Spontaneous zygogenesis in Escherichia coli, a form of true sexuality in prokaryotes

Abstract

A new type of mating, differing from classic conjugation and previously observed in a certain strain of Escherichia coli K-12, has also been found in strains derived from ordinary F " cells of E. coli K-12 exposed to an exogenous factor originating in an E. coli clinical isolate.Immunofluorescence and electron microscopy after single and double labelling of DNA were used to produce evidence in favour of a novel mating mechanism by cell contact at the poles of the bacterial rod. These findings are supported by genetic analyses indicating complete genetic mixing. Unstable complementing diploids were formed, which throw off phenotypically haploid cells, of which some showed a parental phenotype and some were true genetic recombinants. Recombination was observed even when one parent was a UV-inactivated F " RecA " strain. The name 'spontaneous zygogenesis' (Z-mating, for short) is proposed for this kind of mating.

Noncomplementing diploidy resulting from spontaneous zygogenesis in Escherichia coli

“…The most commonly used Szp + strain, MG392, was derived by Z-mating between MG391, an Arg + revertant of the Szp + strain MG388a, and F 2 1485/Nx. The Szp + strain MG401 was created by exposing F 2 strain MG301 to lysates of a lysogenic E. coli clinical isolate (84SV) induced to phage development (Gratia & Thiry, 2003). MG403 was a Szp + recombinant derivative resulting from a cross between MG401 and F 2 1485/Nx.…”

“…Media and chemicals. The media used here have been described previously (Gratia, 1994;Gratia & Thiry, 2003): M9 buffer, Lennox broth (LB), nutrient agar (NA), LB agar, minimal agar (MA; Simmons-citrate agar with added glucose), LCA [Simmons-citrate agar with added lactose, instead of glucose, plus casein acid hydrolysate ('peptone 5'; Gibco), when parents differed in lactose fermentation and were deficient for nutrients not included in peptone 5], and Gratia-Deschuyteneer agar medium (GDA; see below). If necessary, specific substances were added to these media.…”

“…Recent observations with E. coli led to the conclusion that total genetic mixing could occur and persist after contact between distinct populations of intact bacteria without any need to convert them into protoplasts beforehand. This phenomenon, called 'illegitimate mating' in the original report (Gratia, 1994), and later termed 'spontaneous zygogenesis' or Z-mating (Gratia & Thiry, 2003), was observed in an auxotrophic E. coli K-12 derivative (MG352). That strain, fully described in terms of characteristics and origin in the previous papers, was initially F 2 but acquired the ability to promote Z-mating upon infection with defective phage particles from E. coli clinical isolate 84SV.…”

“…That strain, fully described in terms of characteristics and origin in the previous papers, was initially F 2 but acquired the ability to promote Z-mating upon infection with defective phage particles from E. coli clinical isolate 84SV. Examination of mixtures under the fluorescence or electron microscope using immunocytochemical methods revealed junctions between parental cells, at their poles, which appeared to be the possible sites of membrane fusion (Gratia & Thiry, 2003).…”

Eukaryote Evolution: The Importance of the Stem Group

“…Linearity has evolved several times independently in bacteria (Chen et al, 2002;Volff and Altenbuchner, 2000) Meiosis and syngamy Zygogenesis in bacteria Diploids formed, recombination can occur (Gratia, 2005;Gratia, 2007a;Gratia, 2007b;Gratia and Thiry, 2003 Guerrero et al, 1986;Martin, 2002;Sacchi et al, 2004) (von Dohlen et al, 2001) does establish that compartmentation of the genetic material is not an absolute requirement of endosymbiosis. Moreover, the example indicates that there is no obvious problem with the suggestion that the nucleus evolved after the mitochondrial ancestor had gained entry to its protoeukaryotic host.…”