The hydrogen yield (YH2) was expressed as a percentage of the H2 gas produced per CO consumed (mol/mol).
Acetate was the major product with 56.58 mmol produced per mol of CO consumed, followed by ethanol (38.21 mmol produced per mol of CO consumed), butyrate (36.45 mmol produced per mol of CO consumed) and butanol (8.91 mmol produced per mol of CO consumed).
It co-consumed xylose in aerobic and anaerobic glucose-limited chemostat cultures at rates of 0.33 and 0.73 mmol (g biomass)−1 h−1, respectively.
Additionally, the JX123-BTT strain co-consumed glucose, cellobiose, and xylose under continuous culture conditions at a dilution rate of 0.05 h−1 and produced ethanol resulting in 0.38 g/g of ethanol yield and 0.96 g/L⋅h of productivity.
Furthermore, the overexpression of S. cerevisiae ALD6, IDP2, or S. stipitis ZWF1 coding for cytosolic NADP+-dependent dehydrogenases increased the intracellular NADPH availability of the D-10-BT strain, which resulted in a 37 63% improvement in xylitol productivity when cellobiose and xylose were co-consumed.
After mannose was exhausted from the medium, the relatively low amount of galactose (4 g.L−1) was co-consumed together with xylose (data not shown).
Therefore, in batch cultures it is difficult to analyze whether those strains are able to co-consume the sugars or not.
Ethanol productivity would benefit from the design of stable S. cerevisiae strains that would co-consume xylose and arabinose, since both sugars are present in lignocellulosic feedstock.
The ISA1307 strain and also other strains belonging to Z. bailii species are known to have an alleviated Crabtree effect, being able to co-consume glucose and other carbon sources.
Importantly, the N367A mutation in Hxt36 enables the cells to co-consume D-glucose and D-xylose, likely because it improved the Km ratio for xylose over glucose (Table 1) while still maintaining a good Vmax.
The xylose was co-consumed along with glucose for more than 100 h.
