Isolation, characterization and genome sequencing of a soil-borne Citrobacter freundii strain capable of detoxifying trichothecene mycotoxins
Cereals are frequently contaminated with tricthothecene mycotoxins, like deoxynivalenol (DON, vomitoxin), which are toxic to humans, animals and plants. The goals of the research were to discover and characterize microbes capable of detoxifying DON under aerobic conditions and moderate temperatures. To identify microbes capable of detoxifying DON, five soil samples collected from Southern Ontario crop fields were tested for the ability to convert DON to a de-epoxidized derivative. One soil sample showed DON de-epoxidation activity under aerobic conditions at 22-24°C. To isolate the microbes responsible for DON detoxification (de-epoxidation) activity, the mixed culture was grown with antibiotics at 50ºC for 1.5 h and high concentrations of DON. The treatments resulted in the isolation of a pure DON de-epoxidating bacterial strain, ADS47, and phenotypic and molecular analyses identified the bacterium as Citrobacter freundii. The bacterium was also able to de-epoxidize and/or de-acetylate 10 other food-contaminating trichothecene mycotoxins. A fosmid genomic DNA library of strain ADS47 was prepared in E. coli and screened for DON detoxification activity. However, no library clone was found with DON detoxification activity. The whole genome of ADS47 was also sequenced, and from comparative genome analyses, 10 genes (characterized as reductases, oxidoreductases and deacetylase) were identified as potential candidates for DON/trichothecene detoxifying enzymes. Bioinformatic analyses showed that the major animal pathogenic locus of enterocyte effacement (LEE) operon genes absent from the ADS47 genome. Strain ADS47 has the potential to be used for feed detoxification and the development of mycotoxin resistance cereal cultivars.