The genetics of fimbriation inEscherichia coli

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Abstract
(1) Fimbriated cells ofE. coli K-12 are of two types. In the Fim+type the expression of fimbriation is susceptible to reversible environmental suppression. This type gives rise to environment-stable mutants termed Fimσ+.(2) Fimbriated cells can yield two types of non-fimbriated mutant, Fim−and Fimσ−, the latter arising from populations of Fimσ+cells. Neither type reverts to the fimbriated state.(3) Both types of fimbriated and non-fimbriated cells can be distinguished by physiological and genetic criteria.(4) Fimbriation of both types can be transferred to non-fimbriated cells of both types, and segregates among recombinants, in crosses mediated either by transduction or sexual conjugation.(5) The genetic control of fimbriation involves at least two determinants, for one of which a chromosomal location (fim) has been mapped.(6) Certain anomalies offimsegregation are interpreted in terms of negative interference over relatively large regions of the bacterial chromosome.