Mixing control as a device to increase PHB production in batch fermentations with co-cultures of Lactobacillus delbrueckii and Ralstonia eutropha

Poly(β-hydroxybutyric acid) or PHB is a bacterial polymer whose biocompatability, biodegradability and versatile properties make it an eco-friendly substitute for synthetic polymers. It is synthesized by Ralstonia eutropha from glucose as the main carbon source. However, better productivity is obtained through co-cultures of Lactobacillus delbrueckii and R. eutropha. PHB concentrations of 12 g/l have been reported in laboratory experiments and up to 40 g/l are theoretically achievable by fed-batch fermentation with programmable control of carbon and nitrogen feed rates. In this analysis, it is shown that equally high yields are possible in simpler batch fermentations by controlling the mixing intensity. Since mixing in large bioreactors is inherently incomplete, the present approach allows this nonideal feature to be gainfully utilized.