Marion E Fraunhofer (1), Mirko Bunzel (2), Frank Jakob (1), Rudi F Vogel (1), Daniel Wefers (2); (1) Technische Universität München, Freising, Germany
Technical Session 5: Lactic Acid Bacteria
Sunday, August 14 • 2:00–3:15 p.m.
Plaza Building, Concourse Level, Governor’s Square 15
Despite several hurdles, which hinder bacterial growth in beer (e.g., low pH, selective nutrient availability, antimicrobial hop compounds), certain bacteria are still able to grow in and, therefore, spoil beer. Besides strains causing turbidity and off-flavor through growth and metabolite formation, respectively, beer-spoiling bacteria also comprise strains of lactobacilli, which produce slime that increases the viscosity of beer. To get deeper insight into this type of beer spoilage, we characterized Lactobacillus brevis TMW1.2112 isolated from spoiled, viscous beer, with regard to its capability to form exopolysaccharides (EPS), which make up macroscopically observable, slimy material. The strain’s growth dynamics were assessed in different nutrient media, and we found cell growth to correlate with EPS formation. Strongest EPS formation was observed upon growth in liquid culture containing maltose as a carbohydrate source. An agglutination test showed that the major part of these polysaccharides was cell-associated in the form of a capsular polysaccharide (CPS). Since we suspected this ropiness to result from a production of this CPS, we isolated the CPS, as well as the released EPS, from cells or the supernatant, respectively, and analyzed both via NMR spectroscopy and methylation analysis. Both CPS and EPS were identified as identical beta-(1,3)-glucans containing branches in beta-(1,2) positions. Therefore, we suggest that this EPS is mainly produced as CPS, which was partially released into the surrounding medium, causing ropiness of, for example, beer. Since capsule formation is known to protect bacteria from adverse environments in general, it can be speculated that beta-glucan production by beer-spoiling lactobacilli enable a mechanism of passive resistance against the antimicrobial properties of beer.
Marion E. Fraunhofer was born in 1987 in Bad Aibling, Bavaria, Germany. She received a B.S. degree in nutritional science and an M.S. degree in biological chemistry from the University of Vienna, Austria. Currently she is working on her Ph.D. thesis on EPS-forming beer-spoiling lactic acid bacteria at the Technische Universität München under the supervision of Rudi F. Vogel at the Chair of Technische Mikrobiologie in Weihenstephan.