Two-stage continuous cultivation

Fig. 7. Scheme for a two-stage continuous cultivation technique. A = acid, 5 = base, M=medium, P = pump, S = substrate, Cl and C2 = base or acid flow, FI = culture flow, F2 = substrate flow, F3 = outflow, Z1 = medium flow... 

Table 5. Flow rates in a two-stage continuous cultivation of Paracoccus denitrificans with acetic acid as substrate ...

Mothes, G. and Acketmatm, J.U. (2005) Synthesis of Poly(3-hydroxybutyrate-co-4- hydroxybutyrate) with a target mole fraction of 4-hydroxybutyric add units by two-stage continuous cultivation of Delftia acidovorans P4a. Engineering in Life Sciences, S, 58-62. 

Third, as an alternative to the one-stage continuous cultivation technique, especially for the limitation-caused poly(3HB) synthesis discussed above, a two-stage method can be applied. The principle is shown in Fig. 7. 

A few other studies in two-stage continuous systems were conducted with other microorganisms. In the case of P(3HB4HB) production, Delftia acidovorans P4a was cultivated on mixtures of acetic acid and y-butyrolactone here, P(3HB4HB) copolymers with a molar fraction of 2.7-19% 4HB were obtained. The authors state that, especially in the case of toxic substrates like acetic acid and y-butyrolactone, the two-stage continuous production strategy is very convenient [132]. 

In order to reduce the overall cost, there has been many fermentation techniques developed to produce PHAs with high productivity and high yield such as batch, fed-batch and continuous cultivations [5, 13]. Two stage fermentation is the most common and highly productive method to generate high density culture as well as increased amount of PHAs. 

---