Burman L G, Nordström K
J Bacteriol. 1971 Apr;106(1):1-13. doi: 10.1128/jb.106.1.1-13.1971.
A mutant (G11el) of Escherichia coli selected as being resistant to ampicillin and showing signs of an envelope defect was also found to be tolerant to colicins E2 and E3. The colicin tolerance of G11el could be partially repressed by Mg(2+) ions. Transition from tolerance to sensitivity and vice versa by shifting the concentration of Mg(2+) in the growth medium required several generations. This indicated that synthesis of new envelope material was needed for transition. Previous physiological results have indicated a change in the envelope lipopolysaccharide (LPS) of G11el. However, chemical analyses revealed no differences in carbohydrate composition between LPS from G11el and its parent strain G11al. Genetic experiments showed that the mutation in G11el is located at about 20 min on the E. coli K-12 chromosome. The mutation was dominant over wild type in partial diploids with the mutation located on the episome. Because colicin tolerance was the most striking phenotypic effect as a result of mutation in the actual locus, this gene will be named tolD until the exact gene product is known. Spheroplasts formed from G11al and G11el by ethylenediaminetetraacetate-lysozyme treatment did not adsorb colicin E2; however, penicillin spheroplasts of G11al and G11el were tolerant to colicin E2. Thus, colicin tolerance can be induced biochemically. It is suggested that colicin tolerance often is a secondary consequence of a change in the cell envelope.
一株被选作对氨苄青霉素具有抗性且表现出包膜缺陷迹象的大肠杆菌突变体（G11el），也被发现对大肠杆菌素E2和E3具有耐受性。G11el对大肠杆菌素的耐受性可被镁离子部分抑制。通过改变生长培养基中镁离子的浓度，从耐受性转变为敏感性以及反之亦然需要几代时间。这表明转变需要合成新的包膜物质。先前的生理学结果表明G11el的包膜脂多糖（LPS）发生了变化。然而，化学分析显示G11el及其亲本菌株G11al的LPS在碳水化合物组成上没有差异。遗传学实验表明，G11el中的突变位于大肠杆菌K-12染色体上约20分钟处。在突变位于附加体上的部分二倍体中，该突变相对于野生型是显性的。由于在实际位点发生突变导致的最显著表型效应是对大肠杆菌素的耐受性，在确切的基因产物被确定之前，这个基因将被命名为tolD。通过乙二胺四乙酸-溶菌酶处理由G11al和G11el形成的原生质体不吸附大肠杆菌素E2；然而，G11al和G11el的青霉素原生质体对大肠杆菌素E2具有耐受性。因此，大肠杆菌素耐受性可以通过生化方法诱导产生。有人提出，大肠杆菌素耐受性通常是细胞包膜变化的次要结果。
