Nickel and cobalt resistance properties of Sinorhizobium meliloti isolated from Medicago lupulina growing in gold mine tailing

Abstract

Sinorhizobium meliloti CCNWSX0020, isolated from root nodules of Medicago lupulina growing in gold mine tailings in the northwest of China, displayed multiple heavy metal resistance and growth promotion of M. lupulina. In our previous work, the expression level of dmeR and dmeF genes were induced by Cu2+ through comparative transcriptome approach. Based on protein analysis, the dmeF encoded for a protein which showed a 37% similarity to the cation transporter DmeF of Cupriavidus metallidurans, whereas dmeR encoded transcriptional regulator which was highly homologous with DmeR belonging to RcnR/CsoR family metal-responsive transcriptional regulator. In addition to copper, quantitative real-time PCR analysis showed that dmeR and dmeF were also induced by nickel and cobalt. To investigate the functions of dmeR and dmeF in S. meliloti CCNWSX0020, the dmeR and dmeF deletion mutants were constructed. The dmeF mutant was more sensitive to Co2 + and Ni2 + than the wild type strain. Pot experiments were carried out to determine whether the growth of M. lupulina was affected when the dmeF gene was knocked out in the presence of nickel or cobalt. Results indicated that the nodule number of the host plant inoculated with the dmeF deletion mutant was significantly less than the S. meliloti CCNWSX0020 wild-type in the presence of Co2 + or Ni2 +. However, when standardized by nodule fresh weight, the nitrogenase activities of nodules infected by the dmeF deletion mutant was similar to nitrogenase activity of the wild type nodule.

Functional characterization of the Co2+transporter AitP inSinorhizobium meliloti: a new player in Fe2+homeostasis

“…Previous phenotypical characterizations of aitP-like genes in other rhizobial organisms point to a similar role of AitP in Co 2+ export and detoxification [17][18][19] and we have previously shown that AitP homolog in P. aeruginosa is involved in Fe 2+ homeostasis [7].…”

“…Previous phenotypical characterizations of aitP -like genes in other rhizobial organisms point to a similar role of AitP in Co 2+ export and detoxification [17-19], and we have previously shown that the AitP homolog in P. aeruginosa is involved in Fe 2+ homeostasis [7]. However, a P-IB-type ATPase, nia , has been described as participating in Fe 2+ homeostasis in this organism [14], and the identification of an mbfA ortholog in Rm1021 genome led us to hypothesize that AitP in S. meliloti may play a non-classical role in Fe 2+ homeostasis.…”

“…Cobalt is an essential nutrient for S. meliloti and other rhizobia [15], and an uptake system has been identified in this organism [16]. Similarly, the dmeRF system, consisting of a member of the FrmR family of transcriptional regulators (DmeR) and a member of the cation diffusion facilitator (DmeF), has been involved in Co 2+ homeostasis through export, specifically during free-living stages previous to establishing symbiosis and nodulation [17][18][19].…”

The requirement for cobalt in vitamin B12: A paradigm for protein metalation

“…RcnR, and the homologous protein, DmeR, have also been functionally characterised in organisms which can synthesise B 12 de novo such as the human pathogen Salmonella , the leguminous plant symbionts Rhizobium leguminosarum and Sinorhizobium meliloti , and plant pathogen Agrobacterium tumefaciens [ [88] , [89] , [90] , [91] , [92] ]. In each case the genetic architecture differs from E. coli (which does not synthesise B 12 ) : in Salmonella , rcnB is not part of the rcnR operon, and in the plant microbes, DmeR regulates expression of dmeF , encoding a cation diffusion facilitator Ni(II)/Co(II)-efflux pump, distinct from RcnA [ 88 , 89 , 91 ]. The binding affinity, or stability of the Co(II)-RcnR complex as a K D , for Salmonella RcnR is 5 × 10 −10 M. Autoregulation by Salmonella RcnR confers hysteresis: This dampens the response to elevated cobalt and shifts the dynamic range away from what might be predicted from metal-affinity alone [ 93 ].…”

Nickel Metalloregulators and Chaperones

“…DmeR is a Ni(II)-and Co(II)-responsive metalloregulator that has been identified in Rhizobium leguminosarum (R. leguminosarum), Agrobacterium tumefaciens (A. tumefaciens), Sinorhizobium meliloti [81][82][83]. The dmeRF operon encodes both DmeR and DmeF, a cation diffusion facilitator (CDF) [81].…”