Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: May 24, 2007
Publication Date: May 24, 2007
Citation: Bischoff, K.M., Liu, S., Dien, B.S. 2007. Monensin inhibits growth of bacterial contaminants from fuel ethanol plants [abstract]. American Society for Microbiology. Poster #0-010. p. 60. Technical Abstract: Contamination of commercial fermentation cultures by lactic acid bacteria (LAB) is a common and costly problem to the fuel ethanol industry. Virginiamycin (VIR) and penicillin (PEN) are frequently used to control bacterial contamination but extensive use of antibiotics may select for strains with decreased susceptibility to these agents. Samples from the liquefaction tank at a dry-grind ethanol facility using VIR and PEN to control contamination were plated on MRS agar media with and without VIR at 5 ug/ml. Several species of LAB were isolated, including species of Leuconostoc and Weissella with MICs for VIR of equal or greater than 4 ug/ml and strains of Lactococcus lactis with MICs for VIR of >128 ug/ml. All were susceptible to monensin (5 ug/ml), a polyether ionophoric antibiotic that is used in food animal production as a coccidiostat and as a growth promoting agent. Shake-flask fermentations of Saccharomyces cerevisiae experimentally infected with L. lactis had a lower pH (4.10 +/- to 0.04) and a higher concentration of lactic acid (1.0 +/- 0.1 g/l) than control cultures (pH 4.50 +/- 0.03 and < 0.1 g/l lactic acid). Treatment with monensin (5 ug/ml) mitigated the effects of the L. lactis challenge, yielding a final pH of 4.43 +/- 0.05 and decreasing lactic acid to undetectable levels. Treatment with monensin alone did not measurably affect the fermentation. This work demonstrates that monensin may be an effective treatment of ethanol fermentation cultures infected with VIR-resistant lactic acid bacteria.