GENETIC-ANALYSIS OF MUTAGENESIS IN AGING ESCHERICHIA-COLI COLONIES

Bacteria live in unstructured and structured environments, experiencin g feast and famine lifestyles. Bacterial colonies can be viewed as mod el structured environments. SOS induction and mutagenesis have been ob served in aging Escherichia coli colonies, in the absence of exogenous sources of DNA damage. This cAMP-dependent mutagenesis occurring in R esting Organisms in a Structured Environment (ROSE) is unaffected by a umuC mutation and therefore differs from both targeted UV mutagenesis and recA730 (SOS constitutive) untargeted mutagenesis. As a recB muta tion has only a minor effect on ROSE mutagenesis it also differs from both adaptive reversion of the lacI33 allele and from iSDR (inducible Stable DNA Replication) mutagenesis. Besides its recA and lexA depende nce, ROSE mutagenesis is also uvrB and polA dependent. These genetic r equirements are reminiscent of the untargeted mutagenesis in lambda ph age observed when unirradiated lambda infects UV-irradiated E. coli. T hese mutations, which are not observed in aging liquid cultures, accum ulate linearly with the age of the colonies. ROSE mutagenesis might of fer a good model for bacterial mutagenesis in structured environments such as biofilms and for mutagenesis of quiescent eukaryotic cells.