Bioprospecting of thermo- and osmo-tolerant fungi from mango pulp–peel compost for bioethanol production

The persistent edaphic stress on microbial succession due to dynamic changes during composting was explored for selection of multi-stress tolerant microbe(s) desirable for ethanol production. A total of 23 strains were isolated from mango compost using four successive enrichments in YP broth (g l −1 ): glucose, 100; 150; 250 with ethanol (40) and cycloheximide (0.4) at 40 °C, pH 6.0. Based on multi-gene ribotyping, 14 yeasts (61 %) of Saccharomycetaceae , 2 filamentous fungi (8.6 %) and 7 bacteria (30.4 %) were obtained. Phenetic and phylogenetic analysis of the 14 yeasts revealed 64.3 % tolerant to 500 g l −1 glucose, growth at 45 °C and resemblance to Candida sp. (14.3 %), Kluyveromyces marxianus (35.7 %), Pichia kudriavzevii (21.4 %) and Saccharomyces cerevisiae (28.6 %). Assessment of the 14 yeasts in glucose fermentation medium (pH 4.5 at 40 °C) showed ethanol productivity of ≥92 % by 12 yeasts with theoretical yields of 90–97 %. Fermentation of molasses (150 g l −1 glucose equivalent) by P. kudriavzevii D1C at 40 °C resulted in 73.70 ± 0.02 g l −1 ethanol and productivity of 4.91 ± 0.01 g l −1 h −1 . Assessment of P. kudriavzevii D1C revealed multi-stress tolerance towards 5-hydroxymethyl furfural, ethanol (20 %, v/v), high gravity and H 2 O 2 (0.3 M) indicating suitability for ethanol production using high gravity molasses and pre-treated lignocellulosic biomass fermentation.