American Society for Microbiology, Journal of Bacteriology, 15(186), p. 4853-4853, 2004
DOI: 10.1128/jb.186.15.4853.2004
American Society for Microbiology, Journal of Bacteriology, 15(186), p. 4854-4854, 2004
DOI: 10.1128/jb.186.15.4854.2004
Full text: Download
If mutations arose in nongrowing cells, as proposed in Fos- ter's paper (1), then stress-induced mutagenesis would seem inescapable. The plated population certainly grows very little. However, no evidence is provided that reversion occurs in this population and no effort is made to counter evidence to the contrary (see below)—that mutations actually arise in cells growing under selection within developing clones (rendering mutagenesis dispensable). (i) Reversion requires that the lac allele be leaky and lactose be present in the selection medium, suggesting a growth re- quirement. (ii) General mutagenesis is not induced by simple starvation (3) but is seen in the Cairns system when lactose is provided, suggesting dependence on growth. (iii) Clonally related unstable and stable lac cells are found within all revertant colonies, consistent with both types arising sequentially within a growing colony. (iv) Revertant number is strongly reduced if one inhibits growth of cells carrying a lac amplification. (v) Revertant number increases if a lac duplication is pro- vided in the parent cells. (vi) Results of the respreading experiment are not inconsis- tent with reversion within growing clones because single du-