Butanol Tolerance via (p)ppGpp Reduction in Bacterial Strains
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Solution Overview
Problem
Current methods for producing butanol and 2-butanone through fermentation are limited by the toxicity of these chemicals to host microorganisms, leading to inhibited growth and reduced productivity, as most bacteria are not tolerant to low concentrations of butanol.
Innovation Solution
Development of recombinant bacterial hosts with genetic modifications that reduce the accumulation of (p)ppGpp, enhancing their tolerance to butanol and 2-butanone, allowing for increased production and improved growth in the presence of these chemicals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fermentation is used to produce butanol, then chemical synthesis costs are reduced and environmental friendliness is improved, but butanol toxicity to the host microorganism inhibits growth and reduces productivity
Solution Approach 1:
The patent modifies the physiological state of the microorganism by altering its regulatory network through gene knockout (relA and spoT genes), changing the cellular response parameters to butanol toxicity. This allows the organism to maintain growth and productivity in high butanol concentrations where wild-type strains would be inhibited.
Solution Approach 2:
The patent removes the harmful regulatory function by deleting the relA and spoT genes responsible for (p)ppGpp synthesis. This extraction of the toxic regulatory mechanism eliminates the stringent response that causes growth inhibition, thereby resolving the contradiction between using fermentation (cost-effective) and maintaining high productivity.
2Reliability
If (p)ppGpp accumulation is increased to enhance stress response, then microbial tolerance to stressors is improved, but butanol toxicity and growth inhibition worsen
Solution Approach 1:
Instead of increasing (p)ppGpp accumulation to enhance stress tolerance as traditionally done, the patent inverts the approach by deleting the genes (relA and spoT) that synthesize (p)ppGpp. This inversion reveals that reducing (p)ppGpp levels actually confers superior butanol tolerance and growth performance, resolving the contradiction between stress tolerance and butanol toxicity.
3Device complexity
If wild-type bacterial strains are used for butanol fermentation, then genetic modification complexity is minimized, but growth is highly inhibited at low concentrations of butanol
Solution Approach 1:
The patent extracts the harmful regulatory function by deleting the relA and spoT genes from the bacterial genome. This genetic modification removes the stringent response mechanism that causes growth inhibition at low butanol concentrations, enabling the strain to maintain high growth rates and productivity in butanol-rich environments.
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 modified bacterial strains exhibit improved tolerance and productivity, enabling the efficient fermentation of butanol and 2-butanone with reduced accumulation of (p)ppGpp, which enhances their ability to grow in inhibitory concentrations of these chemicals, thus overcoming the limitations of existing fermentation processes.
Implementation Method 1
a bacterial regulatory system involving (p)ppGpp was identified as playing a role in butanol response in bacteria
Data Source
AI summary
Using screening of transposon random insertion mutants, genes involved in accumulation of (p)ppGpp were found to be involved in bacterial cell response to butanol. Reduced production of proteins with enzymatic activity for (p)ppGpp biosynthesis confers increased butanol tolerance. Bacterial strains with reduced (p)ppGpp accumulation and having a butanol or 2-butanone biosynthetic pathway are useful for production of butanol or 2-butanone.