Inhibition of Lactobacillus biofilm growth by Bacillus extracts

Industrial ethanol fermentations are not pure cultures, and are expected to contain contaminant bacteria and fungi.  These additional organisms deplete the feedstock and lower overall ethanol yield.  Severe contamination can lead to “stuck” fermentations, requiring costly shutdowns for cleaning.  As Lactobacillus species are tolerant of low pH and high ethanol conditions, they are often the primary contaminants of ethanol fermenters.  These infections are currently treated by antibiotic addition; however, biofilm formation by Lactobacillus can decrease the efficacy of the antibiotics.  Our laboratory has previously identified Lactobacillus strains with a strong tendency to form biofilms.  Recently, we demonstrated that culture supernatants from two Bacillus strains produced lipopeptides, peptide chains with lipid tails, that inhibited biofilm formation in Lactobacillus.  Lipopeptides are known to have antibacterial activity, and could be good control agents in fermentations as some have activity against both biofilm and planktonic cells.  In this study, a survey was taken of 54 lipopeptide-producing Bacillus species bacteria to identify lipopeptides that inhibit biofilm formation.  Three biofilm-forming strains of Lactobacillus isolated as contaminants of fuel ethanol production were tested.  The biofilm inhibition of Bacillus culture supernatants was measured, and six strains showed significant inhibition of all three Lactobacillus strains.  MALDI-TOF MS analysis showed potential lipopeptides in all six supernatants.  Supernatants are being fractionated to determine the biologically active components.