Process intensification through microbial strain evolution: mixed glucose-xylose fermentation in wheat straw hydrolyzates by three generations of recombinant Saccharomyces cerevisiae

Table 3 Physiological parameters of strains BP10001, IBB10A02 and IBB10B05 obtained from mixed glucose-xylose fermentation in 5% hydrolyzate _X

Parameter	BP10001	IBB10A02	IBB10B05
q_Glucose (g/g_CDW/h)	n.d.	n.d.	n.d.
q_Xylose (g/g_CDW/h)	0.15 ± 0.01	0.53 ± 0.05	0.71 ± 0.01
μ_max^a	0.09 ± 0.01	0.13 ± 0.02	0.43 ± 0.03
Y_Ethanol (g/g)	0.35	0.31	0.30
(Y_{Ethanol/available sugars} (g/g))^b	(0.18)	(0.25)	(0.29)
Y_Glycerol (g/g)	0.06	0.06	0.09
Y_Xylitol (g/g)	0.15	0.22	0.17
Y_Acetate (g/g)	0.04	0.06	0.05
Y_BM (g/g)	0.02	0.03	0.04
C-recovery (%)	98 ± 1	102 ± 1	96 ± 1

Data was obtained from two independent fermentations, mean errors of product coefficients were always below 11%. Fermentation time courses are shown in Figure 2. Fermentation in 5% hydrolyzate_X: glucose to xylose ratio of approximately 0.2.^a Determined in the first 4.5 hours of fermentation;^bY_{Ethanol/available sugars} = c (Ethanol produced in 100 h of fermentation)/c (Available glucose and xylose). Note that utilization of xylose was much lower in strain BP10001 than it was in the evolved strains. This affects the calculated ethanol yield coefficient based on total sugar (glucose and xylose) consumed. The ethanol yield coefficient was therefore also expressed based on total sugars available in the reaction, as shown in parenthesis. n.d., not detectable.

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