Inhibitors of biofilm formation by biofuel fermentation contaminants

Biofuel fermentation contaminants such as Lactobacillus sp. may persist in production facilities by forming recalcitrant biofilms. In this study, biofilm-forming strains of Lactobacillus brevis, Lactobacillus fermentum, and Lactobacillus plantarum were isolated and characterized from a dry-grind fuel ethanol plant. A variety of potential biofilm inhibitors were tested, including microbial polysaccharides, commercial enzymes, ferric ammonium citrate, liamocins, phage endolysin, xylitol, and culture supernatants from Bacillus sp. A commercial enzyme mixture (Novozyme 188) and culture supernatants from Bacillus subtilis strains ALT3A and RPT-82412 were identified as the most promising biofilm inhibitors. In biofilm flow cells, these inhibitors reduced the density of viable biofilm cells by 0.8–0.9 log cfu/cm2. Unlike B. subtilis strain RPT-82412, B. subtilis strain ALT3A and Novozyme 188 did not inhibit planktonic growth of Lactobacillus sp. MALDI-TOF mass spectra showed the production of surfactin-like molecules by both B. subtilis strains, and the coproduction of iturin-like molecules by strain RPT-82412.