All bacterial cells must expand their envelopes during growth. The main load-bearing and shape-determining component of the bacterial envelope is the peptidoglycan cell wall. Bacterial envelope growth and shape changes are often thought to be controlled through enzymatic cell wall insertion. We investigated the role of cell wall insertion for cell shape changes during cell elongation in Gram-negative bacteria. We found that both global and local rates of envelope growth of Escherichia coli remain nearly unperturbed upon arrest of cell wall insertion—up to the point of sudden cell lysis. Specifically, cells continue to expand their surface areas in proportion to biomass growth rate, even if the rate of mass growth changes. Other Gram-negative bacteria behave similarly. Furthermore, cells plastically change cell shape in response to differential mechanical forces. Overall, we conclude that cell wall-cleaving enzymes can control envelope growth independently of synthesis. Accordingly, the strong overexpression of an endopeptidase leads to transiently accelerated bacterial cell elongation. Our study demonstrates that biomass growth and envelope forces can guide cell envelope expansion through mechanisms that are independent of cell wall insertion.

中文翻译：

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革兰氏阴性细菌的细胞包膜生长独立于细胞壁合成

所有细菌细胞在生长过程中都必须扩张其包膜。细菌包膜的主要承载和形状决定成分是肽聚糖细胞壁。通常认为细菌包膜生长和形状变化是通过酶促细胞壁插入来控制的。我们研究了革兰氏阴性细菌细胞伸长过程中细胞壁插入对细胞形状变化的作用。我们发现，在细胞壁插入停止时，大肠杆菌的整体和局部包膜生长率几乎不受干扰，直至细胞突然裂解。具体来说，即使质量增长率发生变化，细胞也会继续按照生物量增长率的比例扩大其表面积。其他革兰氏阴性细菌的行为类似。此外，细胞响应不同的机械力而塑性地改变细胞形状。总的来说，我们得出结论，细胞壁裂解酶可以独立于合成来控制包膜生长。因此，肽链内切酶的强烈过度表达导致细菌细胞伸长瞬时加速。我们的研究表明，生物量生长和包膜力可以通过独立于细胞壁插入的机制引导细胞包膜扩张。