Roles of TroA and TroR in Metalloregulated Growth and Gene Expression in .

The availability of divalent metal cations required as cofactors for microbial metabolism is severely limited in the host environment. Bacteria have evolved highly regulated uptake systems to maintain essential metal homeostasis to meet cellular demands while preventing toxicity. The Tro operon (), present in all sequenced spp., is a member of a highly conserved family of ATP-binding cassette transporters involved in metal cation uptake whose expression is controlled by TroR, a DtxR-like cation-responsive regulatory protein. Transcription of responds to divalent manganese and iron () or manganese and zinc (), and metal-dependent TroR binding to the promoter represses transcription. We report here the construction and complementation of defined Δ and Δ strains to characterize (i) the role of TroA in metal-dependent growth and (ii) the role of TroR in gene expression. We show that TroA expression is required for growth under iron- and manganese-limited conditions. Furthermore, TroR is required for the transcriptional regulation of in response to iron or manganese, and deletion of results in significant differential expression of more than 800 genes in addition to These results suggest that (i) TroA-mediated cation uptake is important in metal homeostasis and may be important for survival in the host environment and (ii) the absence of TroR results in significant dysregulation of nearly one-third of the genome. These effects may be direct (as with ) or indirect due to dysregulation of metal homeostasis. is one of numerous host-associated spirochetes, a group including commensals, pathobionts, and at least one frank pathogen. While most research concerns its role in periodontitis, its relative tractability for growth and genetic manipulation make it a useful model for studying physiology, metabolism, and host-microbe interactions. Metal micronutrient acquisition and homeostasis are highly regulated both in microbial cells and by host innate defense mechanisms that severely limit metal cation bioavailability. Here, we characterized the operon, the role of TroA-mediated iron and manganese uptake in growth, and the effects of TroR on global gene expression. This study contributes to our understanding of the mechanisms involved in cellular metal homeostasis required for survival in the host environment.