Blomfield I C, McClain M S, Princ J A, Calie P J, Eisenstein B I
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620.
J Bacteriol. 1991 Sep;173(17):5298-307. doi: 10.1128/jb.173.17.5298-5307.1991.
We reexamined the influence of fimE, also referred to as hyp, on type 1 fimbriation in Escherichia coli K-12. We found that one strain used previously and extensively in the analysis of type 1 fimbriation, strain CSH50, is in fact a fimE mutant; the fimE gene of CSH50 contains a copy of the insertion sequence IS1. Using a recently described allelic exchange procedure, we transferred the fimE::IS1 allele from CSH50 to our present wild-type strain, MG1655. Characterization of this IS1-containing strain (AAEC137), together with another fimE mutant of MG1655 (AAEC143), led to two conclusions about the role of fimE. First, the formation of phase variant colony types, reported widely in strains of E. coli, depends on mutation of fimE, at least in K-12 strain MG1655. Here we showed that this phenomenon reflects the ability of fimE to stimulate the rapid inversion of the fim invertible element from on to off when the bacteria are grown on agar. Second, our analysis of fimE mutants, which is limited to chromosomal constructs, provided no evidence that they are hyperfimbriate. We believe that these results, which are at odds with a previous study using fim-containing multicopy plasmids, reflect differences in gene copy number.
我们重新研究了fimE（也称为hyp）对大肠杆菌K-12 1型菌毛形成的影响。我们发现，之前在1型菌毛形成分析中广泛使用的一个菌株CSH50，实际上是一个fimE突变体；CSH50的fimE基因含有插入序列IS1的一个拷贝。利用最近描述的等位基因交换程序，我们将fimE::IS1等位基因从CSH50转移到了我们目前的野生型菌株MG1655中。对这个含IS1的菌株（AAEC137）以及MG1655的另一个fimE突变体（AAEC143）的特性分析，得出了关于fimE作用的两个结论。第一，在大肠杆菌菌株中广泛报道的相变菌落类型的形成，至少在K-12菌株MG1655中，依赖于fimE的突变。在这里我们表明，这种现象反映了fimE在细菌在琼脂上生长时刺激fim可逆元件从开启状态快速转变为关闭状态的能力。第二，我们对fimE突变体的分析仅限于染色体构建体，没有证据表明它们是高菌毛的。我们认为，这些结果与之前一项使用含fim多拷贝质粒的研究结果不一致，反映了基因拷贝数的差异。
