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Degree of oxygen satisfaction

Fig. 9.2. The effect of dissolved oxygen on the production of amino acids by Brevibacterium flauum (Hirose and Shibai, 1980).

Degree of oxygen satisfaction

Fig. 9.2. The effect of dissolved oxygen on the production of amino acids by Brevibacterium flauum (Hirose and Shibai, 1980).

DAOC did not accumulate at low oxygen concentrations and, thus, it appears that the most oxygen sensitive step in the pathway is the ring expansion enzyme (expandase) resulting in the accumulation of penicillin N under oxygen limitation.

Erythrose 4-phosphate

Phenylalanine

.Phosphoenol pyruvic acid t

Acetyl-coenzyme A

Oxaloacetic acid

Citric acid

Aspartic acid

Lysine Threonine |

Isoleucine j

.Glutamic acid.

Glutamine Proline Arginine

Fig. 9.3. The biosynthetic routes to the amino acids phenylalanine, valine, leucine, lysine, threonine, /-leucine, glutamic acid, proline, glutamine and arginine in B. flavum.

The requirement for a high dissolved oxygen concentration by many fermentations has resulted in the development of process techniques to ensure that the fermentation does not exceed the oxygen-supply capabilities of the fermentation vessel. The oxygen demand of a fermentation largely depends on the concentration of the biomass and its respiratory activity, which is related to the growth rate. By limiting the initial concentration of the medium, the biomass in the vessel may be kept at a reasonable level and by supplying some nutrient component as a feed, the rate of growth, and hence the respiratory rate, may be controlled. These techniques of medium design and nutrient feed are discussed in Chapters 2 and 4 and later in this chapter.

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