Enzymic activities of cadmium- and zinc-tolerant strains of Klebsiella (Aerobacter) aerogenes growing in glucose-limited chemostats.

The activities of phosphatases and some enzymes of glucose metabolism were determined in K. aerogenes NCIB 418 and in two strains derived from it, resistant to 50 mug Cd2+ ml-1 and 16 mug Zn2+ ml-1 respectively, during growth at D = 0.38 h-1 in medium containing beta-glycerophosphate as sole phosphorus source and supplemented with Cd2+ and Zn2+, as appropriate, for the resistant strains. The pH-activity profiles of the phosphatases differed from strain to strain but all showed maximum activity at an acid pH and this activity was very much lower in the Zn2+-resistant strain than in the control and even lower in the Cd2+-resistant strain. Resistance to either metal was associated with decreased glucose-6-phosphate dehydrogenase activity and increased phosphoglucose isomerase activity, suggesting an increased flow of carbon through the Embden-Meyerhof pathway relative to the pentose phosphate pathway, but the efficiency of the conversion of glucose into biomass was largely unaffected. Glucose phosphoenolpyruvate phosphotransferase activity was also lower in the resistant strains.