Synthetic Biology and Microdevices

Lactic acid bacteria (LAB) are pivotal in food, pharmaceutical, and environmental applications due to their metabolic versatility and probiotic potential. This review explores the advancements in genetic engineering and synthetic biology strategies to enhance LAB functionality. We examine the genomic architecture of key LAB species, such as Lactobacillus and Lactococcus, highlighting their natural genetic traits and metabolic constraints. Emerging genetic tools, including electroporation, conjugation, and CRISPR-Cas systems, have revolutionized LAB modification, enabling precise gene editing and expression control. Synthetic biology approaches, such as genetic circuits, riboswitches, and biosensor development, offer novel pathways for optimizing LAB for functional foods, mucosal therapeutics, and industrial biotechnology. We discuss applications in probiotic delivery, bioremediation, and agricultural enhancement, emphasizing LAB's role in producing bioactive metabolites and combating pathogens. Challenges, including plasmid instability, metabolic burden, and regulatory hurdles, are addressed alongside socio-ethical considerations for genetically modified LAB. The integration of genome-scale engineering and CRISPR-based technologies holds promise for overcoming these barriers, paving the way for next-generation LAB with enhanced stress tolerance and tailored functionalities. This review synthesizes current knowledge and future prospects, underscoring the transformative potential of engineered LAB in addressing global health, environmental, and industrial needs while navigating biosafety and public perception challenges.

Opportunities for artificial intelligence and synthetic biology in designing living drug delivery systems.

Synthetic biology approaches: Towards sustainable exploitation of marine bioactive molecules

The construction of stable and functional synthetic circuits in bacteria is necessary in the areas of systems and synthetic biology. The common approach using plasmids to carry foreign genetic circuits offers convenience in genetic construction but is poor in genetic stability (e.g., variation in copy number). Genome recombination provides the stable genetic maintenance of synthetic circuits, but is often labor intensive and time consuming when the genetic circuits are complex and the DNA fragments become larger. The method introduced here is modified from that reported by Wanner's group and is available for integration of complex genetic circuits into the Escherichia coli chromosome.

BackgroundEvolvability is an intrinsic feature of all living cells. However, newly emerging, evolved features can be undesirable when genetic circuits, designed and fabricated by rational, synthetic biological approaches, are installed in the cell. Streamlined-genome E. coli MDS42 is free of mutation-generating IS elements, and can serve as a host with reduced evolutionary potential.ResultsWe analyze an extreme case of toxic plasmid clone instability, and show that random host IS element hopping, causing inactivation of the toxic cloned sequences, followed by automatic selection of the fast-growing mutants, can prevent the maintenance of a clone developed for vaccine production. Analyzing the molecular details, we identify a hydrophobic protein as the toxic byproduct of the clone, and show that IS elements spontaneously landing in the cloned fragment relieve the cell from the stress by blocking transcription of the toxic gene. Bioinformatics analysis of sequence reads from early shotgun genome sequencing projects, where clone libraries were constructed and maintained in E. coli, suggests that such IS-mediated inactivation of ectopic genes inhibiting the growth of the E. coli cloning host might happen more frequently than generally anticipated, leading to genomic instability and selection of altered clones.ConclusionsDelayed genetic adaptation of clean-genome, IS-free MDS42 host improves maintenance of unstable genetic constructs, and is suggested to be beneficial in both laboratory and industrial settings.

Synthetic genetic circuits are the core research objects in synthetic biology, and the programming of cell behavior is achieved through the combination of engineered gene elements. Mathematical modeling provides crucial support for understanding and designing synthetic genetic circuits, enabling researchers to predict the dynamic behavior of the circuits and guide experimental optimization. This study reviews the categories of synthetic genetic circuits (such as gene switches, oscillators, feedback circuits, etc.) and their biological mechanisms, with a focus on the application of ordinary differential equation (ODE) models, stochastic modeling, and network topology dynamics models in circuit modeling. We expounded on the estimation of model parameters, sensitivity analysis, and the integration methods of experimental data and models, and compared the characteristics of numerical simulation algorithms and commonly used software tools (such as MATLAB, COPASI, BioNetGen, etc.). Through the discussion of the steady-state, oscillation behavior, multiple steady-state and bifurcation analysis of system dynamics, the understanding of the influence of positive and negative feedback mechanisms on system stability is deepened. In addition, we took the classic synthetic gene oscillator Repressilator as a case to conduct modeling and simulation analysis, and compared the model predictions with the experimental data. Finally, the application prospects of synthetic genetic circuits in the fields of bioengineering and medicine were summarized, and the future directions of promoting the design of synthetic circuits with the help of model optimization and artificial intelligence-assisted design were prospected. Research shows that mathematical modeling and computational simulation have become key tools for the study and design of synthetic genetic circuits, providing a theoretical basis and practical guidance for the engineering transformation of complex biological systems.

Reprogramming human fibroblasts to induced pluripotent stem cells (iPSCs) is inefficient, with heterogeneity among transcription factor (TF) trajectories driving divergent cell states. Nevertheless, the impact of TF dynamics on reprogramming efficiency remains uncharted. Here, we identify the successful reprogramming trajectories of the core pluripotency TF, OCT4, and design a genetic controller that enforces such trajectories with high precision. By combining a genetic circuit that generates a wide range of OCT4 trajectories with live-cell imaging, we track OCT4 trajectories with clonal resolution and find that a distinct constant OCT4 trajectory is required for colony formation. We then develop a synthetic genetic circuit that yields a tight OCT4 distribution around the identified trajectory and outperforms in terms of reprogramming efficiency other circuits that less accurately regulate OCT4. Our synthetic biology approach is generalizable for identifying and enforcing TF dynamics for cell fate programming applications.

Paving the way for synthetic biology‐based bioremediation in Europe

Biological systems are inherently stochastic, a fact which is often ignored when simulating genetic circuits. Synthetic biology aims to design genetic circuits de novo, and cannot therefore afford to ignore the effects of stochastic behavior. Since computational design tools will be essential for large-scale synthetic biology, it is important to develop an understanding of the role of stochasticity in molecular biology, and incorporate this understanding into computational tools for genetic circuit design. We report upon an investigation into the combination of evolutionary algorithms and stochastic simulation for genetic circuit design, to design regulatory systems based on the Bacillus subtilis sin operon.

Synthetic biology approaches: the next tools for improved protein production from CHO cells

BackgroundCell population control allows for the maintenance of a specific cell population density. In this study, we use lysis gene BBa_K117000 from the Registry of Standard Biological Parts, formed by MIT, to lyse Escherichia coli (E. coli). The lysis gene is regulated by a synthetic genetic lysis circuit, using an inducer-regulated promoter-RBS component. To make the design more easily, it is necessary to provide a systematic approach for a genetic lysis circuit to achieve control of cell population density.ResultsFirstly, the lytic ability of the constructed genetic lysis circuit is described by the relationship between the promoter-RBS components and inducer concentration in a steady state model. Then, three types of promoter-RBS libraries are established. Finally, according to design specifications, a systematic design approach is proposed to provide synthetic biologists with a prescribed I/O response by selecting proper promoter-RBS component set in combination with suitable inducer concentrations, within a feasible range.ConclusionThis study provides an important systematic design method for the development of next-generation synthetic gene circuits, from component library construction to genetic circuit assembly. In future, when libraries are more complete, more precise cell density control can be achieved.

Compartmentalization is a hallmark of cellular systems and an ingredient actively exploited in evolution. It is also being engineered and exploited in synthetic biology, in multiple ways. While these have demonstrated important experimental capabilities, understanding design principles underpinning compartmentalization of genetic circuits has been elusive. We develop a systems framework to elucidate the interplay between the nature of the genetic circuit, the spatial organization of compartments, and their operational state (well-mixed or otherwise). In so doing, we reveal a number of unexpected features associated with compartmentalizing synthetic and template-based circuits. These include (i) the consequences of distributing circuits including trade-offs and how they may be circumvented, (ii) hidden constraints in realizing a distributed circuit, and (iii) appealing new features of compartmentalized circuits. We build on this to examine exemplar applications, which consolidate and extend the design principles we have obtained. Our insights, which emerge from the most basic and general considerations of compartmentalizing genetic circuits, are relevant in a broad range of settings.

Synthetic biology uses genetically encoded devices and circuits to implement novel complex functions in living cells and organisms. A hallmark of these genetic circuits is the interaction among their individual parts, according to predefined rules, to process cellular information and produce a circuit output or response. As the number of individual components in a genetic circuit increases, so does the number of interactions needed to achieve the correct behavior, and hence, a greater need to fine-tune the levels of expression of each component. Transcriptional promoters play a key regulatory role in genetic circuits, as they influence the levels of RNA and proteins produced. In multicellular organisms, such as plants, they can also determine developmental, spatial, and tissue-specific patterns of gene expression. The 35S promoter from the Cauliflower Mosaic Virus (CaMV 35S) is widely used in plant biotechnology to direct high levels of gene expression in a variety of plant species. We produced a library of 21 variants of the CaMV 35S promoter by introducing all single nucleotide substitutions to the promoter's TATA box sequence. We then characterized the activity of all variants in homozygous transgenic plants and showed that some of these variants have lower activity than the wild type in plants. These promoter variants could be used to fine-tune the behavior of synthetic genetic circuits in plants.

BackgroundThe use of in silico simulations as a basis for designing artificial biological systems (and experiments to characterize them) is one of the tangible differences between Synthetic Biology and “classical” Genetic Engineering. To this end, synthetic biologists have adopted approaches originating from the traditionally non-biological fields of Nonlinear Dynamics and Systems & Control Theory. However, due to the complex molecular interactions affecting the emergent properties of biological systems, mechanistic descriptions of even the simplest genetic circuits (transcriptional feedback oscillators, bi-stable switches) produced by these methods tend to be either oversimplified, or numerically intractable. More comprehensive and realistic models can be approximated by constructing “toy” genetic circuits that provide the experimenter with some degree of control over the transcriptional dynamics, and allow for experimental set-ups that generate reliable data reflecting the intracellular biochemical state in real time. To this end, we designed two genetic circuits (basic and tunable) capable of exhibiting synchronized oscillatory green fluorescent protein (GFP) expression in small populations of Escherichia coli cells. The functionality of the basic circuit was verified microscopically. High-level visualizations of computational simulations were analyzed to determine whether the reliability and utility of a synchronized transcriptional oscillator could be enhanced by the introduction of chemically inducible repressors.ResultsSynchronized oscillations in GFP expression were repeatedly observed in chemically linked sub-populations of cells. Computational simulations predicted that the introduction of independently inducible repressors substantially broaden the range of conditions under which oscillations could occur, in addition to allowing the frequency of the oscillation to be tuned.ConclusionsThe genetic circuits described here may prove to be valuable research tools for the study of synchronized transcriptional feedback loops under a variety of conditions and experimental set-ups. We further demonstrate the benefit of using abstract visualizations to discover subtle non-linear trends in complex dynamic models with large parameter spaces.

With synthetic biology, genetically engineered (GE) cyanobacteria are now a potential photosynthetic platform for bioproducts, in that genetic transformation with a series of transgenes can encode for biosynthetic pathways to enable the conversion of CO2, water and sunlight to biofuels (e.g. butanol). This presentation will disclose designer biosynthetic pathways for photosynthetic production of bioproducts such as butanol and/or related higher alcohols from carbon dioxide and water. The designer photosynthetic organisms are created such that the endogenous photobiological regulation mechanism is tamed, and the reducing power (NADPH) and energy (ATP) acquired from the photosynthetic process are used for synthesis of butanol and/or related higher alcohols from carbon dioxide and water. This photosynthetic biofuels‐production method eliminates the problem of recalcitrant lignocellulosics by bypassing it. Furthermore, this approach enables the use of seawater and/or groundwater for photobiological production of higher alcohols (such as 1‐butanol) without requiring freshwater or agricultural soil, since the designer photosynthetic organisms can be created from certain marine algae and/or cyanobacteria that can use seawater and/or certain groundwater. However, there are still significant challenges. For example, it is also important to understand the bio‐risk of such organisms before the synthetic biology approach could be used for commercial application. Recently, using plasmid‐transformed cyanobacteria, we experimentally demonstrated that the horizontal gene transfer from GE cyanobacteria to E. coli could occur as soon as 1–3 days of liquid co‐cultures. On the other hand, there was no detectable transfer event for the integrated transgenes so far. These results suggested that even though GE cyanobacteria carrying integrated transgenes possess a more permanent change in the genomic DNA, the bio‐risk of these GE organisms in the context of gene sharing is less severe than plasmids‐carrying GE cyanobacteria. In any case, biosafety is still a potential challenge that must also be addressed.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.