Exploiting yeast diversity to produce renewable chemicals from rice straw and husk

Wu, Jia (2018) Exploiting yeast diversity to produce renewable chemicals from rice straw and husk. Doctoral thesis, University of East Anglia.

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Abstract

Exploiting organic lignocellulosic wastes via bio-refining processes has been widely accepted as one of the renewable, environmentally friendly solutions to producing platform chemicals and liquid fuels. Pre-treatment serves as an initial step to improve the accessibility of lignocellulosic polysaccharides to enzymes, and fermentation is a core step to obtain a range of products from the sugars. However, inhibitors of enzymatic saccharification and fermentation are unavoidably generated during hydrothermal pre-treatment. Therefore, the aim of this study has been to assess the associations and possibly correlations between severities of pre-treatment, yield of fermentable sugars and formation of inhibitors, and to evaluate the potential of 11 yeast diverse yeast strains for the potential to produce not only ethanol but also some highly-sought-after platform chemicals.

Air dried rice husk (RH) and rice straw (RS) from the same rice cultivar (Oryza sativa, cv. KhangDan18) were used as substrates. Carbohydrate compositions of each were similar whereas lignin contents differed significantly. Using complementary analytical approaches including a new, rapid NMR screening method, 40 compounds including carbohydrates, organic acids, phenolics and furans were identified from the solids and liquors of pre-treated RH and RS. However, the quantities of compounds differed between the two substrates. Fermentation inhibitors included 5-HMF, 2-FA and phenolic acids such as para-couamric acid (pCA) and trans-ferulic acid (tFA). Differences in lignin, tFA, diferulic acids (DiFA) and pCA between RS and RH reflect differences in cell wall physiology and are probably responsible for the higher recalcitrance of RH. After pre-treatment at a severity of 3.65, ethanol was produced from RS with a yield double that from RH. Above a severity of 5, fermentation was completely inhibited in both RH and RS. More careful control of pre-treatment may be sufficient to reduce the levels of fermentation inhibitors. Such inhibition was found to occur with a range of genetically diverse yeast strains which differed considerably in their metabolic capabilities and production of ethanol. A number could produce significant amounts of ethyl acetate, arabinitol, glycerol and acetate in addition to ethanol, including from hitherto unreported carbon sources. Moreover, a new catabolic property of Rhodotorula mucilaginosa (NCYC 65) was discovered in which sucrose is cleaved into glucose and fructose but they are not metabolised. Engineering some of properties discovered in this study and transferring such properties to conventional industrial yeast strains could greatly expand their biotechnological utility.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Gillian Aldus
Date Deposited: 10 Jan 2019 12:42
Last Modified: 10 Jan 2019 12:42
URI: https://ueaeprints.uea.ac.uk/id/eprint/69533
DOI:

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