Essentiality of the early transcript in the replication origin of the lactococcal prolate phage c2

Lactococcus Ceduovirus Phages Isolated from Industrial Dairy Plants-from Physiological to Genomic Analyses

LactococcusCeduovirus (formerly c2virus) bacteriophages are among the three most prevalent phage types reported in dairy environments. Phages from this group conduct a strictly lytic lifestyle and cause substantial losses during milk fermentation processes, by infecting lactococcal host starter strains. Despite their deleterious activity, there are limited research data concerning Ceduovirus phages. To advance our knowledge on this specific phage group, we sequenced and performed a comparative analysis of 10 new LactococcuslactisCeduovirus phages isolated from distinct dairy environments. Host range studies allowed us to distinguish the differential patterns of infection of L. lactis cells for each phage, and revealed a broad host spectrum for most of them. We showed that 40% of the studied Ceduovirus phages can infect both cremoris and lactis strains. A preference to lyse strains with the C-type cell wall polysaccharide genotype was observed. Phage whole-genome sequencing revealed an average nucleotide identity above 80%, with distinct regions of divergence mapped to several locations. The comparative approach for analyzing genomic data and the phage lytic spectrum suggested that the amino acid sequence of the orf8-encoded putative tape measure protein correlates with host range. Phylogenetic studies revealed separation of the sequenced phages into two subgroups. Finally, we identified three types of phage origin of replication regions, and showed they are able to support plasmid replication without additional phage proteins.

A distinct single-stranded DNA-binding protein encoded by the Lactococcus lactis bacteriophage bIL67

Single-stranded binding proteins (SSBs) are found to participate in various processes of DNA metabolism in all known organisms. We describe here a SSB protein encoded by the Lactococcus lactis phage bIL67 orf14 gene. It is the first noted attempt at characterizing a SSB protein from a lactococcal phage. The purified Orf14(bIL67) binds unspecifically to ssDNA with the same high affinity as the canonical Bacillus subtilis SSB. Electrophoretic mobility-shift assays performed with mutagenized Orf14(bIL67) protein derivatives suggest that ssDNA-binding occurs via a putative OB-fold structure predicted by three-dimensional modeling. The native Orf14(bIL67) forms homotetramers as determined by gel filtration studies. These results allow distinguishing the first lactococcal phage protein with single-strand binding affinity, which defines a novel cluster of phage SSBs proteins. The possible role of Orf14(bIL67) in phage multiplication cycle is also discussed.

Isolation of lactococcal prolate phage-phage recombinants by an enrichment strategy reveals two novel host range determinants

Virulent lactococcal prolate (or c2-like) phages are the second most common phage group that causes fermentation failure in the dairy industry. We have mapped two host range determinants in two lactococcal prolate phages, c2 and 923, for the host strains MG1363 and 112. Each phage replicates on only one of the two host strains: c2 on MG1363 and 923 on 112. Phage-phage recombinants that replicated on both strains were isolated by a new method that does not require direct selection but rather employs an enrichment protocol. After initial mixed infection of strain 112, two rotations, the first of which was carried out on strain MG1363 and the second on 112, permitted continuous amplification of double-plating recombinants while rendering one of the parent phages unamplified in each of the two rotations. Mapping of the recombination endpoints showed that the presence of the N-terminal two-thirds of the tail protein L10 of phage c2 and a 1,562-bp cosR-terminal fragment of phage 923 genome overcame blocks of infection in strains MG1363 and 112, respectively. Both infection inhibition mechanisms act at the stage of DNA entry; in strain MG1363, the infection block acts early, before phage DNA enters the cytoplasm, and in strain 112, it acts late, after most of the DNA has entered the cell but before it undergoes cos-end ligation. These are the first reported host range determinants in bacteriophage of lactic acid bacteria required for overcoming inhibition of infection at the stage of DNA entry and cos-end ligation.