Microbial diversity of the Tibetan tick Haemaphysalis tibetensis (Acari: Ixodidae)

Characterization of the complete mitochondrial genome and phylogenetic analyses of Haemaphysalis tibetensis Hoogstraal, 1965 (Acari: Ixodidae)

Ticks are specialized ectoparasites that feed on blood, causing physical harm to the host and facilitating pathogen transmission. The genus Haemaphysalis contains vectors for numerous infectious agents. These agents cause various diseases in humans and animals. Mitochondrial genome sequences serve as reliable molecular markers, forming a crucial basis for evolutionary analyses, studying species origins, and exploring molecular phylogeny. We extracted mitochondrial genome from the enriched mitochondria of Haemaphysalis tibetensis and obtained a 14,714-bp sequence. The mitochondrial genome consists of 13 protein-coding genes (PCGs), two ribosomal RNA, 22 transfer RNAs (tRNAs), and two control regions. The nucleotide composition of H. tibetensis mitochondrial genome was 38.38 % for A, 9.61 % for G, 39.32 % for T, and 12.69 % for C. The A + T content of H. tibetensis mitochondrial genome was 77.7 %, significantly higher than the G + C content. The repeat units of H. tibetensis exhibited two identical repeat units of 33 bp in length, positioned downstream of nad1 and rrnL genes. Furthermore, phylogenetic analyses based on the 13 PCGs indicated that Haemaphysalis tibetensis (subgenus Allophysalis) formed a monophyletic clade with Haemaphysalis nepalensis (subgenus Herpetobia) and Haemaphysalis danieli (subgenus Allophysalis). Although the species Haemaphysalis inermis, Haemaphysalis kitaokai, Haemaphysalis kolonini, and Haemaphysalis colasbelcouri belong to the subgenus Alloceraea, which were morphologically primitive hemaphysalines just like H. tibetensis, these four tick species cannot form a single clade with H. tibetensis. In this study, the whole mitochondrial genome sequence of H. tibetensis from Tibet was obtained, which enriched the mitochondrial genome data of ticks and provided genetic markers to study the population heredity and molecular evolution of the genus Haemaphysalis.

Microbiota assessment across different developmental stages of Dermacentor silvarum (Acari: Ixodidae) revealed stage-specific signatures

Dermacentor silvarum is an important vector of tick-borne pathogens. The microbiota of ticks has been recognized to influence their development, fitness, and reproduction as well as the acquisition, establishment and transmission of pathogens. Eggs, larvae, nymphs and adults (females and males) of D. silvarum were used in this study to evaluate microbial community and diversity across different developmental stages. The results demonstrated that some developmental stages host different bacterial species, confirming that each stage of development could have a specific associated microbiota. Proteobacteria was the dominant phylum in most stages, while Actinobacteria was the most abundant in nymphs. The abundance of Brevibacterium significantly increased from the egg stage to the following stages, and there was a sharp increase in the abundance of this genus among nymphs. Eggs showed the highest microbial richness and diversity, and the microbial community of eggs exhibited high similarity to that of females. Moreover, the high abundance of Coxiella in eggs and females further indicated that members of this genus are vertically transmitted symbionts. Nymphs showed a microbial composition distinct from those of the other stages, and the microbial community associated with males possessed higher species richness and greater bacterial diversity than that of females. Further investigations are needed to determine the functions of the microbiota and provide information enabling a better understanding of the diversity of the microbial community at different life stages.

Characterization of the bacterial community in Haemaphysalis longicornis (Acari: Ixodidae) throughout developmental stages

As one of the most important vectors, Haemaphysalis longicornis can transmit a variety of pathogens and is widely distributed in China. It has been reported that the bacterial community in ticks can impact tick fitness, development, and reproduction and even the transmission of tick-borne pathogens. In this study, bacterial diversity across all developmental stages (eggs, larvae, nymphs and adults) of H. longicornis was investigated using high-throughput sequencing technology. The results demonstrated that Proteobacteria was the dominant phylum and that Coxiella was the most abundant bacterial genus across all the samples. Alpha diversity analysis demonstrated that the eggs had the highest bacterial richness and diversity, and the bacterial community of the larvae was found to be similar to that of the eggs. However, there was a rapid increase in the relative abundance of Coxiella upon development of larvae to nymphs. Females exhibited the lowest bacterial diversity, and the proportion of Coxiella decreased from 85% in females to 45% in males. Our results suggest that H. longicornis lost most of the bacteria present in the early developmental stages and re-established the bacterial community after bloodmeals and molting.