Biodegradation of Nickel−Citrate and Modulation of Nickel Toxicity by Iron

Abstract

Biodegradation of 1:1 nickel:citric acid by Pseudomonas fluorescens proceeded after a lag (∼17 h) at the rate of 11 ( 1 µmol h -1 , with only partial mineralization of the complex. The incomplete degradation of the complex was not attributed to changes in its structure, but was due to the toxicity of the Ni released. Addition of 1:1 Ni:citric acid inhibited glucose metabolism by the bacterium. The toxicity of the released Ni was evident only when it attained a threshold concentration of >0.3 mM in the culture medium. Speciation calculations showed that Ni released after metabolism of the complex was present as Ni 2+ ion and nickel carbonate. Addition of iron as a ferric hydroxide or 1:1 Fe:citric acid to 1:1 Ni:citric acid resulted in the complete metabolism of the Ni-citrate complex, with concurrent removal of the released Ni from solution by coprecipitation with iron.

Sequestration of Sr-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of a Ca-Citrate-Phosphate Solution

“…Citrate mineralization studies in sediments with different initial biomass did show a general correlation of higher initial biomass with a more rapid mineralization rate, but while biomass in sediments changed 5 orders of magnitude, the mineralization half-life only changed about 1 order of magnitude (Figure 4.4). This conclusion appears inconsistent with results of others (Francis et al 1996), but further investigation into the role of in situ and infiltrating microbial populations (from the river water used) revealed the reason for the apparent difference.…”

Simultaneous biodegradation of Ni–citrate complexes and removal of nickel from solutions by Pseudomonas alcaliphila

“…In the pH range 5-8, Ni and citrate are present predominantly as a mononuclear bidentate [NiCit] À complex (Hedwig et al, 1980). Above pH 8, the complex exists in a tridentate form involving the hydroxyl group of citrate, and above pH 9, it exists in a polymeric form [Ni 4 (OH)Cit 3 ] 5À (Still and Wikberg, 1980;Strouse et al, 1977 complex can be biodegraded by bacteria; however, the tridentate and polymeric Ni-citrate complexes are recalcitrant to biodegradation (Francis et al, 1996). In a medium containing Ni and citrate in a ratio of 1:1, 95 and 100% of the citrate was utilized by Pseudomonas aeruginosa and P. putida, respectively, and the addition of inorganic phosphate as a precipitant promoted Ni removal effectively (Thomas et al, 2000).…”

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

“…Cd remained in solution in all treatments. Cd-citrate complex was formed in the stoichiometry of 1:1, and heavy metals were not toxic to bacteria when complexed with citrate [11]. Therefore, the lag period for excess citrate consumption were not observed in the 1:2 and 1:3 Cd:citrate media.…”

“…When complexed with citrate, metals were nontoxic to bacteria [11]. After degradation inside bacteria cell, toxic metals were released from metal-citrate complex.…”

“…Whereas, for Ni-citrate complex, limited biodegradation of citrate was observed due to the formation of tridentate Ni-citrate complex at alkaline pH [10]. Francis in the complete biotransformation of Ni-citrate complex [11]. Qian et al speculated that displacement-degradation mechanism was responsible for this phenomenon according to the difference in stability of Fe(III)-and Ni-citrate complexes [10].…”