In:
Journal of Bacteriology, American Society for Microbiology, Vol. 203, No. 11 ( 2021-05-07)
Kurzfassung:
In the metallophilic betaproteobacterium Cupriavidus metallidurans , the plasmid-encoded Czc metal homeostasis system adjusts the periplasmic zinc, cobalt, and cadmium concentrations, which influences subsequent uptake of these metals into the cytoplasm. Behind this shield, the P IB2 -type ATPase ZntA is responsible for removal of surplus cytoplasmic zinc ions, thereby providing a second level of defense against toxic zinc concentrations. ZntA is the counterpart to the Zur-regulated zinc uptake system ZupT and other import systems; however, the regulator of zntA expression was unknown. The chromid-encoded zntA gene is adjacent to the genes czcI 2 C 2 B 2 ′, which are located on the cDNA strand and transcribed from a common promoter region. These genes encode homologs of plasmid pMOL30-encoded Czc components. Candidates for possible regulators of zntA were identified and subsequently tested: CzcI, CzcI 2 , and the MerR-type gene products of the locus tags Rmet_2302, Rmet_0102, and Rmet_3456. This led to the identification of Rmet_3456 as ZntR, the main regulator of zntA expression. Moreover, both CzcI proteins decreased Czc-mediated metal resistance, possibly to avoid “overexcretion” of periplasmic zinc ions, which could result in zinc starvation due to diminished zinc uptake into the cytoplasm. Rmet_2302 was identified as CadR, the regulator of the cadA gene for an important cadmium-exporting P IB2 -type ATPase, which provides another system for removal of cytoplasmic zinc and cadmium. Rmet_0102 was not involved in regulation of the metal resistance systems examined here. Thus, ZntR forms a complex regulatory network with CadR, Zur, and the CzcI proteins. Moreover, these discriminating regulatory proteins assign the efflux systems to their particular function. IMPORTANCE Zinc is an essential metal for numerous organisms, from humans to bacteria. The transportome of zinc uptake and efflux systems controls the overall cellular composition and zinc content in a double-feedback loop. Zinc starvation mediates, via the Zur regulator, upregulation of the zinc import capacity via the ZIP-type zinc importer ZupT and amplification of zinc storage capacity, which together raise the cellular zinc content again. On the other hand, an increasing zinc content leads to ZntR-mediated upregulation of the zinc efflux system ZntA, which decreases the zinc content. Together, the Zur regulon components and ZntR/ZntA balance the cellular zinc content under both high external zinc concentrations and zinc starvation conditions.
Materialart:
Online-Ressource
ISSN:
0021-9193
,
1098-5530
Sprache:
Englisch
Verlag:
American Society for Microbiology
Publikationsdatum:
2021
ZDB Id:
1481988-0
SSG:
12
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