BACTERIAL CONTAMINANTS OF FUEL ETHANOL PRODUCTION

Authors: Skinner, Kelly; Leathers, Timothy

Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2004
Publication Date: 10/1/2004
Citation: Skinner, K.A., Leathers, T.D. 2004. Bacterial contaminants of fuel ethanol production. Journal of Industrial Microbiology and Biotechnology. 31:401-408.

Interpretive Summary: Fundamental information is lacking on the problem of bacterial infections of fuel ethanol fermentations. We performed, for the first time, quantitative surveys of bacterial populations in commercial corn-based ethanol facilities. Results will be of interest to ethanol producers and researchers attempting to develop control methods.

Technical 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 nine 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 the order of 10**6 bacteria per ml. Titers from dry grind facilities were more variable but often reached the order of 10**8 per 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 four hours. 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.