COMPLETE MICROBIAL-DEGRADATION OF BOTH ENANTIOMERS OF THE CHIRAL HERBICIDE MECOPROP [(RS)-2-(4-CHLORO-2-METHYLPHENOXY)PROPIONIC ACID] IN ANENANTIOSELECTIVE MANNER BY SPHINGOMONAS HERBICIDOVORANS SP-NOV

Sphingomonas herbicidovorans MH (previously designated Flavobacterium sp. strain MH) was able to utilize the chiral herbicide (RS)-2-(4-chlo ro-2-methylphenoxy)propionic acid (mecoprop) as the sole carbon and en ergy source. When strain MH was offered racemic mecoprop as the growth substrate, it could degrade both the (R) and the (S) enantiomer to co mpletion, as shown by biomass formation, substrate consumption, and st oichiometric chloride release. However, the (S) enantiomer disappeared much faster from the culture medium than the (R) enantiomer. These re sults suggest the involvement of specific enzymes for the degradation of each enantiomer. This view was substantiated by the fact that resti ng 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 l ow rates. Oxygen uptake rates with resting cells confirmed the above v iew, as oxygen consumption was strongly dependent on the growth substr ate. Cells grown on (R)-mecoprop showed oxygen uptake rates more than two times higher upon incubation with the (R) than upon incubation wit h the (S) enantiomer and vice versa.