5.1 Metabolic Oxygen Demand

Metabolic oxygen demand of an organism depends on the biochemical nature of the cell and cultivation conditions. Oxygen need is usually satisfied in most cells if the dissolved oxygen concentraiton in the medium is kept at about 1 mg/L. If the oxygen level is allowed to fall far below this value, oxygen consumption rate decreases with concomitant decrease in biochemical energy production, and as a result cell growth rate also decreases. We described this behavior in Section 4-4. The value of oxygen concentration above which growth rate is at the maximum was described as the critical oxygen concentration, . Characteristic values are summarized in Table 5-1.

Table 5-1 Critical Oxygen Concentration

Organism

in mg L-1

E. coli at 37 C

0.26

S. cerevisiae at 30 C

0.13

Penicillium sp at 24 C

0.78

The oxygen requirement for growth is expressed best in the the parameter, yield coefficient, YX/O2. It represents the amount of oxygen required to grow one gram of cells. Typical values summarized in Table 5-2, show that approximately 0.7 to 1 g of oxygen is needed to produce 1 g of cells. In the same table respiration quotient is also included.

Table 5-2 Stoichiometric Oxygen Demand &Respiration Rate

Organism

Substrate

YX/O2
[g (g cell)-1 h]
qO2
[g O2 (g cell)-1 h]

E. coli

Glucose

1.1

0.20

S.cerevisae

Glucose

0.98

0.30

Candida utilis

Glucose

1.32

Pennicillium sp.

Glucose

1.35

0.18

Hybridoma

CHO cell line