Ecophysiological aspects of algal host–virus interactions in a changing ocean

With this thesis I aimed to obtain a better understanding on how abiotic factors affect virus-phytoplankton interaction, alone and in combination with other relevant environmental variables. The main focus in this thesis is on phosphorus (P) limitation, for the primary reason that phytoplankton growth in many coastal and oceanic systems worldwide is (seasonally) limited in P, and the future (stratified) ocean is expected to become more P-limited than nitrogen (N) limited due to diazotroph N-fixation in the ocean surface. The studies in this thesis were carried out with axenic phytoplankton host-virus model systems under well-controlled experimental set-ups to obtain a mechanistic understanding and allow accurate quantification of virus growth characteristics, i.e., the viral latent period (time until first release of viruses), the viral burst size (number of viruses produced per host cell lysed) and the percentage of infective progeny viruses. Host cell physiology (e.g. photophysiology and lipid composition) was monitored to relate differences in results between treatments to host metabolism.