| Summary: | Microorganisms naturally respond to changes in nutritional conditions by adjusting their morphology and physiology. The cellular response of the fission yeast S. pombe to nitrogen starvation has been extensively studied. Here, we report time course metabolomic analysis during one hour immediately after nitrogen starvation, prior to any visible changes in cell morphology except for a tiny increase of cell length per division cycle. We semi-quantitatively measured 75 distinct metabolites, 60% of which changed their level over 2-fold. The most significant changes occurred during the first 15 min, when trehalose, 2-oxoglutarate, and succinate increased, while purine biosynthesis intermediates rapidly diminished. At 30–60 min, free amino acids decreased, although several modified amino acids—including hercynylcysteine sulfoxide, a precursor to ergothioneine—accumulated. Most high-energy metabolites such as ATP, S-adenosyl-methionine or NAD+ remained stable during the whole time course. Very rapid metabolic changes such as the shut-off of purine biosynthesis and the rise of 2-oxoglutarate and succinate can be explained by the depletion of NH4Cl. The changes in the levels of key metabolites, particularly 2-oxoglutarate, might represent an important mechanistic step to trigger subsequent cellular regulations.
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