Isolation and Characterization of Two Novel Lactococcus lactis Bacteriophages Isolated from Greek Goat Milk

Two novel virulent Lactococcus lactis bacteriophages were isolated from Greek raw goat milk and characterized in this study. Phage PMBT68 infected L. lactis subsp. lactis strain C10, whereas phage PMBT69 infected L. lactis subsp. cremoris strain 3107. Both phages exhibit an isometric capsid head and a long, non-contractile tail, characteristic of members of the class Caudoviricetes. Notably, phage PMBT69 showed cross-subspecies infectivity, as it infected both L. lactis subsp. lactis and subsp. cremoris strains (representing different cell wall polysaccharide types as phage receptors). The linear double-stranded 60,735 bp DNA genome of phage PMBT68 has a GC content of 34.3 mol%, is composed of 100 predicted open reading frames and is circularly permuted. In contrast, the linear double-stranded genome of phage PMBT69 is 127,738 bp in size with 223 predicted open reading frames, a GC content of 32.9 mol% and short direct terminal repeats. Morphological and genomic analyses of the phages demonstrated that phage PMBT68 is a novel species in the genus Teubervirus, whereas PMBT69 represents a novel genus that is most closely related to the genus Audreyjarvisvirus. We therefore propose the establishment of the novel genus Amaltheavirus, with PMBT69 as its type species.