Phage-Associated Mutator Phenotype in Group A Streptococcus

Department of Pharmaceutical Sciences, The University of Oklahoma College of Pharmacy, P.O. Box 26901, Oklahoma City, OK 73190, USA.
Journal of bacteriology (Impact Factor: 2.81). 09/2008; 190(19):6290-301. DOI: 10.1128/JB.01569-07
Source: PubMed


Defects in DNA mismatch repair (MMR) occur frequently in natural populations of pathogenic and commensal bacteria, resulting
in a mutator phenotype. We identified a unique genetic element in Streptococcus pyogenes strain SF370 that controls MMR via a dynamic process of prophage excision and reintegration in response to growth. In S. pyogenes, mutS and mutL are organized on a polycistronic mRNA under control of a common promoter. Prophage SF370.4 is integrated between the two
genes, blocking expression of the downstream gene (mutL) and resulting in a mutator phenotype. However, in rapidly growing cells the prophage excises and replicates as an episome,
allowing mutL to be expressed. Excision of prophage SF370.4 and expression of MutL mRNA occur simultaneously during early logarithmic growth
when cell densities are low; this brief window of MutL gene expression ends as the cell density increases. However, detectable
amounts of MutL protein remain in the cell until the onset of stationary phase. Thus, MMR in S. pyogenes SF370 is functional in exponentially growing cells but defective when resources are limiting. The presence of a prophage
integrated into the 5′ end of mutL correlates with a mutator phenotype (10−7 to 10−8 mutation/generation, an approximately a 100-fold increase in the rate of spontaneous mutation compared with prophage-free
strains [10−9 to 10−10 mutation/generation]). Such genetic elements may be common in S. pyogenes since 6 of 13 completed genomes have related prophages, and a survey of 100 strains found that about 20% of them are positive
for phages occupying the SF370.4 attP site. The dynamic control of a major DNA repair system by a bacteriophage is a novel method for achieving the mutator phenotype
and may allow the organism to respond rapidly to a changing environment while minimizing the risks associated with long-term

Download full-text


Available from: Michael Mcshan
  • Source
    • "It is possible that SpyCI, as well as other Gram-positive phagelike chromosomal islands (Novick et al., 2010), have a complex evolutionary history and their genetic material may have originated from disparate sources. While each chromosomal island shows considerable diversity (Scott et al., 2008), several genes, notably the integrase, primase, and replicase genes, are highly conserved, providing clues to the minimal genome composition needed for a functional CI. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Streptococcus pyogenes is a significant pathogen of humans, annually causing over 700,000,000 infections and 500,000 deaths. Virulence in S. pyogenes is closely linked to mobile genetic elements like phages and chromosomal islands (CI). S. pyogenes phage-like chromosomal islands (SpyCI) confer a complex mutator phenotype on their host. SpyCI integrate into the 5' end of DNA mismatch repair (MMR) gene mutL, which also disrupts downstream operon genes lmrP, ruvA, and tag. During early logarithmic growth, SpyCI excise from the bacterial chromosome and replicate as episomes, relieving the mutator phenotype. As growth slows and the cells enter stationary phase, SpyCI reintegrate into the chromosome, again silencing the MMR operon. This system creates a unique growth-dependent and reversible mutator phenotype. Additional CI using the identical attachment site in mutL have been identified in related species, including Streptococcus dysgalactiae subsp. equisimilis, Streptococcus anginosus, Streptococcus intermedius, Streptococcus parauberis, and Streptococcus canis. These CI have small genomes, which range from 13 to 20 kB, conserved integrase and DNA replication genes, and no identifiable genes encoding capsid proteins. SpyCI may employ a helper phage for packaging and dissemination in a fashion similar to the Staphylococcus aureus pathogenicity islands (SaPI). Outside of the core replication and integration genes, SpyCI and related CI show considerable diversity with the presence of many indels that may contribute to the host cell phenotype or fitness. SpyCI are a subset of a larger family of streptococcal CI who potentially regulate the expression of other host genes. The biological and phylogenetic analysis of streptococcal chromosomal islands provides important clues as to how these chromosomal islands help S. pyogenes and other streptococcal species persist in human populations in spite of antibiotic therapy and immune challenges.
    Full-text · Article · Aug 2014 · Frontiers in Cellular and Infection Microbiology
    • "Prophage SF370.4 is integrated between the mutL and mutS genes. It prevents mutS expression and induces a mutator phenotype at low cell density in S. pyogenes SF370 (Scott et al., 2008). At the onset of the stationary phase, the prophage is excised and replicates as an episome, allowing further re-integration. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Bacteriophages co-exist and co-evolve with their hosts in natural environments. Virulent phages lyse infected cells through lytic cycles, whereas temperate phages often remain dormant and can undergo lysogenic or lytic cycles. In their lysogenic state, prophages are actually part of the host genome and replicate passively in rhythm with host division. However, prophages are far from being passive residents: they can modify or bring new properties to their host. In this review, we focus on two important phage-encoded recombination mechanisms, i.e. site-specific recombination and homologous recombination, and how they remodel bacterial genomes. © The Author 2014. Published by Oxford University Press on behalf of FEMS. All rights reserved. For permissions, please e-mail:
    No preview · Article · Jan 2014 · FEMS Microbiology Letters
  • Source
    • "The integration of SpyCI leads to inactivation of the downstream genes, including mutL, rendering the bacteria defective for MMR. We recently have shown that in strain SF370, SpyCI integration is dependent on the growth phase of the bacterium (Scott et al., 2008). When cells are rapidly dividing during logarithmic growth, the SpyCI excises from the bacterial chromosome and allows both 2 "
    [Show abstract] [Hide abstract]
    ABSTRACT: We recently showed that a prophage-like Streptococcus pyogenes chromosomal island (SpyCI) controls DNA mismatch repair and other repair functions in M1 genome strain SF370 by dynamic excision and reintegration into the 5' end of mutL in response to growth, causing the cell to alternate between a wild type and mutator phenotype. Nine of the 16 completed S. pyogenes genomes contain related SpyCI integrated into the identical attachment site in mutL, and in this study we examined a number of these strains to determine whether they also had a mutator phenotype as in SF370. With the exception of M5 genome strain Manfredo, all demonstrated a mutator phenotype as compared to SpyCI-free strain NZ131. The integrase gene (int) in the SpyCIM5 contains a deletion that rendered it inactive, and this deletion predicts that Manfredo would have a pronounced mutator phenotype. Remarkably, this was found not to be the case, but rather a cryptic promoter within the int ORF was identified that ensured constitutive expression of mutL and the downstream genes encoded on the same mRNA, providing a striking example of rescue of gene function following decay of a mobile genetic element. The frequent occurrence of SpyCI in the group A streptococci may facilitate bacterial survival by conferring an inducible mutator phenotype that promotes adaptation in the face of environmental challenges or host immunity.
    Full-text · Article · Aug 2012 · Frontiers in Microbiology
Show more