title: Shiga toxin 2 is specifically released from bacterial cells by two different mechanisms.
abstract: Shiga toxin 1 (Stx1) is located in the periplasmic fraction, while Stx2 is found in the extracellular fraction, suggesting that enterohemorrhagic Escherichia coli (EHEC) contains a specific Stx2 release system. Both stx(1) and stx(2) are found within the late operons of Stx-encoding phages. Stx2 production is greatly induced by mitomycin C, suggesting that stx(2) can transcribe from the late phage promoter of the Stx2-encoding phage. However, the Stx1 promoter adjacent to stx(1) is a dominant regulatory element in Stx1 production. With the deletion of phage lysis genes of the Stx2-encoding phage, Stx2 remains in the bacterial cells. Further, we demonstrate that the Stx2-encoding phage, but not the Stx1-encoding phage, is spontaneously induced at extremely low rates. These results indicate that spontaneously specific Stx2-encoding phage induction is involved in specific Stx2 release from bacterial cells. Furthermore, to examine whether another system for specific Stx2 release is present in EHEC, we analyze the stx-replaced mutants. As expected, Stx2 derived from the Stx1 promoter is located in both the extracellular and cell-associated fractions, while mutant Stx2 (B subunit, S31N) derived from the Stx1 promoter is found only in the cell-associated fraction. These results indicate that EHEC has another Stx2 release system that strictly recognizes the serine 31 residue of the B subunit. Overall, we present evidence that specific Stx2 release from bacterial cells is involved in both the Stx2-encoding phage induction system and another Stx2 release system.
authors.affiliation: Department of Molecular Infectiology, Graduate School of Medicine, Chiba University, Chiba, Japan. tshimizu@faculty.chiba-u.jp
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ohta
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Noda
mesh_terms: D000818:Animals; D001433:Bacteriolysis; D003090:Coliphages / Q000254:growth & development; D054324:Enterohemorrhagic Escherichia coli / Q000378:metabolism* / Q000821:virology*; D005814:Genes, Viral; D039002:Prophages / Q000254:growth & development; D021381:Protein Transport; D011817:Rabbits; D022641:Shiga Toxin 2 / Q000378:metabolism*
chemical_list: D022641:Shiga Toxin 2