3-Fluorobenzoic acid is a fluorinated organic compound. Little attention has been given to the biodegradation of these compounds. The uses of fluorinated aromatic compounds include herbicides, pesticides, insecticides, refrigerants, and anesthetics (B. D. Key, R. D. Howell, & C. S. Criddle (1997) Environ Sci Technol 31:2445-2454). Fluoroorganics are more stable than their chlorine analogues due to the stability of the C-F bond, which is 25 kcal/mol stronger than the C-Cl bond (D. F. McMillen & D. M. Golden (1982) Ann Rev Phys Chem 33:493). Fluoroorganics pose a potential human health concern. Industrial workers exposed to fluroorganics were shown to have higher serum organic fluorine concentrations than individuals not exposed to fluroorganics (Ubel et al., 1980). The health effects of acute fluoride toxicity are well known; however, it is unclear whether fluorinated organic compounds result in the same problems (Akiniwa. K. (1997) Fluoride 30(2): 89-104).
In organisms that have been surveyed, metabolism of 2-fluorobenzoate and 4-fluorobenzoate is more common than that of 3-fluorobenzoate (Song et al., 2000). Two pathways of 3-fluorobenzoate degradation have been described. In one pathway, degradation is initiated by 1,2-dioxygenation of 3-fluorobenzoate to give 3-fluorohexadiene-cis,cis-1,2-diol-1-carboxylate. This is converted to 3-fluorocatechol, which is slowly metabolized to 2-fluoro-cis,cis-muconate, which is not metabolized further (Schreiber et al., 1980) , leading to accumulation of cytotoxic 3-fluorocatechol. Alternatively, metabolism can begin with 1,6-dioxygenation of 3-fluorobenzoate, which is converted to 5-fluorocyclohexadiene-cis,cis-1,2-diol-1-carboxylate and then sequentially to 4-fluorocatechol, 3-fluoro-cis,cis-muconate, and eventually oxoadipate, which can enter central metabolism (K. H. Engesser, G. Auling, J. Busse, & H.-J. Knackmuss (1990) Arch Microbiol 153:193-199). Fluoride is also released in this pathway. Both pathways are present in strains that metabolize 3-fluorobenzoate, but metabolic flux through each pathway varies among the organisms (Engesser et al., 1990). Cells of Acinetobacter calcoaceticus NCIB 8250 (Clarke et al., 1975) and Pseudomonas sp. B13 (Schreiber et al., 1980) grown on benzoate or 3-chlorobenzoate, respectively, metabolized 3-fluorobenzoate, but the strains could not grow on the compound as a carbon and energy source. In these organisms, the major pathway of 3-fluorobenzoate degradation begins with 1,2-dioxygenation. Strain FLB 300 (alpha-2-subclass of Proteobacteria, Agrobacterium-Rhizobium branch) (Engesser et al., 1990) and Sphingomonas sp. HB-1 (Boersma et al., 2004) were able to grow using 3-fluorobenzoate as a sole carbon and energy source. In these strains that can assimilate 3-fluorobenzoate, the major pathway begins with 1,6-dioxygenation of the substrate, thereby reducing the amount of the toxic 3-fluorocatechol intermediate that is produced.
The following is a text-format 3-fluorobenzoic acid pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (9k) format.
3-Fluorobenzoate Paracoccus denitrificans Pseudomonas sp. B13 Sphingomonas sp. HB-1 Acinetobacter calcoaceticus | | +-------------+-------------+ | | | | benzoate | | benzoate 1,2-dioxygenase | | 1,2-dioxygenase | | | | v v 3-Fluorocyclohexadiene- 5-Fluorocyclohexadiene- cis,cis-1,2-diol- cis,cis-1,2-diol- 1-carboxylate 1-carboxylate | | | | 1,6-dihydroxycyclohexa- | | 1,6-dihydroxycyclohexa- 2,4-diene-1-carboxylate | | 2,4-diene-1-carboxylate dehydrogenase | | dehydrogenase | | | | v v 3-Fluorocatechol 4-Fluorocatechol Pseudomonas sp. B13 | | | | | | | | | | | v v 2-Fluoro-cis,cis-muconate to the 4-Fluorobenzoate Pathway
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