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.