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Pentose sugar utilisation in Clostridium beijerinckii NCIMB 8052 for biobutanol production: genetic and physiological studies

Watson, Julie Elizabeth


Julie Elizabeth Watson


The future of biofuel production hinges on a cheap, readily available feedstock. In terms of resources available, lignocellulose is the most abundant renewable resource on the planet, available from a plethora of sources such as agriculture, forestry, industry and municipals, therefore presenting an attractive resource. Cellulose, hemicellulose and lignin are the three main constituents of lignocellulose. The viability of such a feedstock requires as much of these constituents being converted to product as possible and therefore requires the suitable candidate organism to achieve this. Hemicellulose, an often pentose-rich portion of lignocellulose, can constitute as much as 35%. Traditionally yeasts, namely Saccharomyces cerevisiae, have been employed in biofuel production. However, yeasts are often unable to utilise pentose sugars found in the hemicellulose fraction.In this study the ability of Clostridium beijerinckii to utilise the pentose sugars xylose and arabinose was investigated. The ability of C. beijerinckii to utilise these pentose sugars was established, total solvent yields were 0.34 gram/gram (g.g) of arabinose or xylose consumed, in comparison to 0.41 g.g of glucose consumed. The presence of glucose on low mixed-sugar concentrations (1%), but not on high (6%) hindered the use of both pentoses. The ability of C..beijerinckii to utilise pentose sugars in xylan.C..beijerinckii was capable of fermenting xylan and smaller hydrolysate units of xylan, however the solvent yield was poor. The ability of C..beijerinckii to utilise a pentoserich waste stream, spent dried distillers’ grains (DDGS) was also investigated.
Simultaneous saccharification and fermentation of DDGS produced a total solvent yield of 0.25 g.g in comparison to 0.34 g.g on media containing the equivalent soluble sugars.
The ability of C..beijerinckii to utilise both pentose sugars led to in-silico studies to identify gene systems involved and implicated several genes organised in two distinct clusters, one for each pentose sugar, within the genome. Proteomic analyses by liquid chromatography electrospray ionisation tandem mass spectrometry of whole-cell proteins harvested from cultures of C..beijerinckii grown on either xylose or arabinose as the sole carbon source provided further evidence to implicate the gene systems identified by the in silico analyses. Genes were then targeted for characterisation in-vivo using a number of E. coli knock-out mutants, lacking one or more of key genes involved in pentose sugar use. This identified arabinose isomerase, xylose isomerase and xylulokinase genes.

Thesis Type Thesis
Deposit Date May 27, 2013
Peer Reviewed Not Peer Reviewed
Keywords Biofuel production; lignocellulose; pentose sugars; Cellulose; hemicellulose; lignin; Saccharomyces cerevisiae; Clostridium beijerinckii;
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Award Date 2012-05


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