How nitrogen sources influence Mortierella alpina aging: From the lipid droplet proteome to the whole-cell proteome and metabolome

摘要

Arachidonic acid (ARA) is a valuable polyunsaturated fatty acid produced by Mortierella alpina. Although some strategies such as nitrogen supplementation have shown the potential to affect the aging of M. alpina in ways which enable it to produce more ARA, the underlying mechanism remains elusive. Herein, we conducted a systematical analysis of the lipid droplet proteome, as well as the whole-cell proteome and metabolome, in order to elucidate how and why two different nitrogen sources (KNO3 and urea) affect the aging of M. alpina and the corresponding ARA concentration. We found that KNO3 promoted the ARA concentration, while urea accelerated lipid consumption and stimulated the decomposition of mycelia. Although both KNO3 and urea activated carbohydrate metabolic pathways, KNO3 exerted a stronger promoting effect on the pentose phosphate pathway and induced the lipid droplets to participate in the citrate-pyruvate cycle. The activities of malic enzyme and isocitrate dehydrogenase were also promoted more by KNO3. These pathways provided additional substrates and reducing power for ARA synthesis and ROS elimination. Accordingly, since urea showed a weaker promotion of the related pathways, it caused a depression of the antioxidant system and a consequent increase of ROS. These findings facilitate the design of nitrogen supplementation strategies to achieve higher ARA concentrations, and provide guidance for deciphering the mechanisms of similar aging phenomena in other oleaginous microorganisms.