Physiological characterization of a new thermotolerant yeast strain isolated during Brazilian ethanol production, and its application in high-temperature fermentation

Abstract

Background The use of thermotolerant yeast strains can improve the efficiency of ethanol fermentation, allowing fermentation to occur at temperatures higher than 40 °C. This characteristic could benefit traditional bio-ethanol production and allow simultaneous saccharification and fermentation (SSF) of starch or lignocellulosic biomass. Results We identified and characterized the physiology of a new thermotolerant strain (LBGA-01) able to ferment at 40 °C, which is more resistant to stressors as sucrose, furfural and ethanol than CAT-1 industrial strain. Furthermore, this strain showed similar CAT-1 resistance to acetic acid and lactic acid, and it was also able to change the pattern of genes involved in sucrose assimilation (SUC2 and AGT1). Genes related to the production of proteins involved in secondary products of fermentation were also differentially regulated at 40 °C, with reduced expression of genes involved in the formation of glycerol (GPD2), acetate (ALD6 and ALD4), and acetyl-coenzyme A synthetase 2 (ACS2). Fermentation tests using chemostats showed that LBGA-01 had an excellent performance in ethanol production in high temperature. Conclusion The thermotolerant LBGA-01 strain modulates the production of key genes, changing metabolic pathways during high-temperature fermentation, and increasing its resistance to high concentration of ethanol, sugar, lactic acid, acetic acid, and furfural. Results indicate that this strain can be used to improve first- and second-generation ethanol production in Brazil.

A Fully Defined Synthetic Medium Mimicking Sugar Cane Molasses

“…Raghavendran et al [11] report a glycerol concentration of approximately 4 g.L -1 for PE-2 in molasses at 30 °C. Additionally, Prado et al [39] obtained glycerol titters higher than 4.5 g.L -1 for a thermo-tolerant strain grown at 34°C. Further investigations adjusting the composition of our 2SMol medium (e.g., lower salt concentrations) or in different osmotic pressures can potentially result in similar glycerol concentrations, with similar biomass variation, ethanol yields, and viability.…”

“…Thus, the total nitrogen concentrations were 0, 602.7, and 2401.6 mg.L -1 in 0SMol, 2SMol, and 4SMol, respectively. Initially, results for CO2 loss normalized to wet cell mass were plotted as in previous research [11,39]. Normalization ensures the biomass increase/decrease is considered during the evaluation of the results, and there is no over/underestimation of the outcomes [11].…”

QTL mapping of a Brazilian bioethanol strain links the cell wall protein-encoding gene GAS1 to low pH tolerance in S. cerevisiae

“…As previously stated, the E1G production process in Brazilian mills has the peculiarity of using the Melle-Boinot operation, characterized by fed-batch fermentation cycles with high-density cell recycle. Yeast cells are recycled up to 3 times per day and, between each recycling step, face an acid-wash treatment with sulfuric acid (pH ~ 1.5) that aims to reduce bacterial contamination and flocculation [ 16 , 51 ]. Thus, after linking the GAS1 allele to PE-2 tolerance to growth at low pH, we sought to explore if it is possible to increase tolerance to an acid-wash treatment in a naturally susceptible strain after allele swap (i.e.…”

Identification of a New Endo-β-1,4-xylanase Prospected from the Microbiota of the Termite Heterotermes tenuis

“…Thus, for bioethanol production, enzymes used in the enzymatic step should ideally act at temperatures close to those used for yeast fermentation. Another alternative would be to prospect for enzymes that act in a range of 40 °C so that they can be used in association with thermotolerant yeasts [ 57 , 58 , 59 ]. Our qualitative xylanolytic activity assays indicated that HtpXyl has the potential to be efficient in these two described situations.…”