Inhibition of Lactobacillus biofilm growth in fuel ethanol fermentations by Bacillus.

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.