Effect of single and combined nitrogen sources on lipid production by Rhodotorula kratochvilovae and Rhodotorula paludigena

Oleaginous yeasts of the genus Rhodotorula are promising microbial platforms for sustainable lipid production. However, nitrogen availability critically regulates both biomass formation and lipid production, with nitrogen limitation recognized as a key trigger for lipid overproduction. This study investigated the influence of single and combined organic and inorganic nitrogen sources on biomass formation and lipid production by Rhodotorula kratochvilovae AUMC17237 and R. paludigena AUMC17238. The results revealed strain-specific responses to different nitrogen sources. Among individual nitrogen sources, urea supported the highest biomass production in both strains. Ammonium chloride, when combined with organic nitrogen sources, resulted in enhanced biomass formation. Specifically, its combination with yeast extract yielded the highest biomass in R. kratochvilovae (6.282 ± 0.161 g/L), whereas its combination with urea produced the strongest biomass response in R. paludigena (6.565 ± 0.324 g/L). Organic nitrogen sources generally favored lipid accumulation when applied individually. Urea produced the highest lipid yield in R. kratochvilovae (0.990 ± 0.011 g/L), whereas yeast extract was most effective in R. paludigena (0.947 ± 0.033 g/L). Furthermore, combined organic-inorganic nitrogen sources enhanced lipid production, with maximum lipid yields achieved using ammonium sulfate with yeast extract in R. kratochvilovae (1.219 ± 0.023 g/L) and with urea in R. paludigena (0.909 ± 0.050 g/L). Lipid content varied markedly with nitrogen regime, reaching 32.18 ± 1.023 % of cell dry weight in R. kratochvilovae and 42.51 ± 1.171% in R. paludigena. Overall, these results demonstrate that both nitrogen type and its combination influence biomass formation and lipid accumulation, highlighting the importance of selecting compatible nitrogen regimes to optimize microbial lipid production in applied bioprocesses.