Rewiring Metabolic Flux in Corynebacterium glutamicum Using a CRISPR/dCpf1-Based Bifunctional Regulation System

Tailoring Corynebacterium glutamicum for Sustainable Biomanufacturing: From Traditional to Cutting-Edge Technologies

As the workhorse of industrial amino acid production, Corynebacterium glutamicum is the focus of this review, which provides a comprehensive overview of available techniques employed to engineer strains with desired traits. The review highlights both traditional and cutting-edge approaches with a brief introduction to the bacterium's physiology, serving as a foundation for understanding its metabolic capabilities and potential applications. Genome modulation techniques by contrasting traditional methods with CRISPR-based approaches, as well as transcription modulation strategies that enhance gene expression and metabolic flux, and high-throughput techniques that streamline strain development processes are summarized. Furthermore, the roles of artificial intelligence and machine learning in genetic engineering are explored, emphasizing their growing impact on strain development.

Efficient Biosynthesis of 8-Prenylkaempferol from Kaempferol by Using Flavonoid 8-Dimethylallyltransferase Derived from Epimedium koreanum

The genus Epimedium includes popular Chinese medicinal plants, and icariin and its precursor icaritin are the key bioactive components of Epimedium. Here, we identified flavonoid 8-dimethylallyltransferase (F8DT) in the authentic medicinal material of Epimedium koreanum, which is a key gene in the icariin biosynthesis pathway. This enzyme can catalyze the synthesis of 8-prenylkaempferol (8PK) from kaempferol. The catalytic ability of the rate-limiting enzyme EkF8DT was significantly improved by truncating its N-terminal intrinsically disordered regions (IDRs) and enhancing the flux of the mevalonate pathway. Icaritin was also successfully synthesized by introducing flavonoid 4'-O-methyltransferase into the Saccharomyces cerevisiae strain. Finally, the highest production of 8PK and icaritin (3.6 g/L and 172.0 mg/L, respectively) was obtained in the S. cerevisiae strain.

A rapid and efficient strategy for combinatorial repression of multiple genes in Escherichia coli

BACKGROUND

The regulation of multiple gene expression is pivotal for metabolic engineering. Although CRISPR interference (CRISPRi) has been extensively utilized for multi-gene regulation, the construction of numerous single-guide RNA (sgRNA) expression plasmids for combinatorial regulation remains a significant challenge.

RESULTS

In this study, we developed a combinatorial repression system for multiple genes by optimizing the expression of multi-sgRNA with various inducible promoters in Escherichia coli. We designed a modified Golden Gate Assembly method to rapidly construct the sgRNA expression plasmid p3gRNA-LTA. By optimizing both the promoter and the sgRNA handle sequence, we substantially mitigated undesired repression caused by the leaky expression of sgRNA. This method facilitates the rapid assessment of the effects of various inhibitory combinations on three genes by simply adding different inducers. Using the biosynthesis of N-acetylneuraminic acid (NeuAc) as an example, we found that the optimal combinatorial inhibition of the pta, ptsI, and pykA genes resulted in a 2.4-fold increase in NeuAc yield compared to the control.

CONCLUSION

We anticipate that our combinatorial repression system will greatly simplify the regulation of multiple genes and facilitate the fine-tuning of metabolic flow in the engineered strains.

Application Evaluation and Performance-Directed Improvement of the Native and Engineered Biosensors

Transcription factor (TF)-based biosensors (TFBs) have received considerable attention in various fields due to their capability of converting biosignals, such as molecule concentrations, into analyzable signals, thereby bypassing the dependence on time-consuming and laborious detection techniques. Natural TFs are evolutionarily optimized to maintain microbial survival and metabolic balance rather than for laboratory scenarios. As a result, native TFBs often exhibit poor performance, such as low specificity, narrow dynamic range, and limited sensitivity, hindering their application in laboratory and industrial settings. This work analyzes four types of regulatory mechanisms underlying TFBs and outlines strategies for constructing efficient sensing systems. Recent advances in TFBs across various usage scenarios are reviewed with a particular focus on the challenges of commercialization. The systematic improvement of TFB performance by modifying the constituent elements is thoroughly discussed. Additionally, we propose future directions of TFBs for developing rapid-responsive biosensors and addressing the challenge of application isolation. Furthermore, we look to the potential of artificial intelligence (AI) technologies and various models for programming TFB genetic circuits. This review sheds light on technical suggestions and fundamental instructions for constructing and engineering TFBs to promote their broader applications in Industry 4.0, including smart biomanufacturing, environmental and food contaminants detection, and medical science.

CRISPRi functional genomics in bacteria and its application to medical and industrial research

SUMMARYFunctional genomics is the use of systematic gene perturbation approaches to determine the contributions of genes under conditions of interest. Although functional genomic strategies have been used in bacteria for decades, recent studies have taken advantage of CRISPR (clustered regularly interspaced short palindromic repeats) technologies, such as CRISPRi (CRISPR interference), that are capable of precisely modulating expression of all genes in the genome. Here, we discuss and review the use of CRISPRi and related technologies for bacterial functional genomics. We discuss the strengths and weaknesses of CRISPRi as well as design considerations for CRISPRi genetic screens. We also review examples of how CRISPRi screens have defined relevant genetic targets for medical and industrial applications. Finally, we outline a few of the many possible directions that could be pursued using CRISPR-based functional genomics in bacteria. Our view is that the most exciting screens and discoveries are yet to come.

Application of functional genomics for domestication of novel non-model microbes

With the expansion of domesticated microbes producing biomaterials and chemicals to support a growing circular bioeconomy, the variety of waste and sustainable substrates that can support microbial growth and production will also continue to expand. The diversity of these microbes also requires a range of compatible genetic tools to engineer improved robustness and economic viability. As we still do not fully understand the function of many genes in even highly studied model microbes, engineering improved microbial performance requires introducing genome-scale genetic modifications followed by screening or selecting mutants that enhance growth under prohibitive conditions encountered during production. These approaches include adaptive laboratory evolution, random or directed mutagenesis, transposon-mediated gene disruption, or CRISPR interference (CRISPRi). Although any of these approaches may be applicable for identifying engineering targets, here we focus on using CRISPRi to reduce the time required to engineer more robust microbes for industrial applications.

ONE-SENTENCE SUMMARY

The development of genome scale CRISPR-based libraries in new microbes enables discovery of genetic factors linked to desired traits for engineering more robust microbial systems.