Fig. 1.
An experimental system for tracing plasmid allele dynamics. (A) The model plasmid pTAD and the genetic system. The novel plasmid allele (nptII gene) is introduced into the population by natural transformation via homologous recombination with the model plasmid. The initial population is constituted by hosts of the novel plasmid allele and nonhosts. Hosts are followed for several generations by tracing the presence of the novel allele. (B) An illustration of the two model plasmids; pTAD-R and pTAD-C that are characterized by random and clustered assortment modes, respectively. The model plasmids differ in the lacI repressor allele. The lacI repressor allele in pTAD-C encodes for a LacI repressor that binds two plasmids and thus reduces the unit of segregation of the ancestral plasmid allele. (C) A demonstration of the ability to control the host frequency in the initial population. The frequency of hosts is proportional to the donor DNA concentration. Using 1,000 ng donor DNA for the initial transformation generates a host frequency of 1–5 × 10−4 (∼0.01%), whereas using 100 ng DNA generates a host frequency of 1–5 × 10−5 (∼0.001%).