Bioprospecting Amazonian yeasts for ethanol and xylitol production from sugarcane bagasse hydrolysate

Abstract

The untapped microbial diversity of the Amazon region represents a strategic frontier for biotechnological applications. This study screened, identified, and evaluated the potential of yeasts isolated from Amazonian environments to bioconvert sugarcane bagasse hydrolysate into ethanol and xylitol. The lignocellulosic hydrolysate was obtained by thermochemical treatment using H2SO4 (0.78% v/v) at 121 °C for 68 min, with a 20% solid loading. The yeast-like isolates were identified by sequencing the internal transcribed spacer (ITS) region (5.8S rDNA) and the D1/D2 domain of the 26S rDNA. Fifteen strains belonging to the genera Pichia, Debaryomyces, Meyerozyma, and Cyberlindnera exhibited the native capacity to convert xylose into xylitol and/or ethanol, achieving product yields (YP/S) of up to 0.20 g g− 1 for ethanol and 0.25 g g− 1 for xylitol in synthetic medium. Although initial fermentation in the acid hydrolysate (28.9 g L− 1 xylose, 5.0 g L− 1 arabinose, 1.2 g L− 1 glucose, and 5.9 g L− 1 acetic acid) supported cell growth, product synthesis was strongly inhibited by the high concentration of byproducts. The use of a biomass deacetylation strategy reduced acetic acid levels to 1.0 g L− 1, enabling the conversion of sugars into the desired alcohols. Cyberlindnera saturnus strains achieved YP/S of up to 0.10 g g− 1 for ethanol and 0.14 g g− 1 for xylitol on deacetylated hydrolysate, while simultaneously performing the bioabatement of furans and residual acetic acid. These findings highlight unconventional Amazonian yeasts that, pending bioprocess optimization, exhibit promising metabolic traits for lignocellulosic biorefineries, including potential new yeast taxa.