(463a) High Cell Density Fed-Batch Fermentation of Bacillus Megaterium for Enhanced Polyhydroxybutyrate Production From Sugarcane Molasses

Authors: 
Thongchul, N., Chulalongkorn University
Tolieng, V., Chulalongkorn University



Polyhydroxybutyrate (PHB) which belongs to the group of polyhydroxyalkanoates (PHAs) is one of the most well known compostable biopolymers. It is recognized as the completely biosynthetic polymer with the remarkable biocompatibility properties. PHB as the thermoplastics can be used in various applications including agriculture, marine, and biomedical fields. Due to its renewable property and similar characteristics to the petroleum based polymer (polypropylene), PHB has recently become more attractive.

PHB is commonly synthesized and accumulated by several microorganisms as the intracellular carbon and energy sources. Although PHB has the wide range application, the commercial market is still limited. This is because of the relatively high production cost compared to that of the commodity petroleum based plastics. Many efforts have been developed to reduce the production cost in order that PHB can be more competitive to the petroleum based plastics. Those include 3 major attempts: I. using the low cost feedstocks such as the renewable biomass locally available nearby the production site; II. screening and modifying the robust microorganisms that could rapidly synthesize and accumulate a large amount of PHB inside their inclusion bodies, and III. enhancing the fermentation and recovery processes to obtain high PHB recovery yield.

Bacillus megaterium BA-019 previously screened and identified in our lab is the promising PHB producer because it can produce and accumulate a large amount of PHB inside the cell. This strain has low nutrient requirements and it is also capable of utilizing the low cost substrates such as sugarcane molasses and urea. In this work, enhanced PHB production from low cost sugarcane molasses medium was observed in high cell density cultivation via fed-batch fermentation using the appropriate feeding method. The improved PHB production via high cell density cultivation of B. megaterium BA-019 with balanced initial total sugar concentration and carbon to nitrogen (C/N) weight ratio was observed. In the 10 L stirred fermentor operated at 30 °C, pH 7.0, 600 rpm, and 1.0 vvm air, with the initial total sugar concentration of 60 g/L and urea at the C/N weight ratio of 10:1, 32.48 g/L cell biomass with the corresponding PHB weight content of 26.94% and volumetric productivity of 0.73 g/L×h were obtained from batch cultivation. Continuing cultivation by intermittent feeding of the sugarcane molasses along with urea at the C/N weight ratio of 12.5:1 gave much improved biomass and PHB production (90.71 g/L biomass with 45.84% PHB content and 1.73 g/L×h PHB productivity). Similar biomass and PHB yields were obtained in the 90 L stirred fermentor when using the impeller tip speed as the scale up criterion. It is believed that with the results obtained from this study, further development of commercial PHB production will become more promising.

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