Abstract
Recombinant Escherichia coli is a desirable bacterial chassis for the biosynthesis of many biological compounds including poly(3-hydroxyalkanoates) (PHAs), a class of naturally occurring biodegradable polyesters with promising biomedical and material applications. PHAs are very structurally diverse, and control over their composition allows the production of unique materials with tunable physical and chemical properties. The major limitation to widespread use of PHAs is their high cost and low volumetric productivity, particularly for a desirable class of PHAs with medium chain-length (MCL) side chains. In this work, transcriptional regulators of fatty acid degradation were removed from E. coli in an effort to enhance MCL PHA biosynthesis. Deletion of arcA was successful in improving yields due to increased expression of fadD and fadL in the mutant strains. Although modest improvements in yield were observed in this mutant, a fed-batch high-density fermentation process was developed to further enhance MCL PHA yields using an industrially relevant bioprocess. Through process optimization, some of the highest yields and productivities were achieved to date, including for PHAs with chemically modifiable functional groups. One of these novel functional polymers, a copolymer of 3-hydroxyoctanoate and 3- hydroxy-10-azidodecanoate, was investigated as a targeted nanoparticle drug delivery system. Preliminary results show high encapsulation efficiency of paclitaxel and a surface chemistry amenable to rapid and efficient Click chemistry. In addition to work with MCL PHAs, short chain- length PHAs from a lignocellulosic waste stream, hydrolyzed paper mill waste fines. This work in its entirety demonstrates several successful strategies for improving the availability of PHAs with controlled compositions.