Differential metabolic reprogramming due to nitrogen starvation leads to remobilization of storage metabolites in...

Microalgal stress-related responses to nitrogen (N) deprivation are determined by genetically defined metabolic changes, which are further influenced by cultivation and nutritional conditions. In this study, we evaluated the metabolic responses of five chlorophyte strains to varying N concentrations. The strains included Chlamydomonas reinhardtii and Scenedesmus obliquus, which accumulated higher levels of starch, and Monoraphidium sp., Chlamydomonas sp., and Chlorella vulgaris, characterized by differences in both the levels and compositions of accumulated lipids. Under N-starved condition, all strains exhibited increased starch and neutral lipid content, with strain-specific variations. In this treatment, the content of branched-chain amino acids decreased in Monoraphidium sp., likely due to amino acid catabolism associated with the autophagy and triacylglycerol (TAG) accumulation. Furthermore, we observed a remodeling of lipid classes in S. obliquus, C. vulgaris, Chlamydomonas sp., and Monoraphidium sp., including reductions in digalactosyl diacylglycerol, monogalactosyl diacylglycerol, and sulfoquinovosyl diacylglycerol, accompanied by an increase in TAGs. Under N-starvation several fatty acids of C. vulgaris, Chlamydomonas sp., and C reinhardtii, including α-linolenic acid (C18:3), oleic acid (C18:1), and linoleic acid (C18:2) increase. In contrast, Monoraphidium sp. accumulated long-chain fatty acids such as lumequic acid (C30:1), nervonic acid (C24:1), docosanoic acid (C22:0), and erucic acid (C22:1). Collectively, these results indicate that chlorphyte strains exhibit distinct metabolic responses to N depletion in the medium. These findings highlight the importance of strain-specific assessments when developing the N management strategies for microalgal cultivation and biotechnological applications.