Yeasts and chocolate, the new “BFFs”

by Ângela Carvalho

This friendship discovered by researchers in Belgium promises to revolutionize the way we see and consume chocolate. You may be wondering what yeast and chocolate have in common or the reason behind this special friendship.

Chocolate is produced from the seeds of the Theobroma cacao tree fruit, which literally means “food of the gods”. Continue reading

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The yeast Saccharomyces boulardii and human health

By Manuela Gottardi

When we talk about yeasts we might think of bread, beer and wine but nowadays when associated with human health, yeasts are often seen as pathogens. Continue reading

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Sometimes yeast gets convinced to enter into an unusual partnership

by Matthias Eder .

Ever since the movie “Finding Nemo” the image has been fixed in the mind of the audience: The orange and white striped clownfish which is inseparably connected to its anemone and never moves too far away from it. This unusual partnership has advantages for both sides Continue reading

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Production of essential omega-3 fatty acids by the non-conventional yeast Yarrowia lipolytica

by Leonie Wenning.

The quality of human nutrition is getting more and more into focus in the recent years. For either environmental or ethic reasons as well as  individual health concerns  an increasing number of people is switching from meat and fish based diets to a vegetarian or vegan lifestyle. A critical point related to a vegetarian or vegan lifestyle is sufficient supply of essential nutrients, of which some are highly abundant in animal products. Omega-3 fatty acids are examples for such nutrients considered essential fatty acids for humans. Continue reading

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Session 10

Jensen et al., (2014) EasyClone: method for iterative chromosomal integration of multiple genes in Saccharomyces cerevisiae

Key findings:

In their study Jensen et al. 2014 present a method to simultaneously integrate several genes into the genome of Saccharomyces cerevisiae by the use of different integrative plasmids, corresponding to integration sites on chromosome X, XI and XII. These plasmids were constructed by the USER cloning method (Nour‐Eldin et al. 2006) based on a previously designed vector set by Mikkelsen et al. 2012. The vectors constructed by Mikkelsen et al. 2012 were modified in that way that the selection marker URA, which was flanked by directed repeats, was replaced by a set of 5 different LoxP‐flanked selection markers. These markers can be recycled, enabling repeated cycles of genetic engineering without the loss of the integrated genes. For a proof of concept, Jensen et al. 2014 selected three genes, coding for different fluorescence proteins (CFP, RFP, YFP) and inserted them into three episomal plasmids and three integrative plasmids. The strain CEN.PK102‐5B was either transformed with the three episomal or the three integrative plasmids simultaneously, followed by flow cytometric analysis to test for the presence of the three fluorescent proteins. They could show that the expression of the three proteins is much more uniform in cells containing the three genes integrated in the genome compared to those containing the three episomal plasmids. The standard deviation for cells expressing the fluorescent proteins from additional plasmids was 4‐5 times larger compared to cells containing the integrated genes. In case of the integrated genes, 95% of the cells showed a fluorescence intensity for all three fluorescent proteins within a range of the mean value ± 15%. In contrast, this was only valid for 6% of the cells containing the three genes on episomal plasmids.

Relevance of the article:

In their study Jensen et al. 2014 are able to show the superiority of integrative plasmids compared to episomal plasmids concerning the stability and uniformity of gene expression. Moreover, they are providing a set of 12 different integrative plasmids which can facilitate the simultaneous integration of several genes into the genome of S. cerevisiae. I would rate the article as very good, especially for people who are working in the field of molecular biology, since the article shows a powerful tool for the controllable expression of (foreign) genes in S. cerevisiae.

 

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Session 9

Almeida et al., (2014) A Gondwanan imprint on global diversity and domestication of wine and cider yeast Saccharomyces uvarum

Key Findings:

In a previous work from the same team of Professor Sampaio, they observed a sympatric relationship between Saccharomyces uvarum and S. eubayanus in association with Nothofagus species in Norwestern Patagonia (Libkind et al., 2011). This association prompted them to further study the global genetic diversity and phylogeography of S. uvarum. A set of 54 representative strains were selected for Illumnia sequencing, including isolates from South America and Australasia associated with Nothofagus, as well as Holarctic isolates (from North America, Europe and Far East Asia) mostly associated with oak trees but also from artificial environments as wine and cider. Based on the sequence of 129,096 high-quality polymorphic sites the phylogenetic relationship of these isolates was drawn, enabling the separation in 3 different clades, one including all Holarctic strains and a few South American, another one containing the remaining of the South American isolates and a last one with the Australasia populations. The latter had the higher divergence (4.4%). Most of the genetic diversity was found in the South American isolates (0.689 in 1.248, π x100) in contrast with the Holarctic isolates (0.141). To identify signals of domestication, the genomes were screened for introgressions from other Saccharomyces species. Interestingly none of the Southern Hemisphere isolates had signs of foreign DNA, on the other hand the European isolates possess S. cerevisiae, S. kudriavzevii and most notably S. eubayanus introgressions. Sequence comparison shows that S. kudriavzevii introgressions were acquired from European S. kudriavzevii populations. The S. eubayanus introgressions were the most prevalent and extensive and were 99.5% identical to the type strain of S. eubayanus CRUB 1568 and 99.9% with the S. eubayanus portion of the S. pastorianus genome of the strain Weihenstephan 34/70. These introgressions could have been acquired from S. pastorianus or possibly from a non-yet identified European population of S. eubayanus. Function-specific introgressions were identified, mostly including categories relevant for wine fermentation.

 

Relevance of the article:

This article represents the first geographic characterization of S. uvarum, demonstration the higher diversity in the Southern Hemisphere in association with Nothofagus species, suggesting that the species may be native from the Southern Hemisphere. The multiple introgressions found in the European isolates mainly from S. eubayanus present for the first time signs of domestication of S. uvarum.

 

Rating: Very good article

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Killer yeast or survival instinct

by Nurzhan Kuanyshev.

In order to survive in low nutrient environments, most microorganisms compete with each other to get their best niche, which will allow them to grow and produce progeny. Many different strategies where adopted by microbes to withstand the competition. Some of them evolved to grow in harsh environments with a naturally reduced number of competitors i.e. thermophiles or acidophilic microorganisms. However, what do those microbes do which are growing in normal conditions with thousands of other species fighting for food? Continue reading

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