Direct xylan conversion into glycolipid biosurfactants, mannosylerythritol lipids, by Pseudozyma antarctica PYCC 5048T

Mannosylerythritol lipids (MEL) are glycolipid biosurfactants, produced by Pseudozyma spp., with increasing commercial interest. While MEL can be produced from d-glucose and d-xylose, the direct conversion of the respective lignocellulosic polysaccharides, cellulose and xylan, was not reported yet. The ability of Pseudozyma antarctica PYCC 5048T and Pseudozyma aphidis PYCC 5535T to use cellulose (Avicel®) and xylan (beechwood) as carbon and energy source has been assessed along with their capacity of producing cellulolytic and hemicellulolytic enzymes, toward a consolidated bioprocess (CBP) for MEL production. The yeasts assessed were neither able to grow in medium containing Avicel® nor produce cellulolytic enzymes under the conditions tested. On contrary, both yeasts were able to efficiently grow in xylan, but MEL production was only detected in P. antarctica PYCC 5048T cultures. MEL titers reached 1.3 g/l after 10 days in batch cultures with 40 g/l xylan, and 2.0 g/l in fed-batch cultures with xylan feeding (additional 40 g/l) at day 4. High levels of xylanase activities were detected in xylan cultures, reaching 47-62 U/ml (31-32 U/mg) at 50 °C, and still exhibiting more than 10 U/ml under physiological temperature (28 °C). Total β-xylosidase activities, displayed mainly as wall-bounded and extracellular activity, accounted for 0.154 and 0.176 U/ml in P. antarctica PYCC 5048T and P. aphidis PYCC 5535T cultures, respectively. The present results demonstrate the potential of Pseudozyma spp. for using directly a fraction of lignocellulosic biomass, xylan, and combining in the same bioprocess the production of xylanolytic enzymes with MEL production.