Interaction of the Phi HSIC virus with its host: Lysogeny or pseudolysogeny?

The marine phage Phi HSIC has been previously reported to enter into a lyso genic relationship with its host, HSIC, identified as Listonella pelagia, T his phage produces a variety of plaques on its host, including turbid and h aloed plaques, from which lysogens were previously isolated. These lysogens were unstable during long-term storage at -80 degrees C and were lost, Whe n HSIC was reinfected with phage Phi HSIC, pseudolysogen-like interactions between the phage and its host were observed. The cells (termed HSIC-2 or H SIC-2e) produced high viral titers (10(11) ml(-1)) in the absence of inocul ating phage and yet reached culture densities of nearly 10(9) ml(-1). Proph ages were not induced by mitomycin C or the polyaromatic hydrocarbon naphth alene in cells harboring such infections, However, such cells were homoimmu ne to superinfection, Colonies hybridized strongly with a gene probe from a 100-bp fragment of the Phi HSIC genome, while the host did not. Analysis o f chromosomal DNA preparations suggested the presence of a chromosomally in tegrated prophage, Phage adsorption experiments suggested that HSIC-2 was a dsorption impaired. Because of the chromosomal prophage integration and hom oimmunity, we interpret these results to indicate that Phi HSIC establishes a lysogenic relationship with its host that involves an extremely high lev el of spontaneous induction. This could be caused by a weak repressor of ph age production. Additionally, poor phage adsorption of HSIC-2 compared to t he wild type probably helped maintain this pseudolysogen-like relationship. In many ways, pseudolysogenic phage-host interactions may provide a paradi gm for phage-host interactions in the marine environment.