Isolation and characterization of extracellular polysaccharide Thelebolan produced by a newly isolated psychrophilic Antarctic fungus Thelebolus

The present investigation is on a newly isolated psychrophilic Antarctic filamentous Ascomycetous fungus that has been identified as Thelebolus sp. and given the designation of Thelebolus sp. IITKGP-BT12. The culture was primarily identified through morphological studies, and was further confirmed by 18S rRNA sequencing (GenBank Accession No. KC191572), which revealed its close relatedness with Thelebolus microsporus. The exopolysaccharide (EPS) produced (1.94 g L−1) by the fungus was isolated, purified and characterized as glucan having an average molecular mass of 5 × 105 Da. The structure of EPS was determined by gas chromatography with tandem mass spectrometry (GC–MS/MS), Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) studies (1H, 13C and HSQC). NMR analysis indicated the presence of (1 → 3)-linked β-d-glucan backbone with (1 → 6)-linked branches of β-d-glucopyranosyl units. Antiproliferative activity of EPS was demonstrated in B16-F0 cells, with IC50 of 275.42 μg mL−1. Flow cytometry analysis and DNA fragmentation studies revealed that the cytotoxic action of the EPS mediated apoptosis in cancer cells. This is the first ever report on bioactive EPS thelebolan from Thelebolus sp.