Effect of Adding Cellulose on Lipid Accumulation in Cellobiohydrolase and Delta-6 Desaturase Engineered Mucor circinelloides Strains

Despite microbial production of multifunctional gamma-linolenic acid (GLA) being an important and promising way, the high cost is still a major factor limiting industrial applications. Previously, we proposed a novel approach to promote the production of GLA from cellulose, a widely available and cheapest resource, by overexpression of the cellobiohydrolase (CBH2) and delta-6 desaturase (D6) in Mucor circinelloides. In the present study, an in-depth analysis of growth and lipid accumulation in engineered M. circinelloides strains using cellulosic substrate was to be explored. When cultivated in modified Kendrick and Ratledge (K and R) medium supplemented with the ratio of 1: 1 for glucose and carboxymethyl cellulose (CMC), the cellobiohydrolase and delta-6 desaturase overexpressing strains led to increases in the biomass (up to 10.4 g/L) and lipid yield (up to 2.6 g/L) of 68% and 2.2-fold, respectively, compared with that of the control strain. The yield of GLA in the cellobiohydrolase and delta-6 desaturase co-expression strains reached 415 mg/L, which was a remarkable increase of 3.1-fold compared to that of the control strain. These results proved that the introduction of CBH2 and D6 two key enzymes could significantly enhance the utilization of CMC and effectively convert cellulose into GLA by engineered M. circinelloides. This study provided a reference for the further potential application of the engineered M. circinelloides strains in the conversion of functional GLA from cellulose.