Microbiology Session
Barry Ziola, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
Co-author(s): Emily Ewen and Vanessa Pittet, University of Saskatchewan, Saskatoon, SK, Canada
ABSTRACT: Pediococcus claussenii is a species known to spoil beer. The P. claussenii
ATCC BAA-344T (Pc344) genome was recently sequenced; however, many of
the genes that permit this organism to proliferate amid the harsh
conditions in beer have yet to be identified. It has been determined
that Pc344 carries eight plasmids, six of which have coding capacity and
two of which are cryptic. One of these plasmids has previously been
shown to harbor horA, a well-established beer-spoilage associated
gene involved in hops resistance. To further examine the role that
plasmids may play in the ability of Pc344 to spoil beer, we obtained a
collection of isolates with altered plasmid profiles and put these
isolates through a series of phenotypic analyses designed to mimic the
harsh conditions present in beer. Plasmid-minus Pc344 variants were
generated either by repeatedly culturing in a non-beer medium or by
incubating in a non-beer medium with a sub-lethal concentration of the
antimicrobial compound novobiocin. Single colonies were selected by
spreading onto MRS agar plates and then screened for an altered plasmid
profile using multiplex polymerase chain reactions with primer sets
designed to specific regions of each of the six plasmids with coding
capacity. The plasmid-minus isolates obtained were then subjected to
comparative phenotypic analyses, including monitoring growth in the
presence of varying levels of hops using gradient agar plates, as well
as relative growth rates in beer. Variability in beer-growth rate was
noted among the plasmid-minus variants compared to the typical growth
pattern of the parental Pc344 isolate possessing a complete set of
plasmids. Variability of growth was also observed when analyzing for
hops resistance. The correlation between plasmid elimination and altered
phenotype confirms that the methodology used here is an appropriate
starting point for investigating the role that plasmid genes play in the
beer-spoiling capability of Pc344. Being able to attribute an
organism’s beer-spoiling capacity in part to the presence of specific
plasmids provides a clear direction for a more refined search of
beer-spoilage associated genes.
Barry Ziola received a B.S.
degree (with honors) in botany from McGill University, Montreal, in
1970. After completing a Ph.D. degree in biochemistry at the University
of Alberta, Edmonton, in 1975, he undertook a three-year post-doctoral
stint at the University of Turku, Turku, Finland. He has been at the
University of Saskatchewan, Saskatoon, since 1978, with promotion to
professor coming in 1986. His interest and continuing research in
brewing spoilage bacteria dates to the mid-1980s.
VIEW PRESENTATION 166
