Two-stage syngas fermentation into microbial oils and β-carotene with Clostridium carboxidivorans and engineered Yarrowia lipolytica

Abstract

An engineered Yarrowia lipolytica strain was able to simultaneously accumulate microbial oils and β-carotene from both acetic and butyric acids produced from syngas fermentation by Clostridium carboxidivorans, through the Wood-Ljungdahl pathway, with CO and CO2 as carbon sources. It was first determined that Y. lipolytica showed no inhibition at concentrations < 16 g/L of a mixture of VFAs (Volatile Fatty Acids) containing acetic, butyric, and even hexanoic acids. The yeast was then grown in a bioreactor with a culture medium derived from acetogenic syngas (CO, CO2, H2) fermentation containing all three acids. Y. lipolytica consumed a total of 91 g/L VFAs, progressively supplied through eight successive additions of these acids to the reactor. A maximum lipid content of 36.18% g/g cell was achieved at 61 g/L VFAs consumed and with an airflow rate of 2.0 vvm. Besides, a total of 88.4 mg/g cell and 759 mg/L β-carotene content and concentration were achieved at about 80 g/L VFAs consumed and with a 2.0 vvm airflow rate. It was concluded that; a non-limiting air flow favors the metabolic pathway for β-carotene formation against lipid accumulation.