Effects of cadmium, copper, magnesium, and zinc on the decomposition of citrate by a Klebsiella sp.
The effects of Cd2+, Cu2+, Mg2+, and Zn2+ on the decomposition of citric acid by a Klebsiella sp. were studied by monitoring the degradation of [14C]citrate. The carbon concentration used was 10 micrograms of C liter-1, and the media were designed to provide at least 95% of the citrate complexed to the metal studied. After 72 h of incubation, 80% of the uncomplexed citric acid and 76% of the magnesium citrate had been decomposed. A marked inhibition was observed when Cd2+, Cu2+, or Zn2+ was bound to the organic anion; only 23% of the cadmium citrate, 14% of the zinc citrate, and 5% of the cuprous citrate had been decomposed. The effects were not the result of toxicity, since experiments run with [14C]glucose (nonchelating compound) instead of citrate resulted in similar decomposition rates regardless of the presence of the metal. To examine whether the binding of a metal to citrate enhanced its uptake by the Klebsiella sp., we studied the relative uptake of 65Zn in citrate- and in glucose-containing media. No such effect could be observed, with the uptake of Zn2+ being higher in the glucose-containing media. The study shows that metals may render low-molecular-weight organic acids, such as citric acid, resistant to bacterial degradation. This stresses the importance of metals in influencing microbial decomposition of organic compounds, not only as a result of toxicity.
Department of Water and Environmental Studies, Linköping University, Sweden.
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Brynhildsen
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Rosswall
D001673:Biodegradation, Environmental / Q000187:drug effects; D001693:Biological Transport, Active; D002104:Cadmium / Q000494:pharmacology; D002951:Citrates / Q000378:metabolism*; D019343:Citric Acid; D003300:Copper / Q000494:pharmacology; D007709:Klebsiella / Q000187:drug effects* / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008670:Metals / Q000493:pharmacokinetics / Q000494:pharmacology*; D012988:Soil Microbiology; D015032:Zinc / Q000494:pharmacology
D002951:Citrates; D008670:Metals; D002104:Cadmium; D019343:Citric Acid; D003300:Copper; D008274:Magnesium; D015032:Zinc