Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Osaka, Japan.
Mol Syst Biol. 2011 May 24;7:493. doi: 10.1038/msb.2011.24.
Stochastic switching is considered as a cost-saving strategy for adaptation to environmental challenges. We show here that stochastic switching of a monostable circuit can mediate the adaptation of the engineered OSU12-hisC Escherichia coli strain to histidine starvation. In this strain, the hisC gene was deleted from the His operon and placed under the control of a monostable foreign promoter. In response to histidine depletion, the OSU12-hisC population shifted to a higher HisC expression level, which is beneficial under starving conditions but is not favoured by the monostable circuit. The population shift was accompanied by growth recovery and was reversible upon histidine addition. A weak directionality in stochastic switching of hisC was observed in growing microcolonies under histidine-free conditions. Directionality and fate decision were in part dependent on the initial cellular status. Finally, microarray analysis indicated that OSU12-hisC reorganized its transcriptome to reach the appropriate physiological state upon starvation. These findings suggest that bacteria do not necessarily need to evolve signalling mechanisms to control gene expression appropriately, even for essential genes.
随机切换被认为是一种节省成本的策略，用于适应环境挑战。我们在这里表明，单稳态电路的随机切换可以介导工程化的 OSU12-hisC 大肠杆菌菌株对组氨酸饥饿的适应。在该菌株中，hisC 基因从 His 操纵子中缺失，并置于单稳态外源启动子的控制下。在组氨酸耗尽时，OSU12-hisC 群体转移到更高的 HisC 表达水平，这在饥饿条件下是有益的，但不受单稳态电路的青睐。群体转移伴随着生长恢复，并且在添加组氨酸后是可逆的。在无组氨酸条件下生长的微菌落中观察到 hisC 随机切换的弱方向性。方向性和命运决策部分取决于初始细胞状态。最后，微阵列分析表明，OSU12-hisC 在饥饿时重新组织其转录组以达到适当的生理状态。这些发现表明，细菌甚至不需要进化信号机制来适当地控制基因表达，即使是必需基因。
