Evaluation of Lipid Accumulation From Cellulosic Sugars by Mortierella Isabellina for Biodiesel Production

Mortierella isabellina ATCC42613, a filamentous fungus, was used to assess the lipid production on different carbon sources including glucose, xylose, sulfuric acid and sodium hydroxide treated corn stover enzymatic hydrolysate. The yield of lipid accumulated in fungal biomass kept constant for both glucose (0.41-0.44 g/g biomass) and xylose (0.39-0.44 g/g biomass) as carbon sources with the initial glucose and xylose concentrations varying from 28g/L to 92g/L. The data showed lipid accumulation was independent of carbon to nitrogen ratio from 66 to 309 indicating that this fungus can be cultivated under nitrogen rich medium to increase productivity since microorganisms grow slower in nutrient limited medium. In addition, the lipid conversion yield from xylose was high resulting in a lipid production of 8.8g·L-1, the highest production yet for fungal lipid grown on xylose medium to date. For mixed substrates, diauxic growth was observed as glucose and xylose were consumed subsequently. Lipid accumulation from sulfuric acid and sodium hydroxide treated corn stover enzymatic hydrolysate using a filamentous fungus Mortierella isabellina was investigated for the first time. Sulfuric acid pretreated corn stover enzymatic hydrolysate exhibited quite similar biomass and lipid production compared to synthetic medium. While sodium hydroxide pretreated corn stover enzymatic hydrolysates provided a bit inferior performance compared with mimic sugar medium. Lipid profile analysis showed that intracellular fatty acid composition remained relatively constant at each incremental sugar level for both xylose and glucose cultures. The major fatty acids in each culture were C16:0, C18:1, and C18:2. Predicted biodiesel properties such as iodine value, saponification, and higher heating values analyses indicated the consistence of intracellular fatty acid compositions with jatropha, palm, soybean, and sunflower oils. These results elucidate the great possibility of utilization of filamentous fungal fermentation to accumulate lipids from lignocellulosic biomass for biodiesel production.