Degradation of Fluorobenzene by Rhizobiales Strain F11 via ortho Cleavage of 4-Fluorocatechol and Catechol

Abstract

The aerobic metabolism of fluorobenzene by Rhizobiales sp. strain F11 was investigated. Liquid chromatography-mass spectrometry analysis showed that 4-fluorocatechol and catechol were formed as intermediates during fluorobenzene degradation by cell suspensions. Both these compounds, unlike 3-fluorocatechol, supported growth and oxygen uptake. Cells grown on fluorobenzene contained enzymes for the ortho pathway but not for meta ring cleavage of catechols. The results suggest that fluorobenzene is predominantly degraded via 4-fluorocatechol with subsequent ortho cleavage and also partially via catechol.During the last decades, environmental contamination by fluorinated organic compounds has received increasing attention because of their use as herbicides, fungicides, surfactants, refrigerants, intermediates in organic synthesis, solvents, and pharmaceuticals (11). Whereas the biodegradation of chlorinated compounds has been studied quite extensively (19), little is known about the bacterial metabolism of fluoroaromatic compounds, even though there have been several reports on the degradation of fluorobenzoic acids (5,6,7,16). With chloroaromatics, most degradation routes involve dioxygenase-and dehydrogenase-mediated conversion to the corresponding chlorocatechols, which are further metabolized by a dioxygenase that cleaves the aromatic ring. Dehalogenation occurs during metabolism of the ring-cleavage products (19). Most described strains degrade chlorocatechols via the ortho-cleavage pathway (14,18,19,20), but meta cleavage of 3-chlorocatechol can also occur (13), even though the meta-cleavage route is often unproductive due to the formation of toxic or dead-end products (1,19). Dehalogenation may in some cases occur prior to ring cleavage. For example, mutants of Pseudomonas sp. strain B13 and Alcaligenes eutrophus B9 that grow on 2-fluorobenzoate use a dioxygenase to convert it to catechol, with concomitant decarboxylation and defluorination (5). Pseudomonas putida strain CLB 250, which can use three different 2-halobenzoates, also converts these substrates by initial dehalogenating dioxygenation (6), and a defluorinating 4-fluorobenzoate monooxygenase has been reported as well (16).The present paper describes a metabolic pathway for fluorobenzene (FB). Information about the bacterial metabolism of this compound is scarce, despite studies on its chlorinated analogue (13, 18). Lynch et al. (12) described the oxidation of FB to 3-fluorocatechol by a strain of Pseudomonas putida, but in this study FB was not used as a carbon source. Recently, FB was reported to be completely degraded by a bacterial consortium (2) and by a pure bacterial culture that utilized it as a sole carbon and energy source (3). This gram-negative bacterium, phylogenetically classified within the order Rhizobiales, was named strain F11 and was used here to investigate the metabolism of FB.Intermediates produced during FB degradation. In order to obtain information about the degradation pathway of FB, we tested which intermediates accumulated...

Analysis of Two Gene Clusters Involved in the Degradation of 4-Fluorophenol by Arthrobacter sp. Strain IF1

“…The cleavage of the carbon-fluorine bond is especially interesting in view of its kinetic stability and high bond energy. Defluorination of fluoroaromatics can occur prior to ring cleavage, e.g., via an oxygenase that defluorinates fluorobenzoate (11,36) or fluorobenzene (8). In other cases, defluorination occurs after ring cleavage via the formation of fluorinated muconolactones (42), which can be produced from 4-fluorobenzoate (19) and fluorobenzene (8) via 4-fluorocatechol.…”

The biodegradation vs. biotransformation of fluorosubstituted aromatics

“…Small amounts of cis-dienelactone were detected as a deadend metabolite during growth of Rhizobiales strain F11 on fluorobenzene (Carvalho et al 2006), complying with its role as a minor byproduct rather than a true intermediate of productive 4-fluorocatechol degradation (a possible participation of trans-dienelactone was not addressed). Consistently with this interpretation, no cis-or trans-dienelactone transforming activity was detectable in cells of the fluorobenzoatedegrading strain FLB300 (Engesser et al 1990a).…”

Natural production of fluorinated compounds and biotechnological prospects of the fluorinase enzyme

“…The studies, carried out by Hamilton et al [115,116] with 13 C-and 2 H-labeled precursors, demonstrated a high rate of conversion of glycines and pyruvates into FA and 4-FT, with the carbon atoms of FA and C-3 and C-4 of 4-FT being derived from C-2 of glycine or from C-2 and C-3 of pyruvate, indicating that the substrate for the fluorinating enzyme should be an intermediate between glycerol and pyruvate. It was also shown that the integration of 13 C in the C-1 and C-2 of FA always paralleled that in the C-3 and C-4 of 4-FT, indicating the existence of just one fluorinating enzyme in S. cattleya. Later, Moss et al [117] showed that fluoroacetaldehyde is a common precursor of both FA and 4-FT.…”

“…For many fluoro-organics biodegradation is completely unknown. Monofluorinated compounds like fluorophenols [7][8][9][10], fluorobenzenes [11][12][13][14][15], fluorobenzoates [16][17][18], fluoroanilines [19][20][21], and fluoroacetate (FA) [22][23][24] are more likely to be biodegraded, while polyfluorinated compounds are more prone to be recalcitrant, as is the case with perfluorinated compounds. [1,25,26] In contrast to the countless number of man-made fluorinated molecules, fluorine is rarely found in natural compounds, in spite of constituting the 13th most abundant element on Earth.…”