What gives wine its taste? (We heard it’s on the grapevine…)

ResearchBlogging.orgStacked wine bottlesWine connoisseurs, or oenophiles, possess a seemingly endless vocabulary for describing their tipples of choice. To the uninitiated, it may sound like they are describing an entire gourmet meal, or even a good friend, but this is not just make-believe: those in the know can sometimes pinpoint not just the country or region a wine came from, but the exact vineyard. How can this be possible?

While we cannot hope to distinguish every single chemical in a wine using just our five senses, experienced wine tasters can still perceive hundreds of different compounds that contribute to the drink’s unique flavour and aroma. These compounds are a result of enzymatic and microbial activities during the alcoholic fermentation process, in which yeasts and other microbes convert sugar into ethanol and carbon dioxide.

Getting the mixture right

Winemakers often exert control over the fermentation process by culturing specifically selected yeast strains that they add to their wine in order to achieve certain flavours. However, wild yeasts are also present everywhere in a vineyard, living in the soil and on the processing equipment that turns grapes into ‘must’, the unfiltered, freshly-pressed grape juice that is the precursor of wine. Yeast spores are even found in the air around vines. These wild yeasts all end up in the final product and are called ‘autochthonous’ yeasts, meaning that they are a part of the local environment.

Autochthonous yeasts can impart unique, desirable traits on wines, but as their impact is harder to control detrimental effects can also arise. The effects of local autochthonous microbes on wine are considered to be part of the terroir effect. Many experts credit the effect for the subtle nuances it introduces into wines, and some lament the use of commercially available yeast starter cultures that dilute the terroir effect, make different wines more similar and rob them of their individual “personality”.

Dr Roberto Foschino, a food scientist and microbiologist of the University of Milan, set out to investigate what determines the subtle variations between wines: are they affected more by the year the wine was produced or by terroir, the local impact of the region and vineyard of origin? He and his colleagues journeyed to the Italian wine-growing regions of Franciacorta and Oltrepò Pavese to study the microbial biodiversity of a number of vineyards and cellars over the course of three growing seasons.

To get a complete picture of the autochthonous yeast populations, Dr Foschino and his colleagues sampled the air, must and base wine (the non-sparkling precursor to sparkling wine). To his knowledge, their study is the first to observe the presence of Saccharomyces cerevisiae, a widespread yeast essential for winemaking, in vineyard air.

The researchers isolated over 500 yeast samples from vineyard air, must and base wine and found a total of 31 species of yeast. Must contained the highest species diversity since only the more alcohol-tolerant species survive the fermentation process that turns the liquid into base wine. Furthermore, the winemakers only allowed the team to sample the very top layers of the base wine to avoid disturbing the liquid.

Terroir or vintage?

Dr Foschino and his team made two unexpected findings. Firstly, no strain of the same microbial species was discovered in the same vineyard in consecutive years, suggesting that autochthonous microbial communities vary between years. If no strain is isolated in the same vineyard and cellar over consecutive years, then the microbiota cannot confer a consistent flavour to wines from different years. The effects of terroir and autochthonous microbes may be considered negligible because yeast communities are not specific to geographic areas.

The researchers also found that there was overlap in the species found in samples taken in one year from vineyards up to 100 km apart. The implication is that the vintage – the year in which a wine was made – has an important effect on its flavour. While microbial species and strain varied from year to year in each vineyard, the researchers isolated similar microbes across vineyards in each year of their study.

It appears that the fluctuations of microbial populations over time cause changes in the flavours and characters of wines from different years: the “vintage effect” not only exists but is also more relevant than the “terroir effect”. Oenologists and winemakers may therefore be keen to understand what drives the gradual changes in microbial fauna – microbes may be indicative of environmental changes relevant to their work. Dr Foschino and his team plan to investigate this in the near future, using wild grape varieties in more remote locations to avoid any contamination with artificial microbial cultures.

Jon Fuhrmann

Vigentini, I., De Lorenzis, G., Fabrizio, V., Valdetara, F., Faccincani, M., Panont, C., Picozzi, C., Imazio, S., Failla, O., & Foschino, R. (2014). The vintage effect overcomes the terroir effect: a three year survey on the wine yeast biodiversity in Franciacorta and Oltrepo Pavese, two northern Italian vine-growing areas Microbiology, 161 (Pt_2), 362-373 DOI: 10.1099/mic.0.000004

Image Credit: The Hamster Factor on Flickr under CC BY-NC-ND 2.0

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Q&A: Professor Jeff Errington

Jeff ErrringtonNext month, Society member Professor Jeff Errington FRS will be awarded the prestigious Leeuwenhoek Medal by the Royal Society. The award, named after pioneering Dutch microscopist Antonie van Leeuwenhoek, is awarded triennially and recognises excellence in the fields of bacteriology, virology, mycology, parasitology and microscopy.

Professor Errington’s lecture will focus on his work on the fundamentals of bacterial cell division and how the bacterial cell wall – a flexible layer of proteins and sugars found in almost all bacteria – is important in cell shape. We caught up with him to ask about his work and about his forthcoming prize lecture.

How would you describe your research?

My long-term interests are on some of the most basic questions in biology: “What makes a cell a particular shape?”, “How do chromosomes get replicated and then pulled apart?”, “How do cells know where to divide, and how is division achieved?” I’m investigating the molecular basis for each of these processes. Answers to many of these questions – in bacterial cells at least – relate to cell wall synthesis. In order for bacteria to grow and divide correctly they have to be able to accurately manipulate their cell walls.

How does a bacterium achieve its desired shape?

We’ve found genes that if mutated interfere with a bacterial cell’s shape. The most famous of these genes is mreB, which is a homologue of actin, an important cytoskeletal or “scaffolding” protein found in eukaryotic cells. Before our work, people assumed that bacteria didn’t have cytoskeletons, but we now know they have many proteins that are used in a similar way to the cytoskeletal proteins found in eukaryotic cells, in the sense that they direct the shape of the cell, the division machinery, things like that. If you have a Staphylococcus it’s always a sphere and if you have a Bacillus it’s always elongated. The MreB protein, and the proteins it controls, are pivotal in determining the shape of a cell. Continue reading

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Pathways of resistance: from mercury to methicillin

ResearchBlogging.orgMercury BeadIn a climate of rising fear over the diminishing efficacy of antibiotics, microbiologists from the Universities of Nottingham and East Anglia have looked back at the bacteria-killing substances of the pre-antibiotic era: metals. Dr Jon Hobman and Dr Lisa Crossman’s review, published in the Journal of Medical Microbiology, concludes that the ancient pathways of resistance which bacteria have evolved against these metals may be intimately linked to the antibiotic resistance genes that are circulating in bacterial populations today.

Metals and metallic compounds have been used for medical and biological purposes for millennia: as antiseptics, diuretics, and dental fillings; cosmetics, tonics and chemical weapons. Most are indiscriminately toxic, and you wonder whether some of these historical cures were actually worse than the ailments they were intended to treat – mercury-laced teething powder, anyone?

Metals and their ions can damage cells in multiple ways: binding to enzymes, DNA and membranes, disrupting their function; taking part in reactions that generate harmful free radicals; or binding to the cell’s pool of antioxidants that usually protects against free radicals. It is the lethal damage that these mechanisms can inflict on bacterial cells that underlies the utility of metal compounds in controlling infections in plants, animals and humans. Continue reading

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New to Science – February 2015

Each month, the Society for General Microbiology publishes the International Journal of Systematic and Evolutionary Microbiology, which details newly discovered species of bacteria, fungi and protists. Here are a few of the new species that have been discovered and the places they’ve been found. The full papers are available to journal subscribers, but the abstracts are free to read.

It is the Society for General Microbiology’s 70th birthday this month – it was formally inaugurated on 16 February 1945 and Sir Alexander Fleming became its first President. Such anniversaries are always a time for reflection on the past and its lessons and challenges.

Microbiologists from South Africa and Italy undertook a similar journey into the past, providing New to Science with the most unusual microbe discovery location we have seen so far. The researchers were studying the damage caused by microbial communities in the catacombs of St Callixtus in Rome, which were founded in the very earliest years of Christianity and once housed the tombs of many popes from the first millennium AD. Here, the researchers isolated Kribbella italica from a biofilm growing on the walls of one of the tombs. Continue reading

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Antibiotic resistance transfer: where’s the culprit?

ResearchBlogging.orgColorized low-temperature electron micrograph of a cluster of E. coli bacteriaEscherichia coli is a species of bacteria that forms an essential part of the gut microbiome of many warm-blooded animals, including humans. Most strains are completely harmless to us, but some cause diseases including food poisoning and urinary tract infections. A group of antibiotics known as cephalosporins are often used to treat harmful E. coli infections, but some strains of the bacterium produce substances called extended-spectrum beta-lactamases (ESBL) that confer immunity to these antibiotics.

ESBL-producing E. coli used to be most commonly found in hospital environments, but they are now increasingly causing infections outside of hospitals, as well. The presence of such bacteria in the meat we consume is thought to contribute to the rising prevalence of community-acquired infections. After all, antibiotics are used heavily in the farming industry, so the development of resistant bacterial strains is to be expected.

Previous studies concluded that the ESBL-producing E. coli strains found in farm animals, retail meat and humans were extremely similar, suggesting that consumption of contaminated meat had allowed the bacteria to spread to humans. However, as Mark de Been, a bioinformatician at the Utrecht Medical Centre, explains, this research was based on studies of only a small part of the bacterial genomes. de Been is the lead author of a new study recently published in the journal PLOS Genetics, which shows that the bacteria found in animals and humans are actually significantly different. Continue reading

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Microbe Talk: January 2015

527049831Imagine waking up tomorrow morning to find out that every bacterium and every archeon on the planet had suddenly vanished. What would happen? Could humanity survive? This month, Ben spoke to Dr Jack Gilbert and Dr Josh Neufeld, who have published a thought experiment in PLOS Biology that wonders exactly that…


Show notes:

Don’t forget, you can subscribe to Microbe Talk on iTunes. You can also find us on Stitcher.

Benjamin Thompson

Image Credit: Thinkstock
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World Leprosy Day 2015

World Leprosy Day 2015Leprosy is among the oldest human-specific infections we currently know about. The common ancestor of the two modern bacterial species that cause leprosy, Mycobacterium leprae and M. lepromatosis, is thought to have become a parasite in early humans millions of years ago. This makes it far older than our own species, Homo sapiens. Nevertheless, leprosy continues to afflict hundreds of thousands of people every year.

World Leprosy Day raises awareness of the suffering caused by the disease. It remains endemic in India, where more than half of all worldwide cases occur, and in parts of South East Asia and Africa. World Leprosy Day is observed on the last Sunday of January to coincide with the anniversary of the assassination of Mahatma Gandhi, a vocal supporter of the fight against leprosy.

What is leprosy?
Leprosy is a chronic bacterial infection caused by two members of the genus Mycobacteria. It is usually thought to be transmitted between people via droplets when people breathe or cough, although armadillos may also play a role in transmitting the disease to humans.

Despite its continued prevalence, leprosy is actually one of the least infectious diseases we know. Globally, only about 5% of people are actually susceptible to leprosy due to a malfunction in the gene responsible for conferring immunity; the rest of the human population is immune. Furthermore, of the clinical cases that do occur, some 85% are non-infectious.

The number of new leprosy cases – roughly 200,000 a year – is all the more remarkable given the low risk of acquiring and transmitting the disease. Continue reading

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