Continuous Cultivation of Wautersia eutropha for the Production of A Biodegradable Polymer Poly-(B-Hydroxybutyrate)

* Author for correspondence: , Professor and Head, Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India. Tel: 91-11-26596109, Fax : 91-1126582282, Email : [email protected]. Abstract. Synthetic polymers or plastics have versatile qualities of strength, lightness, and protection and were initially developed for their durability and resistance to degradation. But these very desirable properties of recalcitrant plastics have now become their greatest problem and have made them an environmental hazard. As an alternative to plastics, polyhydroxyalkanoates (PHAs) were found which are 100% degradable polymers. These are polyesters of various hydroxyalkanoates, which are synthesized by numerous microorganisms as energy reserve materials when an essential nutrient such as nitrogen or phosphorus is available in limiting concentrations in the presence of excess carbon source. Polyhydroxybutyrate (PHB) is the most extensively studied member of PHAs. It has been repeatedly reported that the members of the genus Wautersia carry out extensive carbon uptake from media and lead to the accumulation of polyhydroxybutyrate bodies. However, the major problem associated with the industrial production of PHB is the high cost of production. Thus, in order to make the process continuous, cultivation of Wautersia eutropha was carried out in a 7 l bioreactor. The reactor was operated as batch for 15 h after which it was converted to fed-batch so that sufficient biomass and PHB could be produced. Thereafter, it was converted to continuous so that the PHB produced could be continuously maintained and released from the reactor. Media containing 90 g/l fructose and 2.5 g/l nitrogen was fed continuously at a dilution rate of 0.1 h-1. A steady state biomass of 30 g/l with a PHB concentration of 5.5 g/l was obtained. This resulted in a productivity of 0.55 g/l-h. Although the PHB content of the cells was only 20% but the conversion of the overall process to continuous mode made it very useful.