title: Metabolic engineering of Geobacillus thermoglucosidasius for high yield ethanol production.
abstract: We describe the metabolic engineering of two strains of Geobacillus thermoglucosidasius to divert their fermentative carbon flux from a mixed acid pathway, to one in which ethanol becomes the major product. This involved elimination of the lactate dehydrogenase and pyruvate formate lyase pathways by disruption of the ldh and pflB genes, respectively, together with upregulation of expression of pyruvate dehydrogenase. Unlike the situation in Escherichia coli, pyruvate dehydrogenase is active under anaerobic conditions in thermophilic bacilli, but expressed sub-optimally for a role as the primary fermentation pathway. Mutants were initially characterised in batch culture using glucose as carbon substrate and strains with all three modifications shown to form ethanol efficiently and rapidly at temperatures in excess of 60 degrees C in yields in excess of 90% of theoretical. The strain containing the 3 modifications, TM242, was also shown to efficiently ferment cellobiose and a mixed hexose and pentose feed.
authors.affiliation: TMO Renewables Limited, The Surrey Technology Centre, Guildford, Surrey GU2 7YG, UK. roger.cripps@virgin.net
authors.forename: R E
authors.initials: RE
authors.lastname: Cripps
authors.forename: K
authors.initials: K
authors.lastname: Eley
authors.forename: D J
authors.initials: DJ
authors.lastname: Leak
authors.forename: B
authors.initials: B
authors.lastname: Rudd
authors.forename: M
authors.initials: M
authors.lastname: Taylor
authors.forename: M
authors.initials: M
authors.lastname: Todd
authors.forename: S
authors.initials: S
authors.lastname: Boakes
authors.forename: S
authors.initials: S
authors.lastname: Martin
authors.forename: T
authors.initials: T
authors.lastname: Atkinson
mesh_terms: D000123:Acetyltransferases / Q000235:genetics / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D017353:Gene Deletion; D024861:Genetic Enhancement / Q000379:methods*; D056506:Geobacillus / Q000502:physiology*; D007770:L-Lactate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D015202:Protein Engineering / Q000379:methods
chemical_list: D000431:Ethanol; D007770:L-Lactate Dehydrogenase; D000123:Acetyltransferases; C022560:formate C-acetyltransferase