C. butyricum is a gram-positive and strict anaerobic bacteria
strongly established as good H2 and butyrate producer [34,35]
from a vast array of carbohydrates, including starch [36].
Consequently, the strain C. butyricum DSM 10702 was also tested
in this study. BioH2 production from glucose, xylose and fructose
by C. butyricum achieved 472, 424 and 468 mL/g, respectively
(Fig. 1b). These values correspond to H2 yields of 3.47, 2.60 and
3.44 mol H2/mol sugar, respectively, confirming the strain adequacy for bioH2 production. The fermentation of starch would be
of utmost importance, since it is known that not all clostridia
strains are able to ferment raw starch. In this study, C. butyricum
attained a maximum H2 production of 468 mL/g or 3.20 mol
H2/mol glucose equivalents from that substrate. This value is 33%
higher than the volumetric production from Cassava starch by dark
fermentation with a mixed anaerobic bacterial community mainly
composed by Clostridium species [12]. Conversely, xylan and cellulose did not support a significant H2 production by C. butyricum
(Fig. 1b). Considering the characteristics of S. obliquus biomass,
the results obtained show that C. butyricum seems to be an excellent H2 producer for the mentioned biomass.