Comparison of the growth of filamentous fungi and yeasts in lignocellulose-derived media

Five microorganisms of potential interest for on-site enzyme production in lignocellulosic biorefineries were evaluated with regard to inhibitor tolerance and nutrient utilization. Prehydrolysate and hydrolysate of Norway spruce were used in concentrations of 25%, 50%, 75% and 100% and compared to reference media without fermentation inhibitors. Monosaccharide sugars, oligosaccharides, and small aliphatic acids were monitored to investigate nutrient utilization in the lignocellulosic media. The microorganisms studied were the filamentous fungi Aspergillus niger and Trichoderma reesei and the three yeasts Pichia pastoris, Saccharomyces cerevisiae, and Yarrowia lipolytica. All five fungi had the ability to grow in media with 25% prehydrolysate or 25% hydrolysate. The S. cerevisiae strain had the highest inhibitor tolerance of the microorganisms studied and grew in media with 50% prehydrolysate or 75% hydrolysate. In medium with 25% prehydrolysate A. niger and Y. lipolytica gave high biomass yields of 0.46 and 0.32 g/g on initial carbon source, which corresponded to 0.46 and 0.43 g/g on consumed carbon source, respectively. The ethanol yield on consumed carbon source in 50% hydrolysate was 0.29 g/g for P. pastoris and 0.33 g/g for S. cerevisiae. The capability of A. niger to utilize a broad range of nutrients appears especially useful for enzyme production using residual streams. The high tolerance against inhibitors exhibited by S. cerevisiae could be particularly useful in a consolidated bio-process where the fermenting microorganism contributes also by producing enzymes.