Pigment marks ‘key step’ towards isobutanol biofuel production

A red pigment naturally produced by strains of wild yeast could play a pivotal role in developing isobutanol into a large-scale biofuel, according to new research from the University of Wisconsin-Madison (UW-Madison).

The University of Wisconsin-Madison (UW-Madison) revealed a study detailing a new red pigment, pulcherrimin, and its role in developing isobutanol as a large-scale biofuel.

In the study, released in Proceedings of the National Academy of Sciences, a team from UW-Madison based at the Great Lakes Bioenergy Research Center (GLBRC) describe the genetic machinery that the yeasts use to make pulcherrimin, a pigment that binds iron.

They claim that this research is a ‘key step toward harnessing the synthesis pathway for large-scale production of isobutanol as a biofuel.’

“Compared to first-generation biofuels, such as ethanol, isobutanol has a higher energy content, blends better with gasoline, causes less corrosion, and is more compatible with existing engine technology,” said GLBRC researcher Chris Todd Hittinger, a UW–Madison genetics professor.

“Nonetheless, considerable barriers remain to producing this fuel sustainably from dedicated energy crops.”

The early steps of isobutanol synthesis – a budding biofuel prospect – are the same as those used to make pulcherrimin so yeasts that naturally produce this pigment caught the research team’s attention.

“Our thought is that these yeasts that are making pulcherrimin may be primed in a way to make more isobutanol,” said David Krause, a postdoctoral fellow with GLBRC and lead author of the study. “We want to use some of these yeast species that are already putting more carbon into these pathways and see if we can get them to turn that into isobutanol instead of pulcherrimin.”

Using comparative genomics, spanning 90 yeast species to identify the genes involved in pulcherrimin production, the researchers found a cluster of four genes which they named PUL1-4, which seem to play complementary roles.

Through genetic characterisation, they determined that both PUL-1 and PUL-2 are required to create the molecule, whilst PUL-3 and PUL-4 assist the yeast in transporting the pulcherrimin and regulating its production.

UW-Madison describe the discovery as ‘surprising’ because this marks the first time, according to the study, that a gene cluster in budding yeast is responsible for producing a secondary metabolite.

Many secondary metabolites are said to have valuable functions such as toxins, antibiotics or signalling molecules. The study states that whilst such molecules are produced by filamentous fungi and bacteria, the new research suggests that some budding yeasts can produce secondary metabolites too.

Another ‘surprising’ aspect of the study, the report continues, is that many yeast species that do not produce the pulcherrimin pigment, including the most common lab yeast species Saccharomyces cerevisiae, have working PUL-3 and PUL-4 genes.

 “This work really shows how studying diverse genomes can lead to discoveries and new biological insights,” said Hittinger.

“Focusing on a single organism can give us an incomplete picture of a complex biological process. At the same time, we were able to learn more about genes in S. cerevisiae through the lenses of some of these lesser-known species.”