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Lactobacillus sp. brewery isolate: A new threat to the brewing industry?
J. Koob, F. Jacob, F.-J. Methner and M. Hutzler

Only a restricted group of bacterial species is known to be capable to spoil beer. To maintain a good microbiological quality control it is important to know which microbes are hazardous for the brewing industry. Three Lactobacillus (L.) isolates that could not be identified by a commercial realtime PCR system for the detection and identification of beer-spoilage bacteria (Foodproof? Beer Screening Kit, Biotecon Diagnostics, Germany) were obtained from brewery samples. A multivariate study was conducted on the basis of phenotypic, genotypic and beer-related characteristics. The tests were carried out with regard to the two most probable species, L. brevis and L. parabrevis. The comparison of the 16S rRNA gene and the pheS housekeeping gene sequences revealed that the three isolates belong to one species or one operational taxonomic unit (OTU). Furthermore, the unknown brewery isolate could be differentiated from the two most probable species by gene sequence comparisons and DNA-DNA hybridizations. The evaluation of physiological characteristics of the unknown brewery isolate did not demarcate it clearly. The Lactobacillus isolate contained two hop resistance genes and was able to grow in four different beer types resulting in significant compound concentration changes. It was determined that the unknown bacterium did not belong to the species L. brevis or L. parabrevis. In parallel, a species description is submitted to the International Journal of Systematic and Evolutionary Microbiology. Therein, further discrimination of the isolated bacterium from genetically related species (L. yonginensis, L. koreensis, L. hammesii) with no relation to the brewing sector is shown.

Descriptors: lactic acid bacteria, beer spoilage, brewery isolate, Lactobacillus brevis, Lactobacillus parabrevis, multivariate study

BrewingScience - Monatsschrift fr Brauwissenschaft, 69 (July/August 2016), pp. 42-49