Influence of metal complexation on the metabolism of citrate byKlebsiella oxytoca

Abstract

The uptake of 14C-labeled cadmium-, copper-and zinc-citrate into cells of Klebsiella oxytoca was followed.The study was made in order to examine if the earlier reported disability of the bacterium to degrade these complexes was due to an inhibition in transport through the cell membrane. Citrate complexed to cadmium, copper or zinc was taken up at a similar rate to the free citric acid. However, the metal-citrate complexes were not metabolized as shown by the marked accumulation of 14C in the cells as compared with the 14C content in the cells incubated with free citric acid. This was confirmed by the results from trichioroacetic acidprecipitation showing that no 14C was incorporated into macromolecules when the citrate was complexed to the different metals. It is suggested that the inhibited degradation was due to effects on the interaction between enzyme (aconitase) and substrate in the conversion of citrate to iso-citrate. The role of complex configuration on the mineralization of metal-citrate is discussed and also tested in mineralization studies of other metal-citrate complexes (aluminum-, calcium-, cobalt-, manganese-and nickel-citrate).

Thermodynamics of citrate complexation with Mn2+, Co2+, Ni2+ and Zn2+ ions

“…The ions of the citric acid (2-hydroxy-1,2,3-propanetricarboxylic acid; H 4 Cit) occur in small amounts in the majority of living organisms to act as bioactive ligands implicated in a number of biochemical processes [1][2][3][4][5]. Owing to their capacity to form thermodynamically stable complexes with a variety of metal ions, they found widespread use in food and pharmaceutical industries as well as in medicine.…”

Subsurface interactions of actinide species and microorganisms: Implications for the bioremediation of actinide-organic mixtures

“…256 On the other hand, substrate utilization by immobile bacteria often causes significant concentration gradients along the flow path within the aquifer; thus, the expressions describing substrate utilization and biomass synthesis must be coupled to equations describing the flow of water past the stationary organisms. 234,257 Speciation and complex-specific behavior: Recent evidence suggests that the degradation rate of many organic compounds, including organic chelates, is affected by the presence of specific metal cations, 146,226,227,258 indicating that the degradation of many organic compounds is limited to a single chemical species 163,259 or is dependent on the presence of certain metals as co-substrates for key enzymes. 166,225,260 We discussed how the bioavailability of organic compounds is affected by complexation with metals and actinides.…”

“…225 When other, non-preferred metals form the most abundant substrate complex, substrate utilization usually is slowed. 115,145,146,163,226,227 Although several mechanisms have been proposed to account for the reduction in substrate availability and utilization in the presence of various metals, the most general effect comes about when significant metal concentrations reduce substrate availability. This reduction in availability through chemical speciation effects alone occurs when the organic substrate is a strong ligand.…”

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

“…1,5,6 Others, such as those of Cu, Cd and U, are regarded as recalcitrant. 1 In the case of uranium±citrate solutions an additional photodegradation step can be incorporated, 3,7 with uranium then precipitated as uranium trioxide.…”

“…1,8 The recalcitrance was not attributable to toxicity but to resistance to biodegradation. 6,8 The biodegradable complexes are bidentate (with the exception of the tridentate [Fe(II)Cit]…”