Dynamic modulation of DNA replication and gene transcription in deep-sea filamentous phage SW1 in response to changes of host growth and temperature.

Little is known about the response of deep-sea virus and their relationship with their host towards environmental change. Although viruses are thought to play key roles in the deep-sea ecological evolution and biogeochemical cycling, these roles are yet to be defined. This study aims to delineate the relationship between a deep-sea filamentous phage SW1 and its host Shewanella piezotolerans (S. piezotolerans) WP3, and their response towards temperature change. The copy number of SW1's replicative form (RF-) DNA and single-stranded (ss-) DNA along the different growth phases of WP3 were quantified at 20°C and 4°C, respectively. The copy number of SW1 RF-DNA was found to be temperature and growth phase-dependent, while the ssDNA of SW1 was only produced at 4°C. This is the first report showing low-temperature dependence of phage DNA replication. The transcription of SW1 key genes fpsA and fpsR were also found to be induced at low temperature during all the monitored growth periods of WP3. Additionally, the transcription of SW1 was found to be induced by cold-shock while its DNA replication was not changed. Our data demonstrates a dynamic change of virus DNA replication and transcription in accordance with host growth, and the low temperature adapted mechanisms for SW1 activities in the deep sea. This low temperature adapted deep-sea virus-bacterium system could serve as an ideal model to further study the mechanism and relationship of deep-sea virus-bacteria ecosystems.