More Yeast Beasts for Biotech? JGI marks more strains for production possibilities
Yeast, they’re so small that they probably all look like twins, all work the same, do the same things.
Not so, says DOE Joint Genome Insitute’s Robert Riley, who tells The Digest, “We might think of yeasts as simple unicellular, creatures similar to each other, but in fact their genetic diversity is like the difference between human and invertebrate sea squirt,” said Riley.
We’ll think more about that next time we’re paired up by e-Harmony with a sea squirt.
In the meantime, a team led by researchers at JGI conducted a comparative genomic analysis of 29 yeasts. The goal? To discover and facilitate the next generation of biotechnological workhorse yeasts for producing the fuels and products we use in daily life.
In a study just published in Proceedings of the National Academy of Sciences, the team mapped various metabolic pathways to yeast growth profiles.
One of the newly-sequenced yeasts is Pachysolus tannophilus, which can ferment xylose, otherwise known as wood sugar as it is derived from hemicellulose, which along with cellulose, is one of the main constituents of woody biomass. It is only distantly related to well-studied xylose fermenters such as Scheffersomyces stipitis — another yeast sequenced by the DOE JGI.
So that’s the good news. Here’s the bad.
“We also discovered a genetic code change that, if not understood, will impede the yeasts’ biotechnological use,” Riley said.
In P. tannophilus, the team found a change in one of the three-letter codons that represent one of the 20 regularly used amino acids. That change from CUG-Ser to CUG-Ala is only the second observed case of a non-stop codon reassignment (a change from one amino acid to another, rather than from one amino acid to a stop codon) in nuclear genomes.
“While we don’t know why and how this happened,” said Igor Grigoriev, JGI Fungal Program Head and co-senior author of the manuscript.. “Genes with CUG codons may not produce functional proteins when expressed in an organism with different genetic code as will code for a different amino acid.”
“The CUG-Ala reassignment is important to biotechnology,” said Riley, “because in order to express novel biotechnologically useful genes from diverse yeasts into workhorses like Saccharomyces, we need to know if the yeasts’ genetic codes are the same. If they aren’t, expressing the novel genes won’t work because the proteins will be incorrectly translated.”
Among the Yeast Beasts, the usual and unusual suspects
Right now the Big Yeast Beast is Saccharomyces cerevisiae — the one you can buy at the supermarket — used since antiquity to make bread, beer and wine. But yeasts (which belong to the “kingdom” of fungi) can use a wide range of carbon and energy sources, ranging from cellulosic (6-carbon) and hemicellulosic (5-carbon) sugars to methanol, glycerol, and acetic acid. Products include ethanol and other alcohols, esters, organic acids, carotenoids, lipids, and vitamins. In fact vitamin complexes and some nutritional supplements are derived from yeasts.
See the talk
First author Robert Riley talked about finding a fungus in which the 3-letter codon CUG is interpreted as the amino acid serine rather than the expected lysine during the 2016 DOE JGI Genomics of Energy & Environment Meeting. That’s here.
Category: Research
