Lipid production by Mortierella isabellina from pretreated corn cobs and effect of lignocellulose derived inhibitors on growth and lipid synthesis

High production costs of microbial lipids can be reduced by using available and cheap lignocellulosic biomass. The present study optimizes the cultivation conditions of oleaginous fungus Mortierella isabellina and lipid production in corn cobs hydrolysate regarding initial carbon to nitrogen ratio (C:N) in the growth medium, a pretreatment method and, inoculum type. Additionally, we studied the effect of the most abundant lignocellulose-derived inhibitors on lipid synthesis and fungus growth. Low C:N ratios from 5 to 25 mol mol−1 stimulated the fungus growth, while C:N ratios above 50 mol mol−1 gave rise to lipid accumulation. Corn cobs were subjected to dilute acid and alkali pretreatment, using 0.369 g of sulphuric acid and 0.16 g of sodium hydroxide per gram of lignocellulosic biomass, respectively. Growth media based on hydrolysate of alkaline pretreated corn cobs has proved suitable for growth and lipid production. Lipid yield and lipid concentration was 0.13 g g−1 and 8.40 g L−1, respectively. The most toxic inhibitors generated during pretreatment were phenolics, followed by furan aldehydes and aliphatic acids. Using vegetative mycelium instead of spores as inoculum helped cells to overcome the inhibition effect by 5-hydroxymethylfurfural and furan.