Impact of Lead Stress and Adaptation in Escherichia coli

The growth rate of Escherichia coli was stimulated when cells were in media containing lead up to a concentration of 300 ppm. Higher concentrations inhibited growth. Metal analysis revealed that in the presence of lead E. coli concentrates 22.8 mg of lead per gram (dry weight) of cells. Analysis of cellular subfractions indicated that membrane fraction concentrated over 95% of the lead taken up by cells, of which a major portion was found to be associated with membrane lipids. Alterations in alkaline phosphatase, Ca2+–Mg2+ -ATPase activities and the carbohydrate and phospholipid contents in membrane fractions were also observed when cells were grown in the presence of lead. A time- and concentration-dependent increase in the release of carbohydrates by the cells was also evident. The results suggest that besides thriving in higher lead surroundings, E. coli possess a marked ability to concentrate substantial amount of inorganic lead.