Inexpensive fed-batch cultivation for high poly(3-hydroxybutyrate) production by a new isolate of Bacillus megaterium

This research aimed at increasing the cell density and production of the homopolymer polyhydroxybutyrate (PHB) by Bacillus megaterium BA-019, using renewable and inexpensive bioresources as a substrate. A higher cell density and a greater PHB production level were obtained by using sugarcane molasses and urea as carbon and nitrogen sources, respectively. The limitation of nitrogen at a C/N molar ratio of 25 resulted in enhanced cell growth and PHB production in batch cultures. Fed-batch cultivation with the feeding nutrient composed of MSM with sugarcane molasses, urea and trace elements, and controlled by a pH-stat feeding control, lead to a significantly enhanced cell concentration and PHB production. The optimal feeding medium in this system required a higher total sugar concentration (400 g/l) and a C/N molar ratio of 10 mol/mol. Under these conditions the highest attained cell mass (72.6 g/l DW) and PHB content (42% of cell dry wt) were achieved in a short cultivation time (24 h), leading to improved PHB productivity (1.27 g/l/h). However, dissolved oxygen was limiting and thus the system is likely to be suboptimal and capable of even further improvements to the PHB production rate. (C) 2008, The Society for Biotechnology, Japan. All rights reserved.