Characterization of the tick microbiome as a strategy to identify keystone taxa whose manipulation modifies their vector capacity

Abstract

The use of anti-microbiota vaccines is an alternative to control tick-borne diseases. The successful immunization with this type of vaccines in Ixodes ricinus supports the application of this strategy in other tick species. However, for this purpose, the analysis of the microbiome of these ticks and their functional profile, as well as their interactions at the pathogen-pathogen and pathogen-microbial community interfaces, is crucial. The present study demonstrates that the microbiomes of the tick species Rhipicephalus microplus, Ixodes scapularis, Ornithodoros moubata, and Ornithodoros erraticus, are dynamic microbial consortia influenced by their keystone taxa and their biological interactions. Pathogen-pathogen interaction analyzed by detecting simultaneous infections in humans, cattle and ticks detected co-infection with Borrelia lusitaniae and Rickettsia helvetica in I. ricinus. This suggests the absence of interference between these pathogens that may coexist in the vector, probably due to differences in tropism and different pathogenesis mechanisms. On the other hand, the coexistence of Borrelia afzelii and Borrelia miyamotoi in I. ricinus suggested genotypic heterogeneity between these species. Additionally, the variation in temporal interaction patterns between pathogens analyzed in cattle and R. microplus ticks showed the persistence of Anaplasma marginale without clinical signs of anaplasmosis in cattle. However, the variable presence of A. marginale detected in R. microplus could be explained by antagonistic interactions of the pathogen with the microbiome. Indeed, in ticks with simple A. marginale infection, the temporal dynamics of the microbiome showed variations in the pathogen coexistence patterns. The study of I. scapularis ticks infected by Anaplasma phagocytophilum showed differences in the distribution of metabolic pathways in the microbiota, suggesting changes in their functional profiles and new microbial interactions induced during the pathogen colonization process. From all these results, it is inferred that the microbial communities associated with ticks coexist in a dynamic environment subject to selection pressures, such as the presence and multiplication of pathogens. In this context, the study of the microbial community interactions of O. erraticus and O. moubata allowed to analyze their biodiversity and assembly without the selective pressure exerted by the pathogen multiplication rate. Ornithodoros erraticus and O. moubata showed different community assembly patterns, attributed to differences in the transcriptome and midgut anatomy and physiology between both soft tick species, which may support the differences in their previously reported vector competence. This study demonstrated that midgut microbial diversity is higher in O. erraticus compared to O. moubata, suggesting that the microbiota of O. erraticus will offer greater resistance to pathogen colonization and, therefore, will be less competent for transmitting them. Finally, the identification of keystone taxa in the microbiomes of R. microplus, I. scapularis, O. moubata, and O. Erraticus, that significantly modulate microbial community diversity, composition and assembly is an essential result for using them as potential candidates for the development of anti-microbiota vaccines.