PMID:22991467

Citation	Ram, G, Chen, J, Kumar, K, Ross, HF, Ubeda, C, Damle, PK, Lane, KD, Penadés, JR, Christie, GE and Novick, RP (2012) Staphylococcal pathogenicity island interference with helper phage reproduction is a paradigm of molecular parasitism. Proc. Natl. Acad. Sci. U.S.A. 109:16300-5
Abstract	Staphylococcal pathogenicity islands (SaPIs) carry superantigen and resistance genes and are extremely widespread in Staphylococcus aureus and in other Gram-positive bacteria. SaPIs represent a major source of intrageneric horizontal gene transfer and a stealth conduit for intergeneric gene transfer; they are phage satellites that exploit the life cycle of their temperate helper phages with elegant precision to enable their rapid replication and promiscuous spread. SaPIs also interfere with helper phage reproduction, blocking plaque formation, sharply reducing burst size and enhancing the survival of host cells following phage infection. Here, we show that SaPIs use several different strategies for phage interference, presumably the result of convergent evolution. One strategy, not described previously in the bacteriophage microcosm, involves a SaPI-encoded protein that directly and specifically interferes with phage DNA packaging by blocking the phage terminase small subunit. Another strategy involves interference with phage reproduction by diversion of the vast majority of virion proteins to the formation of SaPI-specific small infectious particles. Several SaPIs use both of these strategies, and at least one uses neither but possesses a third. Our studies illuminate a key feature of the evolutionary strategy of these mobile genetic elements, in addition to their carriage of important genes-interference with helper phage reproduction, which could ensure their transferability and long-term persistence.
Links	PubMed PMC3479557 Online version:10.1073/pnas.1204615109
Keywords	Antibiosis/genetics; Cloning, Molecular; Escherichia coli; Gene Transfer, Horizontal/genetics; Genomic Islands/genetics; Microscopy, Electron; Real-Time Polymerase Chain Reaction; Staphylococcus Phages/physiology; Staphylococcus aureus/genetics; Staphylococcus aureus/pathogenicity; Staphylococcus aureus/virology; Two-Hybrid System Techniques; Viral Plaque Assay; Virus Replication/physiology
edit table

Significance

• Staphylococcal pathogenicity islands (SaPIs) are highly mobile, superantigen-encoding genetic elements.
• SaPIs reside at specific sites in the chromosome of their host under control of master repressor.
• Induction is by a helper phage (superinfection, or SOS induction of a resident prophage).
• SaPIs use phage reproduction cycle for their own transduction.
• SaPIs is a major source of intergenic horizontal gene transfer and a stealth conduit for intergeneric gene transfer.
• SaPIs block colony formation and reduce burst size of the helper phage, and increase the survival of phage infected cells.
• The hypothesis is that the diversion of phage virion proteins to the formation of small capsid is responsible for the interferences.
• This article confirms the hypothesis and shows that SapI-encoded protein directly and specifically interferes with phage DNA packaging by blocking the phage terminase small subunit.

*Table 1 and Figure 1.

They used ppi for phage packaging interference and added a subscript to indicate its origin. They cloned ppispb2 gene and tested its role in phage interference. The cloned gene blocked 80α plaque formation completely. Also, its deletion restored plaque formation, and increased the 80α plaque titer (similar to that seen with the host strain lacking any SaPI)

• Conclusion: Ppi interference with phage 80α.

*Figure 2.

Ppispb2 bound strongly to the WT 80α TerSP but not to the mutant protein. In addition, it did not interact with the cognate SaPI TerSS.

These results were confirmed by a pulldown assay using S-tagged Ppispb2.

• Conclusion: Ppispb2 directly and specifically interacts with TerSP and blocks packaging of phage DNA.

*Figure 3.

They deleted two capsid morphogenesis genes, cpmA and cpmB, of SaPI1 and tested this deletion for its effects on 80α plaque formation and phage titer.

• Conclusion: Packaging is sequence-specific and determined by TerS, it is not size-specific (both phage and SaPI DNAs are packaged in capsids of small and large sizes). And, there are at least two different mechanisms of SaPI-mediated interference with helper phages: 1. Ppi-mediated interference with packaging. 2. Cpm-mediated diversion of capsomere proteins for small capsid formation.

*Figure 4.

They used phage 80 and 80alpha to see the effect of SaPI2 interference with different phages.

• Conclusion: SaPI2 uses three mechanisms of phage interference: It uses ORF17 with phage 80, and with phage 80α Ppi and CpmAB.

Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status

References

See Help:References for how to manage references in GONUTS.