Increasing the copper sensitivity of microorganisms by restricting iron supply, a strategy for bio‐management practices

Abstract

Pollution by copper (Cu 2+) extensively used as antimicrobial in agriculture and farming represents a threat to the environment and human health. Finding ways to make microorganisms sensitive to lower metal concentrations could help decreasing the use of Cu 2+ in agriculture. In this respect, we showed that limiting iron (Fe) uptake makes bacteria much more susceptible to Cu 2+ or Cd 2+ poisoning. Using efflux mutants of the purple bacterium Rubrivivax gelatinosus, we showed that Cu + and Cd 2+ resistance relies on the expression of the Fur-regulated FbpABC and Ftr iron transporters. To support this conclusion, inactivation of these Fe-importers in the Cu + or Cd 2+-ATPase efflux mutants gave rise to hypersensitivity towards these ions. Moreover, in metal overloaded cells the expression of FbpA, the periplasmic iron-binding component of the ferric ion transport FbpABC system was induced, suggesting that cells perceived an 'iron-starvation' situation and responded to it by inducing Fe-importers. In this context, the Fe-Sod activity increased in response to Fe homoeostasis dysregulation. Similar results were obtained for Vibrio cholerae and Escherichia coli, suggesting that perturbation of Fe homoeostasis by metal excess appeared as an adaptive response commonly used by a variety of bacteria. The presented data support a model in which metal excess induces Fe-uptake to support [4Fe-4S] synthesis and thereby induce ROS detoxification system.

Additive effects of metal excess and superoxide, a highly toxic mixture in bacteria

“…Nevertheless, if Cd 2+ or Cu + metallates Fur in vivo and allows binding to the Fur box, we may then expect a repression of the iron uptake systems and induction of the Fe‐Sod. Our results showed, however, an induction of Fe‐Sod and the FbpABC iron uptake system (Steunou et al , 2020b), which rather suggest that Fur is unloaded in the presence of Cd 2+ or Cu + .…”

“…Therefore, in these bacteria, there is no other choice but to express SodB in spite of the putative iron limitation status. To corroborate this hypothesis, we have shown that like iron starvation, Cu + and Cd 2+ excess induced iron uptake system as attested by the accumulation of the iron‐binding protein FbpA in the periplasm of R. gelatinosus (Steunou et al , 2020b). The induction of Sod in the ATPase mutants is therefore indirect and is probably the consequence of iron homoeostasis dysregulation by excess Cd 2+ or Cu + .…”

Cadmium and Copper Cross-Tolerance. Cu+ Alleviates Cd2 + Toxicity, and Both Cations Target Heme and Chlorophyll Biosynthesis Pathway in Rubrivivax gelatinosus

“…Induction of SodB expression in the cadA strain suggests an increase in ROS production or a dysregulation of iron homeostasis since SodB is known to be regulated by Fur regulator in bacteria. Together with the degradation of solvent exposed [4Fe-4S] cluster from key metabolic enzymes, iron homeostasis dysregulation and ROS should be considered to account for the Cd 2+ toxicity in the cadA strain (Steunou et al, 2020b).…”

Correlated Transcriptional Responses Provide Insights into the Synergy Mechanisms of the Furazolidone, Vancomycin, and Sodium Deoxycholate Triple Combination in Escherichia coli

“…The observed changes in metal levels could partly explain the observed transcriptional response to FZ and DOC. For example, copper excess has been reported to degrade Fe-S clusters, block Fe-S cluster assembly, and stimulate an iron starvation response in E. coli and other bacteria ( 33 – 36 ). Therefore, copper toxicity could be a contributing factor that results in an iron starvation response to DOC or FVD.…”