食源性致病菌单核细胞增生李斯特菌（Lm）易在食品加工和储藏环境中形成生物被膜，极大增强了抗逆性而难以被彻底清除，因此成为食品卫生安全的重要隐患。前期工作已证实缺失全局转录调控因子CodY能显著影响Lm生物被膜的形成能力，且作用机制可能与其调控细菌碳氮代谢、胞外物质的运输和降解、以及鞭毛形成和运动等相关。因此，本项目拟从以下四个方面深入探讨CodY在Lm生物被膜形成的作用和分子机制：不同营养及CodY效应分子BCAA和GTP浓度变化对CodY调控Lm生物被膜形成的影响；CodY对Lm鞭毛形成和运动的调控作用及对生物被膜形成的影响；CodY在Lm碳氮代谢和转化中的调控作用及对生物被膜形成的影响；CodY在Lm生物被膜胞外蛋白表达中的作用。通过以上研究，建立CodY作用Lm生物被膜形成的分子调控模型，为抑制生物被膜的形成、建立经济有效的食品生产和保藏方法、提高食品卫生安全提供新的思路和理论依据。

The ability of the foodborne pathogen Listeria monocytogenes to develop biofilm in food-processing environment is a major concern for the food safety, because biofilms allow bacteria to better resist environmental stresses. Comparative proteomic and global transcriptional microarray analyses in our previous studies showed that the most striking difference in L. monocytogenes biofilm forming cells was observed for the genes linking central nitrogen and carbon metabolism, glnR (glutamine synthetase repressor, GlnR), glnA (glutamine synthetase, GlnA), gltAB (glutamate synthase), gltC (transcription activator of glutamate synthase operon, GltC) and rocG (glutamate dehydrogenase, RocG). These genes have been demonstrated to be regulated by CodY in many low G+C Gram-positive bacteria, such as Bacillus subtilis, Streptococcus mutans, and so on. CodY is a global transcription regulator that controls dozens of genes involving in adaptation of the bacteria to starvation by highly diverse mechanisms in different bacteria. Biofilm formation was found, in our recent study, to be highly altered in the CodY deletion mutant compared to that of the wild type strain EGDe, suggesting that CodY represses biofilm formation. To illustrate CodY-regulated mechanisms in L. monocytogenes biofilm formation, the objectives of this proposal are to investigate: 1) Whether nutrient availability and the levels of GTP and branched chain amino acids (BCAA) influence on CodY-regulated biofilm formation of L. monocytogenes; 2) Whether the expression of flagellar and motility genes that have been indicated to be important for the initiation of static biofilms of L. monocytogenes is regulated by CodY. 3) Whether the genes of linking central nitrogen and carbon metabolism, glnR, glnA, gltAB, gltC and rocG play a role in L. monocytogenes biofilm formation, and how CodY regluates these genes expression under biofilm status; 4) Whether CodY alters the abundance of exoproteins that affect biofilm formation such as protease. Based on the studies mentioned above, the possible molecular regulation model(s) that the global regulator CodY is involved in biofilm formation of L. monocytogenes will be established to provide insight into potential control mechanisms for this problematic organism.