Higgins M L, Shockman G D
J Bacteriol. 1976 Sep;127(3):1346-58. doi: 10.1128/jb.127.3.1346-1358.1976.
A new ultrastructural method was used to study rounds of envelope synthesis that occur in Streptococcus faecalis in "growth zones" found between pairs of naturally occurring surface markers. The technique consists of producing three-dimensional reconstructions of these growth zones from the mathematical rotation, about a central axis, of measurements taken from central, longitudinal thin sections of cells. A cycle of exponential-phase envelope growth was then simulated by arranging a series of these reconstructions in increasing order of the amount of peripheral wall surface area or the amount of cell volume that each was calculated to contain. Using this simulated cycle of growth, the geometry of a single growth zone during a round of synthesis was studied. Based on this analysis, a model was developed for the assembly of the cell wall of S. faecalis. The model states that new cell wall surface is synthesized by the regulated flow of essentially two channels of cell wall precursors into a single growth zone. One channel of precursors would be involved in the assembly of a bilayered cross wall that would proceed at a fairly constant rate until the cross wall closes. The second channel of precursors would be involved in the separation of the bilayered cross wall into two segments of peripheral wall. These precursors would intercalate into and thicken the separating layers of the cross wall. The flow of precursors through this channel would be progressively reduced through a cycle. These decreases, when coupled with internal hydrostatic pressure, apparently would result in the enlarging peripheral wall becoming increasingly more curved and would also promote cell division by reducing the total amount of cell wall that must be assembled in order for septation to occur.
一种新的超微结构方法被用于研究粪肠球菌中包膜合成的轮次，这些轮次发生在天然存在的表面标记对之间的“生长区”。该技术包括通过对从细胞的中央纵向薄片获取的测量值绕中心轴进行数学旋转，来生成这些生长区的三维重建。然后，通过将一系列这些重建按每个重建所计算包含的外周壁表面积或细胞体积的量的递增顺序排列，来模拟指数生长期包膜生长的一个周期。利用这个模拟的生长周期，研究了一轮合成过程中单个生长区的几何形状。基于这一分析，建立了粪肠球菌细胞壁组装的模型。该模型表明，新的细胞壁表面是通过基本上两个细胞壁前体通道的调节流动合成到单个生长区中的。一个前体通道将参与双层横壁的组装，该组装将以相当恒定的速率进行，直到横壁闭合。第二个前体通道将参与双层横壁分离成两段外周壁。这些前体将插入横壁的分离层并使其增厚。前体通过该通道的流动将在一个周期内逐渐减少。这些减少与内部静水压力相结合，显然会导致扩大的外周壁变得越来越弯曲，并且还会通过减少为了发生隔膜形成而必须组装的细胞壁总量来促进细胞分裂。
