Malherbe A.R., Rose S.H., Viljoen-Bloom M., Van Zyl W.H.
Department of Microbiology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
Malherbe, A.R., Department of Microbiology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa; Rose, S.H., Department of Microbiology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa; Viljoen-Bloom, M., Department of Microbiology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa; Van Zyl, W.H., Department of Microbiology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
The cost-effective production of bioethanol from lignocellulose requires the complete conversion of plant biomass, which contains up to 30 % mannan. To ensure utilisation of galactomannan during consolidated bioprocessing, heterologous production of mannan-degrading enzymes in fungal hosts was explored. The Aspergillus aculeatus endo-β-mannanase (Man1) and Talaromyces emersonii α-galactosidase (Agal) genes were expressed in Saccharomyces cerevisiae Y294, and the Aspergillus niger β-mannosidase (cMndA) and synthetic Cellvibrio mixtus β-mannosidase (Man5A) genes in A. niger. Maximum enzyme activity for Man1 (374 nkat ml-1, pH 5.47), Agal (135 nkat ml-1, pH 2.37), cMndA (12 nkat ml-1, pH 3.40) and Man5A (8 nkat ml-1, pH 3.40) was observed between 60 and 70 °C. Co-expression of the Man1 and Agal genes in S. cerevisiae Y294[Agal-Man1] reduced the extracellular activity relative to individual expression of the respective genes. However, the combined action of crude Man1, Agal and Man5A enzyme preparations significantly decreased the viscosity of galactomannan in locust bean gum, confirming hydrolysis thereof. Furthermore, when complemented with exogenous Man5A, S. cerevisiae Y294[Agal-Man1] produced 56 % of the theoretical ethanol yield, corresponding to a 66 % carbohydrate conversion, on 5 g l-1 mannose and 10 g l-1 locust bean gum. © 2014 Society for Industrial Microbiology and Biotechnology.
algaroba; alpha galactosidase; beta mannosidase; biofuel; galactan; galactomannan; lignin; lignocellulose; mannan; plant gum; Aspergillus; bioreactor; Cellvibrio; enzymology; genetics; hydrolysis; kinetics; metabolism; microbiology; procedures; Saccharomyces cerevisiae; Talaromyces; viscosity; alpha-Galactosidase; Aspergillus; beta-Mannosidase; Biofuels; Bioreactors; Cellvibrio; Galactans; Hydrolysis; Industrial Microbiology; Kinetics; Lignin; Mannans; Plant Gums; Saccharomyces cerevisiae; Talaromyces; Viscosity