Genetics, Vol 144, 871-881, Copyright © 1996


INVESTIGATIONS

Noncomplementing Diploids From Bacillus subtilis Protoplast Fusion: Relationship Between Maintenance of Chromosomal Inactivation and Segregation Capacity

V. Grandjean, Y. Hauck, J. Le-Derout and L. Hirschbein
Institut de Genetique et Microbiologie, Universite Paris-Sud, 91405 Orsay Cedex, France

Fusions of Bacillus subtilis protoplasts from two genetically marked strains produce noncomplementing heterodiploid bacteria. These noncomplementing diploids (Ncds) carry both parental chromosomes, but only one is expressed. Fusion products of strains polymorphic for NotI restriction sites provide new physical evidence to support the conclusion that Ncds are not an artifact of cross feeding or cell adhesion. We show that reversible chromosomal inactivation can only account for the biparental trait of unstable Ncds. Two types of cells were recovered from the late progeny of unstable Ncds: Ncds with irreversible chromosome silencing (stable Ncds) and secondary recombinants that displayed a genomic mosaic NotI profile. Segregants from an unstable Ncd population gave rise to two viable haploid cell types. By contrast, stable Ncds segregated into a population of viable and inviable haploid cells. We propose that the latter are derived from irreversible chromosome silencing. Our results indicate that clonal populations of stable Ncds are heterogenous and suggest that segregation and inactivation are independent parameters.


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J.-P. Gratia
Noncomplementing diploidy resulting from spontaneous zygogenesis in Escherichia coli
Microbiology, September 1, 2005; 151(9): 2947 - 2959.
[Abstract] [Full Text] [PDF]