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

Abstract

The <i>exo-xis</i> 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 <i>exo-xis</i> region and important regulatory elements can significantly influence the regulation of phage development. This report defines specific roles for <i>orf60a</i> and <i>orf61</i> in bacteriophage λ and Φ24_B, a specific Shiga toxin-converting phage with clinical relevance. We observed that mutant phages bearing deletions of <i>orf60a</i> and <i>orf61</i> impaired two central aspects of phage development: the lysis-<i>versus</i>-lysogenization decision and prophage induction. These effects were more pronounced for phage Φ24_B than for λ. Surprisingly, adsorption of phage Φ24_B on <i>Escherichia coli</i> host cells was less efficient in the absence of either <i>orf60a</i> or <i>orf61</i>. 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.