title: Bacterial cytochrome P450 system catabolizing the Fusarium toxin deoxynivalenol.
abstract: Deoxynivalenol (DON) is a natural toxin of fungi that cause Fusarium head blight disease of wheat and other small-grain cereals. DON accumulates in infected grains and promotes the spread of the infection on wheat, posing serious problems to grain production. The elucidation of DON-catabolic genes and enzymes in DON-degrading microbes will provide new approaches to decrease DON contamination. Here, we report a cytochrome P450 system capable of catabolizing DON in Sphingomonas sp. strain KSM1, a DON-utilizing bacterium newly isolated from lake water. The P450 gene ddnA was cloned through an activity-based screening of a KSM1 genomic library. The genes of its redox partner candidates (flavin adenine dinucleotide [FAD]-dependent ferredoxin reductase and mitochondrial-type [2Fe-2S] ferredoxin) were not found adjacent to ddnA; the redox partner candidates were further cloned separately based on conserved motifs. The DON-catabolic activity was reconstituted in vitro in an electron transfer chain comprising the three enzymes and NADH, with a catalytic efficiency (k(cat)/K(m)) of 6.4 mM(-1) s(-1). The reaction product was identified as 16-hydroxy-deoxynivalenol. A bioassay using wheat seedlings revealed that the hydroxylation dramatically reduced the toxicity of DON to wheat. The enzyme system showed similar catalytic efficiencies toward nivalenol and 3-acetyl deoxynivalenol, toxins that frequently cooccur with DON. These findings identify an enzyme system that catabolizes DON, leading to reduced phytotoxicity to wheat.
authors.affiliation: National Institute for Agro-Environmental Sciences, Ibaraki, Japan.
authors.forename: Michihiro
authors.initials: M
authors.lastname: Ito
authors.forename: Ikuo
authors.initials: I
authors.lastname: Sato
authors.forename: Masumi
authors.initials: M
authors.lastname: Ishizaka
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Yoshida
authors.forename: Motoo
authors.initials: M
authors.lastname: Koitabashi
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Yoshida
authors.forename: Seiya
authors.initials: S
authors.lastname: Tsushima
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D003067:Coenzymes / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D007700:Kinetics; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D017422:Sequence Analysis, DNA; D020578:Sphingomonas / Q000201:enzymology* / Q000302:isolation & purification; D014255:Trichothecenes / Q000378:metabolism*; D014871:Water Microbiology
chemical_list: D001426:Bacterial Proteins; D003067:Coenzymes; D004269:DNA, Bacterial; D014255:Trichothecenes; D009243:NAD; D003577:Cytochrome P-450 Enzyme System; C007262:deoxynivalenol