Biotransformations of Fenoxaprop-ethyl by Fluorescent Pseudomonas Strains

Fenoxaprop-ethyl (FE) transformation by pure cultures of four Pseudomonas strains was studied using14C-labeled herbicide, labeled in either the dioxyphenyl (DOP) or the chlorophenyl (CP) ring. Resting cells rapidly hydrolyzed FE to fenoxaprop acid (FA), but cleavage of the ether bond proceeded slowly. Degradation of FE by P. fluorescens strains RA-2 and UA5-40 cultured in tryptic soy broth (TSB) or minimal media with glucose (MMG) or propionate (MMP) was assessed. TSB cultures completely hydrolyzed FE to FA within 5 days. Polar metabolites (predominantly glycylcysteine and cysteine conjugates arising from FE or FA), an unidentified metabolite, and 6-chloro-2,3-dihydrobenzoxazol-2-one (CDHB) accumulated in TSB cultures treated with 14C-CP-labeled FE during an 11-day study, whereas 2-(4-hydroxyphenoxy)propionic acid accumulated in 14C-DOP-labeled FE−TSB cultures. FE transformation by MMP cultures was limited to ester hydrolysis of FE to FA. Hydrolysis of FE to FA was never detected in RA-2 MMG cultures and was low in UA5-40 MMG cultures. Cleavage of the benzoxazolyloxyphenyl ether bond occurred in MMG cultures of both strains; that is, 50% of 14C-CP-labeled FE was recovered as CDHB, and hydroquinone accumulated in MMG 14C-DOP-labeled FE cultures. No mineralization of FE to CO2 was observed, regardless of the 14C label or growth media used as substrate. Strains of P. fluorescens can promote significant cometabolic transformations of FE and may contribute to the dissipation of FE in the environment. Keywords: Herbicide; biodegradation; pseudomonad; microbial metabolism; aryloxyphenoxy propionate