Changes in microbial composition, diversity, and functionality in theAmblyomma maculatummicrobiome following infection withRickettsia parkeri
Authors: Adegoke Abdulsalam , Kumar Deepak , Budachetri Khemraj , Karim Shahid 
Published: October 2021

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 andRickettsia parkeriinfection on changes inAmblyomma maculatummicrobiome 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

TheAmblyomma maculatummicrobiome comprises ten bacterial genera present across tick life cycle stages. Among the top ten bacterial genera (the core tick microbiome),Rickettsia, Francisella,andCandidatus Midichloriaare 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. WhereasR. parkerihad a positive correlation withCandidatus Midichloriaduring 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. parkerireplacesFrancisella,based on the lower level of OTUs representingFrancisellainR. parkeri-infected ticks (in all stages/organs) and negatively correlated according to network and linear discriminant analysis effect size (LEfSe).

Conclusions

We found thatRickettsiaandFrancisellapredominate in the core microbiome of the Gulf Coast tick, whereasCandidatus MidichloriaandCutibacteriumlevels increase with infection. Network analysis and functional annotation suggest thatR. parkeriinteracts positively withCandidatus Midichloriaand negatively withFrancisellaand that metabolic profiles are upregulated with blood meal andR. parkeriinfection. Overall, this is the first study to determine the combinatorial outcome of blood meal and pathogen interaction on microbiome composition over the developmental stages ofAm. maculatum. This new study expands on our existing knowledge of theAm. maculatummicrobiome and further highlights the need to investigate pathogen–symbiont interactions betweenR. parkeriandFrancisellaorCandidatus Midichloriato facilitate the development of strategies for controlling tick-transmitted diseases.

Abstract Figure

Graphical Abstract