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Characterization and detection of the glycosyltransferase (gtf) genes in ropy beer-spoilage lactic acid bacteria
M. Shimokawa, S. Naito, K. Suzuki, and H. Yamagishi

Beer has been generally recognized as a microbiologically stable beverage. However, a limited number of lactic acid bacteria (LAB) species are able to grow in beer. Some strains of LAB produce exopolysaccharides (EPS) and form the encapsulation around the cells, which functions as a protective barrier. For instance, EPS-producing Lactobacillus brevis shows strong heat tolerance (up to 25 PU) and resist disinfectants used in the breweries, making them one of the most difficult beer-spoilage microorganisms to eradicate. Therefore it is important to distinguish EPS-producing L. brevis from other L. brevis strains. To achieve this purpose, we characterized the glycosyltransferase genes (gtf) in beer-spoilage L. brevis strains with the ropy phenotype. As a result of full sequencing, the gtf genes from ropy L. brevis exhibit approximately 98.5% identities with the gtf gene found in wine-spoilage Pediococcus parvulus 2.6, suggesting gtf genes have been horizontally acquired among spoilage LAB in alcoholic beverages. Based on this insight, new primers specific to gtf were designed. The newly developed gtf-specific PCR method was shown to detect not only EPS-producing L. brevis but also beer-spoilage Ped. damnosus and Ped. claussenii with ropy phenotype, suggesting that this PCR method is useful for species-independent identification of EPS-producing beer-spoilage LAB strains. No cross reactions have been observed with the non-ropy LAB strains in various species, as well as other nonspoilage brewery isolates. In conclusion, our newly developed PCR method allows specific and sensitive determination of the EPS-producing ability of beer-spoilage LAB.

Descriptors: lactic acid bacteria, EPS, beer spoilage, ropiness, PCR, horizontal gene transfer

BrewingScience, 69 (January/February 2016), pp. 16-20