Memory and fitness optimization of bacteria under fluctuating environments

Bacteria prudently regulate their metabolic phenotypes by sensing the availability of specific nutrients, expressing the required genes for their metabolism, and repressing them after specific metabolites are depleted. It is unclear, however, how genetic networks maintain and transmit phenotypic states between generations under rapidly fluctuating environments. By subjecting bacteria to fluctuating carbon sources (glucose and lactose) using microfluidics, we discover two types of non-genetic memory in Escherichia coli and analyze their benefits. First, phenotypic memory conferred by transmission of stable intracellular lac proteins dramatically reduces lag phases under cyclical fluctuations with intermediate timescales (1–10 generations). Second, response memory, a hysteretic behavior in which gene expression persists after removal of its external inducer, enhances adaptation when environments fluctuate over short timescales (&lt;1 generation). Using a mathematical model we analyze the ...细菌通过感知特定营养物质的可利用性，表达代谢所需的基因，并在特定代谢物耗尽后抑制相关基因的表达，从而精准调控自身的代谢表型（metabolic phenotypes）。然而，在环境快速波动的条件下，遗传网络如何在代际间维持并传递表型状态，目前仍不明确。本研究借助微流控（microfluidics）技术，使细菌处于碳源（葡萄糖与乳糖）波动的环境中，在大肠杆菌（Escherichia coli）中发现了两类非遗传记忆（non-genetic memory），并对其优势进行了分析。其一，由稳定细胞内乳糖蛋白传递所介导的表型记忆，可在中等时间尺度（1~10代）的周期性波动环境中，显著缩短细菌的延滞期（lag phase）。其二，响应记忆是一种滞后行为：当外部诱导物移除后，基因表达仍会持续一段时间，该机制可在短时间尺度（<1代）的环境波动下增强细菌的适应性。本研究借助数学模型对……进行了分析。