Microbiology Session
Carola C Kern, Technische Universität München, Freising, Germany
Co-author(s): Patrick Preissler, Rudi Vogel, and Jürgen Behr, Technische Universität München, Freising, Germany
ABSTRACT: Lactobacillus brevis is one of the most frequently encountered bacteria in beer-spoilage incidents. The species L. brevis
comprises strains with the ability to grow in low hopped wheat beer, as
well as strains that can grow in lager beer or even highly hopped
pilsner beer. Accordingly, differentiation and classification of L. brevis
based on their beer-spoiling ability improves quality control in
breweries. Matrix assisted laser desorption ionization–time-of-flight
mass spectrometry (MALDI-TOF MS) has been shown as a powerful and rapid
tool for species and subspecies differentiation of bacterial isolates.
In principle, MALDI-TOF MS of microbial samples is based on the
generation of fingerprints of biomarker molecules, where low molecular
weight proteins form a distinctive peak pattern, reflecting protein
expression in the cell. The aim of this work was to elucidate whether
differences in the proteome of two ecotypes of L. brevis are sufficient to differentiate L. brevis below-species ecotypes by MALDI-TOF MS and with special emphasis on their beer-spoiling ability. L. brevis
strains were characterized according to their tolerance to
iso-alpha-acids and their growth in wheat, lager, and pilsner beers. Two
groups of L. brevis strains, each representing a distinct
ecotype, were formed, among which one group showed the ability to grow
in pilsner beer or lager beer and generally had a tolerance to
iso-alpha-acids above 10 µM. The other group was only able to grow in low hopped wheat beer and exhibited an iso-alpha-acids tolerance below 10 µM.
The two groups were analyzed using MALDI-TOF MS. Strain level
identification and cluster analysis of the data were performed. Strain
level identification was achieved in 85% of a total of more than 200
samples. Mis-identification occurred only among strains belonging to the
same ecotype, referring to a strong or weak ability to spoil beer.
Cluster analysis split strains into three subgroups: one closely related
group of strains that were, with the exception of a single strain, able
to grow in lager beer, and two groups of strains, which were only able
to grow in wheat beer. Taken together, MALDI-TOF MS allowed strain level
classification of L. brevis in about 85% of all samples analyzed
and furthermore showed potential to discriminate strains and group them
according to ecotypes based on their ability to grow in beer.
Carola
C. Kern was born in 1984 in Austria. She obtained her master’s degree
in nutritional sciences from the University of Vienna in 2010 and is
currently a Ph.D. student at the Technical University of Munich, where
she’s working on the identification and differentiation of microbial
contaminants in beverages by MALDI-TOF mass spectrometry at the chair of
Technische Mikrobiologie under the supervision of Rudi F. Vogel.
