The solid state ethanol fermentation by F. velutipes was performed for ammonia treated rice straw. Solid state cultivation has a large merit to decrease the ethanol production cost. But it has demerit on the saccharification of biomass. As shown in Fig. 7A, saccharification of biomass at high concentration is quite difficult. Significant amount of cellulase is necessary to obtain enough level of saccharification, and saccharification yield do not increase in proportion to the amount of cellulase if increased the amount of cellulase. Furthermore, saccharification yield will be significantly decreased under the high substrate condition. The hydrolysis rate of 30% w/v biomass was very low (less than 10%). In contrast, ethanol yield was equivalent to 80-90% of hydrolysis rate so that the merit of our process using F. velutipes was proven (Fig. 7B). In the case that enzymes were not added, ethanol production by F. velutipes was only 0.026 l/kg of dry biomass, equivalent to a theoretical ethanol recovery rate of 5.9% from total hexose. In contrast to no enzymes addition, in the case that 1 and 5 mg/ g product of enzymes were added to the fermentation, ethanol production after 15 d by F. velutipes was 0.26 and 0.34 l/kg of dry biomass, respectively. The ethanol conversion rates of 1 and 5 mg/g product enzymes addition were 61.6% and 77.8% for total hexose, respectively. The maximum weight loss was approximately 70% in the case that no enzymes were added to the fermentation, while the maximum weight loss for enzyme addition of 1 and 5 mg/ g product were approximately 90% and 96% respectively (data not shown).

These results suggest F. velutipes has favourable properties for CBP. It could be expected that development of novel bioethanol production process by using F. velutipes.

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Fig. 7. Saccharification and ethanol production at high biomass concentration