90
Chapter 3
Determine the elemental composition of the ash-free biomass and its formula weight per
C-atom. Calculate
Yn
in C-moles (C-mole)'1
.
b.
Calculate the oxygen consumption
(moles 0 2 (C-mole ethane)'1
when it is assumed
that C 02 is the only metabolic product (apart from H20). Write the stoichiometry for
conversion of ethane to SCP.
c.
Measurements show that 10.44 g DW is formed per mole 0 2 consumed. The yield
Y„
is
that calculated above, but the value of RQ is 0.3805. Show that an extra metabolic
product must be formed besides C 02 (and H20). Determine the degree of reduction of
this extra metabolic product. Using your general chemical knowledge you should be able
to identify the extra metabolic product.
Problem 3.3 Production of Penicillin V
Fig. 2.8 recaptures the biosynthesis of penicillin. In the last step of the pathway phenoxyacetic acid
forms an amide with the amino group of 6-APA. Penicillin V can also be formed directly from
isopenicillin N by an exchange of the side chain L-a aminoadipic acid with phenoxyacetic acid. Glucose
(
5
) is the limiting substrate. In a long series of metabolic reactions the three precursor metabolites shown
on Fig. 2.8 at the entry to the penicillin synthesis pathway are finally produced from glucose. Another
substrate is phenoxyacetic acid (j|) which is fed continuously to the reactor with the other substrates
(glucose, ammonia, SO*2
', PO^, minerals etc. in an ideal case. In industry a much cheaper carbon and
nitrogen source is often in part of the fermentation as described in Section 2.2.2). The molecular formula
for penicillin is C|6H|S0 4N2S. What is the molecular formula for phenoxyacetic acid?
a.
On a C-mole basis what is the yield coefficient
Rewrite
Y ^
in g g'1
b.
The composition of
Penicillium chrysogenum
is
X
= CHi
64
O
0
.
52
N
0
i
6
S
0
.
0046
P
0
.
0054
- Determine the
oxygen requirement
if
= 0.127 and
Yv =
0.194. Also find RQ.
c.
Make the assumption that during a fed-batch cultivation of penicillin
rp
will always be
proportional to
rx =
It. Discuss whether this assumption appears to be reasonable. If the
assumption holds then what would be the effect on the specific penicillin production rate if
during the cultivation
YM
starts to increase.
d.
On line RQ measurement show that during the first 120 hours of the production phase (after
biomass has been formed during an initial batch phase) RQ = 0.95 to 1.15 with considerable
scatter of the data. After 150 hours when growth of the fungus has virtually ceased RQ increases
rapidly above 1.20. Discuss probable reasons for this observation. Is it due to break-down of the
assumption in question c? Are other products formed? Could there be some straightforward
experimental error?
Problem 3.4 Checking an anaerobic mass balance for cultivation of
S. cervisiae.
In a steady state, strictly anaerobic chemostat with
V
= 1
L the yeast
S. cerevisiae
grow on a sterile
medium with 23 g L'1
glucose and 1 g L'1
NH3. The feed rate is v = 0.1 L h l. The biomass composition is
X =
C H 1i76O o,56No.[7.
The effluent from the bioreactor has the following composition in g L'1: Glucose
(s),
0.048; ammonia
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