Thermophilic Bacillus Ethanol Production via Formate Dehydrogenase
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Solution Overview
Problem
Current methods for producing ethanol from biomass face challenges in achieving high yields due to metabolic stress and redox imbalance in thermophilic bacteria, which leads to reduced ATP production and ethanol yield, especially at high sugar concentrations and acidic pH conditions.
Innovation Solution
Introduction of a gene encoding an NAD-linked formate dehydrogenase into thermophilic bacteria of the genus Bacillus, which lack lactate dehydrogenase activity, to create a novel pyruvate formate lyase (PFL)-NAD-linked formate dehydrogenase (FDH) pathway, restoring redox balance and enhancing ethanol production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the PDH pathway flux is increased to produce ethanol, then ethanol yield is improved, but cells experience metabolic stress with reduced ATP production
Solution Approach 1:
The patent introduces formate dehydrogenase as an intermediary enzyme that mediates the conversion of formate to CO2 and NADH, enabling the cell to manage redox balance during high-flux ethanol production without experiencing metabolic stress
Solution Approach 2:
The patent modifies the metabolic pathway by changing the redox state parameters through the introduction of formate dehydrogenase, which converts NADH to NAD+, allowing the cell to maintain optimal NADH/NAD+ ratios during high ethanol production flux
2Productivity
If sugar concentration is increased to improve substrate availability, then fermentation rate is improved, but redox imbalance occurs leading to metabolic collapse
Solution Approach 1:
The patent creates a feedback mechanism where formate dehydrogenase continuously converts accumulated NADH back to NAD+, maintaining redox balance and preventing metabolic collapse even at high sugar concentrations and fermentation rates
3Speed
If lactate dehydrogenase activity is present to convert pyruvate to lactate, then rapid sugar consumption is achieved, but ethanol yield is reduced
Solution Approach 1:
The patent extracts or removes lactate dehydrogenase activity from the metabolic pathway, forcing pyruvate to enter the PFL pathway instead, which produces formate that can then be converted to ethanol through the introduced formate dehydrogenase
Solution Approach 2:
The patent inverts the conventional lactate production pathway by introducing formate dehydrogenase, which converts formate to CO2 and NADH, thereby redirecting the metabolic flux toward ethanol production instead of lactate
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 allows for maximal ethanol yields and rapid production by maintaining redox balance and optimal growth conditions, even at high sugar concentrations, preventing metabolic collapse and 'redox death' in thermophilic microorganisms.
Implementation Method 1
The other (encoded by the fdh1 gene) converts formate + NAD into CO2 + NADH2 and is present in many facultative anaerobes
Implementation Method 2
Many micro-organisms contain a pyruvate-formate lyase (PFL) pathway that converts pyruvate into acetyl CoA and formate
Implementation Method 3
These microorganisms first convert input sugars to pyruvate (generally by the EMP pathway of glycolysis)
Implementation Method 4
This is not used for growth but produces heat which causes the ambient temperature to rise and kills mesophilic competitors
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2
AI summary
A thermophilic microorganism lacks lactate dehydrogenase activity and preferably contains an active pyruvate formate lyase pathway. The thermophilic microorganism contains a gene encoding an NAD-linked formate dehydrogenase. The gene encoding an NAD-linked formate dehydrogenase is preferably a codon optimised version of the gene encoding a thermostable NAD-linked formate dehydrogenase. DNA constructs allow stable expression of the gene encoding an NAD-linked formate dehydrogenase in the thermophilic microorganism. The DNA constructs are based upon use of an insertion sequence to achieve stable expression or recombination to insert the gene encoding an NAD-linked formate dehydrogenase into the lactate dehydrogenase gene, thus achieving gene knockout and new functionality in a single step. The microorganisms are useful in fermentation of sugars to produce ethanol.