Abstract
BackgroundThe ColRS two-component system has been shown to contribute to the membrane functionality and stress tolerance of Pseudomonas putida as well as to the virulence of Pseudomonas aeruginosa and plant pathogenic Xanthomonas species. However, the conditions activating the ColRS pathway and the signal(s) sensed by ColS have remained unknown. Here we aimed to analyze the role of the ColRS system in metal tolerance of P. putida and to test whether ColS can respond to metal excess.ResultsWe show that the ColRS system is necessary for P. putida to tolerate the excess of iron and zinc, and that it also contributes to manganese and cadmium tolerance. Excess of iron, zinc, manganese or cadmium activates ColRS signaling and as a result modifies the expression of ColR-regulated genes. Our data suggest that the genes in the ColR regulon are functionally redundant, as several loci have to be deleted to observe a significant decrease in metal tolerance. Site-directed mutagenesis of ColS revealed that excess of iron and, surprisingly, also zinc are sensed by a conserved ExxE motif in ColS’s periplasmic domain. While ColS is able to sense different metals, it still discriminates between the two oxidation states of iron, specifically responding to ferric and not ferrous iron. We propose a signal perception model involving a dimeric ColS, where each monomer donates one ExxE motif for metal binding.ConclusionsSeveral transition metals are essential for living organisms in certain amounts, but toxic in excess. We show that ColRS is a sensor system which detects and responds to the excess of physiologically important metals such as zinc, iron and manganese. Thus, the ColRS system is an important factor for metal homeostasis and tolerance in P. putida.
Highlights
The ColRS two-component system has been shown to contribute to the membrane functionality and stress tolerance of Pseudomonas putida as well as to the virulence of Pseudomonas aeruginosa and plant pathogenic Xanthomonas species
The ColRS system is required for growth in the excess of zinc, iron, manganese and cadmium To test whether the ColRS system is involved in metal resistance, we determined the minimal inhibitory concentrations (MICs) values of different transition metals for wild-type P. putida PaW85 and for its colR-deficient strain (colR)- and colS-deficient strain (colS)-deficient derivatives
Complementation of the colSand colR-deficient strains with an extra copy of colS or colR genes under the control of the tac promoter and LacI repressor enabled normal growth of mutant bacteria under the condition of metal excess (Figure 1)
Summary
The ColRS two-component system has been shown to contribute to the membrane functionality and stress tolerance of Pseudomonas putida as well as to the virulence of Pseudomonas aeruginosa and plant pathogenic Xanthomonas species. The cytosolic metal levels are monitored by different metalloregulators, such as Fur (for iron), Zur (for zinc), MntR (for manganese), etc., which control the expression of highaffinity metal uptake pathways that are able to supply the cell with the limiting metal [12,13,14] These systems regulate the genes necessary for the detoxification of excess metals [15]. The ZraSR two-component system responds to high periplasmic Zn2+ and Pb2+ concentrations by up-regulating the expression of the periplasmic zinctrapping chaperone ZraP, yet the role of this signal pathway in zinc resistance remains ambiguous [21,22] These examples demonstrate that some metal sensor systems can detect more than one metal, they are generally remarkably metal-specific, highlighting the need for a large amount of sensor systems to maintain cellular metal homeostasis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
