SGER: Apoptosis in Bacteria

当细菌细胞死亡时，死亡的原因通常是自溶，而不是有害因素造成的直接损害。肽聚糖的水解是细胞壁合成中的一个必要阶段，自溶被认为是“肽聚糖合成和水解之间的不平衡”的结果，本质上是一个不适应的错误。这个项目探索了这样一种假设，即自溶不是错误，而是适应性程序性死亡。自溶是粘球菌子实体形成和孢子形成的发育过程的一部分。肺炎链球菌自然转化所需的自溶是专门化适应性程序性死亡的另一个例子。细菌表现出许多复杂的组织特征，类似于多细胞生物体。就像在多细胞物种中一样，细菌种群将从消除缺陷细胞中受益。这个项目的目的是测试自溶是细菌适应性细胞凋亡机制这一想法的可行性。具体地说，正在寻找将特定类型的细胞损伤与自溶素激活联系起来的可能的凋亡途径的调节成分。一种遗传学方法正被用来识别假定的凋亡基因。大肠杆菌将被迷你Tn10转座子诱变，并选择存活到致死水平的诱变剂；以及高温。表现出对杀戮的抗性(但在这两个因素存在的情况下不抵抗生长)的突变株将成为编码凋亡化合物的基因的候选对象。“随机”聚合酶链式反应将用于鉴定DNA侧翼区域，扩增的DNA将通过单代测序，携带TN插入的基因将使用大肠杆菌基因组数据库进行鉴定。还将使用一组不同的致死因素来表征突变体的表型。具有已知突变的菌株，例如那些缺乏自溶素的菌株，也将接受致命因素小组的可能生存测试。这一探索性项目将显示大肠杆菌是否具有影响自溶的调控基因，并将为未来详细研究细菌中的细胞凋亡奠定基础。

When a bacterial cell dies, the cause of death is often autolysis, rather than direct damage produced by a harmful factor. Hydrolysis of peptidoglycan is a necessary stage in cell wall synthesis, and autolysis has been viewed as a result of "disbalance between peptidoglycan synthesis and hydrolysis", essentially a maladaptive mistake. This project explores the hypothesis that autolysis is not a mistake, but adaptive programmed death. Autolysis is part of the developmental process of fruiting body formation and sporulation in Myxococcus. Autolysis which is required for natural transformation in S. pneumoniae is another example of specialized adaptive programmed death. Bacteria show many features of complex organization, similar to multicellular organisms. Like in multicellular species, a bacterial population would benefit from eliminating defective cells. The aim of this project is to test the feasibility of the idea that autolysis is the mechanism of adaptive apoptosis in bacteria. Specifically, a search for regulatory components of a possible apoptotic pathway linking particular types of cell damage to activation of autolysins is being undertaken. A genetic approach is being used to identify putative apoptotic genes. E. coli will be mutagenized with mini-Tn10 transposon and selected for survival to lethal levels of a mutagen; and high temperature. Mutants that show resistance to killing (but not resistance to growth in the presence of) both factors will become candidates for being affected in genes coding for apoptotic compounds. "Random" PCR will be used to identify the flanking DNA regions, amplified DNA will be sequenced by single passage, and the genes carrying the Tn insertions will be identified using the database of the E. coli genome. The mutants will also be characterized phenotypically using a panel of different lethal factors. Strains with known mutations, such as those lacking autolysins, will also be tested for possible survival with the panel of lethal factors. This exploratory project will show whether E. coli has regulatory genes affecting autolysis and will lay the basis for future detailed studies of apoptosis in bacteria.