Kim Min-Jeong, Lim Sangyong, Ryu Sangryeol
Department of Food and Animal Biotechnology, School of Agricultural Biotechnology, Center for Agricultural Biomaterials, and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul, Korea.
J Microbiol Biotechnol. 2008 Jun;18(6):1024-32.
Efficient expression of the Salmonella Typhimurium tdcABCDEG operon involved in the degradation of Lserine and L-threonine requires TdcA, the transcriptional activator of the tdc operon. We found that the tdcA gene was transiently activated when bacterial growth condition was changed from aerobic to anaerobic, but this was not observed if Salmonella was grown anaerobically from the beginning of the culture. Expression kinetics of six tdc genes after anaerobic shock demonstrated by a real-time PCR assay showed that the tdcCDEG genes were not induced in tdcA mutant but tdcB maintained its inducibility by anaerobic shock even in the absence of tdcA, suggesting that an additional unknown transcriptional regulation may work for the tdcB expression. We also investigated the effects of nucleoid-associated proteins by primer extension analysis and found that H-NS repressed tdcA under anaerobic shock conditions and fis mutation delayed the peak expression time of the tdc operon. DNA microarray analysis of genes regulated by TdcA revealed that the genes involved in Nacetylmannosamine, maltose, and propanediol utilization were significantly induced in a tdcA mutant. These findings suggest that Tdc enzymes may play a pivotal role in energy metabolism under a sudden change of oxygen tension.
参与L-丝氨酸和L-苏氨酸降解的鼠伤寒沙门氏菌tdcABCDEG操纵子的高效表达需要tdc操纵子的转录激活因子TdcA。我们发现，当细菌生长条件从需氧变为厌氧时，tdcA基因会被短暂激活，但如果沙门氏菌从培养开始就厌氧生长，则不会观察到这种情况。通过实时PCR分析显示的厌氧休克后六个tdc基因的表达动力学表明，tdcCDEG基因在tdcA突变体中未被诱导，但即使在没有tdcA的情况下，tdcB仍通过厌氧休克保持其诱导性，这表明可能存在一种额外的未知转录调控作用于tdcB的表达。我们还通过引物延伸分析研究了类核相关蛋白的作用，发现H-NS在厌氧休克条件下抑制tdcA，fis突变延迟了tdc操纵子的峰值表达时间。对受TdcA调控的基因进行DNA微阵列分析发现，参与N-乙酰甘露糖胺、麦芽糖和丙二醇利用的基因在tdcA突变体中被显著诱导。这些发现表明，Tdc酶可能在氧张力突然变化时的能量代谢中起关键作用。
