Tolerance of natural yeast isolates to inhibitor compounds associated with the fermentation of lignocellulosic hydrolysates to ethanol

Lignocellulosic biomass represents a sustainable feedstock for second-generation bioethanol production; however, the presence of pretreatment-derived inhibitory compounds remains a major challenge to efficient fermentation. This study aimed to isolate and evaluate wild yeast strains for tolerance to lignocellulosic hydrolysate inhibitors and their bioethanol production potential. Yeast isolates were obtained from diverse environmental sources and screened for tolerance to heavy metals, NaCl, and key lignocellulosic inhibitors (acetic acid, formic acid, and furfural). Selected isolates were further assessed for growth performance, sugar utilization, and ethanol production under inhibitor-supplemented synthetic fermentation conditions. Among the inhibitors tested, formic acid exerted the least inhibitory effect on yeast growth and fermentation, while furfural caused the strongest growth suppression. Several isolates demonstrated multi-stress tolerance, with Meyerozyma guilliermondii Y5542 exhibiting the highest ethanol production and conversion efficiency under inhibitor stress, producing up to 10.6 g/L ethanol in the presence of formic acid. Differences in fermentation performance among isolates indicated that sugar consumption did not always correlate with ethanol yield. Overall, the results indicate that wild yeast isolates, particularly M. guilliermondii Y5542, show promising tolerance to lignocellulosic hydrolysate inhibitors and warrant further evaluation for application in bioethanol production under inhibitory conditions. • Increase in quantity of inhibitor does not equate decrease in ethanol production • Meyerozyma guilliermondi can survive in harsh environmental conditions • Wild yeasts of Nigerian origin have potentials in bioethanol production.