Engineered Yeast Host Cells for High Glucose Fermentation
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Solution Overview
Problem
There is a need to improve growth and product production during fermentation of yeasts with increased pyruvate availability due to reduction or elimination of pyruvate decarboxylase activity, as existing methods do not effectively enhance production efficiency.
Innovation Solution
Engineering yeast cells with inactivated pyruvate decarboxylase genes and reduced glucose repression through disruption of a nuclear and cytoplasmic localized hexokinase enzyme, allowing for improved growth and production of products using pyruvate as a substrate, such as isobutanol and 2,3-butanediol, by reducing glucose repression and suppressing competing metabolic pathways.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pyruvate decarboxylase activity is reduced or eliminated to increase pyruvate availability, then product production from pyruvate pathways is improved, but glucose repression remains high which limits respiratory capacity and biomass production
Solution Approach 1:
The patent removes the harmful glucose repression mechanism by deleting the HXK2 gene, which encodes hexokinase 2, a key enzyme in glucose metabolism that mediates glucose repression. This extraction of the repressive element allows pyruvate-dependent pathways to function without the limiting effect of glucose repression, simultaneously improving both product production and respiratory capacity.
2Reliability
If HXK2 gene is deleted to reduce glucose repression, then respiratory capacity and biomass production are improved, but fermentation capacity is reduced by 75%
Solution Approach 1:
The patent changes the metabolic parameters of the yeast cell by combining HXK2 deletion with the introduction of heterologous pyruvate-utilizing pathways. This parameter change shifts the metabolic balance from primarily fermentative to a mixed respiratory-fermentative mode, allowing the cell to maintain growth while producing target chemicals from pyruvate.
Solution Approach 2:
The engineered yeast strain performs multiple functions simultaneously: it maintains biomass production through modified respiratory pathways, produces target chemicals (such as acetolactate, isobutanol, or other pyruvate-derived compounds) through introduced pathways, and adapts its metabolism to balance energy production with product synthesis. This multi-functionality resolves the contradiction between respiratory capacity and fermentation capacity.
3Quantity of substance
If pyruvate decarboxylase is inactivated to redirect metabolite flow toward desired products, then availability of pyruvate for biosynthetic pathways is increased, but competing endogenous pathways continue to consume pyruvate
Solution Approach 1:
The patent converts the potentially harmful effect of competing pyruvate-consuming pathways into a benefit by introducing heterologous pathways that channel pyruvate toward desired product formation. The competing pathways are not completely eliminated but are redirected to produce valuable chemicals rather than wasting pyruvate in unwanted byproducts, thus converting a metabolic disadvantage into a production advantage.
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 engineered yeast cells exhibit enhanced growth and product production, with increased isobutanol and 2,3-butanediol yields, demonstrating improved metabolic efficiency and productivity compared to unmodified strains.
Implementation Method 1
at least one inactivated endogenous gene encoding a pyruvate decarboxylase (pdc) enzyme, wherein the yeast production host cell is pdc-
Implementation Method 2
a genetic modification which has the effect of reducing glucose repression, wherein the unmodified yeast host cell is crabtree-positive and wherein the genetic modification which has the effect of reducing glucose repression is a disruption of a gene encoding a nuclear and cytoplasmic localized hexokinase enzyme
Implementation Method 3
allowing for improved growth and production of products using pyruvate as a substrate, such as isobutanol and 2,3-butanediol
Data Source
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AI summary
Crabtree positive yeast cells that have endogenous expressed pyruvate decarboxylase genes inactivated and an engineered biosynthetic pathway utilizing pyruvate were found to have improved growth and product yield when glucose repression was reduced. These cells were able to grow in media containing a high glucose concentration.