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Stress tolerance to low O2 tension and dissolved CO2

The low oxygen levels in beer selects for microbes capable of anaerobic respiration. LAB, specifically Lactobacillus and Pediococcus isolates, can produce energy in the absence of oxygen by using other electron acceptors to regenerate NAD+ or by substrate-level phosphorylation during fermentation for the regeneration of NAD+ (White et al., 2012a). Fermentation capacities in anaerobic conditions are known to be different across subgroups, even genera, of LAB, nonetheless, the overall anaerobic nature of BSR LAB facilitates their resistance to the stress of low oxygen.

Recently, it was shown that the presence of headspace pressure and dissolved CO2 (dCO2) limits the ability of LAB to grow in and spoil beer (Bergsveinson et al. 2015b). Transcriptomic analysis of dCO2-tolerant isolate L. brevis BSO 464 during growth in packaged beer has since revealed that this environment strongly induces modifications to cellular transcriptional regulation, and to both the cell membrane and wall, relative to what occurs in unpackaged beer (Bergsveinson et al., 2016b). This finding strongly suggests that further analysis of changes in the cell membrane lipid profile of dCO2 beer-tolerant BSR LAB may reveal signature alterations, or biomarkers of tolerance to the packaged beer environment and beer in general. Such information is important, since it is reasonable to expect brewery-adapted BSR LAB to be able to withstand the sudden, additional stress of high dCO2 as a result of headspace flushing with CO2 during packaging.

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