Survey of the genome of opitutus terrae and other organisms for novel carbohydrate-active enzyme specificities

Bawn, Maria (2012) Survey of the genome of opitutus terrae and other organisms for novel carbohydrate-active enzyme specificities. Doctoral thesis, Northumbria University.

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Abstract

Lignocellulose is the major component of the plant cell wall and is a sustainable source of inexpensive abundant biomass. Efficient degradation of the lignocellulosic polysaccharides, cellulose and hemicellulose, is required if the plant cell wall is to be used as a resource for renewable biofuels. Microorganisms have the ability to catalyse the degradation of such bio-material through a cascade of enzyme activities into fermentable sugars and therefore are considered to be a major resource of biocatalysts for the emerging biofuel industry. The stability of the component polysaccharides and the complexity of the plant cell wall are reflected in the diverse range of functions and substrate specificities of lignocellulosic degrading enzymes.

Part of this work describes the identification of a novel GH8 endo-xylanase, OtXyn8A, from the soil bacterium, Opitutus terrae. GH8 is a family in which there is only a limited amount of data available on the xylanase substrate specificity in comparison to families GH10 and GH11 in which xylanases are well established. With this in mind, OtXyn8A is the only endo-xylanase characterised from GH8 that primarily releases xylobiose from its substrates.

Synergy between O. terrae enzymes was partially investigated within this study with the identification of a gene cluster within the bacterial genome. Genes organised within this cluster encoded products required for the degradation of xylan substrates and so the associated enzymes were cloned, expressed and subsequently determined for activity. Combined activities of gene products from the cluster exhibited synergy in the hydrolysis of 4-O-methyl glucuronoxylan.

While surveying the genome of O. terrae, the multiplication of genes encoding GH43 enzymes was also investigated. Genes encoding GH43 enzymes were cloned, expressed and investigated for catalytic activity. Three arabinofuranosidases from O. terrae and one from Lactobacillus brevis were characterised, including the characterisation of an exo-1,5-L-arabinofuranosidase. Furthermore, a β-xylosidase from O. terrae was characterised which exhibited dual functionality as it catalysed the release of arabinose in addition to xylose from arabino-xylooligosaccharides.

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