Enhanced lipid and β-carotene production in fas-knockout Mucor circinelloides by co-supplementation of sodium citrate and soybean oil

Two fatty acid synthase genes (fas1 and fas2) were individually deleted in oleaginous fungus Mucor circinelloides WJ11 in our previous work. In this study, an in-depth analysis on supplement of sodium citrate and soybean oil to achieve high yields of lipid and β-carotene was investigated in fas-knockout M. circinelloides strains. The effects of different concentrations of sodium citrate or soybean oil on cell growth, lipid and β-carotene accumulation in fas-knockout strains were measured, and it was determined that the optimal addition concentrations of sodium citrate and soybean oil were both 15 g/L. Combination use of 15 g/L sodium citrate and 15 g/L soybean oil as additives had a synergistic effect on the cell growth, lipid and β-carotene accumulation in fas-knockout strains, especially for the Mc-fas2Δ strain. The maximum yields of biomass, lipid and β-carotene in Mc-fas2Δ reached 19 g/L, 33.6% and 328 µg/g respectively, which were 25%, 34.4% and 2.2- fold higher than those of the control strain. Moreover, the transcriptional levels of the key genes involved in fatty acid and β-carotene synthesis in the engineered strains were significantly upregulated after adding sodium citrate and soybean oil. This is the first study to systematically evaluate the combined effects of soybean oil and sodium citrate on both lipid and β-carotene production in fas-knockout M. circinelloides strains.