The role of nisin in fuel ethanol production with Saccharomyces cerevisiae
The Key Laboratory of Industrial Biotechnology, Ministry of Education, National Engineering Laboratory for Cereal Fermentation Technology, Jiangnan University, Wuxi, China. Letters in Applied Microbiology
(Impact Factor: 1.66).
06/2012; 55(2):128-34. DOI: 10.1111/j.1472-765X.2012.03275.x
To investigate the effects of nisin on lactobacilli contamination of yeast during ethanol fermentation and to determine the appropriate concentration required to control the growth of selected lactobacilli in a YP/glucose media fermentation model.
The lowest concentration of nisin tested (5 IU ml(-1) ) effectively controlled the contamination of YP/glucose media with 10(6) CFU ml(-1) lactobacilli. Lactic acid yield decreased from 5.0 to 2. 0 g l(-1) and potential ethanol yield losses owing to the growth and metabolism of Lactobacillus plantarum and Lactobacillus brevis were reduced by 11 and 7.8%, respectively. Approximately, equal concentrations of lactic acid were produced by Lact. plantarum and Lact. brevis in the presence of 5 and 2 IU ml(-1) nisin, respectively, thus demonstrating the relatively higher nisin sensitivity of Lact. brevis for the strains in this study. No differences were observed in the final ethanol concentrations produced by yeast in the absence of bacteria at any of the nisin concentrations tested.
Metabolism of contaminating bacteria was reduced in the presence of 5 IU ml(-1) nisin, resulting in reduced lactic acid production and increased ethanol production by the yeast.
Bacteriocins represent an alternative to the use of antibiotics for the control of bacterial contamination in fuel ethanol plants and may be important in preventing the emergence of antibiotic-resistant contaminating strains.
Available from: Admilton G. de Oliveira
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ABSTRACT: This work evaluated the effect of secondary bacterial metabolites produced by Pseudomonas sp LV strain in control of Lactobacillus sp. population in the microcosm of the vat during ethanol fermentation. The fraction F4 produced by Pseudomonas aeruginosa was extracted with dichloromethane and fractionating by vacuum liquid chromatography ob- tained in a methanol phase. The evaluation of antibiotic activity of F4 fraction mixed or not with sulphuric acid and Kamoram®. The antibiotic activity of F4 fraction was determined as well as the fermentation efficiency. Also was de- termined yeast cell viability, budding formation, the viability of budding cells, and number of populations of Sac- charomyces cerevisiae and Lactobacillus sp. The results showed that the F4 fraction had high selective antibiotic ac- tivity against Lactobacillus sp. but not for S. cerevisae, and no inhibitory effect was observed in the fermentation proc- ess by yeast. Also F4 fraction decreased flocculation and foam formation. The F4 has an antibiotic activity against Lac- tobacillus sp. and should be used as an alternative to control bacteria contamination and foam and flocculation forma- tion in the fuel ethanol fermentation process. The F4 fraction could reduce the use of antibiotics in the control of Lac- tobacillus sp. population during the fuel ethanol production.
Available from: Dominic Sauvageau
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ABSTRACT: The emergence of biofuels produced through yeast fermentation represents an important avenue for sustainable energy production. Despite all its advantages, this process is vulnerable to contamination by other organisms – most commonly lactic acid bacteria – that are present in raw feedstocks and/or in production lines. These contaminants compete with the yeast for nutrients, reducing the overall biofuel yield, and release substances that inhibit yeast growth. Here, we investigated the application of bacteriophages as potential antibacterial agents in yeast fermentation.
Experiments conducted to understand the impact of pH on yeast, bacterial, and phage development showed that the yeast Saccharomyces cerevisiae Superstart™ grew in a similar fashion at pH levels ranging from 3 to 6. Growth of Lactobacillus plantarum ATCC® 8014™ was inhibited by pH levels of less than 4, and phages ATCC® 8014-B1™ (phage B1) and ATCC® 8014-B2™ (phage B2) displayed different infectivities within the pH range tested (pH 3.5 to 7). Phage B1 showed the best infectivity at pH 6, while phage B2 was most virulent at pH levels ranging from 4 to 5, and the cocktail of these phages showed highest infectivity in the range from pH 4 to 6. Population dynamics studies in MRS medium at pH 6 showed that, in the presence of bacteria inoculated at 107 cells/ml, yeast cultures were impeded under aerobic and anaerobic conditions, showing major decreases in both cell yield and ethanol production. The addition of the phage cocktail at a low initial multiplicity of infection was sufficient to reduce contamination by over 99%, and to allow yeast and ethanol yields to reach values equivalent to those of axenic cultures.
From the results observed, phages are good candidates as antimicrobial agents, to be used in place of or in conjunction with antibiotics, in yeast fermentation processes. Their implementation with other common contamination abatement/prevention methods could further increase their efficacy.
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ABSTRACT: Current fuel ethanol production using yeasts and starch or sucrose-based feedstocks is referred to as 1st generation (1G) ethanol production. These processes are characterized by the high contribution of sugar prices to the final production costs, by high production volumes, and by low profit margins. In this context, small improvements in the ethanol yield on sugars have a large impact on process economy. Three types of strategies used to achieve this goal are discussed: engineering free-energy conservation, engineering redox-metabolism, and decreasing sugar losses in the process. Whereas the two former strategies lead to decreased biomass and/or glycerol formation, the latter requires increased process and/or yeast robustness.
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