Showing papers in "Journal of Bioprocess Engineering and Biorefinery in 2012"

The Effect of Co-Substrate Feeding on Polyhydroxyalkanoate (PHA) Homopolymer and Copolymer Production in Recombinant Escherichia coli LS5218

Abstract: Polyhydroxyalkanoates (PHAs) are aliphatic polyesters produced by a wide variety of bacteria as carbon and energy storage sources. Copolymers of the short chain length (SCL) 3-hydroxybutyrate (3HB) repeating unit and medium chain length hydroxyalkanoate (MCL-HA) repeating units have better thermal and mechanical properties than poly-3HB homopolymers. In this study, a MCL monomer supplier gene phaJ4 from Pseudomonas putida KT2440, an engineered PHA synthase gene (phaC1) from Pseudomonas sp. 61-3, and the SCL monomer supplier genes, phaA and phaB from Ralstonia eutropha, were coexpressed under the lac promoter in recombinant E. coli LS5218 to produce SCL-MCL copolymers. The recombinant strains were co-fed lauric acid (a fatty acid) and glucose as a carbon source and the ratio of SCL to MCL monomers varied dependant on differences in the timing of the addition of each carbon source during the fermentation. The PHA copolymers produced exhibited a range from 0.4 mol% to 35 mol% MCL repeating units giving rise to wide range of physical properties. The molecular weights and thermal properties of different polymers were studied by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The results suggested the polymers produced by co-feeding with lauric acid and glucose were mixtures of 3HB homopolymers and 3HB-co-MCL copolymers. This conclusion was confirmed by acetone fractionation.

Processes and Bioreactor Designs for Butanol Production from Lignocellulosic Biomass

Abstract: Butanol is a chemical, solvent and a good liquid fuel, which can be produced from lignocellulosic biomass. This paper provides a review on the processes involved in butanol production from lignocellulosic biomass. Processes reviewed include: metabolic pathways of most commonly used microorganisms, lignocellulosic biomass as a potential feedstock for butanol production and bioreactor designs for batch and continuous butanol production. Butanol production from lignocellulosic biomass via different bioreactor designs is compared in terms of butanol concentration, butanol yield and butanol productivity. Factors affecting the fermentative butanol production are summarized and discussed: microbial inhibitors, acetate addition, butyrate addition, hydrogen production, culture stability, anaerobic conditions, agitation, pH, and temperature.