Xylose metabolism
Xylose
XR
NAD(P)H
NAD(P)+
XI
Xylitol
XDH
Bacteria
NAD+
NADH
Xylulose
Anaerobic fungi
Plants
Karhumaa (2007) PhD Thesis, Lund University
Fungi
Xylose fermentation
15
30
10
20
5
10
0
0
20
40
60
80
50
20
Xylose (g/l)
40
XR-XDH
0
100
15
30
10
20
5
10
0
0
20
40
60
Karhumaa et al (2007) Microb Cell Fact Feb 5; 6(1):5
80
0
100
Product (g/l)
XI
Xylose (g/l)
40
Product (g/l)
20
50
Xylose
Ethanol
Xylitol
Glycerol
Arabinose fermentation
L-Arabinose
NAD(P)H
XR
NAD(P)+
L-Arabinose
L-Arabitol
NAD+
AraA
L-ADH
NADH
L-xylulose
L-Ribulose
AraB
NADPH
ATP
L-XR
NADP+
ADP
D-xylitol
L-Ribulose -5 P
AraD
D-xylulose-5-P
NAD+
XDH
NADH
XK
D-Xylulose
ADP ATP
Bacteria
Fungi
Karhumaa K (2006) PhD thesis, Lund University
Arabinose + xylose
co-fermentation I
D-xylose
L-arabinose
Bacterial
arabinose
pathway
NAD(P)H
AraA
XR
L-ribulose
AraB
NAD(P)+
xylose
NAD+
pathway
D-xylitol
ATP
XDH
NADH
D-xylulose
L-ribulose-5-P
XK
AraD
ATP
D-xylulose-5-P
Ethanol
Becker and Boles (2003) Appl Environ Microbiol 69:4144-4150
Karhumaa et al. (2006) Microbial Cell Factories 5:18
Fungal
Arabinose-xylose co-fermentation
20
g/l
15
glucose
xylose
arabinose
arabitol
xylitol
ethanol
10
5
0
0
20
40
60
80
100
time (h)
Karhumaa et al. (2006) Microbial Cell Factories 5:18
Arabitol formation
D-xylose
L-arabinose
XR
AraA
L-ribulose
AraB
NAD(P)H
Km arabinose = 75 mM
NAD(P)+
Km xylose
XR
L-arabitol
D-xylitol
NAD+
ATP
XDH
NADH
D-xylulose
L-ribulose-5-P
XK
AraD
= 95 mM
Rizzi et al. (1989) Appl Microb
Biotechnol 29:148
ATP
D-xylulose-5-P
Ethanol
Karhumaa et al. (2006) Microbial Cell Factories 5:18
Oxygen
Fonseca et al (2008) AEM
(in press)
13C-NMR
pH
5.5
6.5
Experimental conditions
- High density suspension
- Resting cells
- 20 mM L-[2-13C]Arabinose
- Aerobic conditions (O2)
- 30 0C
- pH 5.5
T
Detection zone
50 mL Bioreactor
NADPH NADP
NAD
NADH
NAD
NADH
NAD
NADH
NAD(P)
NAD(P)H
NAD
NADH
NADP
NADPH
NADP
12C
ATP
ADP
ADP
PPP
13C
12C
ATP
or 13C
Pi
NADPH
The real world!!!
Raw
material
Pretreatment
Enzymatic
hydrolysis
SSF
Fermentation
Distillation
Lignin
Ethanol