Technical Session 18: Microbiology II Session
Rudi F Vogel, Technische Universität München, Freising, Germany
Co-author(s): Patrick Preissler, Angel Angelov, and Wolfgang Liebl, Technische Universität München, Freising, Germany
ABSTRACT: Beer is an uncomfortable environment for many
bacteria. Nevertheless, specific bacteria, mainly lactic acid bacteria,
are able to grow in beer and spoil it. In this group of bacteria, Lactobacillus brevis
is the most common beer spoiler found in breweries. Within the large
biodiversity of this genus, different ecotypes exist, some of which
exhibit stress responses enabling survival under the antimicrobial
conditions in beer. Thereby, the tolerance to hop compounds, which are
mainly responsible for inhibition of growth in beer, is a multifactorial
process. For this reason, any approaches to predicting the
physiological differences between beer-spoiling and non-spoiling strains
on the basis of a single marker gene are limited. In addition, most
known genetic determinants that are potentially useful for PCR detection
of beer-spoilage bacteria are widely spread in strains with no
reference to high hop tolerance. Comprehensive and strain specific
information about the ecotype beer spoiler compared with non-spoiler
strains reside in their genomes. In this study we aimed to identify
genes related to the ability to grow in stronger hopped beers (e.g.,
pilsner beer) via comparative genomics of four different strains of L. brevis. The genomes of two beer isolates (L. brevis TMW 1.313 and 1.465) and one strain isolated from feces (L. brevis TMW 1.6T) were determined by next generation pyrosequencing. A fourth sequence of a published genome (L. brevis
ATCC 376, silage isolate) was included in the genome comparison.
Redundant information, which resides in the core genome of all L. brevis
ecotypes or strain-specific sequences were removed, and gene fragments
exclusively occurring in beer-spoiling strains were identified, as well
as ecotype-specific DNA sequences of non-spoiling strains. Subsequently,
targeted arrays derived from these sequences were established and
hybridized with DNA from a bigger set of different L. brevis
strains to identify discriminative marker sequences for the ecotype
“beer-spoiler” or “non-spoiler.” As a result, 34 oligonucleotides could
be identified that are able to differentiate the ecotype “beer-spoiler”
and are useful for predicting beer-spoiling potential. Furthermore, four
oligonucleotides specific for the ecotype “non-spoiler” were found that
can be used as negative markers for beer-spoiling strains. The
cumulative detection of more than one of these marker sequences to a
score enables the establishment of a genetic barcode that can be used by
brewers to predict the beer-spoiling potential of L. brevis
isolates. For practical applications, a multiplex PCR targeted toward a
further reduced set of selected marker sequences proved effective.
Rudi
F. Vogel is a biochemist interested in food microbiology and
biotechnology. As head of Technische Mikrobiologie at the Technische
Universität München he conducts research on starter culture development,
high pressure in food, and biosciences, as well as control of unwanted
microbes in food. A clear focus is on lactic acid bacteria, their
metabolism and genetics, pre- and probiotic functionality, and
mechanisms of stress response and adaptation. In this context
beer-spoiling lactobacilli are used as models to understand molecular
mechanisms of hop resistance.
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