How pirate phage interferes with helper phage: Comparison of the two distinct strategies

Abstract

Pirate phages use the structural proteins encoded by unrelated helper phages to propagate. The best-studied example is the pirate P4 and helper P2 of coliphages, and it has been known that the Staphylococcus aureus pathogenicity islands (SaPIs) that can encode virulence factors act as pirate phages, too.When alone in the host, the pirate phages act as a prophage, but when the helper phage gene is also in the same host cell, the pirate phage has ability to exploit the helper phages structural proteins to produce pirate phage particles and spread, interfering with the helper phage production. The known helper phages in these systems are temperate phage. Interestingly, the interference of the pirate phage to the helper phage occurs in different manner between the SaPI-helper system and the P4-P2 system. The SaPIs cannot lyse the helper lysogen upon infection, while when the helper phage lyse the SaPI lysogen, most of the phage particles produced are SaPI particles. On the contrary, in the P4-P2 system, the pirate P4 can lyse helper P2 lysogens to produce mostly the P4 particles, while when P2 phage lyses a P4 lysogen, most of the produces phages are P2 particles. Here, the consequences of these different strategies in the pirate and helper phage spreading among uninfected host was analyzed by using mathematical model. Both in the well-mixed environment and the spatially structured environment, SaPI's strategy interfere with the helper phage * Corresponding author Email address: mitarai@nbi.dk (Namiko Mitarai) spreading significantly more than the P4's strategy, because SaPI interfere with the helper phage's main reproduction step, while P4 interfere only by forcing the helper lysogens to lyse. However, the interference is weaker in the spatially structured environment, because the system self-organize so that the helper phages take over the front of propagation due to the need of helper phage for the pirate phage spreading.

Microbial Arsenal of Antiviral Defenses. Part II

“…Their induction from the chromosome is dependent on the infection with the helper phages and from the host perspective they can be considered as a version of the Abi response [189,190]. The infected cell is lysed eventually but the burst size of the superinfecting lytic phage progeny is suppressed and majority of the released particles carry the PICI genome instead of the phage genome [191]. Since the PICI elements do not undergo a lytic cycle on their own and limit the spread of helper phages, their pres ence can be beneficial for bacterial population.…”

Sustainable Diversity of Phage-Bacteria Systems

“…In addition, players in these systems exhibit many other strategies that makes the system even more sustainable. We have briefly mentioned the lysis-lysogeny choice in temperate phage [72,73,74,75]; such temperate phage may themselves carry genes that prevent invasion of other phage types [77] or genes that allow using other phage genomes to produce offspring (pirate phages [78,79,80]). A vast number of phage defence mechanisms and anti-phage defence mechanisms obviously contribute to sustaining the phage-bacteria coexistence and diversity arising from coevolution [11,7,8].…”