Metabolic investigation of the microalga Emiliania huxleyi in laboratory and mesocosm experiments with focus on viral infection
The coccolithophore Emiliania huxleyi constitutes a key player of global carbon cycling and its massive algal blooms are frequently terminated by viruses. Thus, the alga is an attractive target for investigations in the context of its ecological role or mechanisms of viral infection, which I addressed by metabolic analysis. Comparative metabolic profiling revealed a unique metabolic composition for both the diploid and haploid life phase. Further, the growth stage of cells influences the metabolic composition, since I observed changes in intensities of specific metabolic classes during growth. For example carbohydrates as mannitol showed highest concentrations in the exponential phase, whereas fatty acids were correlated with the stationary and sterols with the declining phase. A mesocosm study confirmed the complexity of phytoplankton metabolism. Changes in metabolic profiles could partly be tracked back to the plankton group contributing the metabolite and carbon dioxide and iron manipulation affected metabolic profiles. Metabolomic analysis of E. huxleyi infected by a lytic or non-lytic virus aimed to shed light at the hitherto poorly understood processes leading to host cell lysis. A profound rewiring of host metabolism started with changes in energy shuffling facilitating fatty acid production. The importance of fatty acid biosynthesis is reflected in a dose-dependent reduction in viral release, if the pathway was inhibited. Further, specific inhibition of the mevalonate branch of terpene and sterol biosynthesis strongly reducing viral release and the presence of epibrassicasterol, the dominant host sterol, in virion membranes pointed at the pivotal role of this pathway during lytic infection. These results indicate the metabolic variability of E. huxleyi and the tremendous role of the lipid metabolic machinery during both regular cell cycling and lytic viral infection.