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 XynAG3Pp and the CotAPp 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 XynAG3Pp and CotAPp was 150min and 540min, respectively. The relative levels of CotAPp and XynAG3Pp in culture broths were altered by the concentration of methanol used for induction, and CotAPp:XynAG3Pp 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 CotAPp:XynAG3Pp, 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.