{"id":3114,"date":"2024-07-01T11:42:25","date_gmt":"2024-07-01T03:42:25","guid":{"rendered":"https:\/\/opentrons.com.cn\/?post_type=knowledge2&p=3114"},"modified":"2024-09-02T18:29:09","modified_gmt":"2024-09-02T10:29:09","slug":"jygtljhdzdhgj","status":"publish","type":"post","link":"https:\/\/opentrons.com.cn\/en\/news\/jygtljhdzdhgj\/","title":{"rendered":"Automated rational strain construction based on high-throughput binding"},"content":{"rendered":"\n
Molecular cloning is at the core of synthetic biology as it involves the assembly of DNA and its expression in a target host. However, currently cloning is often a manual, time-consuming and repetitive process, and automation would greatly facilitate this process. Automation of the complete rational cloning process (i.e., from DNA creation to expression in the target host) involves the integration of different operations and machines. There are few examples of such workflows, especially when the design is sound (i.e. the DNA sequence design is fixed rather than based on a random library) and the target host is not genetically tractable (e.g. not sensitive to heat shock transformation) . In this study, an automated workflow is presented for the rational construction of plasmids and their subsequent conjugative transfer into the biotechnological platform organism Corynebacterium glutamicum. The entire workflow is equipped with customized software tools. As an application example, a rationally designed transcription factor biosensor library based on the regulator Lrp was constructed and characterized. A sensor with improved dynamic range was obtained, and insights gained from the screen provide evidence for a dual regulatory function of C. glutamicum Lrp.<\/p>\n\n\n\n
Introduction Microbial production of bulk and fine chemicals is an important component in achieving a more sustainable global economy. To facilitate this development, it is necessary to improve the fundamental understanding of microbial life and its engineering to meet society's needs. In recent years, the adoption of the Design-Build-Test-Learn (DBTL) cycle has been proposed as a tool to achieve this goal. (1) Molecular cloning plays an important role in this cycle as it can generate new genotypes with different properties for exploration. A variety of software tools have been developed to assist in the in silico cloning of genotypes, the number of which easily exceeds the number of manual cloning in the laboratory. (2) It is now possible to design hundreds of genotypes in a short time. For example, a production pathway consisting of 5 genes, each with 3 different ribosome binding sites (RBS), has generated 3 5 = 243 variants. However, the design of such a project is relatively simple and the bottleneck now shifts to the actual in vitro creation of these sequences and their expression in the desired industrial host. (3) This problem can be solved by using a one-pot assembly and screening approach, i.e., obtaining many, but not necessarily all, variants and using screening experiments to select the best performing variants. (4) However, these approaches have a drawback: knowledge comes only from a few variants that are successfully constructed and isolated from a one-pot reaction. Variants that are more difficult to construct are less likely to be present in this reaction, making it less likely that their properties will be screened out. For many fundamental biological problems, this is not an ideal solution. Here, rational strain construction and complete traceability of all species within all steps of the workflow are necessary, as is achieved with classical molecular cloning. However, currently molecular cloning is often a manual, time-consuming and repetitive process for which automation would bring huge benefits. (5) Automation of rational cloning workflows has multiple benefits. The hands-on time experimenters spend on strain construction can be significantly reduced. Coupled with the higher throughput that can be achieved, this greatly increases the number of constructs that can be produced in a timely manner. Furthermore, automation introduces standardization into the process by eliminating random variations in the process. These processes can also be more easily monitored and analyzed, making it easier to find room for improvement. Therefore, automation can improve the quantity and quality of cloning workflows. In recent years, microfluidic technology has been used to automate the cloning process. (6,7) Here, a custom microfluidic chip is used to provide liquid separation and liquid transfer for a single unit operation. While this technology has the advantage of combining many unit operations in a single device and being able to scale to a large number of experiments per chip, it requires highly specialized infrastructure and personnel to fabricate the chips and conduct the experiments. A more modular and convenient solution is to use a standard liquid handling system, with auxiliary equipment if required. Such systems can be quite complex, capable of performing a large number of experiments with different tasks, (8\u221211) and there are more cost-effective solutions available. (12) Recently proposed strategies exploit the natural transformation capabilities of specific bacteria, resulting in an efficient and easy-to-use cloning method. (13) However, this approach is limited to a small number of organisms that actively take up exogenous DNA. Most automated cloning workflows published to date focus on E. coli . (14) Escherichia coli is a mature host for molecular cloning and is very easy to manipulate genetically. Many genetic tools have been developed and optimized for E. coli and comprehensive omics data are available. However, E. coli is not always an ideal host for industrial processes due to its low pressure tolerance and risk of phage infection. (15) Therefore, it would be beneficial to expand automated platforms to encompass engineering other genetically more difficult microorganisms. Corynebacterium glutamicum is a widely used industrial bacterium (16) that is more difficult to engineer than E. coli due to its resistance to automation-friendly transformation processes such as heat shock transformation. Although some steps have been taken in this direction, (17) they often fail to automate the actual target biotransformation process, most commonly because electroporation (the preferred method for such organisms) is not easily automated. This study presents a complete workflow for automated rational construction of heat shock-resistant microbial strains. All work was performed using standard liquid handling systems. PCR and Gibson assembly were used to construct a library of 96 plasmids. An automated protocol for heat shock transformation of E. coli was developed as a shuttle system. Colony PCR and sequencing were used as quality controls. For the final step in transforming C. glutamicum, a novel high-throughput conjugation workflow was developed. Conjugation is a well-described and highly relevant bacterial transformation technique. (18) This method is highly efficient, but is often laborious as it requires the use of agar plates and filter paper. In this study, we simplified and automated the procedure by using centrifugation. The entire workflow is equipped with a custom software tool that tracks all constructs and their status in the process. As an application example, the assembly and expression of different Lrp biosensor variants in Corynebacterium glutamicum are shown. The Lrp biosensor has been previously developed for the detection of l -methionine and branched-chain amino acids in Corynebacterium glutamicum. (19) The sensor combines intracellular l -methionine and branched-chain amino acid concentrations with the expression of eyfp, which encodes a fluorescent reporter protein. Increased intracellular concentration results in enhanced fluorescence signal. In general, the design of biosensors is relatively modular; their properties can be changed by modifying ribosome binding sites, promoter length, etc. (20,21) Furthermore, by design, they provide a direct and easily measurable relationship between genotype and phenotype; i.e., changes in Lrp sensor design may result in different measurable fluorescence outputs. Therefore, rational designs of different Lrp biosensors were chosen as application examples to demonstrate the advantages of our cloning automation approach.<\/p>\n\n\n\n
Results and Discussion Automated Genetic Engineering Workflow The automated cloning workflow developed in this study (Fig. 1) can be divided into two stages: assembly and amplification of the plasmid in E. coli and transfer of the plasmid to the target organism (in this case Corynebacterium glutamicum). Plasmids were constructed by in silico design of components, construction of fragments by PCR, and integration into backbone vectors by Gibson assembly. Gibson assembly was chosen because it allows scarless assembly of plasmids. (22) Subsequent transformation into E. coli via heat shock. The resulting clones were cryopreserved and a first step of quality control was performed by colony PCR. This method was chosen due to its cost-effectiveness and short run time. The results of this colony PCR influence the next steps: only E. coli clones with positive colony PCR results, i.e. the resulting DNA fragments are of the expected size, indicating successful assembly of the fragments into the backbone, will be considered for automated plasmid preparation , and simultaneously incorporated into Corynebacterium glutamicum. Purified plasmids were used for sequencing as a final quality control. Afterwards, the automatically constructed strains were screened to characterize altered properties. Best of all, each unit operation is designed to be independent and therefore can be used outside of the workflow.<\/p>\n\n\n\n