EN 18: PHA production from glycerol by bacillus megaterium DSM 90

Abstract

The use bio-plastics made from PHA is not common due to high cost of production. Bio-diesel’s by-product, glycerol, is increasingly looked into as the feedstock for PHA formation due to it being cheap and readily available. However, C:N ratio is widely regarded as one of the critical factor in PHAs production but the optimal ratio for different species may vary. Moreover, the highly reduced glycerol would result in NADH generation when it is converted into PHAs. It is not clear whether additional electron acceptor in the medium would consume NADH, enhancing the overall substrate utilization rate. Acetate, as the intermediate in the glycolysis, would have 3 sinks in the metabolic pathways: PHAs synthesis for carbon storage, biomass synthesis, and TCA cycle for energy generation. From all these aspects, acetate might stimulate cell growth or PHAs synthesis. Therefore, the primary objective of this report is to conduct experiments to analyse how the research gap stated can enhance PHA production. The secondary objective is to test the kinetics of glycerol fermentation. Selections of the best strain from 7 PHA accumulating strains were done. C:N ratio of 4:1, 8:1 and 16:1 was tested to find the optimal ratio for PHA accumulation. Ammonium nitrogen, nitrate and a mixture of both were used to test nitrate as the electron acceptor. Setup with glycerol, acetate and mixture of both were used to test if addition of acetate would act as stimulus for better PHA accumulation. A 3L fermenter was used to test the kinetics of the fermentation process. The results were compared and analysed and it was found that C:N 16:1 produced the most PHA; nitrate is not effective as an electron acceptor to consume NADH to increase PHA production; acetate stimulus did not produce higher PHA accumulation; carbon to PHA efficiency is of 10%.