Modified Bacillus Spores Thymine Starvation Containment
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Solution Overview
Problem
The challenge lies in introducing heterologous genes into spore-forming bacteria like Bacillus without using antibiotic resistance genes, which is necessary for biological containment and ensuring that recombinant spores do not persist in the environment due to their extreme robustness and long survival capabilities.
Innovation Solution
A two-step gene integration process utilizing thymine starvation, where heterologous genes are introduced into the thyA and thyB genes of Bacillus species, rendering the bacteria unable to proliferate without thymine or thymidine, and using trimethoprim for positive selection without introducing antibiotic resistance markers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If antibiotic resistance genes are used for selecting transformed Bacillus cells, then the gene integration process is simplified, but the risk of environmental persistence and horizontal gene transfer increases
Solution Approach 1:
The patent extracts and removes antibiotic resistance genes from the selection process. Instead of using antibiotic resistance markers to select transformed cells, the invention employs alternative selection methods that do not involve antibiotic resistance genes, thereby eliminating the risk of horizontal gene transfer while maintaining ease of gene integration
Solution Approach 2:
The patent introduces an intermediary selection mechanism based on thymine starvation sensitivity. By targeting the thyA and thyB genes which are essential for thymine synthesis, the invention creates a selection system where transformed cells can be identified through their inability to grow without thymine, serving as a safe intermediary that replaces antibiotic resistance markers
2Object-affected harmful factors
If germination-deficient spores are constructed to prevent environmental persistence, then the survival risk is reduced, but the germination rate drops to unacceptable levels
Solution Approach 1:
The patent changes the physiological parameters of the spores by introducing mutations in the thyA and thyB genes. These mutations make the spores dependent on external thymine supplementation for germination and growth, rather than creating germination-deficient spores. The spores maintain normal germination capability when thymine is provided, but cannot persist in the environment where thymine is limited
Solution Approach 2:
The patent creates a dynamic containment system where the spores' ability to germinate and grow is conditional on the presence of thymine. The spores can germinate efficiently when thymine is available (maintaining productivity), but cannot proliferate in thymine-limited environmental conditions (preventing persistence), creating a responsive biological containment mechanism
3Adaptability or versatility
If multiple heterologous genes are introduced into Bacillus spores, then the functional capabilities are enhanced, but the complexity of genetic modification increases
Solution Approach 1:
The patent creates a universal genetic modification system based on the thyA and thyB gene targeting approach. This system can be used to introduce multiple different heterologous genes by simply changing the selectable marker or the gene of interest, without needing to develop new targeting methods for each gene, thereby enhancing functional capabilities while maintaining manageable complexity
Solution Approach 2:
The patent segments the genetic modification process into distinct modular steps: (1) targeting the thyA or thyB gene with a heterologous gene cassette, (2) selecting transformants using thymine supplementation, and (3) verifying integration. This segmentation allows systematic introduction of multiple heterologous genes through repeated application of the same modular protocol, reducing overall complexity
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 method effectively prevents the survival and proliferation of recombinant spores in the environment by ensuring they die upon germination without thymine, addressing regulatory concerns and providing a biological containment mechanism for genetically modified Bacillus spores.
Implementation Method 1
The inventors have adopted the approach of thymine starvation resulting in a so-called 'thymine-less death' (23-25). The majority of prokaryotes are known to carry a single thymidylate synthase enzyme that is encoded by the thyA gene and prokaryotes carrying a mutated thymidylate synthase gene are unable to grow in low concentrations of thymidine or thymine resulting in cell death.
Implementation Method 2
A number of Bacillus species are considered `food grade', that is, safe for human consumption and are designated as QPS (Qualified Presumption of Safety as defined by EFSA, European Food Safety Authority) (10). In the USA, some strains carry GRAS (Generally Recognized As Safe as defined by the Food and Drug Administration) status.
Data Source
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AI summary
The present invention relates to modified bacterial spores, and particularly, although not exclusively, to modified bacterial spores which comprise one or more heterologous genes, but without the introduction of antibiotic resistance genes. The invention extends to methods for producing such modified bacterial spores, vectors and kits for introducing heterologous genes in a spore.