Poster Presentation 2-32

Quantifying Debaryomyces hansenii Tolerance to Selected Inhibitor Compounds Found in Hemicellulosic Hydrolysates

Luís C. Duarte,* Florbela Carvalheiro, Inês Neves 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

Debaryomyces hansenii is a polyol-overproducing yeast that naturally assimilates pentoses and therefore can have potential use for the biotechnological production of pentalditols (e.g. xylitol and arabitol) using lignocellulosic hydrolysates. Therefore it is important to establish its tolerance limits to metabolic inhibitors compounds usually found in hydrolysates.

In this work selected aliphatic acids (acetic and formic acids), phenolic compounds (hydroquinone, syringaldehyde, 4-methylcatechol) and furan derivatives (furfural) were studied. The yeast was cultivated in shake flasks under aerobic conditions, at the initial pH of 5.5, in a chemically defined medium containing glucose, xylose and arabinose.

D. hansenii exhibited an overall higher tolerance over other yeasts reported in literature. Formic acid proved to be more toxic than acetic acid and induced xylitol accumulation with fair yields, reaching a maximum of 0.2 g/g xylose at 1.28 mM (non-dissociated form). All phenolic compounds decreased biomass productivity. Increased toxicity was found for hydroquinone, syringaldehyde and 4-methylcatechol, which is correlated to the compound hydrophobicity. Furfural showed a positive correlation between higher concentrations and longer lag phases. Biomass productivity was also negatively affected. When cells were grown in the presence of furfural and cycloheximide (a protein synthesis inhibitor) a partial decrease of furfural effects was noticed. The hypothesis that apoptotic behavior can be involved in furfural toxicity is currently under study.