CHARACTERIZATION OF BLACK YEAST Aureobasidium spp. ISOLATED FROM THAI COASTAL AREA

Abstract

Aureobasidium spp. is polyextremotolerant microorganism of considerable biotechnological importance that thrives in a broad range of habitats worldwide. This fungus produces valuable products including exopolysaccharides; EPS (pullulan and β-glucan), xylanase, and antifungal agents. Recently, four varieties were separated into four species including A. pullulans, A. melanogenum, A. namibiae and A. subglaciale. A number of Aureobasidium spp. from coastal area was isolated. Among 66 isolates used in this study include 54 new isolates and 12 comparative strains. All new isolates were classified using multi locus sequence analysis from three loci including the rRNA ITS region, TUB, and ELO. Based on the phylogenetic analysis, they were classified into 12 clades, suggesting a vast diversity within the coastal area. However, only two species were found in this study and the dominant species in coastal area was found to be A. melanogenum whereas a few A. thailandense was also found. The color-variant strains that specific and found in only tropical or subtropical zone were obtained and they were located in A. melanogenum clade. Consequently, morphological characteristics, EPS production, and xylanase activity were determined for all isolates in an attempt to identify specific characteristics of each clade, and to compare with terrestrial isolates. The results exhibited different colors on different culture media, type of EPS, and some clades showed high levels of EPS production and/or xylanase activity. Moreover, antifungal activity and multiple abiotic stresses including halotolerance, osmotolerance, thermotolerance, and tolerance against various pH were observed in attempt to discover the useful isolates or extremotolerant for applying in biotechnology. The results showed their ability were strain dependence. To study associations among halotolerance, osmotolerance and EPS production, three strains with different tolerance and EPS production were selected. The results showed halotolerance in A. melanogenum was significantly associated with osmotolerance, but not vice versa. Halo- and/or osmotolerant strains produced low to moderate EPS yield. Moreover, to study the potential application of xylanase in biotechnology, a representative strain was selected and xylanase was produced for xylooligosaccharides (XOS) production. Xylan from Typha angustifolia L. was extracted and used as sole carbon source. The main hydrolysis products yield were xylobiose and small amount of xylose. XOS obtained in this study exhibited antioxidant activity when 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was used for evaluation.