Inhibition of Lactobacillus biofilm growth in fuel ethanol fermentations by Bacillus

Abstract Commercial fuel ethanol fermentations suffer from microbial contaminants, particularly species of Lactobacillus that may persist as antibiotic-resistant biofilms. In this study, culture supernatants from 54 strains of Bacillus known to produce lipopeptides were tested for inhibition of biofilm formation by Lactobacillus fermentum , L. plantarum , and L. brevis strains previously isolated as biofilm-forming contaminants of a commercial fuel ethanol facility. Eleven Bacillus strains inhibited biofilm formation by all three strains by at least 65% of controls. None of these strains inhibited Saccharomyces cerevisiae . Three strains also significantly inhibited planktonic cultures of Lactobacillus . Culture supernatants from B. nakamurai strain NRRL B-41091 were particularly effective. Inhibition was bacteriostatic rather than bacteriocidal, and appeared to be specific for strains of Lactobacillus . Furthermore, the inhibitor from B. nakamurai was shown to prevent stuck fermentations in a corn mash model fermentation system of S. cerevisiae contaminated with L. fermentum .