Comparative Genomic and Morphological Analyses of Listeria Phages Isolated from Farm Environments

The genusListeria is ubiquitous in the environment and includes the globally important food-borne pathogenListeria monocytogenes . While the genomic diversity ofListeria has been well studied, considerably less is known about the genomic and morphological diversity ofListeria bacteriophages. In this study, we sequenced and analyzed the genomes of 14Listeria phages isolated mostly from New York dairy farm environments as well as one relatedEnterococcus faecalis phage to obtain information on genome characteristics and diversity. We also examined 12 of the phages by electron microscopy to characterize their morphology. TheseListeria phages, based on gene orthology and morphology, together with previously sequencedListeria phages could be classified into five orthoclusters, including one novel orthocluster. One orthocluster (orthocluster I) consists of large-genome (∼135-kb) myoviruses belonging to the genus “Twort-like viruses,” three orthoclusters (orthoclusters II to IV) contain small-genome (36- to 43-kb) siphoviruses with icosahedral heads, and the novel orthocluster V contains medium-sized-genome (∼66-kb) siphoviruses with elongated heads. A novel orthocluster (orthocluster VI) ofE. faecalis phages, with medium-sized genomes (∼56 kb), was identified, which grouped together and shares morphological features with the novelListeria phage orthocluster V. This new group of phages (i.e., orthoclusters V and VI) is composed of putative lytic phages that may prove to be useful in phage-based applications for biocontrol, detection, and therapeutic purposes.