Growth of naturally occurring microbial isolates in metal-citrate medium and bioremediation of metal-citrate wastes

The use of citrate as a chelating agent in decontamination operations is of environmental concern as it can mobilize toxic heavy metals if discharged into the environment. Many heavy metal-citrate complexes are recalcitrant to biodegradation. Citrate-utilizing strains of Pseudomonas aeruginosa and Pseudomonas putida were isolated from a mixed culture which had been maintained with EDTA as the carbon source for 2 years. Citrate (5 mM) was used as the sole carbon source in medium supplemented with 5 mM Cd, Zn, Cu, Fe, Co, or Ni. Removal of the metals from the medium was promoted by the incorporation of inorganic phosphate as a precipitant, with formation of nickel and cobalt phosphates confirmed by X-ray powder diffraction analysis. The potential of P putida to biodegrade citrate in a nickel–citrate secondary waste was illustrated using a fill-and-draw reactor supplied with effluent from a bioinorganic ion exchange column that had been used previously to concentrate nickel from aqueous solution. © 2000 Society of Chemical Industry