Functional characterization of a csoR-cueA divergon in Bradyrhizobium liaoningense CCNWSX0360, involved in copper, zinc and cadmium cotolerance

• Published in: Scientific reports 2016-10, Vol.6 (1), p.35155, Article 35155
• Main Authors: Liang, Jianqiang, Zhang, Mingzhe, Lu, Mingmei, Li, Zhefei, Shen, Xihui, Chou, Minxia, Wei, Gehong
• Format: Article
• Language: English
• Subjects: 38/22; 38/23; 38/39; 38/44; 38/70; 38/77; 631/326/171/1818; 631/326/325/1506; Adenosine triphosphatase; Bacteria; Cadmium; Cell division; Clonal deletion; Competitiveness; Complementation; Copper; E coli; Gene deletion; Genes; Gram-negative bacteria; Gram-positive bacteria; Homeostasis; Humanities and Social Sciences; Life sciences; Metals; multidisciplinary; Mutagenesis; Nitrogen; Nitrogen fixation; Nodulation; Oxidation; Phylogenetics; Proteins; Random mutagenesis; Science; Transcription; Tuberculosis; Zinc
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep35155

Random mutagenesis in a symbiotic nitrogen-fixing Bradyrhizobium liaoningense CCNWSX0360 (Bln0360) using Tn 5 identified five copper (Cu) resistance-related genes. They were functionally sorted into three groups: transmembrane transport ( cueA and tolC ); oxidation ( copA ); and protection of the membrane barrier ( lptE and ctpA ). The gene cueA , together with the upstream csoR (Cu-sensitive operon repressor), constituted a csoR-cueA divergon which plays a crucial role in Cu homeostasis. Deletion of cueA decreased the Cu tolerance of cells, and complementation of this mutant restored comparable Cu resistance to that of the wild-type. Transcriptional and fusion expression analysis demonstrated that csoR-cueA divergon was up-regulated by both the monovalent Cu + and divalent Zn 2+ /Cd 2+ , and negatively regulated by transcriptional repressor CsoR, via a bidirectional promoter. Deletion of csoR renders the cell hyper-resistant to Cu, Zn and Cd. Although predicted to encode a Cu transporting P-type ATPase (CueA), cueA also conferred resistance to zinc and cadmium; two putative N-MBDs (N-terminal metal binding domains) of CueA were required for the Cu/Zn/Cd tolerance. Moreover, cueA is needed for nodulation competitiveness of B. liaoningense in Cu rich conditions. Together, the results demonstrated a crucial role for the csoR-cueA divergon as a component of the multiple-metal resistance machinery in B. liaoningense .