Roles of orf60a and orf61 in Development of Bacteriophages λ and Φ24B

The exo-xis region of lambdoid bacteriophage genomes contains several established and potential genes that are evolutionarily conserved, but not essential for phage propagation under laboratory conditions. Nevertheless, deletion or overexpression of either the whole exo-xis region and important regulatory elements can significantly influence the regulation of phage development. This report defines specific roles for orf60a and orf61 in bacteriophage λ and Φ24_B, a specific Shiga toxin-converting phage with clinical relevance. We observed that mutant phages bearing deletions of orf60a and orf61 impaired two central aspects of phage development: the lysis-versus-lysogenization decision and prophage induction. These effects were more pronounced for phage Φ24_B than for λ. Surprisingly, adsorption of phage Φ24_B on Escherichia coli host cells was less efficient in the absence of either orf60a or orf61. We conclude that these open reading frames (ORFs) play important, but not essential, roles in the regulation of lambdoid phage development. Although phages can propagate without these ORFs in nutrient media, we suggest that they may be involved in the regulatory network, ensuring optimization of phage development under various environmental conditions.

Inhibition of Shiga toxin-converting bacteriophage development by novel antioxidant compounds

Oxidative stress may be the major cause of induction of Shiga toxin-converting (Stx) prophages from chromosomes of Shiga toxin-producing Escherichia coli (STEC) in human intestine. Thus, we aimed to test a series of novel antioxidant compounds for their activities against prophage induction, thus, preventing pathogenicity of STEC. Forty-six compounds (derivatives of carbazole, indazole, triazole, quinolone, ninhydrine, and indenoindole) were tested. Fifteen of them gave promising results and were further characterized. Eleven compounds had acceptable profiles in cytotoxicity tests with human HEK-293 and HDFa cell lines. Three of them (selected for molecular studies) prevent the prophage induction at the level of expression of specific phage genes. In bacterial cells treated with hydrogen peroxide, expression of genes involved in the oxidative stress response was significantly less efficient in the presence of the tested compounds. Therefore, they apparently reduce the oxidative stress, which prevents induction of Stx prophage in E. coli.