ENGINEERING XYLITOL AND GLYCINE UTILIZATION IN ESCHERICHIA COLI

Abstract

This thesis focuses on evaluating xylitol and glycine as new feedstocks for microbial fermentation. They can be obtained from lignocellulosic biomass and carbon dioxide. We first engineered an Escherichia coli strain to assimilate xylitol by over-expressing xylitol dehydrogenase (encoded by gutB). The L-tyrosine production yield from xylitol (1.2 g/L) was higher than glucose and xylose. An antibiotic-free plasmid system was developed by replacing antibiotic resistance gene marker with gutB. One protein (a polyethylene terephthalate hydrolase) had five times higher activity when obtained using the xylitol culture compared with using Luria-Bertani medium. To expand the antibiotic-free cell culture concept, we engineered E. coli to utilize glycine. By introducing an in vivo mutagenesis plasmid into the strain and culturing it in a continuous stirred tank reactor, an evolved strain was obtained which was able to grow on glycine without supplementing amino acids and nucleobases.