Lignocellulosic biomass is a challenging ecological niche for microorganisms. Spent sulphite liquor (SSL), which derives from acid hydrolysis of lignocellulosic biomass, is an even greater challenge, due to the presence of toxic phenolic compounds, specific monosaccharides, lignosulphonates and inhibitors, such as HMF, furfural, formic acid and acetic acid. One of these inhibitors is vanillin, a lignin monomeric derivative. Could yeasts that originate from wood tolerate vanillin and grow in the presence of SSL? A basidiomycetous yeast, Cystobasidium laryngis strain FMYD002, grew in vanillin-supplemented media, and biotransformed vanillin into vanillyl alcohol. It is part of a collection of yeasts isolated from decaying wood on the Faroe Islands. The aim of the present study was to determine the vanillin biodegradation profiles and the ability to grow in the presence of SSL.

These yeasts were identified by ITS1–5.8S–ITS2 and D1/D2 sequence homology. The relationship between wood-habitat and vanillin tolerance by cultivating the yeasts in the presence of 1 mM vanillin. The vanillin biodegradation profiles were determined by LC-MS, using the standards: vanillin, vanillyl alcohol and vanillic acid. The growth in different concentrations of SSL was evaluated.

Strains of Cystobasidium laryngis, Cystofilobasidium infirmominiatum, Goffeauzyma gastrica, Goffeauzyma sp., Naganishia sp., Holtermanniella sp., Rhodotorula sp., Nadsonia starkeyi-henricii, Debaryomyces hansenii, Debaryomyces sp., Candida sake and Candida argentea were identified. Most strains were able to grow in vanillin-supplemented medium. The predominant biodegradation product was vanillyl alcohol followed by vanillic acid. Several other biodegradation products were detected. Most strains were able to grow in the presence in SSL. Species of Candida and Debaryomyces were most tolerant, whereas species of Nadsonia, Holtermanniella and Naganishia grew poorly.

Many of the yeast species described herein are associated with wood or cold environments. Ability to grow in the presence of vanillin did not completely correlate with tolerance to SSL. However, the strains that grew at the highest concentration of SSL also grew well in the presence of vanillin, from which they rapidly producedl arge amounts of vanillyl alcohol, and many other biodegradation products. Conversely, the isolates with poor or no growth in vanillin had extremely low or no tolerance to SSL. Thus, high tolerance to vanillin appeared to be a prerequisite for growth in SSL-based medium. Different yeasts have tolerance to different inhibitors present in SSL. A comprehensive analysis of growth and biodegradation of vanillin produced five groups, containing specific yeast genera.