Agrobacterium tumefaciens Zur Regulates the High-Affinity Zinc Uptake System TroCBA and the Putative Metal Chaperone YciC, along with ZinT and ZnuABC, for Survival under Zinc-Limiting Conditions

Agrobacterium tumefaciens has a cluster of genes (Atu3178, Atu3179, and Atu3180) encoding an ABC-type transporter, here namedtroA ,troB , andtroC , respectively, which is shown here to be a zinc-specific uptake system. Reverse transcription (RT)-PCR analysis confirmed thattroA ,troB , andtroC are cotranscribed, withtroC as the first gene of the operon. TheyciC (Atu3181) gene is transcribed in the opposite orientation to that of thetroCBA operon and belongs to a metal-binding GTPase family. Expression oftroCBA andyciC was inducible under zinc-limiting conditions and was controlled by the zinc uptake regulator, Zur. Compared to the wild type, the mutant strain lackingtroC was hypersensitive to a metal chelator, EDTA, and the phenotype could be rescued by the addition of zinc, while the strain with a singleyciC mutation showed no phenotype. However,yciC was important for survival under zinc limitation when eithertroC orzinT was inactivated. The periplasmic zinc-binding protein, ZinT, could not function when TroC was inactivated, suggesting that ZinT may interact with TroCBA in zinc uptake. Unlike many other bacteria, the ABC-type transporter ZnuABC was not the major zinc uptake system inA. tumefaciens . However, the important role ofA. tumefaciens ZnuABC was revealed when TroCBA was impaired. The strain containing double mutations in theznuA andtroC genes exhibited a growth defect in minimal medium.A. tumefaciens requires cooperation of zinc uptake systems and zinc chaperones, including TroCBA, ZnuABC, ZinT, and YciC, for survival under a wide range of zinc-limiting conditions.IMPORTANCE Both host and pathogen battle over access to essential metals, including zinc. In low-zinc environments, physiological responses that make it possible to acquire enough zinc are important for bacterial survival and could determine the outcome of host-pathogen interactions.A. tumefaciens was found to operate a novel pathway for zinc uptake in which ZinT functions in concert with the high-affinity zinc importer TroCBA.