Poster Presentation 2-09

Kluyveromyces marxianus as an Alternative Yeast Cell Factory for Upgrading Lignocellulosic Hydrolysates

Luís C. Duarte,* Sara Esteves, Florbela Carvalheiro and Francisco M. Gírio

INETI, Departamento de Biotecnologia

Estrada do Paço do Lumiar 22

1649-038, Lisboa, Portugal

Phone: +351-217165141

Fax: +351-217163636

E-mail: luis.duarte@ineti.pt

It is currently agreed that there is no suitable microorganism that can be used as an efficient yeast cell factory (YCF) for the upgrade of lignocellulosic hydrolysates.

In this work, the naturally xylose assimilating, GRAS, thermotolerant and genetically manipulable Kluyveromyces marxianus CBS 6556 yeast is proposed and studied as an alternative YCF. The yeast was grown in chemostat at 40ºC, pH 4.5 and 5.5 at dilution rate of 0.05 h^-1, using xylose as the sole carbon and energy source. Steady states were characterized under D-xylose, PO₄^3-, NH₄⁺ and O₂ limitations, through the quantification of metabolic rates and specific enzymatic activities of selected enzymes.

Xylitol was produced as an overflow metabolite in PO₄^3- (pH 5.5) and O₂ limitations. Under the other limitations no other products except biomass and CO₂ were found, although biomass productivity was not as high as compared to other yeasts in similar conditions. Increasing pH from 4.5 to 5.5 lead to ethanol and acetate accumulation under oxygen limitation. Xylose-reductase showed a general specificity for NADPH, whose requirements could always be fulfilled by PP pathway. Xylitol-dehydrogenase specific activities were always higher than xylose-reductase.

The results suggest that xylose metabolism in K. marxianus, conversely to other yeasts, is rigidly controlled for biomass production, not favoring extracellular accumulation of metabolites, which may be advantageous in terms of heterologous protein production.