Complete microbial degradation of both enantiomers of the chiral herbicide mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propionic acid] in an enantioselective manner by Sphingomonas herbicidovorans sp. nov

Abstract

Sphingomonas herbicidovorans MH (previously designated Flavobacterium sp. strain MH) was able to utilize the chiral herbicide (RS)-2-(4-chloro-2-methylphenoxy)propionic acid (mecoprop) as the sole carbon and energy source. When strain MH was offered racemic mecoprop as the growth substrate, it could degrade both the (R) and the (S) enantiomer to completion, as shown by biomass formation, substrate consumption, and stoichiometric chloride release. However, the (S) enantiomer disappeared much faster from the culture medium than the (R) enantiomer. These results suggest the involvement of specific enzymes for the degradation of each enantiomer. This view was substantiated by the fact that resting cells of strain MH grown on (S)-mecoprop were able to degrade the (S) but not the (R) enantiomer of mecoprop. Accordingly, resting cells of strain MH grown on (R)-mecoprop preferentially metabolized the (R) enantiomer. Nevertheless, such cells could transform (S)-mecoprop at low rates. Oxygen uptake rates with resting cells confirmed the above view, as oxygen consumption was strongly dependent on the growth substrate. Cells grown on (R)-mecoprop showed oxygen uptake rates more than two times higher upon incubation with the (R) than upon incubation with the (S) enantiomer and vice versa.

Aerobic biodegradation of chiral phenoxyalkanoic acid derivatives during incubations with activated sludge

“…The (S) enantiomers of mecoprop and dichlorprop, structural analogues of the compounds investigated in this study, are biodegraded before or faster than the corresponding (R) enantiomers in soil and sewage sludge [5,7,20,22]. In one of the studies [7], it was shown that sewage sludge that was acclimatized to pure (R)-mecoprop preferentially degraded the (R) but not the (S) enantiomer within 20 h of incubation; this indicated a selective enrichment of speci¢c populations or regulatory changes in speci¢c strains.…”

“…In order to test and understand the microbial degradation of racemic mixtures of chiral organic compounds, the DOC measurements need to be complemented by enantiomer-speci¢c analysis, because the length of the lag phases as well as the degradation rates may di¡er for the enantiomers. We have reported previously the enantioselective degradation of the chiral herbicides mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propanoic acid] and dichlorprop [(RS)-2-(2,4-dichlorophenoxy)propanoic acid] by Sphingomonas herbicidovorans MH [5,6] and upon incubation with aerobic sewage sludge [7]. Both the (R) and the (S) enantiomers were completely metabolized but the (S) enantiomers were removed from the test medium before the (R) enantiomers.…”

Preferential attack of the (S)-configured ether-linked carbons in bis-(1-chloro-2-propyl) ether by Rhodococcus sp. strain DTB

“…The enantioselective degradation of racemic (R/S)-2-(4-chloro-2methylphenoxy)propionic acid (mecoprop) by Sphingomonas herbicidovorans sp. has been reported (Zipper et al, 1996). Growth experiments have demonstrated that (S)mecoprop was degraded first and when it was spent the organism started to degrade (R)-mecoprop.…”

“…It has been shown that the configuration of a chiral carbon atom next to the ether bond influences the enzyme-catalysed degradation processes. The microbial attack of chiral ether bonds has been found to be stereoselective and the enzymes differ in their enantioselectivity (Zipper et al, 1996). The enzymes involved in the initial breakdown of chiral phenoxyalkanoates have been studied in detail (Fukumori & Hausinger, 1993;Nickel et al, 1997;Westendorf et al, 2003).…”

Posttranslational oxidative modification of (R)‐2‐(2,4‐dichlorophenoxy)propionate/α‐ketoglutarate‐dependent dioxygenases (RdpA) leads to improved degradation of 2,4‐dichlorophenoxyacetate (2,4‐D)

“…In most cases, degradation is initiated by cleavage of the ether bond by α-ketoglutarate-dependent dioxygenases showing pronounced substrate specificity. Whereas phenoxyacetates are cleaved predominantly by 2,4-D/α-ketoglutarate dioxygenases (TfdA) [1,2], degradation of the chiral 2-phenoxypropionates requires two enzymes with opposite enantiospecific characteristics [3][4][5][6][7][8]. (R)-2-(2,4-dichlorophenoxy)propionate/ α-ketoglutarate-dependent dioxygenases (RdpA), which attacks the R-enantiomers of 2-phenoxypropionates, is identical in the primary amino acid sequence in Delftia acidovorans MC1, Sphingobium herbicidovorans MH, and Rhodoferax sp.…”