56
Chapter 3
Table 3.2 Elemental composition of biomass for several microbial species.
Microorganism
Elemental
comoosltion
Ash content
<w/w %t
Condition
Candida utilis
CHi.aOo.4sNo.,,
7.0
Glucose limited, £>=0.05 h
"1
CHi.stOomNojo
7.0
Glucose limited, £>=0.45 h
' 1
CH
1
.
83
o
0
J
4
N
0.10
7.0
Ammonia limited, 2XJ.05 h l
CH
187
O
0
.J
6
N
0.20
7.0
Ammonia limited, Z>=0.45 h
' 1
Klebsiella aerogenes
CH
17
JO
0
.
43
N
0.22
3.6
Glycerol limited, £M).10 h
' 1
CH
1
.
73
O
0
.
43
N
0.24
3.6
Glycerol limited,
D=
0.85 h
' 1
CH i .
75
Q
0
.
47
N
0
. (7
3.6
Ammonia limited, Z>=0.10 h
1
CH
1
.
73
O
0
.
43
N
0
.24
3.6
Ammonia limited, £>=0.85 h
' 1
Saccharomyces cerevisiae
CHi.jîOojgNoift
7.3
Glucose limited, Z>=0.080 h
' 1
CHi.tjOo
.6oNo 19
9.7
Glucose limited, £>=0.255 h
' 1
Escherichia coli
CH
1
94
O
0
.J
2
N
0
.
25
P0,025
5.5
Unlimited growth
CH
1
.
77
O
0
.
49
N
0
.
24
P 0.013
5.5
Unlimited growth
CH
1
j
3
O
0
.j
0
N
0
.
22
P 0,021
5.5
Unlimited growth
CHi.960o.SjNaijP 0.022
5.5
Unlimited growth
Pseudomonas fluorescens
CH] »Oo.jjNo.2jP0.021
5.5
Unlimited growth
Aerobacter aerogenes
CHl.aOojjNo.26P0.024
5.5
Unlimited growth
Pénicillium chrysogenum
CH
1
.
64
O
0
.J
2
N
0.16
7.9
Unlimited growth
Aspergillus niger
CHl.TlO
0
.s
5
N
0
.17
7.5
Unlimited growth
Average
CHiaiOn^Nmi_____
6 .0
Compared to the formula weight and composition of biomass calculated from the macromolecular
composition (3.19) the compositions listed in Table 3.2 seem to contain an added 0.1 H20 per C-
atom. Tentatively this could be ascribed to a systematic error in the elementary analysis: many of
the macromolecules contain strongly bound water, which is not completely released when the
sample is dried before combustion. When the composition (3.19) is rescaled by adding 0.1 H20 per
C atom one obtains the average in Table 3.2 or
2r=CHl8O0JN0.2
(3.20)
which corresponds to a formula weight o f ^ = 2 4 .6 g (C-mole biomass)'1. Unless otherwise stated
we shall throughout the book use (3.20) as the “standard” formula for biomass. Eq. (3.20) is,
however, only applicable in “normal” fermentations where the carbon source is the limiting growth
factor.
As indicated in Table 3.2 the biomass composition is dependent on the growth conditions. This is
further illustrated in Fig. 3.3, which shows results of an anaerobic yeast fermentation carried out in
a batch reactor where nitrogen limitation sets in at 20 hours after the start of the fermentation. The
cells cannot divide when the nitrogen source is used up, but they can still accumulate storage
carbohydrates by polymerization of the substrate, glucose. Consequently the biomass concentration
keeps increasing until all the glucose is used up. Assuming that no “active”, i.e. N-containing
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