Abstract
Bacterial contamination is known as a major cause of the reduction in ethanol yield during bioethanol production by Saccharomyces cerevisiae. Acetate is an effective agent for the prevention of bacterial contamination, but it negatively affects the fermentation ability of S. cerevisiae. We have proposed that the combined use of organic acids including acetate and lactate and yeast strains tolerant to organic acids may be effective for the elimination of principally lactic acid bacterial (LAB) contamination. In a previous study employing laboratory S. cerevisiae strains, we showed that overexpression of the HAA1 gene, which encodes a transcriptional activator, could be a useful molecular breeding method for acetate-tolerant yeast strains. In the present study, we constructed a HAA1-overexpressing diploid strain (MATa/α, named ER HAA1-OP) derived from the industrial bioethanol strain Ethanol Red (ER). ER HAA1-OP showed tolerance not only to acetate but also to lactate, and this tolerance was dependent on the increased expression of HAA1 gene. The ethanol production ability of ER HAA1-OP was almost equivalent to that of the parent strain during the bioethanol production process from sugarcane molasses in the absence of acetate. The addition of acetate at 0.5% (w/v, pH 4.5) inhibited the fermentation ability of the parent strain, but such an inhibition was not observed in the ethanol production process using ER HAA1-OP.
Highlights
The utilization of bioethanol as an alternative to fossil fuels has attracted much attention in the effort to combat global warming and improve energy reserves
Construction of a diploid HAA1-overexpressing strain and confirmation of the HAA1 gene expression level To construct a diploid strain overexpressing HAA1 gene derived from S. cerevisiae Ethanol Red (ER), we employed a strategy of mating haploid strains that overexpressed the HAA1 gene
We reported that an HAA1-overexpressing strain derived from a laboratory strain showed higher acetate tolerance, and that the overexpression of HAA1
Summary
The utilization of bioethanol as an alternative to fossil fuels has attracted much attention in the effort to combat global warming and improve energy reserves. Bacterial contamination is known as a major cause of reductions in the yield of ethanol from such feedstock by yeast, Saccharomyces cerevisiae (Skinner and Leathers 2004) These bacterial contaminants grow under conditions suitable for Various agents have been examined for their potential to control bacteria and thereby avoid the reduction of ethanol yields. It has been reported that potassium metabisulfite and antibiotics effectively inhibit bacterial contamination (Aquarone 1960; Bayrock et al 2003; Hynes et al 1997; Oliva-Neto and Yokoya 1998; William and Carl 1986). Antibiotics such as penicillin and virginiamycin are used in commercial bioethanol production today (Bayrock et al 2003; Hynes et al 1997). In designing a bioethanol production process that eliminates bacterial contamination, we focused on acetate as a control agent
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