Conditional lysis ofEscherichia coli by the fusion of extracellular (STA) to periplasmic (LTB) enterotoxins: Apparent phenotypic suppression of lactose permease |
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Authors: | Dr Yankel M Kupersztoch Frances E Powell Luz-Maria Guzman-Verduzco |
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Institution: | (1) Department of Microbiology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, 75235 Dallas, TX, USA |
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Abstract: | The expression of a methanol-soluble, heat-stable enterotoxin (STA) fused to the B subunit of the heat-labile enterotoxin (LTB) at 35°C or higher temperatures caused strains ofEscherichia coli deficient in lactose permease to behave on indicator media as Lac+; however, at 33°C or lower temperatures the original Lac– phenotype of the host strains was maintained. The apparent phenotypic suppression oflacY was shown to be due to lysis of a fraction of the bacteria and the consequent release of active -galactosidase to the culture supernatant. After incubation at 37°C for 1 h, the cultures were committed to lyse. Plasmid and chromosomal mutants that do not show this phenotype were isolated by selecting Lac– colonies at the unpermissive temperature. The mutations on the plasmids were localized in both the heat-stable and the heat-labile enterotoxin genes. Chromosomal mutants that show normal levels of -galactosidase and fused toxins have also been isolated. |
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