Bio-ethanol production by a novel autochthonous thermo-tolerant yeast isolated from wastewater

Background: It has been known for years that ethanol is a bio-fuel to replace fossil fuels. The ethanol industry requires the utilization of micro-organisms capable production with stresses. The purpose of present study was to isolate and characterize ethanologenic yeast with high potential application at high temperature to produce bio-ethanol. Methods: To isolate ethanologenic yeasts, wastewater samples from a starch producer plant in Varamin, Iran were used. The isolates were identified by molecular characterization. Characteristics of the isolated strains were determined at 30, 35, 40 and 45°C for 48 hours. Results: 50 yeast strains capable of growing well in agar plates in a temperature range of 30–45°C were isolated. Out of the isolated strains, only three strains were screened for their ability to grow at 45°C. Selected yeast, designated as AT-3 strain which showed efficient flocculation capabilities with higher ethanol production and grew faster as compared to the rest of strains in media with 180 g/L glucose at 35°C. The selected yeast was identified as a new strain of Saccharomyces cerevisiae and submitted to the Gene-Bank database. Its’ optimum growth temperature was between 35 and 40°C. The results showed that during the bio-ethanol production 2.5 × 1010 and 8.5 × 109 (CFU/mL) were a good indication of strain capability in heat tolerance. Also, ethanol produced at a raise of 6.9% and 6.85% (w/v) at 35 and 40°C, respectively, whereas glucose-to-ethanol conversion yield was about 75% of the theoretical value. Conclusions: Results emphasized that the isolated strain identified as Saccharomyces cerevisiae. This specific strain has thermo-tolerant, osmo-tolerant, flocculating capabilities with potential for application in developing a low cost ethanol industry.