Degradation of fluorobenzene by a 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...