Search

Microbial contaminations pose a significant concern within the brewing industry, exerting negative effects on the organoleptic quality of the product and leading to substantial economic losses. The exponential proliferation of craft breweries in Argentina in recent years has heightened the demand for constant improvements in processes to ensure excellence in beer production. However, the stringency of microbiological quality controls remains a vulnerable area. This study assesses the prevalence of beer contaminants in samples from 10 breweries located in Buenos Aires City (CABA) and Greater Buenos Aires area (GBA). The results revealed the presence of microorganisms in 70% of the analyzed samples. Fifteen bacteria and 19 yeasts were successfully isolated, with bacteria belonging to the genera Acetobacter and Staphylococcus, and yeasts to the genera Saccharomyces, Lodderomyces, Candida, and Pichia. Accurately identifying these microorganisms provides producers with the necessary information for formulating action plans to improve cleaning and sanitization protocols in their facilities. This proactive approach not only has the potential to mitigate economic losses associated with microbial contamination but also contributes to maintaining and elevating quality standards in regional craft beer production., (Copyright © 2024 The Author(s). Publicado por Elsevier España, S.L.U. All rights reserved.)

The study of natural variation can untap novel alleles with immense value for biotechnological applications. Saccharomyces eubayanus Patagonian isolates exhibit differences in the diauxic shift between glucose and maltose, representing a suitable model to study their natural genetic variation for novel strains for brewing. However, little is known about the genetic variants and chromatin regulators responsible for these differences. Here, we show how genome-wide chromatin accessibility and gene expression differences underlie distinct diauxic shift profiles in S. eubayanus. We identified two strains with a rapid diauxic shift between glucose and maltose (CL467.1 and CBS12357) and one strain with a remarkably low fermentation efficiency and longer lag phase during diauxic shift (QC18). This is associated in the QC18 strain with lower transcriptional activity and chromatin accessibility of specific genes of maltose metabolism and higher expression levels of glucose transporters. These differences are governed by the HAP complex, which differentially regulates gene expression depending on the genetic background. We found in the QC18 strain a contrasting phenotype to those phenotypes described in S. cerevisiae, where hap4Δ , hap5Δ , and cin5Δ knockouts significantly improved the QC18 growth rate in the glucose-maltose shift. The most profound effects were found between CIN5 allelic variants, suggesting that Cin5p could strongly activate a repressor of the diauxic shift in the QC18 strain but not necessarily in the other strains. The differences between strains could originate from the tree host from which the strains were obtained, which might determine the sugar source preference and the brewing potential of the strain. IMPORTANCE The diauxic shift has been studied in budding yeast under laboratory conditions; however, few studies have addressed the diauxic shift between carbon sources under fermentative conditions. Here, we study the transcriptional and chromatin structure differences that explain the natural variation in fermentative capacity and efficiency during diauxic shift of natural isolates of S. eubayanus. Our results show how natural genetic variants in transcription factors impact sugar consumption preferences between strains. These variants have different effects depending on the genetic background, with a contrasting phenotype to those phenotypes previously described in S. cerevisiae. Our study shows how relatively simple genetic/molecular modifications/editing in the lab can facilitate the study of natural variations of microorganisms for the brewing industry.