Maintenance of BSR LAB and importance of biofilms

The mapping of BSR LAB and hop tolerance genes in the brewery by Bokulich et al. (2015) illustrates the risk of cross-contamination between different equipment surfaces, especially in environments where conventional and sour beer types are produced. Cross-contamination of surface areas supports the increase in diversity of the present microbial community, as well as the development of biofilms, thus probably driving spoilage incidence at various production stages (Matoulkova et al., 2012; Timke et al., 2005, 2008; Storgards et al., 2006).

The brewing industry has great concern about biofilms, given that they can be established not only in the brewery, but also in draft beer dispensing lines outside the brewery, which brewers usually do not monitor, nor control (Timke et al., 2005; Thomas and Whitham, 1997). Though biofilms are typically comprised of a variety of microorganisms, they have a known correlation with product-spoiling bacteria and thus require prevention and attention (Timke et al., 2005; Zottola and Sasahara, 1994). Increased analysis of brewery biofilms would be of great utility, especially given that biofilms may be highly individualistic and thus require specific or adapted control treatments. Though some specific strains of LAB have been shown to be able to form biofilms (Kubota et al., 2008), in general, Gram-negative bacteria (and yeasts and moulds) are among the first to colonize surfaces in the brewery, while LAB are opportunistic colonizers that benefit from the multiple interactions within already established communities, especially if the biofilm provides reduced oxygen levels and an acidic environment (Stornsgard et al., 2006).

Involvement in biofilms also increases the likelihood of acquiring genetic material advantageous for the brewing environment through HGT (Kubota et al., 2008; Timke et al., 2005). Biofilm-mediated transfer of beer spoilage virulence genes is evidenced by the finding of plasmid-harboured hop tolerance genes among many LAB species, with the interspecies nucleotide sequence identities of these genes and surrounding regions being highly conserved at approximately 99% (Suzuki et al., 2005, 2008a; Suzuki, 2011). Indeed, a 5.6 kb region that contains horA was found to be 100% identical in L. backii and P inopinatus strains isolated from the same brewery (Iijima et al., 2007) and this same phenomenon is identified in other horA+ isolates recovered from different sources (Pittet et al., 2012a; J. Bergsveinson, unpublished data). As such, HGT among LAB in biofilms is believed to be how hop tolerance genes, and other putative plasmid-mediated beer resistance elements are spread within breweries (Suzuki, 2011).

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