title: Noncomplementing diploidy resulting from spontaneous zygogenesis in Escherichia coli.
abstract: With the aim of understanding sexual reproduction and phenotypic expression, a novel type of mating recently discovered in Escherichia coli was investigated. Termed spontaneous zygogenesis (or Z-mating), it differs from F-mediated conjugation. Its products proved phenotypically unstable, losing part of the phenotype for which they were selected. Inactivation of a parental chromosome in the zygote is strongly suggested by fluctuation tests, respreading experiments, analysis of reisolates, and segregation of non-viable cells detected by epifluorescence staining. Some phenotypically haploid subclones were interpreted as stable noncomplementing diploids carrying an inactivated co-replicating chromosome. Pedigree analysis indicated that the genetic composition of such cells consisted of parental genomes or one parental plus a recombinant genome. Inactivation of a chromosome carrying a prophage resulted in the disappearance of both the ability to produce phage particles and the immunity to superinfection. Phage production signalled transient reactivation of such a chromosome and constituted a sensitive test for stable noncomplementing diploidy. Chromosome inactivation thus appears to be a spontaneous event in bacteria.
authors.affiliation: Laboratory of Phage-typing and Bacterial Genetics, Pasteur Institute of Brussels, Rue Engeland 642, B-1180 Brussels, Belgium.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Gratia
mesh_terms: D002876:Chromosomes, Bacterial; D003227:Conjugation, Genetic / Q000502:physiology*; D003434:Crossing Over, Genetic; D004171:Diploidy; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005816:Genetic Complementation Test; D010957:Plasmids; D011995:Recombination, Genetic