Beer spoiling mechanisms of Lactobacillus brevisGovže, Mateja (Avtor) Čadež, Neža (Mentor) O'Sullivan, Tadhg (Komentor) beerhopHumulus lupulusbeer spoilagelactic acid bacteriaLactobacillus brevisgenomegenome sequencinggenome analysisRNA sequencingtranscriptomic analysisgene expression analysisfenotypic analysisLactobacillus brevis is the most frequently detected lactic acid bacteria in spoiled beer. With phenotypic, genomic and transcriptomic approaches we investigated the beer spoiling mechanisms of L. brevis and determined potential key genes that enable bacterium to grow in beer. For that purpose two L. brevis strains MB124 and MB449 isolated from beer were selected. By sub-culturing at elevated temperature (37°C) and/or in the presence of antibiotic Novobiocin several strains with changed plasmid profiles and reduced/lost beer spoiling ability were isolated. The genomes of three plasmid variants isolated from MB124 and four from MB449 with reduced/lost beer spoiling ability and different hop-resistance gene content (horA, hitA in horC) were sequenced. With comparative genomic analysis of the variants and the parental strain we confirmed that all three hop-resistance genes play a role in hop resistance although their effects differed. When L. brevis MB449 lost all of the three hop-resistance genes it was not able to grow in beer. Further, we showed that genes located on scaffold 2 (putative plasmid) extended adaptation phase of the strain MB449 in beer. Transcriptomic analysis (RNA-seq) of the strain MB124 demonstrated that plasmid-associated gene horC plays a key role in adaptation to beer. Spoilage mechanisms of the strain MB124 determined by chemical and transcriptomic analysis during growth in beer showed that it switched from carbohydrate metabolism into amino (arginine) and organic acids (pyruvate, malate) metabolism. [M. Govže]20172017-09-21 07:51:49Magistrsko delo/naloga95602sl