Changes in microbial composition, diversity, and functionality in the Amblyomma maculatum microbiome following infection with Rickettsia parkeri

Background Ticks are the primary vectors for emerging and resurging pathogens of public health significance worldwide. Examining tick bacterial composition, diversity, and functionality across developmental stages and tissues is necessary for designing new strategies to control ticks and prevent tick-borne diseases. Methods A high-throughput sequencing approach was used to determine the influence of blood meal and Rickettsia parkeri infection on changes in Amblyomma maculatum microbiome composition, diversity, and functionality across the developmental timeline and in different tissues. Quantitative insight into microbial ecology analysis allowed us to determine microbial population structure, composition, and diversity. A non-metric multidimensional scaling, the sparse correlations for compositional data (SparCC) module, and phylogenetic investigation of communities by reconstruction of unobserved states 2 (PICRUSt2) software were used in the assessment. Results The Amblyomma maculatum microbiome comprises ten bacterial genera present across tick life cycle stages. Among the top ten bacterial genera (the core tick microbiome), Rickettsia, Francisella, and Candidatus Midichloria are the key players, with positive interactions within each developmental stage and adult tick organ tested. The bacterial abundances, based on the number of operational taxonomic units (OTUs), increase with blood meal in each stage, helping bacterial floral growth. The growth in bacterial numbers is related to highly abundant energy metabolism orthologs with blood meal, according to functional analysis. Whereas R. parkeri had a positive correlation with Candidatus Midichloria during the tick life cycle, based on the increased number of OTUs and network analysis, this was due to an increased level of metabolic activity. Interestingly, R. parkeri replaces Francisella, based on the lower level of OTUs representing Francisella in R. parkeri -infected ticks (in all stages/organs) and negatively correlated according to network and linear discriminant analysis effect size (LEfSe). Conclusions We found that Rickettsia and Francisella predominate in the core microbiome of the Gulf Coast tick, whereas Candidatus Midichloria and Cutibacterium levels increase with infection. Network analysis and functional annotation suggest that R. parkeri interacts positively with Candidatus Midichloria and negatively with Francisella and that metabolic profiles are upregulated with blood meal and R. parkeri infection. Overall, this is the first study to determine the combinatorial outcome of blood meal and pathogen interaction on microbiome composition over the developmental stages of Am. maculatum . This new study expands on our existing knowledge of the Am. maculatum microbiome and further highlights the need to investigate pathogen–symbiont interactions between R. parkeri and Francisella or Candidatus Midichloria to facilitate the development of strategies for controlling tick-transmitted diseases. ![Figure][1] Graphical Abstract ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes