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  • Title: Mechanisms that Determine the Differential Stability of Stx⁺ and Stx(-) Lysogens.
    Author: Colon MP, Chakraborty D, Pevzner Y, Koudelka GB.
    Journal: Toxins (Basel); 2016 Mar 31; 8(4):96. PubMed ID: 27043626.
    Abstract:
    Phages 933W, BAA2326, 434, and λ are evolutionarily-related temperate lambdoid phages that infect Escherichia coli. Although these are highly-similar phages, BAA2326 and 933W naturally encode Shiga toxin 2 (Stx⁺), but phage 434 and λ do not (Stx(-)). Previous reports suggest that the 933W Stx⁺ prophage forms less stable lysogens in E. coli than does the Stx(-) prophages λ, P22, and 434. The higher spontaneous induction frequency of the Stx⁺ prophage may be correlated with both virulence and dispersion of the Stx2-encoding phage. Here, we examined the hypothesis that lysogen instability is a common feature of Stx⁺ prophages. We found in both the absence and presence of prophage inducers (DNA damaging agents, salts), the Stx⁺ prophages induce at higher frequencies than do Stx(-) prophages. The observed instability of Stx⁺ prophages does not appear to be the result of any differences in phage development properties between Stx⁺ and Stx(-) phages. Our results indicate that differential stability of Stx⁺ and Stx(-) prophages results from both RecA-dependent and RecA-independent effects on the intracellular concentration of the respective cI repressors.
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