Effects of agitation and exogenous H2 on bioconversion of sugarcane bagasse into ethanol by Clostridium thermocellum ATCC 27405

Background: The production of ethanol by a Consolidated Bioprocessing (CBP) strategy, which simultaneously combines cellulase production, lignocellulosic biomass hydrolysis and fermentation of released sugars to ethanol in one bioreactor, is a promising technology for cost reduction in the biological processing of biomass, specially using agroindustrial residues. Clostridium thermocellum is an anaerobic, thermophilic, strictly fermentative gram positive bacterium that meets all the requirements for CBP. Results: Ethanol concentration obtained in the non-stirred fermentation process in flasks with raw bagasse was two times greater than that in the stirred system. The results observed using a pretreated sugarcane bagasse in non-stirred flasks regarding ethanol concentration, were slightly lower than with raw bagasse. The sparging of exogenous H2 into the medium at atmospheric pressure inside the bioreactor showed to be unfavourable to achieve higher ethanol yields. Conclusions: The strain investigated is a promising candidate for thermophilic fermentative ethanol production from dried ground raw sugarcane bagasse in a CBP strategy, although the alcohol concentrations need to be further improved. In future studies, it is recommended to investigate different modes of operation of the fermentation process, including pressurized conditions, as well as to use wet raw sugarcane bagasse aiming to achieve additional improvement in ethanol production and to reduce the costs of the process.

Cellulose hydrolysis and ethanol production by a facultative anaerobe bacteria consortium H and its identification / 生物工程学报

The recalcitrance of lignocellulosic biomass makes its hydrolysis by cellulases less effective, and the consolidated bioprocessing (CBP) strategy that combines enzyme production, cellulose hydrolysis and fermentation, particularly the synergetic role of different microbes in attacking cellulose component could be a solution. In this article, a facultative anaerobe microbial consortium named H was isolated, which exhibited high stability even after 30 subcultures, with pH ranging from 6 to 9. Within three days, 0.5 g filter paper immerged in 100 mL PCS buffer was completely degraded, and 1.54 g/L ethanol was produced, correspondingly. Further analysis on the component of the microbe consortium was carried out though 16S rDNA and DGGE, and Clostridium thermosuccinogene, Clostridium straminisolvens and Clostridium isatidis that can directly convert cellulose to ethanol were identified, indicating that Clostridium spp. played important role in cellulose degradation through the synergistic coordination of different species, and the characterization of the consortium will benefit the analysis of the underlying mechanisms as well as the optimization of the CBP process for more efficient cellulose degradation and ethanol production.