Effects of infection by bacteriophages APSE-2 and APSE-3 on the pea aphid (Acyrthosiphon pisum) bacterial symbiont Hamiltonella defensa

Symbiotic associations are ubiquitous in nature and play a key role in the success of insects in particular. Symbioses with bacteria are especially common and are often maternally transmitted with a net fitness benefit driving the persistence of the symbiosis. These bacterial symbionts are often infected with bacteriophages which have the ability to impact these symbioses in critical ways. Perhaps the most interesting aspect of bacteriophage infection is the potential to bring new traits that benefit both bacterial symbiont and the insect host. The novel genes could alter bacterial titers and lytic events that are important in the maintenance of symbiosis. Currently though, the role of bacteriophages in the upkeep of host-bacterial symbiosis is poorly understood. There are seven strains of APSE (A.pisum secondary endosymbionts) currently described with two found in pea aphid (A.pisum) populations in the US. These stains, APSE-2 and APSE-3 provide different levels of protection against parasitoid wasps for their aphid hosts. APSE-2 persists mostly as an integrated prophage in H. defensa while APSE-3 persists as an episomal prophage. We used ­in vitro cultures of H.defensa and APSE- 2 and APSE-3 to better understand how different strains of APSE effect the growth and interaction of H.defensa and insect cells under different environmental and culture conditions.