There is an article in Wine Spectator (Seen on the JGI feed) on sequencing the wine spoilage yeast bruxellensis (correct name is now Dekkera bruxellensis)which adds the not-so-excellent taste of “sweaty horse” to wines. There is already some survey sequencing done by Ken Wolfe and Jurge Piskur’s groups so a full genome sequencing project will help work out how this yeast is able to out compete Saccharomyces and cause dramatic wine spoilage. This is also relevant on the bio-fuel side since this yeast can also taint an ethanol bio-reactor. It is an interesting ecology inside the wine bottle and this competition for resources can lead to bad tasting wine. The competition presumably originated in some form in the rotting fruit where these yeasts compete for space and use different approaches in their niche including the fermentation process which produces the revered ethanol by-product and helps establish a chemical-warfare driven landgrab. The ethanol also helps prevent and of course this has implications for the Drosophila (Sophophora)flies that land there and eat yeast. They needed a good way to overcome the ethanol like the well studied Adh gene.
We may have to reevaluate whether Saccharomyces cerevisiae alone is the species used to brew beer. A paper from Gonzalez et al describes results from PCR-RFLP comparison of 24 brewing strains identifies evidence for S. cerevisiae x S. kudriavzevii hybrids. Although this hybridization is not unprecedented, most seem to be related to cultivated brewing or fermentation strains. It seems that the hybrids are better able to cope with the stress associated with fermentation process.
It seems these would also be a great test system for more whole genome sequencing or at least more polymorphism comparisons to try and determine the proportion of the genome that comes from different parents and estimate timing and frequency of hybridization. It seems possible that the hybridizations are occurring multiple times in nature so are the same regions from each parental genome kept in the hybrid offspring that are selected for fitness under fermentation stress?
Gonzalez, S.S., Barrio, E., Querol, A. (2008). Molecular Characterization of New Natural Hybrids of Saccharomyces cerevisiae and S. kudriavzevii in Brewing . Applied and Environmental Microbiology, 74(8), 2314-2320. DOI: 10.1128/AEM.01867-07
Researchers from Technical University of Denmark published some interesting results from comparing expression across the very distinct Aspergillus species.
Kudos also goes to making it Open Access. I am posting a few key figures below the fold because I can! They grew the fungi in bioreactors fermenting glucose or xylose. After calibrating the growth curves they were able to sample the appropriate time points for comparison of gene expression across these three species. They found a set of genes commonly expressed.
David Carter at the Sanger Centre emailed a message that new assemblies of Saccharomyces strain resequencing project have been posted including a new three-way alignment of S. bayanus-S.paradoxus-S.cerevisiae. This updates the Dec 2007 release.
Dettman, Anderson, and Kohn recently published a paper in BMC Evolutionary Biology on reproductive experimental evolution in two Neurospora crassa populations evolved under different selective conditions. This is a great study that complements work published last year in Nature on experimental evolution in Saccharomyces cerevisiae populations. Neurospora populations were evolved under high salt and low temperature and were started from either high diversity (interspecific crosses, N. crassa vs N. intermedia) or low diversity (intraspecific cross, two N. crassa isolates D143 (Louisiana, USA)and D69 (Ivory Coast)) as described in Figure 1. The experimentally evolved populations were then tested for asexual and sexual fitness (they were taken through complete meiotic cycle throughout the experiment to avoid insure there was selection on the sexual reproduction pathway.
I’ve paraphrased an email sent by David Carter to folks interested in Saccharomyces resequencing project.
The latest version of the SGRP data is on the web site and ftp site. This release is somewhat provisional, and motivated more by the fact that we have a paper deadline coming up than by any claim to finality. It should be quite a bit better than what was there before, but doesn’t have a correct treatment of transposons.
There are a few new features in the browser which [David] is going to document over the next couple of days.
Major new features of the data are that there should be much better consistency between alignments; Solexa/Illumina data has been incorporated for the strains that had it; and the S. paradoxus alignments are based on a new assembly that created a few weeks ago and which covers about 95% of the genome; a description is at http://www.sanger.ac.uk/Teams/Team71/durbin/sgrp/spara_assembly.shtml
Ed Louis at Nottingham sent out an email today outlining plans for publishing analyses of the Saccharomyces Genome Resequencing Project. They are in process of analyzing the data and ask that people respect their use of the data, but also invite collaborations and companion papers.
“If anyone has done or plans on doing a global analysis with a tight clean result which you think should be included in the overview paper, please contact us [Richard Durbin and Ed Louis; emails available through above links]. The analysis would have to be complete by 14 December and you would have to be willing to have the details transparently displayed on the web pages associated with the project.”
A recent PLoS One article “A Genetic Code Alteration Is a Phenotype Diversity Generator in the Human Pathogen Candida albicans” finds some pretty dramatic changes in gene expression and phenotypes by replacing the tRNAs for CUG back to Leucine (Leu; in the standard genetic code) from their meaning of Serine (Ser) in these Candida species. The CUG codon transition in some Candida spp has been of interest since it is an example of a recent change in the genetic code and provides a comparative system to study the mechanism and genome changes of how a genetic code shift is manifested.
Few organisms are as well understood at the genetic level as Saccharomyces cerevisiae. Given that there are more yeast geneticists than yeast genes and exemplary resources for the community (largely a result of their size), this comes as no surprise. What is curious is the large number of yeast genes for which we’ve been unable to characterize. Of the ~6000 genes currently identified in the yeast genome, 1253 have no verified function (for the uninclined, this is roughly 21% of the yeast proteome). Egads! If we can’t figure this out in yeast, what hope do we have in non-model organisms?Lourdes Peña-Castillo and Timothy R. Hughes discuss this curious observation and its cause in their report in Genetics.