-specific bacterial microbiota in the engorged female <i>Haemaphysalis longicornis</i> ticks

Bacterial microbiota are involved in tick physiology and varies with various factors. The variation of bacterial microbiota among tick organs is less investigated. In this study, the bacterial microbiota of four organs (ovaries, salivary glands, midgut, and Malpighian tubules) from the engorged female Haemaphysalis longicornis were surveyed using 16S rRNA high-throughput sequencing. Results indicated that the bacterial richness and diversity varied among tick organs, and ovaries had the lowest level of bacterial richness and diversity. The ovaries and salivary glands had relatively stable bacterial compositions when considering bacterial abundance. Proteobacteria was the dominant bacterial phylum in the four organs, followed by Firmicutes, Bacteroidota and Actinobacteriota. The ovaries carried more Proteobacteria, while the Firmicutes abundance was higher in salivary glands. The environmental bacteria including Staphylococcus, Pseudomonas, Brevundimonas, Acinetobacter, Enterobacter, and Stenotrophomonas had high abundance in the midgut and salivary glands, suggesting that ticks can acquire environmental bacteria through blood meals or host skin. The predominant proportion of Coxiella in ovaries ensures its vertical transmission, and Coxiella in Malpighian tubules can provide nutrients to the host. In conclusion, organ-specific bacterial microbiota was observed in the engorged female H. longicornis, and the functions of these bacteria in organs remain to be investigated.