Different adsorption strategies affect cyanophage infection of cyanobacteria under light-dark cycles

Abstract

The unicellular cyanobacteria Prochlorococcus and Synechococcus account for a major portion of the carbon fixation in aquatic environments. Their viruses (cyanophages) are abundant and are estimated to infect 15% of marine cyanobacteria at any given time. Cyanophage infection eventually results in killing its cyanobacterial host through burst, which releases dissolve organic matter into the marine ecosystem. Therefore, they play significant roles in global biogeochemical cycles. Cyanobacteria can perform oxygenic photosynthesis, and the life cycle of cyanophages is also influenced by light. Previous studies showed that there are two different adsorption strategies, one is light-dependent adsorption, and the other is light-independent adsorption. We hypothesize that light-dependent adsorption is a selective strategy developed by cyanophages to adapt to the host metabolism, which is driven by the daily light-dark cycle. In our experiments, we used myoviruses P-HM1, P-HM2, podoviruses P-SSP7, P-GSP1, and siphovirus P-HS2 to infect their host Prochlorococcus MED4 under different conditions to check their adsorption strategies. Then we did single infection experiments with P-HM2 (light-dependent adsorption) and P-SSP7 (light-independent adsorption) at different times of the day and compared their diel infection patterns. After that, we carried out competition experiments by using different cyanophages to co-infect their host Prochlorococcus MED4 at different times of a simulated day to investigate that which adsorption strategies might confer a fitness advantage to cyanophages under light-dark cycles. We found that adsorption of P-HM1 and P-HM2 to MED4 were light-dependent, while P-SSP7, P-GSP1 and P-HS2 were light-independent. When infections were initiated at different times of an experimental day, extracellular P-HM2 can be synchronized to the light-dark cycle through light-dependent adsorption while P-SSP7 cannot. And the competition experiments suggested that the daily light-dark cycle provides a temporal niche for cyanophages with different adsorption strategies. Our work will give us valuable insights into the intrinsic role of light in shaping cyanophage and cyanobacteria interactions in aquatic environments.

Date of Award	2016
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology