Molecular Characterization and Lytic Activities of Streptococcus agalactiae Bacteriophages and Determination of Lysogenic-Strain Features

Abstract

The application of mitomycin C induction to 114 genetically diverse Streptococcus agalactiae strains generated 36 phage suspensions. On electron microscopy of the phage suspensions, it was possible to assign the phages to the Siphoviridae family, with three different morphotypes (A, B, and C). Phage genetic diversity was evaluated by a PCR-based multilocus typing method targeting key modules located in the packaging, structural, host lysis, lysogeny, replication, and transcriptional regulation clusters and in the integrase genes and by DNA digestion with EcoRI, HindIII, and ClaI. Thirty-three phages clustering in six distantly related molecular phage groups (I to VI) were identified. Each molecular group was morphotype specific except for morphotype A phages, which were found in five of the six phage groups. The various phage groups defined on the basis of molecular group and morphotype had specific lytic activities, suggesting that each recognized particular host cell targets and had particular lytic mechanisms. Comparison of the characteristics of lysogenic and propagating strains showed no difference in the serotype or clonal complex (CC) identified by multilocus sequence typing. However, all the lysogenic CC17 and CC19 strains presented catabolic losses due to a lack of catabolic decay of DL-alpha-glycerol-phosphate substrates (CC17) and of alpha-D-glucose-1-phosphate (CC19). Moreover, the phages from CC17 lysogenic strains displayed lytic replication in bacterial hosts from all S. agalactiae phylogenetic lineages other than CC23, whereas phages obtained from non-CC17 lysogenic strains lysed bacteria of similar evolutionary origin. Our findings suggest that the adaptive evolution of S. agalactiae exposed the bacteria of this species to various phage-mediated horizontal gene transfers, which may have affected the fitness of the more virulent clones.The Lancefield group B Streptococcus, Streptococcus agalactiae-a major cause of neonatal infections-has increasingly been reported as a common pathogen in nonpregnant adults since the 1970s (40). The proportion of neonatal infections caused by serotype III multilocus sequence type 17 (ST-17) strains is higher than would be expected on the basis of the proportion of women and infants colonized by ST-17 strains in control populations (3,5,24,26,30,33). The major clonal complexes (CC) 1, 12, 17, 19, and 23 have been associated with infections in adults (4, 5, 14, 21). The presence in the S. agalactiae genome of particular insertion sequences, a group II intron, and prophage DNA fragments (17,36,49) suggests that horizontal genetic transfer may play an important role in genome diversification and the emergence of virulent clones in S. agalactiae.Temperate phages affect bacterial fitness by modifying anchor points for genome rearrangements, by disrupting genes, by protecting against lytic infection, by lysing competing strains through prophage induction, and by introducing new fitness factors (8, 18). Little is currently known about these phages. S. agalactiae phages we...

Molecular Characterization and Prophage DNA Contents of Streptococcus agalactiae Strains Isolated from Adult Skin and Osteoarticular Infections

“…We previously identified and characterized bacteriophages and prophage remnants from S. agalactiae strain genomes and designed primer pairs recognizing the prophage sequences of S. agalactiae bacteriophages for use in PCR (12,47). Ten of these primer pairs were used here for the evaluation, by PCR, of the prophage content of S. agalactiae strains ( Table 1).…”

“…They were first isolated in 1969 (39), and more-recent analyses of sequenced S. agalactiae strains have revealed the presence of abundant regions resembling prophages (16,44,45). We recently induced phages from S. agalactiae strains of various phylogenetic lineages, characterized them molecularly, and determined their lytic activities (12). The various molecular phage groups were found to correspond to particular strain lineages, with specific morphological features and lytic activities, suggesting a role for phage-mediated horizontal gene transfer in the evolution of the species and the emergence of lineages with a more specific role in particular diseases.…”

“…We used a PCR-based method recognizing S. agalactiae prophages to determine the prophage content of strain genomes (12). The genetic relationships between prophage DNA regions of strains were determined by hierarchical analysis.…”

Comparative genomics and the role of lateral gene transfer in the evolution of bovine adapted Streptococcus agalactiae

“…Furthermore, LGT via ICE may also occur between S. agalactiae and other Streptococcus species (Davies et al, 2005, 2009; Haenni et al, 2010). Additional mobile genetic elements (MGE) such as phages have also been implicated in LGT within and among various Streptococcus species (Beres and Musser, 2007; Domelier et al, 2009; Ferretti et al, 2001; Holden et al, 2004; Salloum et al, 2010). …”

Analysis of Streptococcus agalactiae pan-genome for prevalence, diversity and functionality of integrative and conjugative or mobilizable elements integrated in the tRNALys CTT gene

“…Most of strain-specific genes of S. agalactiae cluster in chromosomal genomic islands (Glaser et al 2002;Tettelin et al 2005). Several chromosomal prophages have been detected in this species, but they are less abundant in S. agalactiae than in S. pyogenes (Canchaya et al 2003;Domelier et al 2009). In addition, a first analysis carried out on the genome of eight human S. agalactiae strains indicated that a large part of the chromosomal genomic islands could be transferable by conjugation (Brochet et al 2008).…”