Quantitative proteomic profiling of the Escherichia coli response to metallic copper surfaces

Abstract

Metallic copper surfaces have strong antimicrobial properties and kill bacteria, such as Escherichia coli, within minutes in a process called contact killing. These bacteria are exposed to acute copper stress under dry conditions which is different from chronic copper stress in growing liquid cultures. Currently, the physiological changes of E. coli during the acute contact killing process are largely unknown. Here, a label-free, quantitative proteomic approach was employed to identify the differential proteome profiles of E. coli cells after sub-lethal and lethal exposure to dry metallic copper. Of the 509 proteins identified, 110 proteins were differentially expressed after sub-lethal exposure, whereas 136 proteins had significant differences in their abundance levels after lethal exposure to copper compared to unexposed cells. A total of 210 proteins were identified only in copper-responsive proteomes. Copper surface stress coincided with increased abundance of proteins involved in secondary metabolite biosynthesis, transport and catabolism, including efflux proteins and multidrug resistance proteins. Proteins involved in translation, ribosomal structure and biogenesis functions were down-regulated after contact to metallic copper. The set of changes invoked by copper surface-exposure was diverse without a clear connection to copper ion stress but was different from that caused by exposure to stainless steel. Oxidative posttranslational modifications of proteins were observed in cells exposed to copper but also from stainless steel surfaces. However, proteins from copper stressed cells exhibited a higher degree of oxidative proline and threonine modifications.

Copper Reduction and Contact Killing of Bacteria by Iron Surfaces

“…A mutant strain with higher levels of unsaturated fatty acids and thus more sensitive to ROS exhibited an earlier rise in lipid peroxidation, higher sensitivity to contact killing, and an earlier onset of DNA degradation (26). Evidence for oxidative damage was also apparent from the proteome of E. coli exposed to metallic copper by the increased presence of oxidatively modified proteins (27). Although ROS clearly cause cell damage in contact killing, it is probably an accompanying effect rather than the primary cause of cell death.…”

Contact Killing of Bacteria on Copper Is Suppressed if Bacterial-Metal Contact Is Prevented and Is Induced on Iron by Copper Ions

“…A mutant strain with higher levels of unsaturated fatty acids and thus more sensitive to ROS exhibited an earlier rise in lipid peroxidation, higher sensitivity to contact killing, and an earlier onset of DNA degradation (28). Evidence for oxidative damage was also apparent from the proteome of E. coli exposed to metallic copper by the increased presence of oxidatively modified proteins (35).…”

“…E. coli exposed to metallic copper had upregulated cell envelope and capsule polysaccharide biogenesis proteins (35), indicative of stress on the microorganism's envelope (35). Proteins involved in translation, ribosomal structure, and biogenesis functions, on the other hand, were downregulated.…”

RpiR Homologues May Link Staphylococcus aureus RNAIII Synthesis and Pentose Phosphate Pathway Regulation

“…The samples were homogenized for 40 s at 6.0 m/s in a FastPrep instrument (MP Biomedical), and the lysate was centrifuged for 5 min at 20,800 ϫ g and 4°C. Bacterial proteins were subjected to in-solution trypsin digestion as described previously (28). Briefly, the proteins were reduced with 10 mM dithiothreitol and were alkylated with 40 mM iodoacetamide, followed by trypsin (Roche) digestion (trypsin/protein ratio, 1:50) overnight at 37°C.…”