Metal complexation by histidine-rich peptides confers protective roles against cadmium stress inEscherichia colias revealed by proteomics analysis

Abstract

The underlying mechanism and cellular responses of bacteria against toxic cadmium ions is still not fully understood. Herein, Escherichia coli TG1 expressing hexahistidine-green fluorescent protein (His6GFP) and cells expressing polyhistidine-fused to the outer membrane protein A (His-OmpA) were applied as models to investigate roles of cytoplasmic metal complexation and metal chelation at the surface membrane, respectively, upon exposure to cadmium stress. Two-dimensional gel electrophoresis (2-DE) and two-dimensional difference in gel electrophoresis (2D-DIGE) in conjunction with mass spectrometry-based protein identification had successfully revealed the low level expression of antioxidative enzymes and stress-responsive proteins such as manganese-superoxide dismutase (MnSOD; +1.65 fold), alkyl hydroperoxide reductase subunit C (AhpC; +1.03 fold) and DNA starvation/stationary phase protection protein (Dps; −1.02 fold) in cells expressing His6GFP in the presence of 0.2 mM cadmium ions. By contrarily, cadmium exposure led to the up-regulation of MnSOD of up to +7.20 and +3.08 fold in TG1-carrying pUC19 control plasmid and TG1 expressing native GFP, respectively, for defensive purposes against Cd-induced oxidative cell damage. Our findings strongly support the idea that complex formation between cadmium ions and His6GFP could prevent reactive oxygen species (ROS) caused by interaction between Cd2+ and electron transport chain. This coincided with the evidence that cells expressing His6GFP could maintain their growth pattern in a similar fashion as that of the control cells even in the presence of harmful cadmium. Interestingly, overexpression of either OmpA or His-OmpA in E. coli cells has also been proven to confer protection against cadmium toxicity as comparable to that observed in cells expressing His6GFP. Blockage of metal uptake as a consequence of anchored polyhistidine residues on surface membrane limited certain amount of cadmium ions in which some portion could pass through and exert their toxic effects to cells as observed by the increased expression of MnSOD of up to +9.91 and +3.31 fold in case of TG1 expressing only OmpA and His-OmpA, respectively. Plausible mechanisms of cellular responses and protein mapping in the presence of cadmium ions were discussed. Taken together, we propose that the intracellular complexation of cadmium ions by metal-binding regions provides more efficiency to cope with cadmium stress than the blockage of metal uptake at the surface membrane. Such findings provide insights into the molecular mechanism and cellular adaptation against cadmium toxicity in bacteria.

Transcriptional analysis reveals specific niche factors and response to environmental stresses of enterohemorrhagic Escherichia coli O157:H7 in bovine digestive contents

“…Industrial processing and intensive agricultural practices can result in the contamination of forage, feed and water by heavy metals, which can then be sources of exposure for farmed ruminants [42]. In this report, EHEC EDL933 induced a large number of genes functionally associated with response to cadmium in the bovine DCs, but we quantified low concentrations of Cd (from 4 to 12 μg/Kg) that cannot be considered as toxic for E. coli [43]. Efflux systems required to protect the bacteria against exposure to other metal ions were also activated, together with genes required to sense and face oxidative stresses.…”

Genomic Insights Into Cadmium Resistance of a Newly Isolated, Plasmid-Free Cellulomonas sp. Strain Y8

“…Modern omics tool has revealed a variety of basic metabolic pathways involved in metal resistance (Sheng et al, 2016; Isarankura- Na-Ayudhya et al, 2018;Alviz-Gazitua et al, 2019), and for either prokaryotic or eukaryotic cells possession of specific Cd resistance genes/operons is essential for Cd resistance (Intorne et al, 2012;Schwager et al, 2012;Chaoprasid et al, 2015;Zhang et al, 2015). A genome-wide annotation of strain Y8 led to the identification of 54 heavy metal-related genes (Figure 2), including potential metal resistance genes homologous to zntA of E. coli, czcD of C. metallidurans, copAB of Legionella pneumophila (Purohit et al, 2018), cutC of Enterococcus faecalis (Latorre et al, 2011), znuA of E. coli (Patzer and Hantke, 1998), etc.…”

Proteomics and bioinformatics analysis reveal potential roles of cadmium-binding proteins in cadmium tolerance and accumulation ofEnterobacter cloacae

“…1). These toxic effects possibly derived from the generation of reactive oxygen and nitrogen species (ROS and RNS) (Brennan & Schiestl, 1996; Isarankura-Na-Ayudhya et al, 2018; Stohs & Bagchi, 1995). Such free radical was not mainly produced by cadmium itself, however, indirect formation of ROS and RNS e.g., superoxide radical, hydroxyl radical and nitric oxide has been reported (Waisberg et al, 2003).…”