The role of cell-envelope synthesis for envelope growth and cytoplasmic density in Bacillus subtilis

All cells must increase their volumes in response to biomass growth to maintain intracellular mass density within physiologically permissive bounds. Here, we investigate the regulation of volume growth in the Gram-positive bacterium Bacillus subtilis. To increase volume, bacteria enzymatically expand their cell envelopes and insert new envelope material. First, we demonstrate that cell-volume growth is determined indirectly, by expanding their envelopes in proportion to mass growth, similarly to the Gram-negative Escherichia coli, despite their fundamentally different envelope structures. Next, we studied, which pathways might be responsible for robust surface-to-mass coupling: We found that both peptidoglycan synthesis and membrane synthesis are required for proper surface-to-mass coupling. However, surprisingly, neither pathway is solely rate-limiting, contrary to wide-spread belief, since envelope growth continues at a reduced rate upon complete inhibition of either process. To arres...

所有细胞均需伴随生物量增长而增大体积，以将胞内质量密度维持在生理许可的范围内。本研究针对革兰氏阳性菌枯草芽孢杆菌（Bacillus subtilis）的体积生长调控机制展开探究。细菌若要增大体积，需通过酶促反应扩增细胞被膜并嵌入新的被膜物质。首先，我们证实：尽管革兰氏阴性大肠杆菌（Escherichia coli）与枯草芽孢杆菌的被膜结构存在本质差异，但枯草芽孢杆菌的细胞体积增长同样通过使被膜扩增速率与生物量生长速率相匹配来间接实现，这一点与大肠杆菌一致。随后，我们对介导稳定表面-质量耦合的潜在通路进行了研究：结果发现，肽聚糖（peptidoglycan）合成与膜合成均是维持正常表面-质量耦合的必要条件。然而令人意外的是，与学界广泛持有的观点相悖，这两条通路均并非单一的速率限制因子——因为当任意一条通路被完全抑制时，被膜的生长仍会以减缓的速率持续进行。[原文末尾截断为"To arres..."]