Iron Reduction in Dermacentor andersoni Tick Cells Inhibits Anaplasma marginale Replication

Anaplasma spp. are obligate intracellular, tick-borne, bacterial pathogens that cause bovine and human anaplasmosis. We lack tools to prevent these diseases in part due to major knowledge gaps in our fundamental understanding of the tick-pathogen interface, including the requirement for and molecules involved in iron transport during tick colonization. We determine that iron is required for the pathogen Anaplasma marginale, which causes bovine anaplasmosis, to replicate in Dermacentor andersoni tick cells. Using bioinformatics and protein modeling, we identified three orthologs of the Gram-negative siderophore-independent iron uptake system, FbpABC. Am069, the A. marginale ortholog of FbpA, lacks predicted iron-binding residues according to the NCBI conserved domain database. However, according to protein modeling, the best structural orthologs of Am069 are iron transport proteins from Cyanobacteria and Campylobacterjejuni. We then determined that all three A. marginale genes are modestly differentially expressed in response to altered host cell iron levels, despite the lack of a Ferric uptake regulator or operon structure. This work is foundational for building a mechanistic understanding of iron uptake, which could lead to interventions to prevent bovine and human anaplasmosis.