New data on excisions of Mu from E. coli MCS2 cast doubt on directed mutation hypothesis

Nature. 1990 Mar 8;344(6262):173-5. doi: 10.1038/344173a0.


According to the directed mutation hypothesis, certain mutations in bacteria occur more frequently in environments in which the resulting phenotype is selectively favoured than in non-selective environments. This hypothesis therefore challenges the fundamental tenet that mutations occur spontaneously, irrespective of effects on the organism's fitness. One purported case of directed mutation is the excision of a Mu sequence from Escherichia coli strain MCS2 in minimal lactose-arabinose medium. Here, we show that this case can be more simply explained by an accelerated rate of excision mutation in response to non-specific physiological stresses of starvation and by slight growth of MCS2 on minimal lactose-arabinose medium.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Arabinose / metabolism
  • Chromosome Deletion*
  • Escherichia coli / genetics*
  • Escherichia coli / growth & development
  • Lactose / metabolism
  • Mutation*


  • Arabinose
  • Lactose