The rate-controlling substrate of nitrilotriacetate for biodegradation by Chelatobacter heintzii

Codisoposal of anthropogenic chelating agents such as nitrilotriacetate (NT A) with radio active and heavy metals can enhance environmental transport o f the metals, extending subsurface contamination and threatening groundwate r sources. The biodegradation of the chelating agent can lead to the immobi lization of the chelated metal and radionuclide contaminants. The rate of b iodegradation of the organic complexing agent may depend on the concentrati on of a specific, biologically available form of the chelate. In mixtures o f metals and chelating agents, the relative distribution of different chemi cal forms of the chelate at equilibrium is controlled by the total concentr ations of organic and inorganic constituents and thermodynamic stability co nstants for the aqueous complexes that form. In this paper, we evaluate exp erimental results for biodegradation of NTA by Chelatobacter heintzii in di fferent metal/NTA systems in order to identify the chelate form controlling the rate of degradation. The CaNTA(-) is the only species that can control the rate of NTA degradation in our systems. Our analysis of the potentiall y rate-limiting reactions in the biodegradation of NTA indicates that kinet ically controlled complexation in the NTA system is not affecting the biode gradation of the chelate. The rate of transport of CaNTA- into the cell app ears to control the overall rate of NTA degradation. Thus, we expect enhanc ed rates of biological degradation of the chelate and immobilization of cod isposed metals when CaNTA(-) is available to C. heintzii.