REDUNDANT TRANSFER OF F' PLASMIDS OCCURS BETWEEN ESCHERICHIA-COLI-CELLS DURING NONLETHAL SELECTIONS

Surface exclusion is the mechanism by which F plasmids prevent the red undant entry of additional F plasmids into the host cell during expone ntial growth. This mechanism is relaxed in cells that are in stationar y phase. Using genetically marked F' plasmids and host strains, we ext end this finding to Escherichia coli populations during extended nonle thal selection in bacterial lawns. We show that a high level of redund ant transfer occurs between these nongrowing cells during the selectio n. This result has implications for the mechanism of adaptive mutagene sis.