Weiss A A, Falkow S
Infect Immun. 1984 Jan;43(1):263-9. doi: 10.1128/iai.43.1.263-269.1984.
Avirulent-phase derivatives of Bordetella pertussis (those which have simultaneously lost the ability to synthesize several virulence-associated factors) and the genetic mechanism of the phase change were studied. Increased tolerance to erythromycin was shown to be an avirulent-phase marker. By the use of efficiency of plating on erythromycin, the proportion of avirulent-phase (Vir) variants in a virulent-phase (Vir+) population was determined to be between 10(-3) and 10(-6), depending on the strain. We showed that the phase shift is reversible and detected a complete Vir- to Vir+ to Vir- to cycle. In other experiments, hybridization studies with avirulent-phase mutants obtained by Tn5 mutagenesis suggested that a single region located at a unique site in the B. pertussis chromosome controls the phase change. One of the avirulent Tn5 mutants was used as a recipient in a conjugative cross with a virulent-phase donor. All recombinants which had reacquired the virulence-associated factors also lost Tn5, indicating the loss of Tn5 was required to restore the Vir+ phenotype. The Tn5 avirulent-phase mutants behave as if the insertion interrupted the function of a transacting gene product which is required for the expression of the other virulent-phase genes. A model of the molecular basis of the phase regulation is presented.
对百日咳博德特氏菌的无毒力阶段衍生物（即那些同时丧失合成多种毒力相关因子能力的衍生物）及其相变的遗传机制进行了研究。结果表明，对红霉素耐受性的增加是无毒力阶段的一个标志。通过在红霉素上的平板接种效率，确定了无毒力阶段（Vir）变体在有毒力阶段（Vir+）群体中的比例在10^(-3)至10^(-6)之间，具体取决于菌株。我们表明相变是可逆的，并检测到一个完整的从Vir-到Vir+再到Vir-的循环。在其他实验中，对通过Tn5诱变获得的无毒力阶段突变体进行的杂交研究表明，位于百日咳博德特氏菌染色体独特位点的单个区域控制着相变。其中一个无毒力Tn5突变体在与有毒力阶段供体的接合杂交中用作受体。所有重新获得毒力相关因子的重组体也失去了Tn5，这表明恢复Vir+表型需要丢失Tn5。Tn5无毒力阶段突变体的行为就好像插入中断了一种反式作用基因产物的功能，而这种产物是其他有毒力阶段基因表达所必需的。本文提出了相变调控分子基础的模型。
