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Abstract
Summary: Previous work has shown that Escherichia coli K 12 ColE2+ cells undergo a form of partial lysisand exhibit increases in lysophosphatidylethanolamine (lysoPE) and free fatty acid content due to activation of phospholipase A when induced to produce and release colicin E2. The increase in lysoPE content was assumed to be essential for efficientcolicin release. These same characteristics are also presented by some natural ColE2+ isolates, and by other representatives of the Enterobacteriaceae after transformation with derivatives of a ColE2 plasmid. However, Salmonella typhimurium strains carrying ColE2 plasmids released colicin without partial lysis and without increasing their lysoPEcontent. A previously undetected minor phospholipid, which appeared in these and other strains only when they were induced to produce colicin, may be an important factor in colicin release. In ColE2+ E. coli K 12, production of this new lipid was dependent on phospholipase A activation following expression of the ColE2 lysis gene. Some other ColE2+ strains did not respond to induction of colicin production in the same way as ColE2+ E. coli K 12. These strains were less sensitive to inducer (mitomycin C) or unable to produce increased amounts of colicin in response to induction, or unable to degrade colicin once it was released. In general, the results suggest that colicin release occurs by the same or similar processes in the various strains tested, and support the continued use of E.coli K 12 as the model strain for studying the mechanisms of colicin release.
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