This chemical acts by inhibiting elongases andthebiosynthesisofgibberellicacid,resultinginplantdeath when absorbed through the roots and shoots just above the seed of the target plants. TheUSEPAestimatedthat59 64millionpoundsofmetolachlor was applied in 1995, and its use has been steadily declining duringrecentyears. Recommendedapplicationlevelsofthechemical were 1. 2 5 lb/acre in 1995. In 1999, however, Syngenta Crop Protection, one of the main manufacturers of this herbicide, dis continued sales of metolachlor and replaced it with the reduced risk compound S metolachlor. This enantiomer is more effective in weed control than racemic metolachlor, providing the same weed control but requiring 35% less applied chemical.

Meto lachlor use in the United States was subsequently reduced by 15 24 million pounds in 2001, as herbicides containing this chemical were replaced SNX-5422 with S metolachlor, of which 20 24 million pounds wasappliedduringthatyear. Thisisthelargestreductionofpesticide use in the United States to date. Since atrazine was banned in Europe in 2003, there had been increasing use of metolachlor combinedwithpostemergence herbicidesuntil S metolachlorwas substituted for use of the mixed enantiomer. The European Union presently allows application of only S metolachlor for weed control. In Spain, it has been estimated that 5000 t of S metola chlor is applied on 1. 3 million hectares per year Metolachlorisslightlysolubleinwater and is moderately sorbed by most soils, with greater sorption occurring on soils having greater organic matter and clay contents.

Extensive leaching of 2010 American Chemical Society Published on Web 12/29/2010 PDE Inhibitors pubs. acs. org/JAFC metolachlor is reported to occur,especially insoilswithlow organic content. Metolachlor is relatively more persistent in soils as compared to other widely used chloroacetanilide herbicides, such as alachlor and propachlor. Metolachlor half lives ranging from 15 to 70 days have been observed in different soils. The herbicide is highly persistent in water, over a wide range of pH values, with reported half life values of g200 and 97 days in highly acid and basic conditions, respectively. Metolachlor is also relatively stable in water, and under natural sunlight, only about 6. 6% was degraded in 30 days. Because very little metolachlor volatilizes from soil, photodegradation is thought to be a pathway for loss, but only in the top few centimeters of soil.

On the basis of these observations, it has been postulated that metolachlor dissipation in soil mainly occurs via biological degrada tion, rather than chemical processes. The degradation of metolachlor Cannabinoid Receptor in soils has been proposed to occur via co metabolic processes that are affected by soil texture, microbial activity, and bioavailability. The limited number of reports on the micro bial degradation of metolachlor, and its long half life, led to contrasting hypotheses that microbial consortia are likely needed for metolachlor catabolism in soils or that metolachlor is not readily metabolized bysoilmicroorganisms. More over, previous attempts to enhance metolachlor degradation in natural fields have generally not been successful.

This was, in part, attributed to the low bioavailability of this herbicide to microorganisms. However, the half life of metolachlor in sterile soil was reduced from 97 to 12 days after the addition of an active HDAC-42 microbial community, indicating that other biotic factors influence metolachlor degradation in soils. Whereas pure cultures of an actinomycete, a streptomycete, and a fungus capableofmetabolizingmetolachlorhavebeenreported,degradation times were long, and only small amounts of the herbi cide were degraded or mineralized. Similarly, low rates of mineralization of the chloroacetanilide herbicide alachlor have also been reported, only 3 % of the herbicide was mineralized after 30 122 days. Pure microbial cultures have also been reported to be relatively ineffective in mineralizing acetochlor, a related herbicide, with maximum rates of 24%.

Recently, Xu et al. reported that 89, 63, and 39% of the chloroacetanilide HSP herbicides propachlor, alachlor, and meto lachlor were degraded, respectively, after 21 days of incubation. The major dissipation routes for both alachlor and acetochlor appear to be due to microbiologically mediated degradation, runoff, and leaching. Most chloroacetanilide degrading microorganisms reported to date are fungi, and metolachlor is thought to be more persistent and recalcitrant to degradation thanthe other chloroacetanilide herbicidesinsoils and water. In this study, we examined Spanish soils with a history of metolachlor application for the presence of pure microbial cultures capable of catabolizing this herbicide. Here we report the isolation and characterization of a pure culture of a yeast, Candida xestobii, and a bacterium, Bacillus simplex, that have the ability of catabolize metolachlor and use this herbicide as a sole source of carbon for growth. We also report that the yeast is also capable of rapidly catabolizing other chloroacetanilide herbi cides, such as acetochlor and alachlor.