76
Chapter 3
Example 3.9. Production of lysine from glucose with acetic acid as byproduct
L-lysine (CHt^O^N,^ - see Table 3.3.) can be produced from glucose in very high yields by aerobic
fermentation using the bacterium
Corynebacterium glutamicum
. With NHj as nitrogen source and a
standard biomass composition the stoichiometry of the total reaction is given in (1). Some carbon is lost to
the undesired byproduct acetic acid.
- C H 20 - Y snN H 3 - YS0O2 +YsxCH]&O05N a2 + Y CH 2nOv lN in + Y
CH 20 +
)
YsCc o 2 + yswh 2o =
0
There are 8 rates and 4 constraints. 4 rates can be calculated, and the formal method (3.33) is needed to
avoid algebraic errors.
Choose <7j,
qPl, qPl
and
as the four measured rates
V
r0
1
1
0"
(1
1
1
0"
f
0.1905
i
9
0.1905
-0.1905"
9,
3
1.8
0
2
2
7
3
2
0
-0.9524
__ 10
9
-0.9524
0.9524
9c
0
0.5
2
l
1
l
3
1
2
9P1
-0.0476
9
-0.0476
- 0.9524
k9 w)
,1
0.2
0
0;
l
I
0
0.4286
0
-0.4286
-0.5714
j
(
2
)
From equation (2) the yield coefficients in reaction (1) are obtained:
Y„
=0.1905 + | r w -0.19051;, -0.19057„
Y„
= 0.9524- f
-0.95241;, -0.95241;
Y„ =
0.0476 + 4
Ym
- 0.0476
Yn +
0.9524
Y„
<3)
Y„
=0.4286
-0.42861;,+0.57141;
It is easily proved that the carbon, nitrogen and redox balances close:
1 = ^ + ^ , + ^ + ^
^ « 0 . 2 ^ + ! ^
(4)
-4 r„ + 4 = 4 2 0 Y „ + 4 jrv i +4rvi
Note that the occurrence of a product (acetate) with the same formula per C-atom as a substrate (glucose)
does not disturb the calculations. When stoichiometric calculations such as these are made as a preliminary
to a process design it is of first importance to see whether a sufficiently high yield of the desired product
can be obtained to make the process economically viable.
Based on our simple stoichiometric model and assuming that
YK
must be positive (oxygen is also used to