J. BERGSVEINSON (1), B. Ziola (1);
(1) University of Saskatchewan, Saskatoon, SK, Canada
Technical Session 6 - Yeast and Microbiology
Monday, June 15
2:00–3:45 p.m.
Flores 1–2
The search for a small set of universal genetic markers for beer-spoilage by lactic acid bacteria (LAB) has long been of interest for researchers and brewers alike. To date, only a few genes have been proposed to confer the ability to spoil beer and all are purported to solely mediate the stress of hops. Unfortunately, these hop-tolerance genes are not the “Holy Grail” of genetic indicators, as they are not foolproof markers of beer-spoilage. Specifically, these genes are not found in all LAB that cause spoilage and, conversely, are sometimes found in LAB with limited beer-spoilage ability. Thus much remains to be investigated regarding the genetics and physiology of LAB beer-spoilage isolates in relation to other physiological stresses present in beer, such as dissolved CO2/pressure. The impetus to expand the focus of investigation of these isolates is increased in light of the recent appreciation of the role some LAB isolates play in fermenting lambic beers and selected specialty craft brews. Under certain circumstances, flavor compounds produced by LAB contribute favorably to the flavor profile of a beer, though when these compounds are over produced or are “undesired,” they spoil the beer. This suggests that there is either a relative scale of brewing-related virulence for LAB isolates (i.e., the extent to which an isolate can grow and metabolize in beer) or that differences in the physiochemical properties of a given beer limits which LAB isolates can grow in it. This poses an interesting dilemma as to how best to define brewing-related LAB and how to detect virulent, spoilage-LAB versus their non-spoilage counterparts. To investigate differences in LAB genetics and the resulting physiology of isolates with different beer-growth capabilities, we have sequenced the genomes of six LAB isolates via the Illumina MiSeq platform and performed subsequent comparative genomics and detailed plasmid profile analysis. We also assessed the transcriptional activity of three of these isolates via RNA sequencing with the Illumina HiSeq platform under conditions of varying hop concentrations, as well as dissolved CO2 levels, in beer. Further, we assessed alterations in the fatty acid profile of 10 LAB isolates of interest under conditions of varying dissolved CO2 levels in beer via gas chromatography. Analysis of these data sets indicates that the search for beer-spoilage indicator genes must be expanded beyond hop-tolerance genes to include conserved regulatory elements such as non-coding RNAs and DNAs, and that strong beer-spoilage potential is indicated by selected genetic pathways. Additionally, the data reveal the importance of fatty acid adaptations in correlation with dissolved CO2/pressure, as this is clearly a selective pressure for the virulence of LAB in beer. In sum, the expectation of finding a small subset of “universal” or “Holy Grail” genes in relation to beer-spoilage must be curtailed. Instead, expression of genes from multiple physiological systems needs to be further analyzed vis-à-vis relevance to LAB growth in and spoilage of beer.
Jordyn Bergsveinson graduated from the University of Saskatchewan in 2010 with a B.S. (honors) degree in microbiology and immunology. She then began a master’s program under the supervision of Barry Ziola in the area of brewing microbiology at the University of Saskatchewan and converted from an M.S. program to a Ph.D. program in December 2011 and is looking to finish her Ph.D. degree in August 2015. Her Ph.D. work is focused on the detailed genetic and physiological mechanisms of lactic acid bacteria for the purpose of correctly identifying true beer-spoiling organisms.
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