Date of Award

4-4-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Applied Science

First Advisor

Qingfang He

Abstract

The wood sugars present in the lignocellulosic biomass can be used to support microbial growth to synthesize a number of value added products. The objective of this research was to metabolically engineer model cyanobacterium Synechocystis to enable it to harvest carbon and energy stored in the wood sugars in addition to the light energy. In the xylose-specific work, we generated five Synechocystis strains that heterologously expressed XylAB enzymes, which mediate xylose catabolism, either in combination with or without one of four xylose transporters, namely XylE, XylFGH, GalP, or Glf. In terms of dry biomass accumulation and xylose consumption, the strains possessing the XylE and Glf transporters were found to be the most efficient, and the strain lacking a heterologous transporter was the least efficient. In the arabinose-specific work, twelve Synechocystis strains were constructed with four strains each expressing arabinose catabolic enzymes, AraBAD coded by the unmodified araBAD, modified araBAD-I and modified araBAD-II gene sets, either in combination with or without one of three arabinose transporters, namely AraE, AraFGH, or AraJ. Overall, the strains expressing AraBAD enzymes coded by the unmodified gene set were found to be the most efficient, among which the strain expressing AraJ showed the most remarkable results while the strain expressing AraE transporter was found to be the least efficient. This work reports a rare example where a non-functional protein AraJ from E. coli has been shown to perform efficiently when expressed heterologously, across the genera. This work demonstrates that various bacterial xylose and arabinose transporters can boost catabolism of the respective sugars in the engineered Synechocystis strains, and paves the way for the sustainable production of bio-compounds and green fuels from lignocellulosic biomass.

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