Mutant Yeast Cells for Lactic Acid Production
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Solution Overview
Problem
Current yeast fermentation processes for producing lactic acid face challenges due to glycerol production, which consumes carbon, directs energy away from product formation, and complicates product recovery, and most bacteria struggle in acidic environments, necessitating pH buffering.
Innovation Solution
Development of mutant yeast cells with deletions or disruptions in native metabolic pathways from dihydroxyacetone phosphate to glycerol, specifically targeting glycerol-3-phosphate dehydrogenase, glycerol-3-phosphatase, dihydroxyacetone phosphate phosphatase, and glycerol dehydrogenase genes, to reduce or eliminate glycerol production, thereby improving acid tolerance and product yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If yeast cells are genetically modified to produce lactic acid by disrupting the pyruvate decarboxylase gene, then lactic acid production is improved, but glycerol production increases significantly
Solution Approach 1:
The patent extracts and removes the harmful glycerol production pathway from the yeast cell by deleting the GPD1 and GPD2 genes. This extraction eliminates the competing carbon sink while preserving the desired lactic acid production pathway, directly resolving the contradiction between productivity and carbon loss.
Solution Approach 2:
The patent changes the metabolic parameter by altering the gene expression profile through gene deletion. By removing GPD1 and GPD2 genes, the cell's metabolic flux is redirected from glycerol production to lactic acid production, optimizing carbon utilization while maintaining productivity.
2Loss of substance
If glycerol production is reduced by deleting glycerol-3-phosphate dehydrogenase genes, then carbon efficiency is improved, but cell growth is compromised
Solution Approach 1:
The patent introduces an intermediary mechanism by co-deleting the GPP1 and GPP2 genes along with GPD1 and GPD2. This multi-gene deletion strategy creates a coordinated metabolic shift that maintains redox balance and cellular energy management, thereby preserving cell growth while eliminating glycerol production.
Solution Approach 2:
The patent applies a universal approach by targeting multiple genes (GPD1, GPD2, GPP1, GPP2) that collectively control glycerol metabolism. This multi-functional deletion strategy ensures comprehensive glycerol production elimination while maintaining cellular homeostasis and growth capabilities.
3Ease of manufacture
If fermentation is conducted at low pH to maintain product in acid form, then product recovery is simplified, but bacterial survival is compromised
Solution Approach 1:
The patent uses a copying strategy by employing yeast cells (Saccharomyces cerevisiae) as model organisms to study and optimize low-pH fermentation. The yeast's natural ability to tolerate acidic environments provides a template for understanding bacterial survival mechanisms and developing strategies to maintain low pH without compromising microbial life.
4Reliability
If pH buffering is applied to maintain higher pH during fermentation, then bacterial survival is improved, but product recovery becomes difficult
Solution Approach 1:
The patent applies an inversion strategy by rejecting the conventional approach of buffering to maintain high pH. Instead, it inverts the logic by allowing the pH to drop naturally to acidic levels, which simplifies product recovery. The yeast-based system compensates for the harsh conditions, eliminating the need for buffering while achieving both survival and ease of manufacture.
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 mutant yeast cells produce very low levels of glycerol while maintaining growth capabilities, achieving high yields of lactic acid and simplifying product recovery, with glycerol production reduced to less than 2% of the carbon source consumed.
Implementation Method 1
DHAP is reduced by a glycerol-3-phosphate dehydrogenase (GPD, systematic name sn-glycerol-3-phosphate:NAD+2-oxidoreductase, EC 1.1.1.8) enzyme to form glycerol-3-phosphate (G3P). G3P is dephosphorylated to glycerol by a glycerol-3-phosphatase enzyme (GPP, systematic name glycerol-1-phosphate phosphohydrolase, EC 3.1.3.21).
Implementation Method 2
Yeast are used as biocatalysts in a number of industrial fermentations. There is an increasing interest in using yeast to ferment sugars to organic acids such as lactic acid.
Implementation Method 3
mutant yeast cells with deletions or disruptions in native metabolic pathways from dihydroxyacetone phosphate to glycerol, specifically targeting glycerol-3-phosphate dehydrogenase, glycerol-3-phosphatase, dihydroxyacetone phosphate phosphatase, and glycerol dehydrogenase genes
Data Source
AI summary
Yeast cells are genetically modified to disrupt a native metabolic pathway from dihydroxyacetone to glycerol. In certain aspects, the yeast cell is of the genera Kluyveromyces, Candida or Issatchenkia. In other aspects, the yeast cell is capable of producing at least one organic acid, such as lactate. The yeast cells produce significantly less glycerol than the wild-type strains, and usually produce greater yields of desired fermentation products. Yeast cells of the invention often grow well when cultivated, despite their curtailed glycerol production.