Cu transport and distribution in different cellular fractions of Klebsiella oxytoca strain CAV 1374

This study elucidated copper (Cu) transport and trafficking mechanisms at the cellular interface using the Cu resistant strain Klebsiella oxytoca CAV 1374. The optimum conditions for biosorption were determined by investigating uptake rates due to initial pH, initial Cu concentrations, and maximum tolerated concentrations (MTC) of Cu. Cellular fraction analysis and depth-profiling XPS were used to comprehensively evaluate the spatial-temporal distribution of Cu on cellular interfaces during biosorption. Potential uptake mechanisms were then further examined by biosorption kinetics analyses, ion exchange experiments, FTIR analysis, and K+ channel blocking experiments. The results indicated that Cu was primarily absorbed by extracellular polymeric substances through chemical interactions and little Cu penetrated inside cells under low Cu stress conditions (<= 20 mg/L). In contrast, an intracellular rate-controlling physical interaction was predominant under high Cu stress conditions (>= 30 mg/L). Further, Cu2+ could be bound by functional groups, followed first by replacement of Ca2+ at the cell surface. Subsequently, some of the Cu2+ in cell walls was reduced to Cu+, and only Cu+ could then penetrate into cell membranes. These results indicate that strain Klebsiella oxytoca CAV 1374 is a suitable biosorbent agent for Cu removal and can provide critical insights into Cu-uptake mechanisms of microorganisms.

Automated summary

This study investigated the copper transport and trafficking mechanisms using the Cu resistant strain Klebsiella oxytoca CAV 1374, and found that the strain is a suitable biosorbent for copper removal. Different uptake mechanisms and pathways were identified under different copper concentrations, providing critical insights into copper-uptake mechanisms of microorganisms.