Koch A L
Biology Department, Indiana University, Bloomington 47405-6801, USA.
Crit Rev Microbiol. 1998;24(1):23-59. doi: 10.1080/10408419891294172.
When subject to an osmotic 'up-shock', water flows outward from bacterial cytoplasm of the bacterium. Lipid bilayers can shrink very little in area and therefore must wrinkle to accommodate the smaller volume. The usual consequence is that all the layers of the cell envelope must become wrinkled together because they adhere to each other and must now cover a smaller surface. Plasmolysis spaces are formed if the cytoplasmic membrane (CM) separates from the other components of the wall. However, because the CM bilayer is essentially an incompressible two-dimensional liquid, this constraint restricts the location and shape of plasmolysis spaces. With mild up-shocks they form at the pole and around constricting regions in the cell. Elsewhere their creation requires the formation of endocytotic or exocytotic vesicles. The formation of endocytotic vesicles occurs in animal and plant cells as well as in bacterial cells. With stronger up-shocks tubular structures (Bayer adhesion sites), or other special geometric shapes (e.g., Scheie structures) allow the bilayer to surround an irregular shaped cytoplast. Periosmotic agents, that is, those that extract water from the periplasm as well as the cytoplasm, are molecules such as poly-vinyl-pyrrolidone and alpha-cyclodextrin that are too large to pass through the porins in the outer membrane. They were found to significantly inhibit the formation of plasmolysis spaces. Presumably, they inhibit the plasmolysis process, which requires that extracellular fluid enter between the CM and the outer membrane (OM). In the extreme case, with the dehydrating action of both osmotic agents and periosmotic agents, periplasmic space formation tends to be prevented and a new kind of space develops within the cytoplasm. We have designated these as 'cytoplasmic voids'. These novel structures are not bounded by lipid bilayers, in contrast to the endocytotic vesicles. These new spaces appear to result from the negative turgor pressure generated by the application of the combination of osmotic and periosmotic agents causing bubble formation. Several ideas in the literature about the wall biology (periseptal annuli, leading edge, osmotic pressure in the periplasm) are presented and critiqued. The basic criticism of these is that much of the phenomena can be explained because of the physics of the phospholipid bilayers and osmotic forces and thus does not imply the existence of a special control mechanism to regulate growth and division.
当受到渗透“向上冲击”时，水从细菌的细胞质向外流动。脂质双层在面积上几乎不会收缩，因此必须起皱以适应较小的体积。通常的结果是，细胞膜的所有层必须一起起皱，因为它们相互粘附，现在必须覆盖更小的表面。如果细胞质膜（CM）与细胞壁的其他成分分离，就会形成质壁分离空间。然而，由于CM双层本质上是一种不可压缩的二维液体，这种限制限制了质壁分离空间的位置和形状。在轻度向上冲击下，它们在细胞的极点和收缩区域周围形成。在其他地方，它们的形成需要内吞或外排小泡的形成。内吞小泡的形成发生在动物、植物细胞以及细菌细胞中。在更强的向上冲击下，管状结构（拜耳粘附位点）或其他特殊的几何形状（如谢伊结构）使双层围绕不规则形状的原生质体。渗透剂，即那些从周质以及细胞质中提取水分的物质，是诸如聚乙烯吡咯烷酮和α-环糊精等分子，它们太大而无法穿过外膜中的孔蛋白。发现它们能显著抑制质壁分离空间的形成。据推测，它们抑制质壁分离过程，质壁分离过程需要细胞外液进入CM和外膜（OM）之间。在极端情况下，由于渗透剂和反渗透剂的脱水作用，往往会阻止周质空间的形成，并且在细胞质内会形成一种新的空间。我们将这些称为“细胞质空隙”。与内吞小泡不同，这些新结构不是由脂质双层界定的。这些新空间似乎是由渗透剂和反渗透剂组合施加产生的负膨压导致气泡形成而产生的。文中提出并批判了文献中关于细胞壁生物学（周质隔膜环、前沿、周质中的渗透压）的几种观点。对这些观点的基本批评是，许多现象可以用磷脂双层的物理性质和渗透力来解释，因此并不意味着存在一种特殊的控制机制来调节生长和分裂。
