Production and Chemical Characterization of Exopolysaccharides by Antarctic Yeasts Vishniacozyma victoriae and Tremellomycetes sp.

Abstract

The study aimed to investigate exopolysaccharides (EPSs) produced by two Antarctic yeasts isolated from Livingston Island. The species were identified as Vishniacozyma victoriae (V) and Tremellomycetes sp. (T) based on a molecular genetic analysis of ITS1-5.8S-ITS4 regions of the 18S rRNA gene. The EPS production was investigated under stress conditions in culture flasks and a bioreactor. Different chromatographic (HPLC-RID, HPSEC-RID) and spectral (FT-IR) analyses were employed to characterize EPSs. Tremellomycetes sp. accumulated 7 g/L biomass and 4.5 g/L EPS after 120 h of cultivation. The total carbohydrate content of V-EPS and T-EPS was 75.4% and 79.0%, respectively. The EPSs mainly consisted of mannose (30–32%), which was followed by glucose, xylose, galactose, and small amounts of uronic acids (6.3–7.0%). EPSs had appreciable amounts of proteins (11–12%). The FT-IR spectra contained absorption bands typical for hetero-mannans and β-glucans (797–1033 cm−1). EPSs were heterogeneous with a broad molecular weight distribution range (47 × 104–68 × 104 g/mol). In conclusion, both yeasts synthesized high-molecular-weight heteromannans, and Tremellomycetes sp. stood out as being a better producer than V. victoriae. The current study also formed a basis for a better assessment of the potential for practical application of EPSs and yeasts in biochemical engineering and biotechnology.