Inhibition factors of hydrogen production by the
extreme thermophile Caldicellulosiruptor
saccharolyticus
E.W.J. van Niel1, P.A.M. Claassen2 and A.J.M. Stams1
Introduction
At a partial H2 pressure >1.7·104 Pa also lactate starts
Model
fittingaccording to:
being produced
The inhibition kinetics was determined in growing
- +4H
+
acetate,
cultures
with
various
inhibitors (H2, sucrose,
C12H22O11
+ H
2O → 4 CH3CHOHCOO
lactate, and NaCl). The data were fitted according to
Han & Levenspiel (1988) using the least squares
method:
rH2 =
rH2max·( S/(KS+S))·(1-
Results
I/ICRIT
)n
The inhibition kinetics are shown in Fig. 1 and parameter
values in Table 1. High concentrations of sodium acetate
caused lysis of 20% of the culture (Fig. 2).
200
Biomass
H2
150
600
100
300
Acetate
Sucrose
50
0
Concentration (mmol/L)
biomass (mg DW/L)
900
0
0
20
Fig. 3
40
60
80
Time (h)
r(H2) (mmol H2/h)
0.4
0.2
20000
40000
60000
0.1
0.05
0
0
partial hydrogen pressure (Pa)
20
40
60
80
100
4.5
1.6
3
1.5
0
1.2
0.8
0.4
0
0
100
200
300
400
0
100
Sodium acetate (mM)
200
300
Han & Levenspiel (1988) Biotechnol Bioeng 32:430.
Joliffe et al. (1981) Cell 25:753.
1Laboratory
for Microbiology, Wageningen University, Hesselink van
Suchtelenweg 4, 6703 CT Wageningen, The Netherlands
for Agrotechnological Research (ATO), Industrial (Agro) biotechnology
Subdivsion, P.O. Box 17, 6700 AA Wageningen, The Netherlands
2Institute
400
NaCl (mmol/L)
Fig. 1
Table 1. Parameter values.
30
20
Inhibitor
ICRIT
(mM)
n
(-)
H2
Sucrose
Na-acetate
Sodium
0.1
292
370
255
3.1
1.6
1
1
10
0
-10
0
100
200
300
-20
Fig. 2
Sodium acetate (mM)
According to model fitting, growth in batch culture was
inhibited by sodium acetate. Figure 3: data points are fitted
with the equation:
X = X0 ·exp{(µMAX·S/(KS+S))·(1- A/ACRIT)·(t-t0)}
with X = biomass, µMAX= 0.125 h-1, KS = 2.3 mM, A = acetate (mM),
ACRIT= critical acetate (370 mM), t = time (h)
Yield factors found: YSX = 45.1 g DW/mol sucrose; YATP = 14.1 g/mol ATP
(under assumption: 1ATP/acetate)
Conclusions
- C. saccharolyticus is about 10 times less sensitive to H2 than other
References
120
Sucrose concentration (g/L)
r(H2) (mmol/h/L)
+ 4 CO2 + 8 H2 +
0.6
0
r(H) mmol/h/L
C12H22O11 + 9 H2O → 4 CH3
4H+
COO-
0.15
0
Increase in OD (%)
Little is known yet about the metabolic properties of
(hyper)
thermophilic anaerobes. We studied the effect of
various
compounds present in the culture, on the production of
H2
by Caldicellulosiruptor saccharolyticus. Sucrose was
used
as a model substrate. It is mainly fermented according to:
r(H2) (mmol H2/h/L)
0.8
thermophiles described in the literature
- H2 production is influenced most by acetate and Na+
- Like observed with Bacillus subtilis (Joliffe et al, 1981), acetate and/or
Na+ at high concentrations cause autolysis
- Unlike B. subtilis, lysis is restricted to only about 20% of the culture