STOICHIOMETRY OF MICROBIAL GROWTH AND

PRODUCT FORMATION

PTT 203 Biochemical Engineering

W E E K 1 3BY:

M A D A M N O O R U L N A J WA D I YA N A YA A C O B

Lets Try

Assume that experimental measurement for certain organisms have shown that cells can convert two-thirds (wt/wt) of the substrate carbon (alkane or glucose) to biomass

a) Calculate the stoichiometric coefficients for the following biological reactions:

Hexadane: C16H34 + aO2 + bNH3 c (C 4.4 H 7.3 N 0.86 O 1.2) + dH2O + eCO2

Glucose: C6H12O6 + aO2 + bNH3 c (C 4.4 H 7.3 N 0.86 O 1.2) + dH2O + eCO2

b) Calculate the yiels coeeficients Yx/s (g dw cell/g substrate), Yx/o2 (g dw cwll/ g O2)

7.4 Theoretical Predictions of Yield Coefficient

In aerobic fermentation, the growth yield per available electron in oxygen molecules is approximately 3.14 gdw/electron when ammonia is used as the nitrogen sources.

The number of available electron per oxygen molecule is four.

When the number of oxygen molecules per mole of substrate is known, the growth yield coefficient Yx/s can easily be calculated

Consider the aerobic catabolism of glucose:C6H12O6 + 6O2 6 CO2 + 6 H2OThe total number of available electrons in 1

mole glucose is 24.The cellular yield per available electron is

Yx/s = 24 (3.14)= 76gdw cell/molThe predicted growth yield coefficient is

Yx/s= 76/180= 0.4 gdw cell/g glucose

The ATP yield (Y x/ATP ) in many anaerobic fermentation is approximately 10.5 gdw cells/ mol ATP. In aerobic fermentation this yield varies between 6-29.

When the energy yield of metabolic pathway is known (N moles of AT produced per gram of substrate consumed), the growth yield Yx/s can be calculated using the following equation

Y x/s = Y x/ATP N

Do it Yourself

Example 7.2