Recently Evolved Francisella-Like Endosymbiont Outcompetes an Ancient and Evolutionarily Associated Coxiella-Like Endosymbiont in the Lone Star Tick (Amblyomma americanum) Linked to the Alpha-Gal Syndrome

Abstract

BackgroundTicks are hematophagous arthropods that transmit various bacterial, viral, and protozoan pathogens of public health significance. The lone star tick (Amblyomma americanum) is an aggressive human-biting tick that transmits bacterial and viral pathogens, and its bites are suspected of eliciting the alpha-gal syndrome, a newly emerged delayed hypersensitivity following consumption of red meat in the United States. While ongoing studies have attempted to investigate the contribution of different tick-inherent factors to the induction of alpha-gal syndrome, an otherwise understudied aspect is the contribution of the tick microbiome and specifically obligate endosymbionts to the establishment of the alpha-gal syndrome in humans.Materials and MethodsHere we utilized a high-throughput metagenomic sequencing approach to cataloging the entire microbial communities residing within different developmental stages and tissues of unfed and blood-fed ticks from laboratory-maintained ticks and three new geographical locations in the United States. The Quantitative Insights Into Microbial Ecology (QIIME2) pipeline was used to perform data analysis and taxonomic classification. Moreover, using a SparCC (Sparse Correlations for Compositional data) network construction model, we investigated potential interactions between members of the microbial communities from laboratory-maintained and field-collected ticks.ResultsOverall, Francisellaceae was the most dominant bacteria identified in the microbiome of both laboratory-raised and field-collected Am. americanum across all tissues and developmental stages. Likewise, microbial diversity was seen to be significantly higher in field-collected ticks compared with laboratory-maintained ticks as seen with a higher number of both Operational Taxonomic Units and measures of species richness. Several potential positive and negative correlations were identified from our network analysis. We observed a strong positive correlation between Francisellaceae, Rickettsiaceae, and Midichloriaceae in both developmental stages and tissues from laboratory-maintained ticks, whereas ovarian tissues had a strong positive correlation of bacteria in the family Xanthobacteraceae and Rhizobiaceae. A negative interaction was observed between Coxiellaceae and Francisellaceae in Illinois, and all the bacteria detected from ticks from Delaware were negatively correlated.ConclusionThis study is the first to catalog the microbiome of Am. americanum throughout its developmental stages and different tissue niches and report the potential replacement of Coxiellaceae by Francisellaceae across developmental stages and tissues tested except in ovarian tissues. These unique and significant findings advance our knowledge and open a new avenue of research to further understand the role of tick microbiome in tick-borne diseases and develop a holistic strategy to control alpha-gal syndrome.

Tick-borne pathogens identified inHyalomma marginatum(Acari: Ixodidae) collected from various vertebrate hosts in the South of France

“…Francisella-like and Coxiella-like endosymbionts detected in our study are non-pathogenic mutualistic and/or commensal microbes, which play a key role in the tick's developmental process and pathogen transmission (Buysse et al 2021;Hussain et al 2022). In our study, about 97% of H. marginatum were infected by FLE, and only one tick was positive for CLE, which is coherent with previous observations that FLE outcompetes CLE in ixodid ticks (Kumar et al 2022). High prevalence of FLE in H. marginatum ticks was previously observed, as it seems to be an ancestral primary endosymbiotic organism (mandatory to tick survival), being involved in nutritional symbiotic interactions including folate and riboflavin biosynthesis pathways plus biotin biosynthesis that are crucial for tick metabolism (Buysse et al 2021).…”

High levels of alpha-gal with large variation in the salivary glands of lone star ticks fed on human blood

“…Another interesting aspect of tick bites causing AGS was the possible involvement of tick microbiomes including endosymbionts. A recent study proposed that an invasion of Francisella -like endosymbiont (FLE) replacing Coxiella-like endosymbiont (CLE) in A. americanum is associated with AGS 25 , although the genome sequences of the FLE, CLE, and another common endosymbiont, Rickettsia amblyommatis , do not contain bacterial alpha-1,3-galactosyltransferase gene in our search on the genome sequences. In addition to endosymbionts, other tick gut microbes may be involved, as a study in human gut microbiome found Enterobacteriaceae with alpha-1,3-galactosyltransferase genes.…”

Another tick bites the dust: exploring the association of microbial composition with a broad transmission competence of tick vector species

“…Considering the bacteria genera with LinDA’s log 2 > 0.5 and BH adjusted P < 0.05, the Francisella genus was associated with the MCV group, suggesting that bacteria belonging to this genus should direct tick species toward transmitting less pathogens. This genus is composed of pathogenic species as well as endosymbionts that have been identified in many tick species ( 21 ). In particular, the latter which are detected in all life stages both in colony-reared and in field-collected ticks ( 21 ).…”

“…This genus is composed of pathogenic species as well as endosymbionts that have been identified in many tick species ( 21 ). In particular, the latter which are detected in all life stages both in colony-reared and in field-collected ticks ( 21 ). High prevalence of Francisella was associated with decreased Rickettsia genus, which impairs tick borne pathogen transmission by outcompeting other bacterial genera ( 22 , 23 ).…”