Biodegradation of metal citrate complexes and implications for toxic-metal mobility

Presence of Fe3+ and Zn2+ promoted biotransformation of Cd–citrate complex and removal of metals from solutions

“…MBR were similar to that by Pseudomonas fluorescens [7,8,15] [7]. Therefore, the non-biodegradable tridentate Fe(III)-citrate complex was the predominant complex in the 1:1 Fe:citrate medium at pH Table 2 Distribution and uptake of metals in Pseudomonas sp.…”

“…Bidentate complexes, such as Fe(III)-and Zn-citrate can be transported as intact complex inside the bacteria and then was biodegraded [7]. Tridentate and binuclear complexes, such as Cd-and U-citrate are recalcitrant to biodegradation due to the lack of transport systems for metal-citrate complexes or the inability of the citrate degrading enzymes to utilize the complexes as substrate or both [8].…”

Microbial Transformations of Uranium Complexed with Organic and Inorganic Ligands

“…Biodegradation of metal citrate complexes is dependent upon the type of complex formed between the metal and citric acid; bidentate complexes are readily biodegraded whereas the tridentate complexes are recalcitrant (Francis et al 1992). Pseudomonas fluorescens metabolized the bidentate complexes whereas complexes involving the hydroxyl group of citric acid, and the binuclear U-citrate complex are not (Francis et al 1992). The presence of the free hydroxyl group of citric acid is the key determinant in effecting biodegradation of the metal complex.…”

“…It forms different types of complexes with transition metals and actinides including formation of a bidentate, tridentate, binuclear, or polynuclear complex species. Biodegradation of metal citrate complexes is dependent upon the type of complex formed between the metal and citric acid; bidentate complexes are readily biodegraded whereas the tridentate complexes are recalcitrant (Francis et al 1992). Pseudomonas fluorescens metabolized the bidentate complexes whereas complexes involving the hydroxyl group of citric acid, and the binuclear U-citrate complex are not (Francis et al 1992).…”

“…We have shown that the metabolism of the metal-citrate complex is dependent upon the type of complex formed between the metal and citric acid. Fe(III) forms a bidentate complex with citric acid and was metabolized, whereas U forms a binuclear complex with citric acid and was recalcitrant (Francis et al 1992;Francis and Dodge,1993;Joshi-Tope and Francis 1995). The resting cells of the sulfate-reducing Desulfovibrio desulfuricans and the facultative iron-reducing Shewanella halotolerans bacteria reduced U(VI) complexed with oxalate or citrate to U(IV) under anaerobic conditions with little precipitation of uranium.…”