Characterization of Dev-CD-23823 and Dev-CT57, new Autographivirinae bacteriophages infecting Cronobacter spp.

Cronobacter spp. are opportunistic pathogenic bacteria responsible for severe infections in neonates. Powdered infant formula has been confirmed to be the source of infection in some cases. Bacteriophages offer a safe means for eliminating this pathogen. In the present study, we characterized two closely related Cronobacter-specific bacteriophages of the proposed genus "GAP227virus". The phages Dev-CD-23823 and Dev-CT57 possessed broad host specificity, as they infected 88% and 80% of the Cronobacter strains tested. Genome sequence comparisons of phages Dev-CD-23823 and Dev-CT57 showed different levels of similarity to the prototype GAP227 phage. The Dev-CT57 phage was highly similar, whereas the Dev-CD-23823 phage showed only 75% sequence identity. A phylogenic tree based on the RNA polymerase (RNAP) gene from selected representatives of the subfamily Autographivirinae confirmed the grouping of Dev-CD-23823, Dev-CT57 and GAP227 in one cluster together with phages PP2, Phi80-18 and PhiR8-01. A common conserved motif was also detected in the RNAP promoters of these phages. The functional activity of these RNAP promoters was confirmed experimentally using a promoter probe vector, and a phage-specific signal was observed; however, some cross-specificity of Dev-CD-23823 and Dev-CT57 promoters was also detected. These results will contribute to our understanding of the biology and evolution of Autographivirinae phages.