Environmental Engineering Reference
In-Depth Information
TABLE 13.9 Major sugar composition (wt%) of common
agricultural lignocellulosic feedstocks
a
Wheat straw
Bagasse
Sugar beet pulp
Hexoses
(C
6
)
Glucose
32.6
39.0
24.1
Mannose
0.3
0.4
4.6
Galactose
0.8
0.5
0.9
Pentoses
(C
5
)
Xylose
19.2
22.1
18.2
Arabinose
2.4
2.1
1.5
Other components
44.7
35.9
50.7
a
Adapted from Van Maris et al. (2006).
Hexose pathway in
S. cerevisiae
d-xylose
d-mannose
d-glucose
d-galactose
Glucose-6-P
Xylose pathway in
fungi and yeast
Mannose-6-P
Xylose pathway in
engineered
S.cerevisiae
Fructose-6-P
Xylitol
Fructose-1,6-biP
d-xylulose
Pentose
phosphate
pathway
DHAP
G-3-P
d-xylulose-5-P
Glycerol
PEP
Pyruvate
Ethanol
FIGURE 13.10
Simplified hexoses and xylose pathways for the production of ethanol.
the workhorse, as described in Section 13.2. The main features of
S. cerevisiae
for
industrial ethanol production are (i) high ethanol productivity, (ii) high tolerance to
ethanol, and (iii) tolerance to relatively low pH. The last two features are especially
relevant for minimizing contamination by other microorganisms. This allows for the
use of low-cost equipment and microorganism recycle, among others. Additionally,
S. cerevisiae
is able to ferment other hexoses (mannose and galactose) to ethanol (see
Figure 13.10), and it shows tolerance to inhibitory compounds formed during pretreat-
ment. Native strains, however, are unable to utilize xylose for growth or fermentation
to ethanol.
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