Shiga toxin 2 is specifically released from bacterial cells by two different mechanisms

Infect Immun. 2009 Jul;77(7):2813-23. doi: 10.1128/IAI.00060-09. Epub 2009 Apr 20.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacteriolysis*
  • Coliphages / growth & development
  • Enterohemorrhagic Escherichia coli / metabolism*
  • Enterohemorrhagic Escherichia coli / virology*
  • Genes, Viral
  • Prophages / growth & development
  • Protein Transport
  • Rabbits
  • Shiga Toxin 2 / metabolism*

Substances

  • Shiga Toxin 2