Abstract:N-nitrosodiethylamine（NDEA）is a strong carcinogen easily produced during food processing.As reported，some Lactobacillus spp.could degrade NDEA，but the degradation mechanism remained unclear.Therefore，this study investigated the effects of environmental factors including cultivating temperature，time，pH value，and aerobic/anaerobic conditions on the degradation capacity of Enterococcus faecium 15A，a Lactobacillus strain with NDEA-degrading ability isolated from the gut of a healthy person.As revealed by the results，the degradation of this strain was positively related to its growth，and environmental pH value could alter its effect.To be specific，E.faecium 15A showed a degrading effect on NDEA at pH2-7，whereas promoted NDEA production at pH8.The effect of E.faecium 15A on NDEA was found to be a process with multiple gene targets and involving multiple metabolic pathways by transcriptomics analysis.Among these metabolic pathways，the purine biosynthetic/metabolic process might be the crucial pathway.Then corresponding up-regulated genes（xpt，hpt，Pyk，and Ndk）and down-regulated gene（guaA）were verified by real-time reverse transcriptase polymerase chain reaction.This study revealed the degradation regularity of E.faecium 15A and explored the degradation mechanism of the strain from the molecular level.The findings could provide a basis for efficient microbial degradation of NDEA and novel thoughts for Lactobacillus used as culture starters and probiotics.