Hua Qiang, Yang Chen, Oshima Taku, Mori Hirotada, Shimizu Kazuyuki
Institute for Advanced Biosciences, Keio University, Tsuruoka 997-0017, Japan.
Appl Environ Microbiol. 2004 Apr;70(4):2354-66. doi: 10.1128/AEM.70.4.2354-2366.2004.
Studies of steady-state metabolic fluxes in Escherichia coli grown in nutrient-limited chemostat cultures suggest remarkable flux alterations in response to changes of growth-limiting nutrient in the medium (Hua et al., J. Bacteriol. 185:7053-7067, 2003). To elucidate the physiological adaptation of cells to the nutrient condition through the flux change and understand the molecular mechanisms underlying the change in the flux, information on gene expression is of great importance. DNA microarray analysis was performed to investigate the global transcriptional responses of steady-state cells grown in chemostat cultures with limited glucose or ammonia while other environmental conditions and the growth rate were kept constant. In slow-growing cells (specific growth rate of 0.10 h(-1)), 9.8% of a total of 4,071 genes investigated, especially those involved in amino acid metabolism, central carbon and energy metabolism, transport system and cell envelope, were observed to be differentially expressed between the two nutrient-limited cultures. One important characteristic of E. coli grown under nutrient limitation was its capacity to scavenge carbon or nitrogen from the medium through elevating the expression of the corresponding transport and assimilation genes. The number of differentially expressed genes in faster-growing cells (specific growth rate of 0.55 h(-1)), however, decreased to below half of that in slow-growing cells, which could be explained by diverse transcriptional responses to the growth rate under different nutrient limitations. Independent of the growth rate, 92 genes were identified as being differentially expressed. Genes tightly related to the culture conditions were highlighted, some of which may be used to characterize nutrient-limited growth.
对在营养受限的恒化器培养中生长的大肠杆菌进行的稳态代谢通量研究表明，响应培养基中生长限制营养物的变化，通量会发生显著改变（Hua等人，《细菌学杂志》185:7053 - 7067，2003年）。为了通过通量变化阐明细胞对营养条件的生理适应，并理解通量变化背后的分子机制，基因表达信息至关重要。进行了DNA微阵列分析，以研究在葡萄糖或氨受限的恒化器培养中生长的稳态细胞的全局转录反应，同时保持其他环境条件和生长速率恒定。在生长缓慢的细胞（比生长速率为0.10 h⁻¹）中，在所研究的总共4071个基因中，有9.8%被观察到在两种营养受限培养之间差异表达，特别是那些参与氨基酸代谢、中心碳和能量代谢、转运系统和细胞包膜的基因。在营养限制条件下生长的大肠杆菌的一个重要特征是其通过提高相应转运和同化基因的表达从培养基中清除碳或氮的能力。然而，在生长较快的细胞（比生长速率为0.55 h⁻¹）中，差异表达基因的数量降至生长缓慢细胞中的一半以下，这可以通过在不同营养限制下对生长速率的不同转录反应来解释。与生长速率无关，有92个基因被鉴定为差异表达。突出了与培养条件密切相关的基因，其中一些可用于表征营养受限生长。
