Chapter 15 : Biodegradation of Synthetic Chelating Agents

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This chapter discusses the current state of knowledge of the biodegradation of the synthetic chelating agents nitrilotriacetate (NTA) and EDTA. The understanding of the biodegradation of chelating agents requires a mechanistic coupled understanding of geochemistry and microbiology, including the way chelated metal influences biodegradation, the way metal in the metal-chelate complex can exchange with other metals, the way adsorption of the chelating agent influences biodegradation, the biodegradation of chelating agents by whole cells, the cellular transport of chelating agents into the cell, its enzymatic biodegradation, and, finally, the genetics of biodegradation. The identity of the metal-NTA complex present in solution after desorption, that is, the "desorbed metal-NTA complex," is important for understanding and predicting NTA biodegradation when sorbents are present. The variation in NTA biodegradation by whole cells was proposed to be influenced by the lability of the metal-NTA complex or the frequency of making and breaking the metal-carboxyl oxygen and the metal-nitrogen bonds of the complex. The specificity of NTA monooxygenase indicated that an intact metal-NTA complex was necessary for biodegradation and that the lability of the metal-NTA complex did not influence its biodegradation by the enzyme. Future areas of research on the biochemistry and genetics of NTA biodegradation include the purification of IDA dehydrogenase and the cloning, sequencing, and characterization of the corresponding gene(s).

Citation: Bolton H, Girvin D, Xun L. 2000. Biodegradation of Synthetic Chelating Agents, p 363-383. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch15
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Figure 1

Structures of NTA, EDTA, CoNTA, and CoEDTA.

Citation: Bolton H, Girvin D, Xun L. 2000. Biodegradation of Synthetic Chelating Agents, p 363-383. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch15
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Figure 2

Speciation of 1 µM NTA in equilibrium with gibbsite (A1[OH]; log K = 8.77) in a 0.01 M NaClO solution.

Citation: Bolton H, Girvin D, Xun L. 2000. Biodegradation of Synthetic Chelating Agents, p 363-383. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch15
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Figure 3

Biodegradation of 1 M EDTA to CO at pH 7 by BNC1 with different metals added. Error bars indicate ± 1 standard deviation of the mean.

Citation: Bolton H, Girvin D, Xun L. 2000. Biodegradation of Synthetic Chelating Agents, p 363-383. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch15
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Figure 4

(A) Structures of NTA, IDA, and glyoxylate. (B) Reactions catalyzed by NADH:FMNB oxidoreductase (cB) and NTA monooxygenase (cA).

Citation: Bolton H, Girvin D, Xun L. 2000. Biodegradation of Synthetic Chelating Agents, p 363-383. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch15
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Figure 5

Overview of the gene cluster encoding NTA monooxygenase of . The genes , . . and and their directions of transcription are indicated by arrows. Cloned DNA fragments are indicated by open bars.

Citation: Bolton H, Girvin D, Xun L. 2000. Biodegradation of Synthetic Chelating Agents, p 363-383. In Lovley D (ed), Environmental Microbe-Metal Interactions. ASM Press, Washington, DC. doi: 10.1128/9781555818098.ch15
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