Turner M A, Arellano F, Kozloff L M
Department of Microbiology, University of California, San Francisco 94143-0404.
J Bacteriol. 1990 May;172(5):2521-6. doi: 10.1128/jb.172.5.2521-2526.1990.
Studies of the properties of the ice nucleation structure exposed on the surfaces of various bacteria such as Pseudomonas syringae, Erwinia herbicola, or various strains of Ice+ recombinant Escherichia coli have shown that there are clearly three major related but chemically distinct types of structures on these cells. First, the ability of Ice+ cells to nucleate super-cooled D2O has been examined, and it has been found that this ability (relative to the ability of the same cells to nucleate super-cooled H2O) exhibited three characteristic nucleating patterns. The rarest structure, called class A, is found on only a small fraction of cells in a culture, nucleates H2O at temperatures above -4.4 degrees C, and is an effective nucleator of super-cooled D2O. A second class of structure, called class B, is found on a larger portion of the cells, nucleates H2O between -4.8 and -5.7 degrees C, and is a relatively poor nucleator of super-cooled D2O. The class C structure is found on almost all cells and nucleates at -7.6 degrees C or colder. These three classes of structures were also differentiated by their sensitivities to low concentrations of water-miscible organic solvents such as dioxane or dimethyl sulfoxide. Depending on the specific bacterial strain, the addition of these solvents to bacterial suspensions lowered the nucleation activity of the class A structure by 1,000-fold or more. The nucleation activities of class B structures in the same culture were highly resistant to these compounds and were lowered only by 20 to 40%. The class C structures were more sensitive than Class B structures were, and the nucleation activities decreased 70 to 90%. Finally, the pH sensitivity of these three classes of structures was examined. The class A structure was destroyed in buffers at pH 4.5 lower but was stable in buffers at higher pHs. The class B structure was less sensitive to acidic buffers but was destroyed at pH 5.5 or lower and was stable at higher pHs. However, the class C structure was unaffected by incubation in buffers with pHs of 3.5 to 9.0. Suggestions for the actual nucleation structures of the three classes are proposed.
对诸如丁香假单胞菌、草生欧文氏菌等各种细菌表面以及不同菌株的冰核形成重组大肠杆菌表面所暴露的冰核形成结构特性进行的研究表明，这些细胞上明显存在三种主要的、相互关联但化学性质不同的结构类型。首先，研究了冰核阳性（Ice+）细胞使过冷重水（D2O）成核的能力，结果发现这种能力（相对于相同细胞使过冷普通水（H2O）成核的能力）呈现出三种特征性的成核模式。最罕见的结构类型，称为A类，仅在培养物中的一小部分细胞上发现，在高于-4.4摄氏度的温度下使普通水成核，并且是过冷重水的有效成核剂。第二类结构，称为B类，在较大比例的细胞上发现，在-4.8至-5.7摄氏度之间使普通水成核，并且是过冷重水相对较差的成核剂。C类结构在几乎所有细胞上都能发现，在-7.6摄氏度或更低温度下成核。这三类结构对低浓度的与水混溶的有机溶剂（如二氧六环或二甲基亚砜）的敏感性也有所不同。根据具体的细菌菌株，向细菌悬液中添加这些溶剂会使A类结构的成核活性降低1000倍或更多。同一培养物中B类结构的成核活性对这些化合物具有高度抗性，仅降低20%至40%。C类结构比B类结构更敏感，成核活性降低70%至90%。最后，研究了这三类结构的pH敏感性。A类结构在pH值低于4.5的缓冲液中被破坏，但在较高pH值的缓冲液中稳定。B类结构对酸性缓冲液不太敏感，但在pH值为5.5或更低时被破坏，在较高pH值时稳定。然而，C类结构在pH值为3.5至9.0的缓冲液中孵育时不受影响。文中还对这三类结构的实际成核结构提出了建议。
