The Catabolism of Complex Carbohydrates in Four Representative Examples of the Geobacillus Genus

Abstract

The ever-increasing demand for transportation fuels, the decrease in global petroleum reserves, and the negative impact of greenhouse gases make renewable and sustainable biofuels an imperative for the future. First-generation biofuels produced from food crops are limited by cost and competition with food supply. Despite considerable effort to produce fuels from lignocellulosic biomass, chemical and enzymatic pretreatment to solubilise the biomass prior to microbial bioconversion remains a major economic barrier to the development of an industrial process. Here we report the complete genomic surveys of complex carbohydrate catabolism in four representative examples of the Geobacillus genus: G. thermodenitrificans, G. thermoglucosidans, G. stearothermophilus and G. kaustophilus. In concordance with the genomic survey the empirical confirmation of mono-, di- and poly- saccharide degradation in each species was investigated. The data collected indicates that all four species were able to utilise a wide range of C5 and C6 monosaccharides and the disaccharide cellobiose, which are all catabolic products of lignocellulosic biomass. G. thermodenitrificans was also able to catabolise one of the major carbohydrates of lignocellulose, xylan. G. thermoglucosidans, G. stearothermophilus and G. kaustophilus however were unable to utilise xylan for growth. Comparison of the G. thermodenitrificans and G. thermoglucosidans xylan degradation genes highlighted a xylan 1,4-β-xylosidase predicted in G. thermodenitrificans but not predicted in G. thermoglucosidans, which suggested an incomplete pathway. We created several constructs with Gtn xynB to test sub-cellular localisation of this enzyme and whether introduction allows xylan utilisation in G. thermoglucosidans.