[GAR+] Prion Inactivates Glucose Repression in Yeast Fermentation
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Solution Overview
Problem
Saccharomyces cerevisiae yeasts exhibit inefficient sugar utilization and lower ethanol yields due to glucose-associated repression and diauxic shift when switching from glucose to other carbon sources, such as xylose and arabinose, in cellulosic feedstocks, leading to inefficient fermentation kinetics.
Innovation Solution
Introduction of the [GAR+] prion, which forms a complex with Pma1 and Std1 proteins, inactivating glucose-associated repression, allowing yeasts to non-preferentially utilize a mixture of sugars, including C5 and C6 sugars simultaneously during the exponential phase of fermentation, thereby improving fermentation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If yeast utilizes glucose preferentially through glucose-associated repression, then fast growth and out-competition of other organisms is achieved, but utilization of other carbon sources like xylose and arabinose is repressed
Solution Approach 1:
The invention changes the physiological state of the yeast by inducing the [GAR+] prion form, which alters the glucose signaling pathway parameters. This prion formation modifies the interaction between Pma1 and Std1 proteins, thereby changing the repression parameters to allow simultaneous utilization of multiple carbon sources while maintaining growth speed
2Adaptability or versatility
If yeast switches from glucose to other carbon sources, then metabolism of secondary carbon source is initiated, but a pronounced lag phase known as diauxic shift occurs
Solution Approach 1:
The [GAR+] prion prepares the yeast metabolism in advance by pre-activating the transcriptional programs for alternative carbon source utilization. This preliminary action occurs during glucose consumption, so when other sugars need to be metabolized, the enzymes are already present, eliminating the lag phase
3Adaptability or versatility
If targeted metabolic engineering is used to increase transcription or activity of genes involved in xylose metabolism, then xylose utilization is improved, but fermentation kinetics remain inefficient due to sequential growth stages
Solution Approach 1:
The invention creates a dynamic system where the yeast can simultaneously metabolize multiple carbon sources through the [GAR+] prion state. This dynamic capability allows the fermentation process to proceed in parallel rather than sequential stages, dramatically improving productivity while maintaining enhanced xylose utilization from metabolic engineering
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of [GAR+] yeast strains, such as Saccharomyces cerevisiae strain UCD932, enhances ethanol yield and fermentation rate by enabling simultaneous conversion of multiple sugars, including glucose, mannose, galactose, xylose, and arabinose, particularly in mixed carbon source feedstocks like red liquor waste from the pulp and paper industry, improving overall fermentation efficiency and viability.
Implementation Method 1
Saccharomyces cerevisiae are specialized organisms that ferment glucose to ethanol
Data Source
AI summary
Genetically modified microorganisms useful in fermentation and methods of using such microorganisms are provided. Such microorganisms contain a [GAR+] prion or are modified to contain a [GAR+] prion. Exemplary microorganisms include yeast such as S. cerevisiae. The microorganisms can be further modified to convert xylose and/or arabinose. Methods of fermentation using such microorganisms exhibit improved fermentation efficiency and improved microorganism viability.