McCalla D R, Kaiser C, Green M H
J Bacteriol. 1978 Jan;133(1):10-6. doi: 10.1128/jb.133.1.10-16.1978.
Wild-type Escherichia coli cells are sensitive to nitrofurazone (NF) and many other nitrofuran derivatives. A variety of evidence indicated that these compounds are converted to toxic "active" metabolites by reductases present in the bacteria. Sensitive E. coli K-12 acquired threefold-greater resistance to NF in one mutational step. These partially resistant mutants could undergo a second mutation that made them 10 times as resistant as the wild type. Mutation of wild-type strain K-12 to the higher level of resistance in a single step was not observed. The first mutational step was associated with partial loss of reduced nicotinamide adenine dinucleotide phosphate-linked, O(2)-insensitive NF reductase activity, and the second step was associated with loss of the remaining activity. The two-step mutants did, however, contain other NF reductases that were inhibited by O(2) and reduced NF only under anaerobic conditions. We designated the genes that control reductase activity "nitrofuran sensitivity genes" (nfsA and nfsB). Thus, wild-type strains are nfsA(+)nfsB(+), and the resistant double mutants are nfsA nfsB. A variety of crosses established that these genes are both located close to gal, that the most probable sequence is lac nfsB gal nfsA, and that the single-step mutants with an intermediate level of resistance are nfsA nfsB(+). The nfsA(+)nfsB strains contained about 70 to 80% of the wild-type reductase I activity-apparently enough to confer wild-type sensitivity. This reductase activity was resistant to 2 M urea. The nfsA nfsB(+) strains had only 20 to 30% of the wild-type activity, and this residual activity was sensitive to 2 M urea.
野生型大肠杆菌细胞对呋喃西林（NF）和许多其他硝基呋喃衍生物敏感。多种证据表明，这些化合物会被细菌中存在的还原酶转化为有毒的“活性”代谢物。敏感的大肠杆菌K-12在一个突变步骤中对NF的抗性提高了三倍。这些部分抗性突变体可能会发生第二次突变，使其抗性比野生型高10倍。未观察到野生型菌株K-12在单个步骤中突变为更高水平的抗性。第一个突变步骤与烟酰胺腺嘌呤二核苷酸磷酸还原型（NADPH）连接的、对O₂不敏感的NF还原酶活性部分丧失有关，第二个步骤与剩余活性丧失有关。然而，两步突变体确实含有其他NF还原酶，这些酶被O₂抑制，并且仅在厌氧条件下还原NF。我们将控制还原酶活性的基因命名为“硝基呋喃敏感性基因”（nfsA和nfsB）。因此，野生型菌株为nfsA(+)nfsB(+)，抗性双突变体为nfsA nfsB。各种杂交实验表明，这些基因都位于gal附近，最可能的顺序是lac nfsB gal nfsA，具有中等抗性水平的单步突变体为nfsA nfsB(+)。nfsA(+)nfsB菌株含有约70%至80%的野生型还原酶I活性——显然足以赋予野生型敏感性。这种还原酶活性对2M尿素具有抗性。nfsA nfsB(+)菌株仅具有20%至30%的野生型活性，并且这种残余活性对2M尿素敏感。
