Fig. 2. Pathway activity variation of core metabolism in photoautotrophic (left) and heterotrophic (right) organisms after nitrogen depletion.

The solution space of the models was sampled according to a previously reported methodology⁵³; employing functions available in The COBRA Toolbox (see Methods). Significant upregulations or downregulations was assessed by performing a Student’s t test on the distributions of each reaction at the initial and final time points. Included organisms are abbreviated as follows: Chlorella vulgaris (Cv), Phaeodactylum tricornutum (Pt), Saccharomyces cerevisiae (Sc), Yarrowia lipolytica (Yl), and Chinese Hamster Ovary cells (CHO).