Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2010
Publication Date: 12/29/2010
Citation: Munoz, A.M., Koskinen, W.C., Sadowsky, M.J. 2011. Biodegradation and mineralization of metolachlor by Candida xestobii. Journal of Agricultural and Food Chemistry. 59(2):619-627. Interpretive Summary: Metolachor degradation by a yeast and bacterium. Metolachlor is one of the most extensively used chloroacetamide herbicides. In this study, we examined soils with a history of metolachlor application for the presence of pure microbial cultures capable of degradation (catabolism) of this herbicide. We were able to isolate and characterize of pure cultures of a yeast, Candida xestobii, and a bacterium, Bacillus simplex, that have the ability to catabolize metolachlor and use this herbicide as a sole source of carbon for growth. We also report that the yeast is able to rapidly degrade and mineralize other acetanilide herbicides, such as acetochlor and alachlor. These newly isolated organisms will allow us to obtain a better understanding of the biochemistry and genetics of acetanilide herbicides catabolism by microorganism, and will provide new tools for the bioremediation of environments impacted by these herbicides.
Technical Abstract: Metolachlor (2-chloro-6’-ethyl-N-(2-methoxy-1-methylethyl) aceto-o-toluidide) is a pre-emergent chloroacetanilide herbicide used to control broadleaf and annual grassy weeds in a variety of crops. The S enantiomer of metolachlor, S-metolachlor, is the most effective form for weed control. While the degradation of metolachlor in soils is thought to occur primarily by microbial activity, little is known about the microorganisms that carry out this process and the mechanisms by which this occurs. In this study we examined a silty-clay soil (a Luvisol) from Spain with 10 and 2 year histories of metolachlor and S-metolachlor applications, respectively, for microorganisms that had the ability to degrade this herbicide. We report here on the isolation and characterization of pure cultures of Candida xestobii and Bacillus simplex that have the ability to use metolachlor as a sole source of carbon for growth. Species assignment was confirmed by morphological and biochemical criteria, and by sequence analysis of 18S and 16S rRNA, respectively. HLPC and LC-MS analyses indicated that Bacillus simplex biodegraded 30% of metolachlor following 5 d of growth in minimal medium, while Candida xestobii degraded 60% after 4 d of growth and converted up to 25% of the compound into CO2 after 240 h (10 days). Moreover, the yeast degraded other acetanilide compounds; a 80% of acetochlor and alachlor were degraded in 15 h and 41 h respectively. Results of these studies indicate that microorganism comprising two main branches of the tree of life have acquired the ability to degrade the same novel chlorinated herbicide that has been recently added to the biosphere.