Koch A L, Doyle R J
J Theor Biol. 1985 Nov 7;117(1):137-57. doi: 10.1016/s0022-5193(85)80169-7.
Gram-positive, rod-shaped bacteria, given a pulse of peptidoglycan precursors, first exhibit a lag before the second or turnover phase of peptidoglycan commences. This is because new material is inserted on the inner face of the wall and gradually displaced through the wall. Based on this experimental observation, a mathematical model was constructed and compared with experimental data obtained in several laboratories for the first and second phases of wall turnover of Bacillus subtilis. The model allows the parameters of the process to be estimated for experiments with any labeling time. According to the surface stress theory the wall which is layed down immediately outside the cytoplasmic layer is in an unextended conformation. As subsequent additions of murein occur, the wall moves outward, becomes stretched, and bears the stress due to hydrostatic pressure. Ultimately, peptide and glycosyl bonds become cleaved. At the end of the lag phase the cleavage becomes so extensive that wall fragments are liberated into the medium. This strategy permits rod-shaped growth. In some experimental situations the half-life of wall radioactivity in this second phase roughly equals the doubling time; consequently, the exponential release probably does not represent random turnover but instead is the result of expansion of the underlying wall that continues to create strain which favors autolysis action. The slower turnover of the third phase, where there is a much slower loss, is also included in the analysis.
革兰氏阳性杆状细菌在给予肽聚糖前体脉冲后，在肽聚糖的第二阶段或周转阶段开始之前首先会出现一个延迟期。这是因为新材料插入到细胞壁的内表面，并逐渐穿过细胞壁移位。基于这一实验观察结果，构建了一个数学模型，并将其与在几个实验室中获得的枯草芽孢杆菌细胞壁周转第一阶段和第二阶段的实验数据进行了比较。该模型允许针对任何标记时间的实验估算该过程的参数。根据表面应力理论，紧挨着细胞质层外侧形成的细胞壁处于未伸展的构象。随着随后胞壁质的添加，细胞壁向外移动，被拉伸，并承受由于静水压力产生的应力。最终，肽键和糖基键断裂。在延迟期结束时，断裂变得非常广泛，以至于细胞壁碎片被释放到培养基中。这种策略允许杆状生长。在某些实验情况下，这个第二阶段细胞壁放射性的半衰期大致等于倍增时间；因此，指数释放可能并不代表随机周转，而是底层细胞壁扩张的结果，这种扩张持续产生有利于自溶作用的应变。分析中还包括了第三阶段较慢的周转，在这个阶段损失要慢得多。
