Arumugam, Deyvanai
(2021)
Production Of Polyhydroxyalkanoates From Xylose By Escherichia Coli Carrying Wild Type And Mutant Xyle.
Masters thesis, Perpustakaan Hamzah Sendut.
Abstract
The abundance of xylose in agricultural waste represents an opportunity to turn it into energy or chemical feedstock. This study explores using E. coli JM109(DE3) harbouring pACYCxylE coding for a xylose transporter and pGEMCABcn carrying the PHA operon from C. necator to convert xylose into polyhydroxyalkanoate. Based on the criteria of fast growing, plasmid stability and ability to grow on minimal medium, strain JM109(DE3) was found to be the most suitable host for PHA production from xylose. The two plasmids were found to be stable after 10 serial overnight subcultures even without antibiotics selection. The strain was able to accumulate PHA up 62% CDW after 120 hours of incubation in mineral medium containing 1% xylose. Increasing xylose concentration up to 5% did not cause any further increase in PHA content, nor toxicity. Even at 1% xylose or glucose, the data suggests that the mineral medium was already limiting. When grown in 1% glucose, JM109(DE3) yield only 12% CDW PHA. Increasing glucose concentration to 5% leads to lower PHA content of only 6% CDW, implying glucose inhibition. In an experiment using a range of xylose:glucose ratio of 1:0.1 to 1:1, the PHA content fell from 58% to 32% CDW. In order to overcome glucose toxicity, six XylE mutants were tested for PHA production.
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