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.