Microbial contamination of fuel ethanol fermentations

Beckner, Margaret Elizabeth; Ivey, Melissa L.; Phister, Trevor G.

doi:10.1111/j.1472-765x.2011.03124.x

Cited by 145 publications

(112 citation statements)

References 41 publications

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“…LAB are also used to ferment plant-based substrates into industrial-grade lactic acid for the manufacture of polylactide bioplastics (5). Conversely, LAB are frequent contaminants of bioethanol fermentations (6).…”

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confidence: 99%

Lactococcus lactis Metabolism and Gene Expression during Growth on Plant Tissues

Golomb

Marco

2014

J. Bacteriol.

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Lactic acid bacteria have been isolated from living, harvested, and fermented plant materials; however, the adaptations these bacteria possess for growth on plant tissues are largely unknown. In this study, we investigated plant habitat-specific traits of Lactococcus lactis during growth in an Arabidopsis thaliana leaf tissue lysate (ATL). L. lactis KF147, a strain originally isolated from plants, exhibited a higher growth rate and reached 7.9-fold-greater cell densities during growth in ATL than the dairy-associated strain L. lactis IL1403. Transcriptome profiling (RNA-seq) of KF147 identified 853 induced and 264 repressed genes during growth in ATL compared to that in GM17 laboratory culture medium. Genes induced in ATL included those involved in the arginine deiminase pathway and a total of 140 carbohydrate transport and metabolism genes, many of which are involved in xylose, arabinose, cellobiose, and hemicellulose metabolism. The induction of those genes corresponded with L. lactis KF147 nutrient consumption and production of metabolic end products in ATL as measured by gas chromatography-time of flight mass spectrometry (GC-TOF/MS) untargeted metabolomic profiling. To assess the importance of specific plant-inducible genes for L. lactis growth in ATL, xylose metabolism was targeted for gene knockout mutagenesis. Wild-type L. lactis strain KF147 but not an xylA deletion mutant was able to grow using xylose as the sole carbon source. However, both strains grew to similarly high levels in ATL, indicating redundancy in L. lactis carbohydrate metabolism on plant tissues. These findings show that certain strains of L. lactis are well adapted for growth on plants and possess specific traits relevant for plant-based food, fuel, and feed fermentations. L actic acid bacteria (LAB) found on plants are essential for the production of a wide variety of plant-derived fermented foods with desirable organoleptic properties, improved nutritional attributes, and extended shelf life (1). LAB are a diverse group of bacterial species in the Firmicutes phylum that are characterized by the production of lactic acid as the main end product of carbohydrate metabolism. Some of the most commonly recognized genera among the LAB include Lactococcus, Lactobacillus, Leuconostoc, Pediococcus, and Oenococcus. LAB-fermented plantbased food products include sauerkraut, sourdough, and olives, as well as diverse foods unique to different ethnic groups (e.g., pulque, nukadoko, or gundruk [2,3]). LAB are responsible for the conversion of plant tissues such as alfalfa into silage for animal feed with enhanced nutritional content and stability (4). LAB are also used to ferment plant-based substrates into industrial-grade lactic acid for the manufacture of polylactide bioplastics (5). Conversely, LAB are frequent contaminants of bioethanol fermentations (6).In contrast to commercial dairy fermentations that utilize starter cultures, initiation of plant-based fermentations typically relies on the LAB that are located on or associated with plant tis...

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confidence: 99%

Lactococcus lactis Metabolism and Gene Expression during Growth on Plant Tissues

Golomb

Marco

2014

J. Bacteriol.

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“…Bacterial contamination is still a major challenge in industrial ethanol fermentations despite a lot of effort devoted to the subject (Skinner and Leathers 2004;Kádár et al 2007;Bischoff et al 2009;Albers et al 2011;Beckner et al 2011). Bacteria compete with the yeasts by consuming the sugars available for ethanol production and the nutrients needed by the yeast for growth (Skinner and Leathers 2004).…”

Section: Introductionmentioning

confidence: 99%

“…The use of low pH frequently fails, as some bacterial strains can thrive in low pH media (Bischoff et al 2009). Antibiotics generate difficult-to-treat waste and can contribute to the development of antibiotic-resistant bacteria (Beckner et al 2011). The early detection methods are laborious and offer no real solution to the problem.…”

Section: Introductionmentioning

confidence: 99%

Effect of High Solids Loading on Bacterial Contamination in Lignocellulosic Ethanol Production

et al. 2013

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aContamination by lactic acid-producing bacteria is frequently a major challenge in ethanol processes. In this work, high solids loading was used both to keep bacterial infection under control in simultaneous saccharification and fermentation (SSF) of lignocellulosic biomass and to increase the ethanol productivity of the process. With no sterilization of the substrates, lactic acid bacteria contaminated the fermentation process with 8 and 10% suspended solids (SS) substrates, consumed both pentoses and hexoses, and produced lactic acid. However, a high solids loading of 12% SS prevented lactic acid formation, which resulted in higher ethanol yield during the SSF process. This high SS resulted in an ethanol concentration of 47.2 g/L, which satisfies the requirement for industrial lignocellulosic ethanol production.

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“…Acute infections are unpredictable and are characterized by the accumulation of bacterial by-products such as lactic acid and acetic acid. These organic acids inhibit yeast growth [8][9][10][11][12][13][14][15] and may cause stuck fermentations (incomplete conversion of glucose to ethanol) that require costly shutdowns of facilities for cleaning and disinfecting [4,7,9,16]. Lactobacilli flourish in the glucose-rich fermentation environment and are well adapted for survival under the high ethanol, low pH, and low oxygen conditions present during fermentation [6,17,18].…”

Section: Introductionmentioning

confidence: 99%

“…Fuel ethanol production is not performed under aseptic conditions, and the economics of fuel ethanol production are threatened by Gram-positive and Gram-negative bacteria that contaminate commercial fuel ethanol plants and reduce ethanol yields [4][5][6][7]. Lactic acid bacteria (LAB) are the primary bacterial contaminants of fuel ethanol fermentations with species of Lactobacillus predominating.…”

Section: Introductionmentioning

confidence: 99%

Saccharomyces cerevisiae expressing bacteriophage endolysins reduce Lactobacillus contamination during fermentation

Khatibi

Roach

Donovan

et al. 2014

Biotechnol Biofuels

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Background: One of the challenges facing the fuel ethanol industry is the management of bacterial contamination during fermentation. Lactobacillus species are the predominant contaminants that decrease the profitability of biofuel production by reducing ethanol yields and causing "stuck" fermentations, which incur additional economic losses via expensive antibiotic treatments and disinfection costs. The current use of antibiotic treatments has led to the emergence of drug-resistant bacterial strains, and antibiotic residues in distillers dried grains with solubles (DDGS) are a concern for the feed and food industries. This underscores the need for new, non-antibiotic, eco-friendly mitigation strategies for bacterial contamination. The specific objectives of this work were to (1) express genes encoding bacteriophage lytic enzymes (endolysins) in Saccharomyces cerevisiae, (2) assess the lytic activity of the yeast-expressed enzymes against different species of Lactobacillus that commonly contaminate fuel ethanol fermentations, and (3) test the ability of yeast expressing lytic enzymes to reduce Lactobacillus fermentum during fermentation. Implementing antibiotic-free strategies to reduce fermentation contaminants will enable more cost-effective fuel ethanol production and will impact both producers and consumers in the farm-to-fork continuum. Results: Two genes encoding the lytic enzymes LysA and LysA2 were individually expressed in S. cerevisiae on multi-copy plasmids under the control of a galactose-inducible promoter. The enzymes purified from yeast were lytic against Lactobacillus isolates collected from fermentors at a commercial dry grind ethanol facility including Lactobacillus fermentum, Lactobacillus brevis, and Lactobacillus mucosae. Reductions of L. fermentum in experimentally infected fermentations with yeast expressing LysA or LysA2 ranged from 0.5 log 10 colony-forming units per mL (CFU/mL) to 1.8 log 10 (CFU/mL) over 72 h and fermentations treated with transformed yeast lysate showed reductions that ranged from 0.9 log 10 (CFU/mL) to 3.3 log 10 (CFU/mL). Likewise, lactic acid and acetic acid levels were reduced in all experimentally infected fermentations containing transformed yeast (harboring endolysin expressing plasmids) relative to the corresponding fermentations with untransformed yeast.

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Microbial contamination of fuel ethanol fermentations

Cited by 145 publications

References 41 publications

Lactococcus lactis Metabolism and Gene Expression during Growth on Plant Tissues

Lactococcus lactis Metabolism and Gene Expression during Growth on Plant Tissues

Effect of High Solids Loading on Bacterial Contamination in Lignocellulosic Ethanol Production

Saccharomyces cerevisiae expressing bacteriophage endolysins reduce Lactobacillus contamination during fermentation

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