Usage of the Fungus and the Bacterium in a Biorefinery System for Biochemical Production on Grass Hydrolysates.

Utilization of various biomasses as raw materials in biorefineries represents a promising alternative for the production of valuable chemicals and biofuels. This study investigates the potential of the fungus DSM 2158, cultivated on media containing the liquid phase of grass hydrolysates (LGH) and various nitrogen sources (yeast extract and corn steep liquor), for the production of valuable metabolites, such as ethanol, chitin, chitosan, and fatty acids. The ethanol yield varied depending on the cultivation media and conditions. The highest substrate-into-ethanol conversion coefficients (0.14-0.2 g g) were achieved during cultivation on the LGH medium containing 5 g L CSL in Erlenmeyer flasks and a bubble column bioreactor. In these cultivations, the highest fungal biomass concentrations (5.61-5.91 g L) were also observed. In flask cultivations, the highest content of total lipids in fungal dry biomass (15.76%) was observed. The obtained fungal biomass contained up to 22 fatty acids, with oleic acid (≈50%) being the most predominant. Chitin and chitosan yields were from 0.1 g g to 0.3 g g of dry biomass depending on the cultivation media and conditions. The residual media from the cultivation of were used for the growth of the non-sulfur purple bacterium DSM 2781. Cultivations of DSM 2781 on the residual media, in Erlenmeyer flasks and a stirred-tank bioreactor, resulted in a biomass yield of 0.50 to 2.26 g L. After extraction of bacterial biomass, total pigments (expressed as bacteriochlorophyll-a) were obtained in the range from 1.8 to 48.1 mg g dry biomass depending on the media and cultivation conditions. The highest titer of bacteriochlorophyll-a was achieved during cultivation on the exhausted LGH medium with 5 g L yeast extract. The established biorefinery system has to be optimized in order to reach capacity for transfer to a larger scale.