Biodegradation and Mineralization of Metolachlor and Alachlor by Candida xestobii

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, S-metolachlor, is the most effective form for weed control. Although 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. This study 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. Tis paper reports 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. High-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) analyses indicated that C. xestobii degraded 60% of the added metolachlor after 4 days of growth and converted up to 25% of the compound into CO(2) after 10 days. In contrast, B. simplex biodegraded 30% of metolachlor following 5 days of growth in minimal medium. In contrast, moreover, the yeast degraded other acetanilide compounds and 80% of acetochlor (2-chloro-N-ethoxymethyl-6'-ethylaceto-o-toluidide) and alachlor (2-chloro-2',6'-diethyl-N-methoxymethylacetanilide) were degraded after 15 and 41 h of growth, respectively. The results of these studies indicate that microorganisms 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.

Alachlor oxidation by the filamentous fungus Paecilomyces marquandii

“…One route leads to a loss of chloracetaldehyde and methanol from alachlor and the other one leads to hydroxylation of the ethyl group attached to a benzene ring after previous dechlorination of the chloracetaldehyde substituent (6). Alachlor byproducts have been often identified in bacteria enriched soil samples or microbial cultures [18,27,28]. Nevertheless, only few papers presented metabolic pathway of alachlor transformation by microorganisms.…”

“…The genus of Paecilomyces represents ubiquitous soil fungi, often isolated from heavy metal polluted areas [21][22][23]. Its remarkable enzyme activity and degradative abilities were also documented [24][25][26] Literature data concerning alachlor degradation by soil microbial communities or pure microorganism cultures and their metabolic pathways are limited and usually reveal only a few byproducts [27][28]. Only Tiedje and Hagedorn, [29] and Sette et al [30] documented the degradation of alachlor by pure cultures of soil fungus Chaetomium globosum and soil streptomycetes and proposed a microbial pathway of herbicide transformation.…”

Mechanism study of alachlor biodegradation by Paecilomyces marquandii with proteomic and metabolomic methods

“…Some of these intermediates are toxic or mutagenic e.g., 2,6-diethylaniline (DEA) [4,5]. Microbial degradation, or rather transformation, plays a pivotal role in the rate of alachlor elimination from the environment [6][7][8]. There are many studies concerning the both the characterization of selected microbial consortium or microorganisms in pure culture capable of degrading alachlor and the identification of byproducts, but little is known about the molecular mechanisms of conversions.…”

S-metolachlor efficacy on the control of Brachiaria decumbens, Digitaria horizontalis, and Panicum maximum in mechanically green harvested sugarcane

“…In both works, the authors ascribed the results to the retention of the herbicide by the plant residues covering the soil surface and to increased losses of the herbicides to the surrounding environment. It is worth noting that S-metolachlor is a stereoisomer of metolachlor (Blaser, 2002) with a higher biological activity (Munoz et al, 2011) and that the amount of rain and the period during which the rainfall occurred after the herbicide was applied may have had an important effect on the retention of the herbicide. Oliveira et al (2001) observed that the low precipitation during the first days after the mixture of atrazine and metolachlor was applied may explain the low removal of the metolachlor from the plant residues to the soil.…”

“…However, more detailed information about S-metolachlor is lacking. This herbicide is a metolachlor stereoisomer (Blaser, 2002) that presents higher biological activity (Munoz et al, 2011). In Brazil, S-metolachlor is recommended for preemergence control of monocots and some dicots species in soybean, corn, beans, cotton, and sugar cane crops.…”