By directly monitoring single cell growth in a microfluidic platform, we interrogated genome-deletion effects in Escherichia coli strains. We compared the growth dynamics of a wild type strain with a clean genome strain, and their derived mutants at the single-cell level. A decreased average growth rate and extended average lag time were found for the clean genome strain, compared to those of the wild type strain. Direct correlation between the growth rate and lag time of individual cells showed that the clean genome population was more heterogeneous. Cell culturability (the ratio of growing cells to the sum of growing and nongrowing cells) of the clean genome population was also lower. Interestingly, after the random mutations induced by a glucose starvation treatment, for the clean genome population mutants that had survived the competition of chemostat culture, each parameter markedly improved (i.e., the average growth rate and cell culturability increased, and the lag time and heterogeneity decreased). However, this effect was not seen in the wild type strain; the wild type mutants cultured in a chemostat retained a high diversity of growth phenotypes. These results suggest that quasi-essential genes that were deleted in the clean genome might be required to retain a diversity of growth characteristics at the individual cell level under environmental stress. These observations highlight that single-cell microfluidics can reveal subtle individual cellular responses, enabling in-depth understanding of the population.

中文翻译：

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单细胞微流控技术研究基因组缺失对细菌生长行为的影响

通过直接监测微流控平台中的单细胞生长，我们询问了大肠杆菌中的基因组缺失效应株。我们将野生型菌株与干净的基因组菌株及其在单细胞水平上的衍生突变体的生长动力学进行了比较。与野生型菌株相比，清洁基因组菌株的平均生长速率降低，平均滞后时间延长。单个细胞的生长速度和滞后时间之间的直接相关性表明，纯净的基因组种群具有更高的异质性。干净的基因组群体的细胞可培养性（生长的细胞与生长的和未生长的细胞之比）也较低。有趣的是，在葡萄糖饥饿处理诱导的随机突变之后，对于在化学恒温器培养的竞争中幸存下来的干净的基因组种群突变体，每个参数都得到了显着改善（即，平均生长速度和细胞可培养性增加，滞后时间和异质性降低）。但是，在野生型菌株中未观察到这种作用。在恒化器中培养的野生型突变体保留了高度的生长表型多样性。这些结果表明，在环境压力下，可能需要在干净的基因组中删除的准必需基因才能在单个细胞水平上保留多种生长特征。这些观察结果表明，单细胞微流控技术可以揭示细微的个体细胞反应，从而使人们能够深入了解该群体。