Bacterial defluorination of 4-fluoroglutamic acid

Bacterial degradation of the anti-depressant drug fluoxetine produces trifluoroacetic acid and fluoride ion

Fluoxetine (FLX) is a blockbuster drug with annual sales in the billions of dollars. Its widespread use has resulted in its detection in water courses, where it impacts aquatic life. Investigations on the biodegradation of FLX by microorganisms are important, since augmentation of secondary wastewater treatment by an effective degrader may be one method of improving the drug's removal. In this paper, we demonstrate that common environmental bacteria can use FLX as a sole carbon and energy source. Investigations into the metabolites formed using fluorine-19 nuclear magnetic resonance spectroscopy (¹⁹F NMR) and gas chromatography-mass spectrometry indicated that the drug was initially hydrolysed to yield 4-(trifluoromethyl)phenol (TFMP) and 3-(methylamino)-1-phenylpropan-1-ol. Since the fluorometabolite accumulated, the bacteria presumably used the latter compound for carbon and energy. Further growth studies revealed that TFMP could also be used as a sole carbon and energy source and was most likely catabolised via meta-cleavage, since semialdehyde products were detected in culture supernatants. The final products of the degradation pathway were trifluoroacetate and fluoride ion; the former is a dead-end product and was not further catabolised. Fluoride ion most likely arises owing to spontaneous defluorination of the meta-cleavage products that were shown to be photolabile.Key points• Bacteria can use FLX and TFMP as sole carbon and energy sources for their growth.• Biodegradation produces fluorometabolites that were detected by ¹⁹F NMR and GC-MS.• Trifluoroacetic acid and fluoride ion were identified as end products.

Development of a colorimetric colony-screening assay for detection of defluorination by micro-organisms

AIMS

To develop a colorimetric colony-screening assay to facilitate the isolation of micro-organisms capable of defluorination.

METHODS AND RESULTS

A metal-dye chelate, zirconium-xylenol orange was used to detect fluoride ions released from a fluorinated substrate through microbial metabolism. Depolymerised zirconium reagent gave the greatest visual contrast for the presence of fluoride compared to more polymerised forms of zirconium reagent. The sensitivity of the assay was greatest when the molar ratio of depolymerised zirconium to xylenol orange was 1:2. Using depolymerised zirconium and xylenol orange (150 and 300 nmol l(-1) respectively), the assay could detect a fluoride application spot (5 mmol l(-1)) containing 50 nmoles of fluoride ions. Most media constituents were well tolerated by the assay, although phosphate ions needed to be restricted to 0.1 g l(-1) and some proteins digest to between 1 and 5 g l(-1). A microbial enrichment culture growing on solidified medium containing 20 mmol l(-1) fluoroacetate was screened using the assay, and defluorinating bacteria belonging to the genus Burkholderia isolated.

CONCLUSIONS

A method was developed that is sensitive, rapid and reliable for detecting defluorination by micro-organisms growing on solidified medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

This method can be used to facilitate the isolation of micro-organisms capable of defluorination.

Biology of fluoro-organic compounds

Investigations on diverse aspects of fluoro-organic compounds have rapidly increased during the past decades. Because natural sources of fluoro-organic compounds are extremely rare, the industrial synthesis of fluorinated organic compounds and production of fluorinated natural product derivatives have greatly expanded in recent years because of their increasing importance in the agrochemical and pharmaceutical industries. Due to structural complexity or instability, synthetic modification is often not possible, and various biofluorination strategies have been developed in recent years for applications in the anti-cancer, anti-viral and anti-infection fields. Despite the industrial importance of fluorinated compounds, there have been serious concerns worldwide over the levels and synthetic routes of certain fluorinated organic compounds, in particular perfluorinated chemicals (PFCs). PFCs are emerging and recalcitrant pollutants which are widely distributed in the environment and have been detected in humans and wildlife globally. PFCs have been demonstrated to be potentially carcinogenic, adversely affect the neuroendocrine and immune systems, and produce neurotoxicity, heptatotoxicity and endocrine disrupting effects in vertebrate animals. Here, we provide an overview of recent advances in our understanding of the biology of various fluoro-organic compounds and perspectives for new enzymes and metabolic pathways for bioremediation of these chemicals.

Metabolism of fluoroorganic compounds in microorganisms: impacts for the environment and the production of fine chemicals

Incorporation of fluorine into an organic compound can favourably alter its physicochemical properties with respect to biological activity, stability and lipophilicity. Accordingly, this element is found in many pharmaceutical and industrial chemicals. Organofluorine compounds are accepted as substrates by many enzymes, and the interactions of microorganisms with these compounds are of relevance to the environment and the fine chemicals industry. On the one hand, the microbial transformation of organofluorines can lead to the generation of toxic compounds that are of environmental concern, yet similar biotransformations can yield difficult-to-synthesise products and intermediates, in particular derivatives of biologically active secondary metabolites. In this paper, we review the historical and recent developments of organofluorine biotransformation in microorganisms and highlight the possibility of using microbes as models of fluorinated drug metabolism in mammals.