Antibacterial T6SS1 cluster identification and bioinformatics characterization of their putative effectors in Shiga toxin-producing Escherichia coli

Shiga toxing-producing Escherichia coli (STEC) O22:H8 strain is a serotype occasionally isolated in Argentinian cattle. Preliminary works showed that the cattle carrying STEC O22:H8 strains could not be experimentally colonized by EHEC O157:H7 strain. The type 6 secretion system (T6SS) is one of the most versatile virulence mechanisms involved in delivering effectors, particularly the T6SS1 translocate antibacterial toxins effectors during bacterial competition for niche-space. In this work, we could evidence the molecular bases of the success of STEC O22:H8 (154) strain during bacterial competition against EHEC O157:H7 strains. The genome sequence of STEC O22:H8 (154) allowed us to identify a complete T6SS1 cluster. In addition, we identify and characterized several putative T6SS1-antibacterial effectors encoded inside the T6SS1 clusters and in genomic pathogenic islands. Competition assays against EHEC O157:H7 strain confirmed the antibacterial activity of STEC O22:H8 (154) strain in vitro. Considering the absent of T6SS1 in STEC strains, we proposed the recent horizontal transfer acquisition and the most probably donor belong to the same Escherichia coli species. A safe STEC O22:H8 (154){Delta} stx would be used as a new strategy to fight STECs in bovine intestinal colonization, leading in a reduction in beef contamination and consequently HUS cases in humans.