Efficient Polyhydroxyalkanoate Production by Rhodopseudomonas palustris from Lignocellulosic Biomass

Authors

Brandi Brown, University of Nebraska-LincolnFollow

First Advisor

Mark Wilkins

Second Advisor

Rajib Saha

Date of this Version

Summer 7-30-2021

Citation

Brown, Brandi. EFFICIENT POLYHYDROXYALKANOATE PRODUCTION BY RHODOPSEUDOMONAS PALUSTRIS FROM LIGNOCELLULOSIC BIOMASS: A DISSERTATION. University of Nebraska-Lincoln. 2021.

Comments

A DISSERTATION Presented to the Faculty of the Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Engineering (Agricultural and Biological Systems Engineering), Under the Supervision of Professors Rajib Saha and Mark Wilkins. Lincoln, Nebraska: July, 2021

Copyright © 2021 Brandi J. Brown

Abstract

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 CGA009 is 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-co-3-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 on LBPs. 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.

Advisors: Rajib Saha and Mark Wilkins