Mass production of poly(3-hydroxybutyrate) by fed-batch cultures of Ralstonia eutropha with nitrogen and phosphate limitation

Abstract

For mass production of poly(3-hydroxybutyrate) (PHB), high cell density cultures of Ralstonia eutropka were carried out in 2.5-1 and 60-1 fermenters by two fed-batch culture techniques of nitrogen and phosphate limitation. When the nitrogen limitation technique was employed using both an on-line glucose monitoring and control system, a high concentration level of PHB (121 g/l) was obtained in the small-scale fermenter of 2.5 1. However, the PHB concentration obtained in a large-scale fermenter of 60 1 only turned out to be 60 g/l. In contrast, when another fed-batch culture technique of the phosphate-limitation employing dissolved oxygen (DO) stat glucose feeding was used, a large amount of PHB was successfully produced in both 60-1 and 2.5-1 fermenters. In a 2.5-1 fermenter, concentrations of PHB and cells obtained in 58 h were 175 and 210 g/l, respectively, which corresponded to the PHB productivity level of 3.02 g/l/h. In a 60-1 fermenter, a final cell concentration of 221 g/l and a PHB concentration of 180 g/l with PHB productivity level of 3.75 g/l/h were obtained in 48 h. PHB content and yield from glucose were 81% and 0.38 g PHB/g glucose, respectively. These data suggest that the phosphate limitation technique is more effective compared to nitrogen limitation in the mass production of PHB by R. eutropha of a large scale.