Effect of oxygen on the fermentation performance of Candida intermedia: a study case for lignocellulosic bioethanol production

Conference poster, 2015

Microbial robustness is considered one of the remaining challenges for a cost-effective lignocellulosic bioethanol production. This concept stands for the efficient conversion of all sugars present in lignocellulose while dealing with the inhibitory compounds generated during biomass processing (furan derivatives, short chain organic acids and phenolic compounds) and fermentation (ethanol). In this context, efficient xylose conversion is crucial as it represents the second most abundant sugar in lignocellulosic biomass. We have isolated a clone of the non-conventional xylose-fermenting yeast species Candida intermedia that shows great potential for being a non-genetically modified alternative for lignocellulosic bioethanol production. To understand its potential for industrial use, we performed a thorough physiological investigation of the strain. In the present work, the fermentation performance of the isolated clone was evaluated in glucose/xylose medium under different oxygen-limiting conditions to promote ethanol production. When oxygen was supplied with a flow rate of 1 vvm and a concentration ranging from 1% to 21% in the gas flow, a xylose consumption rate of 0.10-0.78 g/L h was observed. After glucose depletion, ethanol concentration remained constant and only xylitol (0.34-0.61 g/g) and cell biomass were further produced. When no oxygen was supplied, a maximum xylose consumption rate of 0.53 ± 0.04 g/L h was observed. Furthermore, almost 90% of the initial xylose concentration was consumed within the first 48 h and ethanol was produced continuously, even after glucose depletion. Regarding xylitol accumulation, a yield of 0.14 ± 0.04 g/g was found at 48 h of fermentation. In brief, we can conclude that C. intermedia requires low oxygen concentrations for triggering ethanol production, and that the presence of even low amounts of oxygen further on in the process has a detrimental effect in the conversion of xylose to ethanol.