A strategy to prevent the occurrence of Lactobacillus strains using lactate-tolerant yeast Candida glabrata in bioethanol production

Abstract

Contamination of Lactobacillus sp. in the fermentation broth of bioethanol production decreases ethanol production efficiency. Although the addition of lactate to the broth can effectively inhibit the growth of Lactobacillus sp., it also greatly reduces the fermentation ability of Saccharomyces cerevisiae. To overcome this conflict, lactate-tolerant yeast strains were screened. Candida glabrata strain NFRI 3164 was found to exhibit both higher levels of lactate tolerance and fermentation ability. Co-cultivation of C. glabrata was performed with Lactobacillus brevis and Lb. fermentum, which were reported as major contaminating bacteria during bioethanol production, in culture medium containing 2% lactate. Under these culture conditions, the growth of Lactobacillus strains was greatly inhibited, but the ethanol production of C. glabrata was not significantly affected. Our data show the possibility of designing an effective fuel ethanol production process that eliminates contamination by Lactobacillus strains through the combined use of lactate addition and C. glabrata.

Capability of Candidas to Ferment Mixtures of Carbohydrates to Alcohol in Free Cells and Co-Culture

“…The alcohol production with C. tropicalis strain was 35% higher than the alcohol concentration obtained by C. glabrata, which can be explained by the lower consumption of glucose and fructose observed with C. glabrata and by the influence of the agitation that favors C. glabrata microbial growth, and also oxygen dissolution in the medium, reducing alcohol production. Nevertheless, the ability of alcohol production by C. glabrata has been reported with similar characteristics with those of S.cerevisiae that showed increment in alcohol concentration under limited oxygen conditions [7]. In both strains alcohol production started after 0.5 days of fermentation, production rate was higher with C. glabrata (0.040 ± 0.01 gh -1 ), while a higher production of 44.5 ± 0.04 gL -1 was obtained with C.…”

“…Yeasts of the genus Candida sp. have shown the ability to ferment pentoses and hexoses carbohydrates from degradation of hemicellulose and cellulose, individually and in co-culture [5][6][7]. The co-culture system appears to be an advantageous system over individual cultures because of the potential for synergistic utilization of the metabolic pathways of the strains involved [8,9].…”

Enhancement of Acetic Acid Tolerance in Saccharomyces cerevisiae by Overexpression of the HAA1 Gene, Encoding a Transcriptional Activator

“…It is therefore particularly desirable to establish a method preventing bacterial contamination without using antibiotics. Weak organic acids, such as acetic acid and lactic acid, are effective and safe inhibitors used in the prevention of such contamination (14,18). However, the fermentation ability of yeast is also limited by the presence of high concentrations of weak organic acids.…”

Control of Lactobacillus plantarum Contamination in Bioethanol Fermentation by Adding Plantaricins

“…Firstly, Lactobacillus can compete against S. cerevisiae for saccharides and other micronutrients in fermentation broth (Narendranath and Power, 2005). Secondly, lactate generated by Lactobacillus can decrease the fermentation pH value, thus inhibiting yeast biomass and bioethanol yield (Watanabe et al, 2008;Katakura et al, 2011). Addition of 4% (w/v) exogenous lactic acid can significantly decrease the bioethanol yield (Graves et al, 2006).…”

“…Various methods have been attempted to prevent the adverse effects of bacterial contamination, such as adding antibiotics (Narendranath and Power, 2005;Bischoff et al, 2009), exogenous ethanol (Katakura et al, 2011), lactate (Watanabe et al, 2008), and acetate (Saithong et al, 2009). Antibiotics are widely used to eliminate bacterial contamination.…”