Efficient Polyhydroxyalkanoate Production by Rhodopseudomonas Palustris from Lignocellulosic Biomass

Polyhydroxyalkanoates (PHAs) are biopolymers produced by bacteria with the potential to replace conventional plastics. However, the relatively high production costs of PHAs are keeping them from market acceptance, with approximately half of the production costs derived from the feedstock. Thus, engineering a microbe for PHA production from cheaper and renewable carbon sources is necessary to promote the valorization of PHAs. Lignocellulosic biomass is considered to be one of the most economic carbon sources in the world, and is thus an attractive candidate for cheaper production of bioplastics. Rhodopseudomonas palustris CGA009is a metabolically robust bacterium capable of catabolizing lignin breakdown products (LBPs),and also has the ability to produce several high-value bioproducts like bioplastics and biohydrogen. Thus, the goal of this research was aimed at producing and optimizing PHA production from R. palustris from LBPs. The first study produced poly-3-hydroxybutyrate(PHB) from R. palustris from the LBP p-coumarate with a PHB titer of 0.41 g/L and 68.4%carbon conversion efficiency. This study also optimized a high-throughput quantification method for PHB that employed flow cytometry. The second study produced poly(3-hydroxybutyrate-co3-hydroxyvalerate) (PHBV) from the LBPs p-coumarate and coniferyl alcohol, and utilized an integrated experimental and computational modeling approach to infer metabolic factors controlling PHB production that can be expanded to any PHB-producing microbe with similar metabolic features. The third study expressed the phaP1 phasin gene from the PHB-producing model bacterium Cupriavidus necator H16 in R. palustris for the overproduction of PHBV onLBPs. Expression of phaP1 yielded PHBV production from R. palustris aerobically (0.7 g/L),which does not occur in the wild type strain and provides more flexibility for industrial production. The 3-hydroxyvalerate fractions were also significantly increased under both anaerobic and aerobic conditions, which boosts thermomechanical properties compared to PHB alone. Taken together, these studies contributed to development of R. palustris as a biotechnology chassis for the production of bioplastics from lignocellosic biomass