Cornell Team Identifies a Sugar-Sensing Regulator Enhancing Yeast-Based Biofuel Production
Cornell University researchers have identified Cbr1, a protein that lets the yeast Rhodotorula toruloides keep using complex sugars even when glucose is available, according to a study in PLOS Biology.
Using transcriptomics, which measures the activity of every gene in a genome, the team found that Cbr1 switches on sugar-digesting genes and overrides the cell's usual feedback loop that suppresses them.
The authors say the work could inform metabolic engineering of fungi for biofuels and plastics, and the search for new targets against fungal pathogens.
A Yeast With Industrial Appeal
Researchers at Cornell University have identified a regulator that helps a lipid-rich yeast decide what to eat. The protein, called Cbr1, is a transcription factor: a protein that turns genes on and off and so governs which genes a cell expresses. The study, published on 1 September 2026 in PLOS Biology, describes its role in Rhodotorula toruloides, a single-celled fungus.
The organism interests biotechnologists because it can accumulate up to 70% of its biomass as lipids, or fats. Lori Huberman, an assistant professor in Cornell's School of Integrative Plant Science, says groups are working to engineer the yeast to steer those lipids towards other useful molecules, including environmentally friendly plastics and biofuel. She adds that it can consume all the breakdown products of plant cell walls, so it could in principle be fed grasses grown on marginal land or agricultural waste. Similar feedstock logic appears in other work on fungal fermentation of agricultural and food waste and in research on shiitake mushrooms and wood-derived fuel.
How Fungal Nutrient Sensing Works
Fungi, Huberman explains, prefer glucose, a six-carbon sugar that is the most accessible form of carbon in plant tissue. When glucose is present, they repress genes needed to use carbon sources that cost more energy to digest. This is known as carbon catabolite repression.
That creates a problem for sugars such as cellobiose, a plant sugar made of two linked glucose molecules. Once glucose appears, the cell suppresses the genes that would split cellobiose, which limits access to the glucose locked inside it. The result is a negative feedback loop.
Using transcriptomics on the wild-type yeast and on strains the team had engineered, the researchers identified genes under Cbr1's control. One encodes an enzyme that cleaves cellobiose. Cbr1 activates that gene and also inhibits the mechanism that would normally repress it. In Huberman's description, this lets the cell keep detecting carbon sources that are being broken down into glucose. The study found Cbr1 does the same for other complex sugars built from two glucose molecules. The paper's model also covers gentiobiose, fucose and intermediates of the tricarboxylic acid (TCA) cycle, a core metabolic pathway.
The first authors are Brandon Reyes-Chavez, a graduate student, and Joshua Kerkaert, a postdoctoral associate, both in Huberman's laboratory. The paper is titled "The carbohydrate utilization regulator Cbr1 coordinates nutrient-specific gene activation with selective carbon catabolite repression in a basidiomycete yeast" (DOI: 10.1371/journal.pbio.3003983).
Relevance for Disease Control
The Cornell release frames the finding as relevant beyond biofuels. It states that fungal diseases can contribute to up to 20% of staple crop losses before and after harvest, and that rising drug-resistant fungal infections in humans can lead to roughly 3.8 million deaths globally each year. Understanding how fungi sense nutrients, the release says, could identify targets for treating diseases caused by pathogenic fungi. The commercial pressure around resistance is visible elsewhere, for instance in a fungicide partnership aimed at disease resistance in European cereals.
Huberman stresses that R. toruloides is not a serious pathogen. Her argument is one of principle: many fungi that do infect plants or animals could be disrupted by altering their ability to sense and respond to nutrients. The study does not test this on any pathogen.
Limitations and the Road Ahead
The work is a mechanistic advance rather than a product. As described by Cornell, it identifies how Cbr1 operates in one yeast species; it does not report engineered strains producing fuels or plastics, nor any antifungal intervention. Whether the mechanism is conserved in pathogenic fungi is not addressed in the source material. Huberman describes the findings as important for future metabolic engineering and for controlling fungal infections, so the practical value depends on follow-up studies that put the regulator to work, whether in industrial strains or as a drug or crop-protection target.
