xestobii wasalsoshownheretorapidlymineralizeup to 25% of metolachlor after 10 days of growth. Because differ ences in mineralization rates among microorganisms in soils are likely due to both biotic and abiotic factors, more studies are needed to assess the contribution of mineralization to loss of this herbicide in soils. Results of mass balance analyses indicated that 5% of metolachlor in the culture medium was present in C. xestobii and B. simplex cells following incubation with metolachlor. This result indicated that metolachlor was not significantly incorporated into biomass and, thus, metabolites that were not mineralized were likely released into the growth medium. Our results are in contrast to those reported in ref 17, which reported that 80% of ring labeled metolachlor added to a microbial community was removed from the medium and accumulated inside cells.
Mechanism of Degradation. The mechanism by which metola chlor is transformed by C. xestobii is not clear. Because Pazopanib analytical standards of possible metolachlor metabolites were not available, we used the University of Minnesota Biocatalysis/Biodegrada tion Database Pathway Prediction System to predict plausible pathways for the microbial degradation of metola chlor. The PPS identi fied 22 possible molecules with molecular ions 190. Comparison of the possible molecular ions from the total ion current plot of culture medium obtained following growth of C. xestobii on metolachlor resulted in no positive matches. Also, HPLC fractionation of the spent medium following growth of C.
xestobii in uniformly ring labeled metolachlor did not result in any peaks that had 2% of the applied C, other than the metolachlor Pazopanib peak, leading to difficulty in extrapolating a degra dation pathway. Although it is tempting to speculate that dechlorination was not a major mechanism for the degradation of metolachlor by the isolated yeast, too few data are available to accurately determine this. Consequently, the pathway by which metolachlor is transformed by C. xestobii is currently unknown and awaits further analyses. In summary, in this study we report on the isolation of a bacte rium and yeast that have the ability to catabolize metolachlor. We also show that the yeast C. xestobii uses metolachlor as a sole C and energy source for growth and is able to mineralize t. this compound under controlled laboratory conditions.
Although otherfungalandbacterialstrainshavebeenisolatedthatareableto Cannabinoid Receptor partially transform metolachlor, most attempts to isolate pure or mixed microbial cultures capable of mineralizing metolachlor have been unsuccessful. Whereas the degradation of metola chlor has been previously studied with a pure culture of the fungus Ch. globosum, which also used this herbicide as a sole source of C and energy, gas liquid chromatographic analysis of the concen trated extract from resting cell experiments with this fungus showed that at least eight extractable products were produced fromtheoriginalcompound. TiedjeandHagedorn reported that the major product of alachlor degradation by this fungus was likely 2,6 diethyl N aniline, and McGahen and Tiedje reported that the co metabolism of metolachlor by Ch.
globosum is thought to occur by removal of one or both R groups from the nitrogen atom and subsequent dehydrogenation of the ethyl substituent. These authors also postulated that the HDAC-42 fungus may eventually remove the chloro, methoxy, or ethoxy substituent from the R groups. In addition to fungi, bacteria have also been reported to transform alachlor. For example, Sette et al. reported that a Streptomycetes sp. strain degraded ??60 75% of the alachlor within days to produce indole and quinoline deriv atives, and Villareal et al. reported that Moraxella sp. strain DAK3 respired and grew on N substituted acylanilides containing methyl, ethyl, or isopropyl substitutions, but failed to grow on alachlor and metolachlor. In contrast to previous studies with fungi, the isolated C.
xestobii strain degraded 50% of metolachlor after 4 days of growth, and no metabolites, such as the ethanesulfonic acid and oxanilic acid, were detected in the growthmediumbyHPLCanalysis. A. flavus and A. terr ??cola PARP have been also described as metolachlor degrading fungi, reducing the half life of this herbicide from 189 to 3. 6 and 6. 4 days, respec tively. Coupled with data showing that some fungicides significantly reduce metolachlor dissipation in soils, results from our studies are consistent with the notion that soil yeast and other fungi may be responsible for significant transformation of metolachlor in soils. Moreover, because degradation of metola chlor by C. xestobii was fairly rapid and resulted in the miner alization of this herbicide, our data suggest that this yeast may eventually prove to be useful for metolachlor bioremediation efforts. More studies, however, are needed to determine whether this yeast is also able to metabolize and mineralize other aniline herbicide compounds and to identify metabolites produced dur ing the degradation process.