2,4-Dichlorophenoxyacetic acid (2,4-D), a chlorinated phenoxy compound, functions as a systemic herbicide and is used to control many types of broadleaf weeds. It is used in cultivated agriculture and in pasture and rangeland applications, forest management, home and garden situations and for the control of aquatic vegetation. The wide use of this compound has prompted interest in its biodegradation. Alcaligenes eutrophus and other bacteria can degrade 2,4-D through 2,4-dichlorophenol, 3,5-dichlorocatechol, and ortho cleavage of this catechol ([http://www.ncbi.nlm.nih.gov/pubmed/8226980|Fukumori & Hausinger, 1993]). Alternatively, Axotobacter chroococcum first removes the chloride in the 2 position to produce 4-chlorophenoxyacetate, 4-chlorophenol, and 4-chlorocatechol, again with ortho cleavage of this catechol ([http://www.ncbi.nlm.nih.gov/pubmed/2219955|Balajee and Mahadevan, 1993]). 2,4-D biodegradation by this pathway branch may produce a byproduct antibiotic protoanemonin, which can be degraded to cis-acetylacrylate by a dienelactone hydrolase of Pseudomonas sp. strain B13 ([http://www.ncbi.nlm.nih.gov/pubmed/9440530|Brueckmann et al., 1998]). Comamonas testosteroni JH5 can cleave 4-chlorocatechol by a meta pathway, forming 5-chloro-2-hydroxymuonate semialdehyde which can be further transformed by a 2-hydroxymuconic semialdehyde dehydrogenase or a 2-hydroxymuconic semialdehyde hydrolase. Dehydrogenation is the major route, however the hydrolase step is also of physiological significance. Both branches lead to 5-chloro-2-oxopent-4-eneoate. This does not accumulate, and stoichiometric chloride is quickly released, but the exact route of chloride elimination is not known ([http://www.ncbi.nlm.nih.gov/pubmed/1510672|Hollender et al., 1997]). Pseudomonas cepacia P166 can move the chloride in 5-chloro-2-oxopent-4-eneoate through 5-chloro-4-hydroxy-2-oxopentanate to chloroacetate. Chloroacetate accumulates transiently, and stoichiometric dehalogenation is observed ([http://www.ncbi.nlm.nih.gov/pubmed/7574580|Arensdorf & Focht, 1995]).