AUTHORS: Domek MJ, Robbins JE, Anderson ME, and McFeters GA
PUBLICATION REF: Canadian Journal of Microbiology 33: 57-62,1987
PURPOSE OF STUDY:
Based on evidence that the presence of copper in drinking water, which frequently occurs naturally, can cause injury to Escherichia coli (E. coli) and other coliforms, the authors performed experiments to elucidate the physiologic mechanisms responsible of cellular injury.
MATERIALS AND METHODS:
E. coli was isolated from river water and cultured in broth. Washed cells were placed in an inorganic carbon buffer and the pH adjusted. High concentrations of copper were introduced to produce injury to the 95% level. The injured populations were analyzed using a series of tests: oxygen uptake measurements by oxygraph and differential respirometer, nuclear magnetic resonance spectroscopy, gas chromatography, and spectrophotometric respiration measurements.
As compared to normal cells, short-term oxygen uptake was reduced by 75% in copper-injured cells. Similarly, long-term respirometry experiments showed that the rate of oxygen uptake of the injured cells was approximately 47% of the rate in normal cells.
Nuclear magnetic resonance spectra revealed that the rate of glucose utilization was 64% compared to normal cells. Similar trends were evident in lactate, ethanol, acetate, and glutamine accumulation under both aerobic and anaerobic conditions. The slow utilization of succinate and decreased production of CO2 under aerobic conditions suggested that copper has major effect on the aerobic metabolic function of E. coli.
Copper-injured cells reduced six times greater quantities of 2 (p-iodophenyl) -3- (p-nitrophenyl) -5- phenyltetrazolium chloride (INT) than control cells when NADH was used as a substrate. A comparison of metabolic end products demonstrated marked differences in carbon flow in injured cells.
Exposure of E. coli in drinking water to copper produces a variety of injurious effects. The mechanism include decreased oxygen utilization of glucose, and lowered accumulation of metabolic products such as lactate and ethanol. The fact that aerobic succinate was lowered and less glutamine produced suggest that tricarboxylic acid (TCA) activity is also inhibited.