Synergistic action of co-expressed xylanase/laccase mixtures against milled sugar cane bagasse

Abstract The primary plant cell wall is composed of cellulose, hemicellulose, lignin and protein in a stable matrix. The concomitant depolymerization of lignin by laccase and of hemicelluloses by xylanase can improve lignocellulose degradation in the production of second generation biofuels. A thermophilic variant of xylanase A (XynAG3) and the thermostable laccase (CotA), both from Bacillus subtilis , were produced in co-transformed Pichia pastoris strain GS115. Mobility changes in SDS-PAGE after Endo H digestion indicated that both enzymes were glycosylated. The maximum catalytic activity of the XynAG3 Pp and the CotA Pp was observed at 58 °C and 75 °C, respectively, and both enzymes presented high activity at pH 5.0. The half-life at 60 °C of XynAG3 Pp and CotA Pp was 150 min and 540 min, respectively. The relative levels of CotA Pp and XynAG3 Pp in culture broths were altered by the concentration of methanol used for induction, and CotA Pp :XynAG3 Pp ratios of 1:1.5 and 1:2 were evaluated against milled sugar-cane bagasse. The highest activity was observed at a 1:2 ratio of CotA Pp :XynAG3 Pp , and was 44% higher as compared to the sum of the activities of the individual enzymes in the same assay conditions. These results demonstrate the synergistic action between an endoxylanase and a laccase against the natural lignocellulosic substrate.