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Bacterial contaminants of fuel ethanol production

  • Kelly A. Skinner
  • Timothy D. Leathers
Original Paper

Abstract

Bacterial contamination is an ongoing problem for commercial fuel ethanol production facilities. Both chronic and acute infections are of concern, due to the fact that bacteria compete with the ethanol-producing yeast for sugar substrates and micronutrients. Lactic acid levels often rise during bouts of contamination, suggesting that the most common contaminants are lactic acid bacteria. However, quantitative surveys of commercial corn-based fuel ethanol facilities are lacking. For this study, samples were collected from one wet mill and two dry grind fuel ethanol facilities over a 9 month period at strategic time points and locations along the production lines, and bacterial contaminants were isolated and identified. Contamination in the wet mill facility consistently reached 106 bacteria/ml. Titers from dry grind facilities were more variable but often reached 108/ml. Antibiotics were not used in the wet mill operation. One dry grind facility added antibiotic to the yeast propagation tank only, while the second facility dosed the fermentation with antibiotic every 4 h. Neither dosing procedure appeared to reliably reduce overall contamination, although the second facility showed less diversity among contaminants. Lactobacillus species were the most abundant isolates from all three plants, averaging 51, 38, and 77% of total isolates from the wet mill and the first and second dry grind facilities, respectively. Although populations varied over time, individual facilities tended to exhibit characteristic bacterial profiles, suggesting the occurrence of persistent endemic infections.

Keywords

Bacterial contamination Dry grind Fuel ethanol Lactobacillus Wet mill 

Notes

Acknowledgements

The authors thank the fuel ethanol companies that participated in this study, who requested that their contributions remain anonymous. Expert technical assistance was provided by Melinda S. Nunnally.

References

  1. 1.
    Anonymous (2003) Building a secure energy future. Ethanol industry outlook 2003. Renewable Fuels Association, WashingtonGoogle Scholar
  2. 2.
    Anonymous (2003) The world of corn. National Corn Growers Association, St. LouisGoogle Scholar
  3. 3.
    Aquarone E (1960) Penicillin and tetracycline as contamination control agents in alcoholic fermentation of sugar cane molasses. Appl Microbiol 8:263–268PubMedGoogle Scholar
  4. 4.
    Bayrock D, Ingledew WM (2001) Changes in steady state on introduction of a Lactobacillus contaminant to a continuous culture ethanol fermentation. J Ind Microbiol Biotechnol 27:39–45CrossRefPubMedGoogle Scholar
  5. 5.
    Chang IS, Kim BH, Shin PK, Lee WK (1995) Bacterial contamination and its effects on ethanol fermentation. J Microbiol Biotechnol 5:309–314Google Scholar
  6. 6.
    Chang IS, Kim BH, Shin PK (1997) Use of sulfite and hydrogen peroxide to control bacterial contamination in ethanol fermentation. Appl Environ Microbiol 63:1PubMedGoogle Scholar
  7. 7.
    Chin PM, Ingledew WM (1994) Effect of lactic acid bacteria on wheat mash fermentations prepared with laboratory backset. Enzyme Microbial Technol 16:311–317CrossRefGoogle Scholar
  8. 8.
    Connolly C (1999) Bacterial contaminants and their effects on alcohol production. In: Jacques K, Lyons TP, Kelsall DR (eds) The alcohol textbook, 3rd edn. Nottingham University Press, Nottingham, pp 317–334Google Scholar
  9. 9.
    Dien BS, Bothast RJ, Nichols NJ, Cotta MA (2002) The U.S. corn ethanol industry: an overview of current technology and future prospects. Int Sugar J 104:204–211Google Scholar
  10. 10.
    Essia Ngang JJ, Letourneau F, Wolniewicz E, Villa P (1990) Inhibition of beet molasses alcoholic fermentation by lactobacilli. Appl Microbiol Biotechnol 33:490–493Google Scholar
  11. 11.
    Gibbons WR, Westby CA (1986) Use of potassium metabisulfite to control bacterial contaminants during fermentation of fodder beet cubes for fuel ethanol. Biomass 11:99–113CrossRefGoogle Scholar
  12. 12.
    Hough JS, Briggs DE, Stevens R, Young TW (1982) Microbial contamination in breweries. In: Malting and brewing science: hopped wart and beer, vol 2. Chapman and Hall, London, pp 741–775Google Scholar
  13. 13.
    Hynes SH, Kjarsgaard DM, Thomas KC, Ingledew WM (1997) Use of virginiamycin to control the growth of lactic acid bacteria during alcohol fermentation. J Ind Microbiol 18:284–291CrossRefGoogle Scholar
  14. 14.
    Ingledew WM (1999) Alcohol production by Saccharomyces cerevisiae: a yeast primer. In: Jacques K, Lyons TP, Kelsall DR (eds) The alcohol textbook, 3rd edn. Nottingham University Press, Nottingham, pp 49–87Google Scholar
  15. 15.
    Johnson LA, May JB (2003) Wet milling: the basis for corn biorefineries. In: White PJ, Johnson LA (eds) Corn: chemistry and technology, 2nd edn. Am Assoc Cereal Chem, St. Paul, pp 449–494Google Scholar
  16. 16.
    Keim CR (1999) The wet-milling process: the basis for corn wet milling alcohol production. In: Jacques K, Lyons TP, Kelsall DR (eds) The alcohol textbook, 3rd edn. Nottingham University Press, Nottingham, pp 39–48Google Scholar
  17. 17.
    Leathers TD (1998) Upgrading fuel ethanol coproducts. Soc Ind Microbiol News 48:210–217Google Scholar
  18. 18.
    MacDonald T, Yowell G, McCormack M (2001) U.S. ethanol industry; production capacity outlook. California Energy Commission. P600-01-017Google Scholar
  19. 19.
    Maiorella B, Blanch HW, Wilke CR (1983) By-product inhibition effects on ethanolic fermentation by Saccharomyces cerevisiae. Biotechnol Bioeng 25:103–121Google Scholar
  20. 20.
    Maisch WF (2003) Fermentation products and processes. In: White PJ, Johnson LA (eds) Corn: chemistry and technology, 2nd edn. Am Assoc Cereal Chem, St. Paul, pp 695–721Google Scholar
  21. 21.
    Makanjuola DB, Tymon A, Springham DG (1992) Some effects of lactic acid bacteria on laboratory-scale yeast fermentation. Enzyme Microb Technol 14:350–357CrossRefGoogle Scholar
  22. 22.
    Narendranath NV, Hynes SH, Thomas KC, Ingledew WM (1997) Effects of lactobacilli on yeast-catalyzed ethanol fermentations. Appl Environ Microbiol 63:4158–4163PubMedGoogle Scholar
  23. 23.
    Narendranath NV, Thomas KC, Ingledew WM (2000) Urea hydrogen peroxide reduces the numbers of lactobacilli, nourishes yeast, and leaves no residues in the ethanol fermentation. Appl Environ Microbiol 66:4187–4192CrossRefPubMedGoogle Scholar
  24. 24.
    Narendranath NV, Thomas KC, Ingledew WM (2001) Acetic acid and lactic acid inhibition of growth of Saccharomyces cerevisiae by different mechanisms. J Am Soc Brew Chem 59:187–194Google Scholar
  25. 25.
    Oliva-Neto P, Yokoya F (1998) Effect of 3,4,4′-trichlorocarbanilide on growth of lactic acid bacteria contaminants in alcoholic fermentation. Bioresour Technol 63:17CrossRefGoogle Scholar
  26. 26.
    Oliva-Neto P, Yokoya F (1994) Evaluation of bacterial contamination in a fed-batch alcoholic fermentation process. World J Microbiol Biotechnol 10:697–699Google Scholar
  27. 27.
    Rainbow C (1971) Spoilage organisms in breweries. Process Biochem 6:15–17, 31Google Scholar
  28. 28.
    Stroppa CT, Andrietta MGS, Andrietta SR, Steckelberg C, Serra GE (2000) Use of penicillin and monensin to control bacterial contamination of Brazilian alcohol fermentations. Int Sugar J 102:78–82Google Scholar
  29. 29.
    Thomas KC, Hynes SH, Ingledew WM (2001) Effect of lactobacilli on yeast growth, viability and batch and semi-continuous alcoholic fermentation of corn mash. J Appl Microbiol 90:819–828CrossRefPubMedGoogle Scholar
  30. 30.
    Thomas KC, Hynes SH, Ingledew WM (2002) Influence of medium buffering capacity on inhibition of Saccharomyces cerevisiae growth by acetic and lactic acids. Appl Environ Microbiol 68:1616–1623CrossRefPubMedGoogle Scholar
  31. 31.
    Torre P (1999) Co-products from ethanol fermentation: alternatives for the future. In: Jacques K, Lyons TP, Kelsall DR (eds) The alcohol textbook. Nottingham University Press, Nottingham, pp 335–346Google Scholar

Copyright information

© Society for Industrial Microbiology 2004

Authors and Affiliations

  1. 1.Fermentation Biotechnology Research Unit National Center for Agricultural Utilization Research, USDA, Agricultural Research ServicePeoriaUSA

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