Abstract
Many contaminant yeast strains that survive inside fuel ethanol industrial vats show detrimental cell surface phenotypes. These harmful effects may include filamentation, invasive growth, flocculation, biofilm formation, and excessive foam production. Previous studies have linked some of these phenotypes to the expression of FLO genes, and the presence of gene length polymorphisms causing the expansion of FLO gene size appears to result in stronger flocculation and biofilm formation phenotypes. We performed here a molecular analysis of FLO1 and FLO11 gene polymorphisms present in contaminant strains of Saccharomyces cerevisiae from Brazilian fuel ethanol distilleries showing vigorous foaming phenotypes during fermentation. The size variability of these genes was correlated with cellular hydrophobicity, flocculation, and highly foaming phenotypes in these yeast strains. Our results also showed that deleting the primary activator of FLO genes (the FLO8 gene) from the genome of a contaminant and highly foaming industrial strain avoids complex foam formation, flocculation, invasive growth, and biofilm production by the engineered (flo8∆::BleR/flo8Δ::kanMX) yeast strain. Thus, the characterization of highly foaming yeasts and the influence of FLO8 in this phenotype open new perspectives for yeast strain engineering and optimization in the sugarcane fuel-ethanol industry.
Highlights
The renewable Brazilian sugarcane first-generation fuel-ethanol industry is highly competitive, when compared with ethanol production processes from other crops, as it shows the highest percentage of greenhouse gas emissions’ reduction, highest energy balance and yields per hectare, and the lowest production costs [1,2]
The productivity of the Brazilian fuel ethanol industry has increased steadily since 1975, an increase possibly due to several improvements, including the selection of new sugarcane varieties with an increased amount of sugarcane biomass per hectare and the amount of ethanol produced from each ton of sugarcane, as the industrial sector responsible for this, including the fermentation process, has reached high industrial efficiency [3,4,5]
We analyzed 15 industrial yeast strains isolated during fermentative fuel-ethanol production processes in Brazil
Summary
The renewable Brazilian sugarcane first-generation fuel-ethanol industry is highly competitive, when compared with ethanol production processes from other crops (e.g., corn and sugarbeet), as it shows the highest percentage of greenhouse gas emissions’ reduction, highest energy balance and yields per hectare, and the lowest production costs [1,2]. The productivity of the Brazilian fuel ethanol industry has increased steadily since 1975, an increase possibly due to several improvements, including the selection of new sugarcane varieties with an increased amount of sugarcane biomass per hectare and the amount of ethanol produced from each ton of sugarcane, as the industrial sector responsible for this, including the fermentation process, has reached high industrial efficiency [3,4,5]. As many industrial processes, the substrate (sugarcane juice and/or diluted molasses) is not sterile and, a continuous input of contaminant microorganisms is observed [9,10]. While lactic acid bacteria are contaminants of concern in industrial ethanol fermentations [11,12], wild yeasts affect the productivity of these fermentations, leading to decreased efficiency and stuck fermentations that cause plants to shut down for cleaning before beginning a new fermentation [13,14,15,16]
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