Identification and molecular characterization of Serratia marcescens phages vB_SmaA_2050H1 and vB_SmaM_2050HW

Serratia marcescens is a rod-shaped, Gram-negative bacterium causing nosocomially acquired infections. Bacteriophages are natural opponents of their pathogenic bacterial hosts and could be an alternative to traditional antibiotic treatments. In this study, two S. marcescens-specific bacteriophages, vB_SmaA_2050H1 and vB_SmaM_2050HW, were isolated from two different waste samples in China. Phage plaque assays, transmission electron microscopy, host-range determination, and one-step growth curve analyses were performed for both phages. vB_SmaA_2050H1 was classified as belonging to the family Ackermannviridae, and vB_SmaM_2050HW was classified as belonging to the family Myoviridae. One-step growth curve analysis showed that the latent and rise period of vB_SmaA_2050H1 were 80 min and 50 min, respectively, with a burst size of approximately 10 phage particles per infected cell. For vB_SmaM_2050HW, latent and rise periods of 40 min and 60 min, respectively, were determined, with a burst size of approximately 110 phage particles per infected cell. vB_SmaA_2050H1 infected 10 of the 15 (66.67%) S. marcescens strains tested, while vB_SmaM_2050HW infected 12 (80%) of the strains. Whole-genome sequencing and annotation of each of the phage genomes revealed genome sizes of 159,631 bp and 276,025 bp for vB_SmaA_2050H1 and vB_SmaM_2050HW, respectively, with the respective genomes containing 213 and 363 putative open reading frames. Sequence analysis of the genomes revealed that vB_SmaA_2050H1 is a member of the ViI-like family, while vB_SmaM_2050HW is a novel virulent bacteriophage. These findings provide further insights into the genomic structures of S. marcescens bacteriophages.