Optimal Medium Composition to Enhance Poly-β-hydroxybutyrate Production by Ralstonia eutropha Using Cane Molasses as Sole Carbon Source

In order to reduce the costs associated with Poly-β-hydroxybutyrate production, growth and Poly-β-hydroxybutyrate production of Ralstonia eutropha were studied in batch culture on different carbon sources. Experiments were designed and conducted to not only lower the cost of Poly-β-hydroxybutyrate production by using inexpensive substrates, but also to increase Poly-β-hydroxybutyrate production by optimizing the culture medium composition. Low cost, abundant carbon sources, including cane molasses, beet molasses, soya bean, and corn steep liquor were used to investigate the possibility of Poly-β-hydroxybutyrate production in such renewable carbon sources. Based on the experimental results, cane molasses with production of 0.49 g/L Poly-β-hydroxybutyrate was selected as the most efficient carbon source. To improve bacterial growth and Poly-β-hydroxybutyrate production, different chemicals were then used to pretreat the cane molasses. Sulfuric acid, with 33% enhancement in Poly-β-hydroxybutyrate production, revealed the highest efficiency in removing heavy metals and suspended impurities and was used to pretreat cane molasses in the subsequent experiments. Additionally, to make the process even more efficient and ultimately more effective, urea and corn steep liquor were used as nitrogen/minerals and vitamin sources, respectively. Using the Response Surface Methodology and through a 2n factorial Central Composite Design, the medium composition was then optimized, and maximum biomass concentration of 5.03 g/L and Poly-β-hydroxybutyrate concentration of 1.63 g/L were obtained.