125th Anniversary Review: Microbiological Instability of Beer Caused by Spoilage Bacteria

Effects of Ultradisperse Humic Sapropel Suspension on Microbial Growth and Fermentation Parameters of Barley Distillate

Barley and other cereal grains can be used in the production of ethanol. The quality and safety of the grains utilized have enormous effects on the overall yield and quality of the final product (ethanol). Therefore, the present paper seeks to elucidate the antimicrobial activities of ultradisperse humic sapropel suspensions (UDHSS) on barley, wort, fermentation, and the quality of the final product. A standard microbiological method was used to assess the biocidal activities. Physicochemical parameters and volatile compounds were determined. Treated samples exhibited least microbial growth (for grain: 1.145 ± 0.120 × 104 cfu/g) when compared to the control (3.425 ± 0.33 × 105 cfu/g). Mash from the treated sample had less Free Amino Nitrogen (35.14 ± 0.02 mg/L) than the control experiment (41.42 ± 0.01). However, the levels of °Brix and Free Amino Nitrogen (FAN) were unaffected by the UDHSS treatments. After the chromatographic analysis, it was revealed that the barley distillate obtained from treated grains had high volatiles concentration when compared to the control experiment. The volume of the methanol quantified in the distillate was low, and hence safe, and might find applications in the food industries or in domestic consumption after rectification.

Lactobacillus backii and Pediococcus damnosus isolated from 170-year-old beer recovered from a shipwreck lack the metabolic activities required to grow in modern lager beer

In 2010, bottles of beer containing viable bacteria of the common beer-spoilage species Lactobacillus backii and Pediococcus damnosus were recovered from a shipwreck near the Åland Islands, Finland. The 170-year quiescent state maintained by the shipwreck bacteria presented a unique opportunity to study lactic acid bacteria (LAB) evolution vis-a-vis growth and survival in the beer environment. Three shipwreck bacteria (one L. backii strain and two P. damnosus strains) and modern-day beer-spoilage isolates of the same two species were genome sequenced, characterized for hop iso-α-acid tolerance, and growth in degassed lager and wheat beer. In addition, plasmid variants of the modern-day P. damnosus strain were analyzed for the effect of plasmid-encoded genes on growth in lager beer. Coding content on two plasmids was identified as essential for LAB growth in modern lager beer. Three chromosomal regions containing genes related to sugar transport and cell wall polysaccharides were shared by pediococci able to grow in beer. Our results show that the three shipwreck bacteria lack the necessary plasmid-located genetic content to grow in modern lager beer, but carry additional genes related to acid tolerance and biofilm formation compared to their modern counterparts.

Microbial acidification, alcoholization, and aroma production during spontaneous lambic beer production

Acidic beers, such as Belgian lambic beers and American and other coolship ales, are becoming increasingly popular worldwide thanks to their refreshing acidity and fruity notes. The traditional fermentation used to produce them does not apply pure yeast cultures but relies on spontaneous, environmental inoculation. The fermentation and maturation process is carried out in wooden barrels and can take up to three years. It is characterized by different microbial species belonging to the enterobacteria, acetic acid bacteria, lactic acid bacteria, and yeasts. This review provides an introduction to the technology and four fermentation strategies of beer production, followed by the microbiology of acidic beer production, focusing on the main microorganisms present during the long process used for the production of Belgian lambic beers. © 2018 Society of Chemical Industry.

The Interior Surfaces of Wooden Barrels Are an Additional Microbial Inoculation Source for Lambic Beer Production

Traditional lambic beer production takes place through wort inoculation with environmental air and fermentation and maturation in wooden barrels. These wooden casks or foeders are possible additional inoculation sources of microorganisms for lambic worts. To date, however, these lambic barrels have been examined only with culture-dependent techniques, thereby missing a portion of the microorganisms present. Moreover, the effects of the cleaning procedures (involving high-pressure water and/or fumigation) and the barrel type on the microbial community structures of the interior surfaces of wooden lambic barrels were unclear. The culture-dependent plating and culture-independent amplicon sequencing of swab samples obtained from the interior surfaces of different wooden casks and foeders used for traditional lambic beer production in Belgium revealed that the microbial compositions of these surfaces differed statistically throughout the barrel-cleaning procedures applied. At the end of the cleaning procedures, amplicon sequencing still detected fermentation- and maturation-related microorganisms, although only a few colonies were still detectable using culture-dependent methods. It is possible that some of the surviving microorganisms were missed due to the presence of many of these cells in a viable but not culturable state and/or engrained deeper in the wood. These surviving microorganisms could act as an additional inoculation source, besides brewery air and brewery equipment, thereby helping to establish a stable microbial community in the wort to diminish batch-to-batch variations in fermentation profiles. Furthermore, the microbial compositions of the interior barrel surfaces differed statistically based on the barrel type, possibly reflecting different characteristics of the lambic barrels in terms of age, wood thickness, and wood porosity.IMPORTANCE Although the coolship step is generally regarded as the main contributor to the spontaneous inoculation by environmental air of fresh worts for lambic beer production, it is known that microorganisms often associate with specific surfaces present in a brewery. However, knowledge about the association of microorganisms with the interior surfaces of wooden lambic barrels is limited. To clarify the role of casks and foeders as additional microbial inoculation sources, it was important to determine the influence of the barrel characteristics and the cleaning procedures on the microbial communities of the interior barrel surfaces. Moreover, this helped to elucidate the complex spontaneous lambic beer fermentation and maturation process. It will allow further optimization of the lambic beer production process, as well as the wooden-barrel-cleaning procedures applied.

Multiple Genome Sequences of Exopolysaccharide-Producing, Brewery-Associated Lactobacillus brevis Strains

Lactobacillus brevis represents one of the most relevant beer-spoiling bacteria. Besides strains causing turbidity and off flavors upon growth and metabolite formation, this species also comprises strains that produce exopolysaccharides (EPSs), which increase the viscosity of beer. Here, we report the complete genome sequences of three EPS-producing, brewery-associated L. brevis strains.

Heterogeneity between and within Strains of Lactobacillus brevis Exposed to Beer Compounds

This study attempted to investigate the physiological response of six Lactobacillus brevis strains to hop stress, with and without the addition of Mn²⁺ or ethanol. Based on the use of different fluorescent probes, cell viability and intracellular pH (pHi) were assessed by fluorescence microscopy combined with flow cytometry, at the single cell level. The combined approach was faster than the traditional colony based method, but also provided additional information about population heterogeneity with regard to membrane damage and cell size reduction, when exposed to hop compounds. Different physiological subpopulations were detected under hop stress in both hop tolerant and sensitive strains. A large proportion of cells were killed in all the tested strains, but a small subpopulation from the hop tolerant strains eventually recovered as revealed by pHi measurements. Furthermore, a short term protection against hop compounds was obtained for both hop tolerant and sensitive strains, by addition of high concentration of Mn²⁺. Addition of ethanol in combination with hop compounds caused an additional short term increase in damaged subpopulation, but the subsequent growth suggested that the presence of ethanol provides a slight cross resistance toward hop compounds.

Multiple Genome Sequences of Important Beer-Spoiling Lactic Acid Bacteria

Seven strains of important beer-spoiling lactic acid bacteria were sequenced using single-molecule real-time sequencing. Complete genomes were obtained for strains of Lactobacillus paracollinoides, Lactobacillus lindneri, and Pediococcus claussenii. The analysis of these genomes emphasizes the role of plasmids as the genomic foundation of beer-spoiling ability.

Multiple Genome Sequences of the Important Beer-Spoiling Species Lactobacillus backii

Lactobacillus backii is an important beer-spoiling species. Five strains isolated from four different breweries were sequenced using single-molecule real-time sequencing. Five complete genomes were generated, which will help to understand niche adaptation to beer and provide the basis for consecutive analyses.

The Identification of Novel Diagnostic Marker Genes for the Detection of Beer Spoiling Pediococcus damnosus Strains Using the BlAst Diagnostic Gene findEr

As the number of bacterial genomes increases dramatically, the demand for easy to use tools with transparent functionality and comprehensible output for applied comparative genomics grows as well. We present BlAst Diagnostic Gene findEr (BADGE), a tool for the rapid prediction of diagnostic marker genes (DMGs) for the differentiation of bacterial groups (e.g. pathogenic / nonpathogenic). DMG identification settings can be modified easily and installing and running BADGE does not require specific bioinformatics skills. During the BADGE run the user is informed step by step about the DMG finding process, thus making it easy to evaluate the impact of chosen settings and options. On the basis of an example with relevance for beer brewing, being one of the oldest biotechnological processes known, we show a straightforward procedure, from phenotyping, genome sequencing, assembly and annotation, up to a discriminant marker gene PCR assay, making comparative genomics a means to an end. The value and the functionality of BADGE were thoroughly examined, resulting in the successful identification and validation of an outstanding novel DMG (fabZ) for the discrimination of harmless and harmful contaminations of Pediococcus damnosus, which can be applied for spoilage risk determination in breweries. Concomitantly, we present and compare five complete P. damnosus genomes sequenced in this study, finding that the ability to produce the unwanted, spoilage associated off-flavor diacetyl is a plasmid encoded trait in this important beer spoiling species.

Metabolic strategies of beer spoilage lactic acid bacteria in beer

Beer contains only limited amounts of readily fermentable carbohydrates and amino acids. Beer spoilage lactic acid bacteria (LAB) have to come up with metabolic strategies in order to deal with selective nutrient content, high energy demand of hop tolerance mechanisms and a low pH. The metabolism of 26 LAB strains of 6 species and varying spoilage potentialwas investigated in order to define and compare their metabolic capabilities using multivariate statistics and outline possible metabolic strategies. Metabolic capabilities of beer spoilage LAB regarding carbohydrate and amino acids did not correlate with spoilage potential, but with fermentation type (heterofermentative/homofermentative) and species. A shift to mixed acid fermentation by homofermentative (hof) Pediococcus claussenii and Lactobacillus backii was observed as a specific feature of their growth in beer. For heterofermentative (hef) LAB a mostly versatile carbohydrate metabolism could be demonstrated, supplementing the known relevance of organic acids for their growth in beer. For hef LAB a distinct amino acid metabolism, resulting in biogenic amine production, was observed, presumably contributing to energy supply and pH homeostasis.

Development of a PCR assay based on the 16S-23S rDNA internal transcribed spacer for identification of strictly anaerobic bacterium Zymophilus

PCR-primers were designed for identification of strictly anaerobic bacteria of the genus Zymophilus based on genus-specific sequences of the 16S-23S rDNA internal transcribed spacer region. The specificity of the primers was tested against 37 brewery-related non-target microorganisms that could potentially occur in the same brewery specimens. None DNA was amplified from any of the non-Zymophilus strains tested including genera from the same family (Pectinatus, Megasphaera, Selenomonas), showing thus 100% specificity. PCR assay developed in this study allows an extension of the spectra of detected beer spoilage microorganisms in brewery laboratories.

In situ examination of Lactobacillus brevis after exposure to an oxidizing disinfectant

Beer is a hostile environment for most microorganisms, but some lactic acid bacteria can grow in this environment. This is primarily because these organisms have developed the ability to grow in the presence of hops. It has been speculated that hop resistance is inversely correlated to resistance against oxidation, and this would have great impact on the use of various disinfectants in the brewing industry. In this study, we cultivated bacteria under aerobic and anaerobic conditions, and then investigated the in situ outgrowth of individual cells into microcolonies on de Man Rogosa Sharpe (MRS) agar after exposure to the oxidizing agent peracetic acid (PAA). An automated microscope stage allowed us to analyse a much larger number of cells over extended periods of incubation. After PAA treatment, the lag time increased markedly, and extensive variation in morphology, μmax as well as stress resistance was observed between and within the tested Lactobacillus brevis strains. The results suggest that aerobic cultivation increased the oxidative stress tolerance in Lactobacillus brevis. The results also show that dead cells are randomly distributed in a microcolony and the majority of non-growing individual cells do not stain with a membrane impermanent dye (Propidium iodide), which indicates that PAA may not destroy the plasma membrane. In conclusion, the developed microscopic analysis of individual cells on MRS agar can provides faster results and more details of cell physiology compared to the traditional CFU method.

Development of a species-specific PCR assay for identification of the strictly anaerobic bacterium Selenomonas lacticifex found in biofilm-covered surfaces in brewery bottling halls

AIMS

In recent years, beer-spoilage cases from strictly anaerobic bacteria have risen in frequency, in connection with the production of non-pasteurized, non-alcohol and low-alcoholic beers and with the lowering of dissolved oxygen in the packaged beer. Selenomonas lacticifex, found in brewer's yeast and in biofilms covering some surfaces in brewery bottling area, is considered to be a beer-spoilage organism. This study aims to develop S. lacticifex-specific PCR assay. The objective of this study was also evaluation of the specificity and reproducibility of the developed PCR assay in real brewery samples.

METHODS AND RESULTS

Three primers (one forward and two reverse) were designed for identification of the strictly anaerobic bacterium S. lacticifex on the basis of the species-specific sequences of the 16S rDNA region. The specificity of the primers was tested against 44 brewery-related non-target micro-organisms that could potentially occur in the same brewery specimens. None of the primer pairs amplified DNA from any of the non-S. lacticifex strains tested including genera from the same family (Pectinatus, Megasphaera, Zymophilus) and the closely related species Selenomonas ruminantium, showing thus 100% specificity.

CONCLUSIONS

The PCR assay developed in this study enables the detection of the strictly anaerobic bacterium S. lacticifex in real brewery samples including pitching yeast.

SIGNIFICANCE AND IMPACT OF THE STUDY

Selenomonas lacticifex-specific PCR assay developed in this study allows for the extension of the spectra of detected beer-spoilage micro-organisms in brewing laboratories and thus lowering the risk of contamination of the final product.

Differentiation of Lactobacillus brevis strains using Matrix-Assisted-Laser-Desorption-Ionization-Time-of-Flight Mass Spectrometry with respect to their beer spoilage potential

Lactobacillus (L.) brevis is one of the most frequently encountered bacteria in beer-spoilage incidents. As the species Lactobacillus brevis comprises strains showing varying ability to grow in beer, ranging from growth in low hopped wheat to highly hopped pilsner beer, differentiation and classification of L. brevis with regard to their beer-spoiling ability is of vital interest for the brewing industry. Matrix-Assisted-Laser-Desorption-Ionization-Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) has been shown as a powerful tool for species and sub-species differentiation of bacterial isolates and is increasingly used for strain-level differentiation. Seventeen L. brevis strains, representative of different spoilage types, were characterized according to their tolerance to iso-alpha-acids and their growth in wheat-, lager- and pilsner beer. MALDI-TOF MS spectra were acquired to perform strain-level identification, cluster analysis and biomarker detection. Strain-level identification was achieved in 90% out of 204 spectra. Misidentification occurred nearly exclusively among strains belonging to the same spoilage type. Though spectra of strongly beer-spoiling strains showed remarkable similarity, no decisive single markers were detected to be present in all strains of one group. However, MALDI-TOF MS spectra can be reliably assigned to the corresponding strain and thus allow to track single strains and connect them to their physiological properties.

Comparative analysis of the Oenococcus oeni pan genome reveals genetic diversity in industrially-relevant pathways

Background

Oenococcus oeni, a member of the lactic acid bacteria, is one of a limited number of microorganisms that not only survive, but actively proliferate in wine. It is also unusual as, unlike the majority of bacteria present in wine, it is beneficial to wine quality rather than causing spoilage. These benefits are realised primarily through catalysing malolactic fermentation, but also through imparting other positive sensory properties. However, many of these industrially-important secondary attributes have been shown to be strain-dependent and their genetic basis it yet to be determined.

Results

In order to investigate the scale and scope of genetic variation in O. oeni, we have performed whole-genome sequencing on eleven strains of this bacterium, bringing the total number of strains for which genome sequences are available to fourteen. While any single strain of O. oeni was shown to contain around 1800 protein-coding genes, in-depth comparative annotation based on genomic synteny and protein orthology identified over 2800 orthologous open reading frames that comprise the pan genome of this species, and less than 1200 genes that make up the conserved genomic core present in all of the strains. The expansion of the pan genome relative to the coding potential of individual strains was shown to be due to the varied presence and location of multiple distinct bacteriophage sequences and also in various metabolic functions with potential impacts on the industrial performance of this species, including cell wall exopolysaccharide biosynthesis, sugar transport and utilisation and amino acid biosynthesis.

Conclusions

By providing a large cohort of sequenced strains, this study provides a broad insight into the genetic variation present within O. oeni. This data is vital to understanding and harnessing the phenotypic variation present in this economically-important species.