Degradation of the thiocarbamate herbicide EPTC (S-ethyl dipropylcarbamothioate) and biosafening by Rhodococcus sp. strain NI86/21 involve an inducible cytochrome P-450 system and aldehyde dehydrogenase.
Determination of the N-terminal sequences of two EPTC (S-ethyl dipropylcarbamothioate)-induced proteins from thiocarbamate-degrading Rhodococcus sp. strain NI86/21 resolved by two-dimensional electrophoresis enabled the localization of the respective structural genes on two distinct DNA fragments. One of these strongly induced proteins is a NAD(+)-dependent dehydrogenase active on aliphatic aldehydes. The second protein was identified as a cytochrome P-450 enzyme. The cytochrome P-450 gene represents the first member of a new family, CYP116. Downstream of the cytochrome P-450 gene, two genes for a [2Fe-2S] ferredoxin (rhodocoxin) and a ferredoxin reductase are located. A putative regulatory gene encoding a new member of the AraC-XylS family of positive transcriptional regulators is divergently transcribed from the cytochrome P-450 gene. By hybridization, it was demonstrated that the aldehyde dehydrogenase gene is widespread in the Rhodococcus genus, but the components of the cytochrome P-450 system are unique to Rhodococcus sp. strain NI86/21. Overexpression in Escherichia coli was achieved for all of these proteins except for the regulatory protein. Evidence for the involvement of this cytochrome P-450 system in EPTC degradation and herbicide biosafening for maize was obtained by complementation experiments using EPTC-negative Rhodococcus erythropolis SQ1 and mutant FAJ2027 as acceptor strains. N dealkylation by cytochrome P-450 and conversion of the released aldehyde into the corresponding carboxylic acid by aldehyde dehydrogenase are proposed as the reactions initiating thiocarbamate catabolism in Rhodococcus sp. strain NI86/21. In addition to the major metabolite N-depropyl EPTC, another degradation product was identified, EPTC-sulfoxide.
Nagy
I
I
F. A. Janssens Laboratory of Genetics, Catholic University of Leuven, Heverless, Belgium.
Schoofs
G
G
Compernolle
F
F
Proost
P
P
Vanderleyden
J
J
de Mot
R
R
D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000502:physiology*; D000595:Amino Acid Sequence; D001483:Base Sequence; D001673:Biodegradation, Environmental; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000502:physiology*; D004790:Enzyme Induction; D005798:Genes, Bacterial; D006540:Herbicides / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D012240:Rhodococcus / Q000235:genetics / Q000378:metabolism*; D013859:Thiocarbamates / Q000378:metabolism*
D006540:Herbicides; D013859:Thiocarbamates; D003577:Cytochrome P-450 Enzyme System; D000444:Aldehyde Dehydrogenase; C036251:EPTC