Abstract

The coccolithophore Emiliania huxleyi is a microalga with biogeochemical and biotechnological relevance, due to its high abundance in the ocean and its ability to form intricate calcium carbonate structures. Depletion of macronutrients in oceanic waters is very common and will likely enhance with advancing climate change. We present the first comprehensive metabolome study analyzing the effect of phosphorus (P) and nitrogen (N) starvation on the diploid and haploid life-cycle stage, applying various metabolome analysis methods to gain new insights in intracellular mechanisms to cope with nutrient starvation. P-starvation led to an accumulation of many generic and especially N-rich metabolites, including lipids, osmolytes, and pigments. This suggests that P-starvation primarily arrests cell-cycling due to lacking P for nucleic acid synthesis, but that enzymatic functionality is widely preserved. Also, the de-epoxidation ratio of the xanthophyll cycle was upregulated in the diploid stage under P-starvation, indicating increased nonphotochemical quenching, a response typically observed under high light stress. In contrast, N-starvation resulted in a decrease of most
central metabolites, also P-containing ones, especially in the diploid stage, indicating that most enzymatic functionality ceased. The two investigated nutrient starvation conditions caused significantly different responses, contrary to previous assumptions derived from transcriptomic studies. Data highlight that instantaneous biochemical flux is a more dominant driver of the metabolome than the transcriptomically rearranged pathway patterns. Due to the fundamental nature of the observed responses it may be speculated that microalgae with similar nutrient requirements can cope better with P-starvation than with N-starvation.

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