Modified Saccharomyces cerevisiae for D-lactic acid production
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Solution Overview
Problem
Current methods for producing lactic acid, such as chemical synthesis and biological fermentation, face challenges in controlling the composition ratio of D-type and L-type lactic acid, leading to low melting point polylactic acid and inefficient fermentation productivity due to limitations in cell growth and enzyme activity control.
Innovation Solution
A modified Saccharomyces cerevisiae microorganism with inactivated PDC1 activity and decreased PDC5 activity, combined with enhanced aldehyde dehydrogenase (ALD) and acetyl-CoA synthetase (ACS) activities, achieved through genetic modifications and enzyme regulation, to optimize lactic acid production and cell growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If gene manipulations are performed to strengthen lactic acid dehydrogenase activity and decrease pyruvate decarboxylase activity, then lactic acid production is improved, but cell growth is inhibited and overall fermentation productivity remains low
Solution Approach 1:
The invention changes the kinetic parameters of enzyme reactions by introducing heterologous enzymes with different catalytic properties. Specifically, it introduces D-lactic acid dehydrogenase from Lactobacillus plantarum with high D-lactic acid production capability, and simultaneously introduces pyruvate decarboxylase from Zymomonas mobilis with optimized kinetic parameters, thereby improving both lactic acid production and cell growth rates
Solution Approach 2:
The invention creates a composite enzymatic system by combining multiple enzymes from different sources within the same microorganism (Saccharomyces cerevisiae). This includes endogenous L-lactic acid dehydrogenase, heterologous D-lactic acid dehydrogenase, endogenous pyruvate decarboxylase, and heterologous pyruvate decarboxylase, forming a composite catalytic system that achieves both high lactic acid production and maintained cell growth
2Quantity of substance
If pyruvate decarboxylase activity is decreased to improve lactic acid yield, then lactic acid production is enhanced, but cell growth rate is reduced
Solution Approach 1:
Instead of completely inactivating pyruvate decarboxylase, the invention introduces an additional pyruvate decarboxylase gene from Zymomonas mobilis that provides partial activity. This partial action is sufficient to support cell growth requirements while allowing the majority of pyruvate flux to be directed toward lactic acid production through the introduced D-lactic acid dehydrogenase pathway
Solution Approach 2:
The heterologous pyruvate decarboxylase from Zymomonas mobilis acts as an intermediary enzyme that bridges the gap between reduced endogenous PDC activity and cell growth requirements. It provides the necessary acetaldehyde and ethanol production for maintaining cell viability while allowing optimized lactic acid production through the engineered pathway
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
This approach significantly increases lactic acid fermentation productivity while maintaining cell growth rates, improving the yield and efficiency of D-lactic acid production.
Implementation Method 1
the biological fermentation process allows to selectively produce D-type lactic acid or L-type lactic acid depending on the strain used
Implementation Method 2
the method for producing lactic acid includes a traditional chemical synthesis and a biological fermentation process
Data Source
Figure 1
AI summary
The present invention relates to Saccharomyces sp. capable of producing lactic acid with a decreased activity of pyruvate decarboxylase (PDC) and increased activities of aldehyde dehydrogenase (ALD) and acetyl-CoA synthetase (ACS), and a method of producing lactic acid from the culture medium obtained by culturing the microorganism.