To determine whether increasing the amount of cellulase affects
glucose conversion and subsequent ethanol productivity, we
increased the load of T. reesei culture supernatant to 15 mg and
carried out SSF with varying amounts of yeast, supplemented by
heterologous expression of AaBGL1 or addition of Novozyme 188.
Interestingly, we observed a marked difference in the manner in
which the sugars were metabolized between AaBGL1 and Novozyme
188 at this T. reesei culture supernatant protein load. The
pattern was very different with immediate glucose consumption in
the presence of Novozyme 188 (Fig. 6A). Ethanol production of
recombinant AaBGL1 increased to 13.3 g/L, corresponding to 54.6%
ethanol production efficiency at 72 h of SSF, and 10.5 g/L of glucose
remained in the supernatant at 72 h of SSF. With Novozyme 188
and S. cerevisiae INVSc1, the highest ethanol concentration obtained
was 17.5 g/L, corresponding to 72% ethanol production efficiency
at 24 h of SSF, with almost complete glucose consumption
by the yeast (Fig. 6A and Table S4). However, the ethanol produced
by Novozyme 188 and S. cerevisiae INVSc1 decreased after 24 h of
SSF. In contrast, complete glucose consumption of recombinant
AaBGL1 was observed at 48 h of SSF when a higher dcw of yeast
(15 mg) was used (Fig. 6B).