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

Abstract

Agrobacterium tumefaciens has a cluster of genes (Atu3178, Atu3179, and Atu3180) encoding an ABC-type transporter, here named troA, troB, and troC, respectively, which is shown here to be a zinc-specific uptake system. Reverse transcription (RT)-PCR analysis confirmed that troA, troB, and troC are cotranscribed, with troC as the first gene of the operon. The yciC (Atu3181) gene is transcribed in the opposite orientation to that of the troCBA operon and belongs to a metal-binding GTPase family. Expression of troCBA and yciC was inducible under zinc-limiting conditions and was controlled by the zinc uptake regulator, Zur. Compared to the wild type, the mutant strain lacking troC was hypersensitive to a metal chelator, EDTA, and the phenotype could be rescued by the addition of zinc, while the strain with a single yciC mutation showed no phenotype. However, yciC was important for survival under zinc limitation when either troC or zinT 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 in A. tumefaciens. However, the important role of A. tumefaciens ZnuABC was revealed when TroCBA was impaired. The strain containing double mutations in the znuA and troC 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. IMPORTANCEBoth 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 hostpathogen 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. Zinc is an essential metal for bacteria because it is required for the functions of many enzymes and proteins (1, 2). However, zinc overload is toxic to cells (3-7). Bacteria have mechanisms to maintain zinc homeostasis via the coordinated response of genes involved in zinc uptake, efflux, and storage (8-13). The zinc uptake regulator Zur is a transcriptional regulator belonging to the Fur family and functions as a repressor of zinc uptake genes, including znuABC and zinT (10). To prevent excessive amounts of zinc in cells under high-zinc conditions, Zur uses Zn 2ϩ as its cofactor to bind to a conserved AT-rich sequence, called the Zur box (14), found in the promoter region of the zinc uptake genes, leading to inhibition of gene expression (15)(16)(17). ZnuA is a periplasmic protein that binds zinc and transfers it to the membrane permease ZnuB and the ATPase ZnuC (15). The ZinT protein is a periplasmic zinc-binding protein (18-21) that has been shown to directly interact with and assist ZnuABC i...

Modulation of Symbiotic Compatibility by Rhizobial Zinc Starvation Machinery

“…A similar conclusion was drawn for ZupT of Salmonella enterica (9). In contrast to the less-studied low-affinity zinc transporter, the conserved ZnuABC has been widely studied in many bacteria, such as E. coli, S. enterica, Bacillus subtilis, Yersinia pestis, Yersinia ruckeri, Streptomyces coelicolor, and Agrobacterium tumefaciens (6,(10)(11)(12)(13)(14)(15)(16). It has been established that ZnuABC plays an essential role in bacterial growth under zinc-deplete conditions and dramatically affects virulence of diverse bacteria (14,(17)(18)(19).…”

“…by Zur (zinc uptake regulator), belonging to the well-known Fur (iron-uptake regulator) family, which acts as a repressor for zinc uptake genes (3,(5)(6)(7). However, this regulation can be complex due to the variation in the number and characteristics of zinc uptake systems in different genomic backgrounds.…”

Phytochrome mediated responses in Agrobacterium fabrum: growth, swimming, plant infection and interbacterial competition

“…Atu1049 is annotated as a hypothetical protein and was found involved in GABA responses. atu3178, atu3179, atu3181 belong to an operon of a Zn 2+ ABC transporter (35). The fact that three out of four genes of the same operon appear light regulated underpins the reliability of the assays.…”

Interplay between the Zur Regulon Components and Metal Resistance in Cupriavidus metallidurans

“…Consequently, a role of the three CobWs of C. metallidurans in zinc homeostasis had been predicted (41). CobW-like proteins have been characterized from several bacteria, i.e., YeiR and YjiA from E. coli (41,42) YciC from Bacillus subtilis (54) and Agrobacterium tumefaciens (55), and ZigA from Acinetobacter baumannii (56). The Zur regulon of A. tumefaciens encodes in addition to a ZnuACB a second ABC import system (TroABC), the periplasmic zinc-binding protein ZinT, and YciC, which are upregulated under zinc-limited conditions.…”

“…The Zur regulon of A. tumefaciens encodes in addition to a ZnuACB a second ABC import system (TroABC), the periplasmic zinc-binding protein ZinT, and YciC, which are upregulated under zinc-limited conditions. YciC is important for survival under these conditions but only in a Δtro or ΔzinT deletion mutant (55). Expression control of yciC from B. subtilis is very similar to that of the cobW1 cluster with two Zur-binding sites, which also results in a tight repression when sufficient zinc is available (54).…”