Title
Kluyveromyces lactis as an expression host for enzymes that degrade lignocellulosic biomass
Authors
CAMILLA LAMBERTZCHRISTIAN ECKERT RAINER FISCHER and ULRICH COMMANDEUR

Published Volume 50 Issue 3-4 March-April
Keywords Kluyveromyces lactis, heterologous expression, protein secretion, cellulose, lignin, cellulase, laccase

Abstract
Lignocellulose is the most abundant regenerative raw material in the world and is therefore an important substrate for the conversion of biomass into biofuels and other high-value products. The efficient microbial degradation of plant biomass in nature requires a set of different enzymes that act in concert to degrade different parts of the lignocellulose molecule. For example, cellulases are responsible for cellulose hydrolysis, and peroxidases and laccases are the main enzymes for lignin degradation. One strategy for the generation of tailor-made enzyme cocktails is the production of specific combinations of different enzymes for different biomass sources.
Because the best known biomass degraders are fungi, a eukaryotic expression system is preferable for the expression of biomass-degrading enzymes. We therefore chose the yeast Kluyveromyces lactis for the over expression of enzymes from fungi such as Trichoderma reesei and Pycnoporus cinnabarinus. K. lactis combines eukaryotic post-translational modifications with easy single-cell fermentation conditions. Furthermore, it can secrete the recombinant enzymes to avoid expensive and time-consuming downstream processing steps.
Here, we demonstrate that K. lactis is an appropriate host for the production of recombinant enzymes that degrade lignocellulose, using the endoglucanase TrCel5A and the laccase PcLCC3-1 as examples. Both enzymes were secreted efficiently into the culture medium, and following affinity purification were active against the model substrates Azo CMC (TrCel5A) and ABTS (PcLCC3-1).