Nectar Yeast Community of Tropical Flowering Plants and Assessment of Their Osmotolerance and Xylitol-Producing Potential.

Floral nectar is colonised by microbes, especially yeasts which alter the scent, temperature, and chemical composition of nectar, thereby playing an essential role in pollination. The yeast communities inhabiting the nectar of tropical flowers of India are not well explored. We isolated 48 yeast strains from seven different tropical flowering plants. Post MSP-PCR-based screening, 23 yeast isolates and two yeast-like fungi were identified, which belonged to 16 species of 12 genera viz. Candida (2 species), Aureobasidium (2 species), Metschnikowia (2 species), Meyerozyma (1 species), Saitozyma (1 species), Wickerhamomyces (1 species), Kodamaea (2 species), Pseudozyma (1 species), Starmerella (1 species), Hanseniaspora (1 species), Rhodosporidiobolus (1 species), Moesziomyces (1 species), and two putative novel species. All yeast strains were assessed for their osmotolerance abilities in high salt and sugar concentration. Among all the isolates, C. nivariensis (SRA2.2, SRA1.1 and SRA2.1), M. caribbica (SRA4.8 and SRA4.6), S. flava SRA4.2, and M. reukaufii SRA3.2 showed significant growth in high concentrations of sugar (40-50% glucose), as well as salt (12-15% NaCl). All 25 strains were also screened for their ability to utilise xylose to produce xylitol. Meyerozyma caribbica was the most efficient xylitol producer, wherein three strains of this species (SRA4.6, SRA4.1, and SRA4.8) generated 18.61 to 21.56 g l-1 of xylitol, with 0.465-0.539 g g-1 yields. Through this study, we draw attention towards the tropical floral nectar as a potential niche for the isolation of diverse, osmotolerant, and xylitol-producing yeasts. Such osmotolerant yeasts have potential applications in food industries and biofuel production.