Near-infrared light responsive synthetic c-di-GMP module for optogenetic applications

Accelerating Genetic Sensor Development, Scale-up, and Deployment Using Synthetic Biology

Living cells are exquisitely tuned to sense and respond to changes in their environment. Repurposing these systems to create engineered biosensors has seen growing interest in the field of synthetic biology and provides a foundation for many innovative applications spanning environmental monitoring to improved biobased production. In this review, we present a detailed overview of currently available biosensors and the methods that have supported their development, scale-up, and deployment. We focus on genetic sensors in living cells whose outputs affect gene expression. We find that emerging high-throughput experimental assays and evolutionary approaches combined with advanced bioinformatics and machine learning are establishing pipelines to produce genetic sensors for virtually any small molecule, protein, or nucleic acid. However, more complex sensing tasks based on classifying compositions of many stimuli and the reliable deployment of these systems into real-world settings remain challenges. We suggest that recent advances in our ability to precisely modify nonmodel organisms and the integration of proven control engineering principles (e.g., feedback) into the broader design of genetic sensing systems will be necessary to overcome these hurdles and realize the immense potential of the field.

Selective induction of programmed cell death using synthetic biology tools

Regulated cell death (RCD) controls the removal of dispensable, infected or malignant cells, and is thus essential for development, homeostasis and immunity of multicellular organisms. Over the last years different forms of RCD have been described (among them apoptosis, necroptosis, pyroptosis and ferroptosis), and the cellular signaling pathways that control their induction and execution have been characterized at the molecular level. It has also become apparent that different forms of RCD differ in their capacity to elicit inflammation or an immune response, and that RCD pathways show a remarkable plasticity. Biochemical and genetic studies revealed that inhibition of a given pathway often results in the activation of back-up cell death mechanisms, highlighting close interconnectivity based on shared signaling components and the assembly of multivalent signaling platforms that can initiate different forms of RCD. Due to this interconnectivity and the pleiotropic effects of 'classical' cell death inducers, it is challenging to study RCD pathways in isolation. This has led to the development of tools based on synthetic biology that allow the targeted induction of RCD using chemogenetic or optogenetic methods. Here we discuss recent advances in the development of such toolset, highlighting their advantages and limitations, and their application for the study of RCD in cells and animals.

Engineering Bacteriophytochrome-coupled Photoactivated Adenylyl Cyclases for Enhanced Optogenetic cAMP Modulation

Sensory photoreceptors abound in nature and enable organisms to adapt behavior, development, and physiology to environmental light. In optogenetics, photoreceptors allow spatiotemporally precise, reversible, and non-invasive control by light of cellular processes. Notwithstanding the development of numerous optogenetic circuits, an unmet demand exists for efficient systems sensitive to red light, given its superior penetration of biological tissue. Bacteriophytochrome photoreceptors sense the ratio of red and far-red light to regulate the activity of enzymatic effector modules. The recombination of bacteriophytochrome photosensor modules with cyclase effectors underlies photoactivated adenylyl cyclases (PAC) that catalyze the synthesis of the ubiquitous second messenger 3', 5'-cyclic adenosine monophosphate (cAMP). Via homologous exchanges of the photosensor unit, we devised novel PACs, with the variant DmPAC exhibiting 40-fold activation of cyclase activity under red light, thus surpassing previous red-light-responsive PACs. Modifications of the PHY tongue modulated the responses to red and far-red light. Exchanges of the cyclase effector offer an avenue to further enhancing PACs but require optimization of the linker to the photosensor. DmPAC and a derivative for 3', 5'-cyclic guanosine monophosphate allow the manipulation of cyclic-nucleotide-dependent processes in mammalian cells by red light. Taken together, we advance the optogenetic control of second-messenger signaling and provide insight into the signaling and design of bacteriophytochrome receptors.

Current Trends of Bacterial and Fungal Optoproteins for Novel Optical Applications

Photoproteins, luminescent proteins or optoproteins are a kind of light-response protein responsible for the conversion of light into biochemical energy that is used by some bacteria or fungi to regulate specific biological processes. Within these specific proteins, there are groups such as the photoreceptors that respond to a given light wavelength and generate reactions susceptible to being used for the development of high-novel applications, such as the optocontrol of metabolic pathways. Photoswitchable proteins play important roles during the development of new materials due to their capacity to change their conformational structure by providing/eliminating a specific light stimulus. Additionally, there are bioluminescent proteins that produce light during a heatless chemical reaction and are useful to be employed as biomarkers in several fields such as imaging, cell biology, disease tracking and pollutant detection. The classification of these optoproteins from bacteria and fungi as photoreceptors or photoresponse elements according to the excitation-emission spectrum (UV-Vis-IR), as well as their potential use in novel applications, is addressed in this article by providing a structured scheme for this broad area of knowledge.

Remotely Controllable Engineered Bacteria for Targeted Therapy of Pseudomonas aeruginosa Infection

Pseudomonas aeruginosa (P. aeruginosa) infection has become an intractable problem worldwide due to the decreasing efficacy of the mainstay therapy, antibiotic treatment. Hence, exploring new drugs and therapies to address this issue is crucial. Here, we construct a chimeric pyocin (ChPy) to specifically kill P. aeruginosa and engineer a near-infrared (NIR) light-responsive strain to produce and deliver this drug. Our engineered bacterial strain can continuously produce ChPy in the absence of light and release it to kill P. aeruginosa via remotely and precisely controlled bacterial lysis induced by NIR light. We demonstrate that our engineered bacterial strain is effective in P. aeruginosa-infected wound therapy in the mouse model, as it eradicated PAO1 in mouse wounds and shortened the wound healing time. Our work presents a potentially spatiotemporal and noninvasively controlled therapeutic strategy of engineered bacteria for the targeted treatment of P. aeruginosa infections.

The clinical potential of optogenetic interrogation of pathogenesis

BACKGROUND

Opsin-based optogenetics has emerged as a powerful biomedical tool using light to control protein conformation. Such capacity has been initially demonstrated to control ion flow across the cell membrane, enabling precise control of action potential in excitable cells such as neurons or muscle cells. Further advancement in optogenetics incorporates a greater variety of photoactivatable proteins and results in flexible control of biological processes, such as gene expression and signal transduction, with commonly employed light sources such as LEDs or lasers in optical microscopy. Blessed by the precise genetic targeting specificity and superior spatiotemporal resolution, optogenetics offers new biological insights into physiological and pathological mechanisms underlying health and diseases. Recently, its clinical potential has started to be capitalized, particularly for blindness treatment, due to the convenient light delivery into the eye.

AIMS AND METHODS

This work summarizes the progress of current clinical trials and provides a brief overview of basic structures and photophysics of commonly used photoactivable proteins. We highlight recent achievements such as optogenetic control of the chimeric antigen receptor, CRISPR-Cas system, gene expression, and organelle dynamics. We discuss conceptual innovation and technical challenges faced by current optogenetic research.

CONCLUSION

In doing so, we provide a framework that showcases ever-growing applications of optogenetics in biomedical research and may inform novel precise medicine strategies based on this enabling technology.

Optogenetics for transcriptional programming and genetic engineering

Optogenetics combines genetics and biophotonics to enable noninvasive control of biological processes with high spatiotemporal precision. When engineered into protein machineries that govern the cellular information flow as depicted in the central dogma, multiple genetically encoded non-opsin photosensory modules have been harnessed to modulate gene transcription, DNA or RNA modifications, DNA recombination, and genome engineering by utilizing photons emitting in the wide range of 200-1000 nm. We present herein generally applicable modular strategies for optogenetic engineering and highlight latest advances in the broad applications of opsin-free optogenetics to program transcriptional outputs and precisely manipulate the mammalian genome, epigenome, and epitranscriptome. We also discuss current challenges and future trends in opsin-free optogenetics, which has been rapidly evolving to meet the growing needs in synthetic biology and genetics research.

Bioelectronic cell-based device provides a strategy for the treatment of the experimental model of multiple sclerosis

Wireless powered optogenetic cell-based implant provides a strategy to deliver subcutaneously therapeutic proteins. Immortalize Human Mesenchymal Stem Cells (hMSC-TERT) expressing the bacteriophytochrome diguanylate cyclase (DGCL) were validated for optogenetic controlled interferon-β delivery (Optoferon cells) in a bioelectronic cell-based implant. Optoferon cells transcriptomic profiling was used to elaborate an in-silico model of the recombinant interferon-β production. Wireless optoelectronic device integration was developed using additive manufacturing and injection molding. Implant cell-based optoelectronic interface manufacturing was established to integrate industrial flexible compact low-resistance screen-printed Near Field Communication (NFC) coil antenna. Optogenetic cell-based implant biocompatibility, and device performances were evaluated in the Experimental Autoimmune Encephalomyelitis (EAE) mouse model of multiple sclerosis.

Light-Dependent Control of Bacterial Expression at the mRNA Level

Sensory photoreceptors mediate numerous light-dependent adaptations across organisms. In optogenetics, photoreceptors achieve the reversible, non-invasive, and spatiotemporally precise control by light of gene expression and other cellular processes. The light-oxygen-voltage receptor PAL binds to small RNA aptamers with sequence specificity upon blue-light illumination. By embedding the responsive aptamer in the ribosome-binding sequence of genes of interest, their expression can be downregulated by light. We developed the pCrepusculo and pAurora optogenetic systems that are based on PAL and allow to down- and upregulate, respectively, bacterial gene expression using blue light. Both systems are realized as compact, single plasmids that exhibit stringent blue-light responses with low basal activity and up to several 10-fold dynamic range. As PAL exerts light-dependent control at the RNA level, it can be combined with other optogenetic circuits that control transcription initiation. By integrating regulatory mechanisms operating at the DNA and mRNA levels, optogenetic circuits with emergent properties can thus be devised. As a case in point, the pEnumbra setup permits to upregulate gene expression under moderate blue light whereas strong blue light shuts off expression again. Beyond providing novel signal-responsive expression systems for diverse applications in biotechnology and synthetic biology, our work also illustrates how the light-dependent PAL-aptamer interaction can be harnessed for the control and interrogation of RNA-based processes.

Light-regulated gene expression in Bacteria: Fundamentals, advances, and perspectives

Numerous photoreceptors and genetic circuits emerged over the past two decades and now enable the light-dependent i.e., optogenetic, regulation of gene expression in bacteria. Prompted by light cues in the near-ultraviolet to near-infrared region of the electromagnetic spectrum, gene expression can be up- or downregulated stringently, reversibly, non-invasively, and with precision in space and time. Here, we survey the underlying principles, available options, and prominent examples of optogenetically regulated gene expression in bacteria. While transcription initiation and elongation remain most important for optogenetic intervention, other processes e.g., translation and downstream events, were also rendered light-dependent. The optogenetic control of bacterial expression predominantly employs but three fundamental strategies: light-sensitive two-component systems, oligomerization reactions, and second-messenger signaling. Certain optogenetic circuits moved beyond the proof-of-principle and stood the test of practice. They enable unprecedented applications in three major areas. First, light-dependent expression underpins novel concepts and strategies for enhanced yields in microbial production processes. Second, light-responsive bacteria can be optogenetically stimulated while residing within the bodies of animals, thus prompting the secretion of compounds that grant health benefits to the animal host. Third, optogenetics allows the generation of precisely structured, novel biomaterials. These applications jointly testify to the maturity of the optogenetic approach and serve as blueprints bound to inspire and template innovative use cases of light-regulated gene expression in bacteria. Researchers pursuing these lines can choose from an ever-growing, versatile, and efficient toolkit of optogenetic circuits.

An adaptive tracking illumination system for optogenetic control of single bacterial cells

Single-cell behaviors are essential during early-stage biofilm formation. In this study, we aimed to evaluate whether single-cell behaviors could be precisely and continuously manipulated by optogenetics. We thus established adaptive tracking illumination (ATI), a novel illumination method to precisely manipulate the gene expression and bacterial behavior of Pseudomonas aeruginosa on the surface at the single-cell level by using the combination of a high-throughput bacterial tracking algorithm, optogenetic manipulation, and adaptive microscopy. ATI enables precise gene expression control by manipulating the optogenetic module gene expression and type IV pili (TFP)-mediated motility and microcolony formation during biofilm formation through bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) level modifications in single cells. Moreover, we showed that the spatial organization of single cells in mature biofilms could be controlled using ATI. Therefore, this novel method we established might markedly answer various questions or resolve problems in microbiology. KEY POINTS: • High-resolution spatial and continuous optogenetic control of individual bacteria. • Phenotype-specific optogenetic control of individual bacteria. • Capacity to control biologically relevant processes in engineered single cells.

Engineering of optogenetic devices for biomedical applications in mammalian synthetic biology

Gene- and cell-based therapies are the next frontiers in the field of medicine. Both are transformative and innovative therapies; however, a lack of safety data limits the translation of such promising technologies to the clinic. Improving the safety and promoting the clinical translation of these therapies can be achieved by tightly regulating the release and delivery of therapeutic outputs. In recent years, the rapid development of optogenetic technology has provided opportunities to develop precision-controlled gene- and cell-based therapies, in which light is introduced to precisely and spatiotemporally manipulate the behaviour of genes and cells. This review focuses on the development of optogenetic tools and their applications in biomedicine, including photoactivated genome engineering and phototherapy for diabetes and tumours. The prospects and challenges of optogenetic tools for future clinical applications are also discussed.

Optogenetics Illuminates Applications in Microbial Engineering

Optogenetics has been used in a variety of microbial engineering applications, such as chemical and protein production, studies of cell physiology, and engineered microbe-host interactions. These diverse applications benefit from the precise spatiotemporal control that light affords, as well as its tunability, reversibility, and orthogonality. This combination of unique capabilities has enabled a surge of studies in recent years investigating complex biological systems with completely new approaches. We briefly describe the optogenetic tools that have been developed for microbial engineering, emphasizing the scientific advancements that they have enabled. In particular, we focus on the unique benefits and applications of implementing optogenetic control, from bacterial therapeutics to cybergenetics. Finally, we discuss future research directions, with special attention given to the development of orthogonal multichromatic controls. With an abundance of advantages offered by optogenetics, the future is bright in microbial engineering. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Far-Red Light Triggered Production of Bispecific T Cell Engagers (BiTEs) from Engineered Cells for Antitumor Application

Bispecific T-cell engagers (BiTEs), which have shown potent antitumor activity in humans, are emerging as one of the most promising immunotherapeutic strategies for cancer treatment in recent years. However, the clinical application of BiTEs nowadays has been hampered by their short half-life in the circulatory system due to their low molecular weight and rapid renal clearance. Inevitable continuous infusion of BiTEs has become a routine operation in order to achieve effective treatment, although it is costly, inconvenient, time-consuming, and even painful for patients in some cases. To develop an on-demand, tunable, and reversible approach to overcome these limitations, we assembled a transcription-control device into mammalian cells based on a bacterial far-red light (FRL) responsive signaling pathway to drive the expression of a BiTE against Glypican 3 (GPC3), which is a highly tumor-specific antigen expressed in most hepatocellular carcinomas (HCC). As demonstrated in in vitro experiments, we proved that the FRL sensitive device spatiotemporally responded to the control of FRL illumination and produced a therapeutic level of BiTEs that recruited and activated human T cells to eliminate GPC3 positive tumor cells. By functionally harnessing the power of optogenetics to remotely regulate the production of BiTEs from bioengineered cells and demonstrating its effectiveness in treating tumor cells, this study provides a novel approach to achieve an in vivo supply of BiTEs, which could be potentially applied to other formats of bispecific antibodies and facilitate their clinical applications.

Toward Multiplexed Optogenetic Circuits

Owing to its ubiquity and easy availability in nature, light has been widely employed to control complex cellular behaviors. Light-sensitive proteins are the foundation to such diverse and multilevel adaptive regulations in a large range of organisms. Due to their remarkable properties and potential applications in engineered systems, exploration and engineering of natural light-sensitive proteins have significantly contributed to expand optogenetic toolboxes with tailor-made performances in synthetic genetic circuits. Progressively, more complex systems have been designed in which multiple photoreceptors, each sensing its dedicated wavelength, are combined to simultaneously coordinate cellular responses in a single cell. In this review, we highlight recent works and challenges on multiplexed optogenetic circuits in natural and engineered systems for a dynamic regulation breakthrough in biotechnological applications.

The Red Edge: Bilin-Binding Photoreceptors as Optogenetic Tools and Fluorescence Reporters

This review adds the bilin-binding phytochromes to the Chemical Reviews thematic issue "Optogenetics and Photopharmacology". The work is structured into two parts. We first outline the photochemistry of the covalently bound tetrapyrrole chromophore and summarize relevant spectroscopic, kinetic, biochemical, and physiological properties of the different families of phytochromes. Based on this knowledge, we then describe the engineering of phytochromes to further improve these chromoproteins as photoswitches and review their employment in an ever-growing number of different optogenetic applications. Most applications rely on the light-controlled complex formation between the plant photoreceptor PhyB and phytochrome-interacting factors (PIFs) or C-terminal light-regulated domains with enzymatic functions present in many bacterial and algal phytochromes. Phytochrome-based optogenetic tools are currently implemented in bacteria, yeast, plants, and animals to achieve light control of a wide range of biological activities. These cover the regulation of gene expression, protein transport into cell organelles, and the recruitment of phytochrome- or PIF-tagged proteins to membranes and other cellular compartments. This compilation illustrates the intrinsic advantages of phytochromes compared to other photoreceptor classes, e.g., their bidirectional dual-wavelength control enabling instant ON and OFF regulation. In particular, the long wavelength range of absorption and fluorescence within the "transparent window" makes phytochromes attractive for complex applications requiring deep tissue penetration or dual-wavelength control in combination with blue and UV light-sensing photoreceptors. In addition to the wide variability of applications employing natural and engineered phytochromes, we also discuss recent progress in the development of bilin-based fluorescent proteins.

A far-red light-inducible CRISPR-Cas12a platform for remote-controlled genome editing and gene activation

The CRISPR-Cas12a has been harnessed as a powerful tool for manipulating targeted gene expression. The possibility to manipulate the activity of CRISPR-Cas12a with a more precise spatiotemporal resolution and deep tissue permeability will enable targeted genome engineering and deepen our understanding of the gene functions underlying complex cellular behaviors. However, currently available inducible CRISPR-Cas12a systems are limited by diffusion, cytotoxicity, and poor tissue permeability. Here, we developed a far-red light (FRL)–inducible CRISPR-Cas12a (FICA) system that can robustly induce gene editing in mammalian cells, and an FRL-inducible CRISPR-dCas12a (FIdCA) system based on the protein-tagging system SUperNova (SunTag) that can be used for gene activation under light-emitting diode–based FRL. Moreover, we show that the FIdCA system can be deployed to activate target genes in mouse livers. These results demonstrate that these systems developed here provide robust and efficient platforms for programmable genome manipulation in a noninvasive and spatiotemporal fashion.

Reprogramming microbial populations using a programmed lysis system to improve chemical production

Microbial populations are a promising model for achieving microbial cooperation to produce valuable chemicals. However, regulating the phenotypic structure of microbial populations remains challenging. In this study, a programmed lysis system (PLS) is developed to reprogram microbial cooperation to enhance chemical production. First, a colicin M -based lysis unit is constructed to lyse Escherichia coli. Then, a programmed switch, based on proteases, is designed to regulate the effective lysis unit time. Next, a PLS is constructed for chemical production by combining the lysis unit with a programmed switch. As a result, poly (lactate-co-3-hydroxybutyrate) production is switched from PLH synthesis to PLH release, and the content of free PLH is increased by 283%. Furthermore, butyrate production with E. coli consortia is switched from E. coli BUT003 to E. coli BUT004, thereby increasing butyrate production to 41.61 g/L. These results indicate the applicability of engineered microbial populations for improving the metabolic division of labor to increase the efficiency of microbial cell factories.

Protein-Based Systems for Translational Regulation of Synthetic mRNAs in Mammalian Cells

Synthetic mRNAs, which are produced by in vitro transcription, have been recently attracting attention because they can express any transgenes without the risk of insertional mutagenesis. Although current synthetic mRNA medicine is not designed for spatiotemporal or cell-selective regulation, many preclinical studies have developed the systems for the translational regulation of synthetic mRNAs. Such translational regulation systems will cope with high efficacy and low adverse effects by producing the appropriate amount of therapeutic proteins, depending on the context. Protein-based regulation is one of the most promising approaches for the translational regulation of synthetic mRNAs. As synthetic mRNAs can encode not only output proteins but also regulator proteins, all components of protein-based regulation systems can be delivered as synthetic mRNAs. In addition, in the protein-based regulation systems, the output protein can be utilized as the input for the subsequent regulation to construct multi-layered gene circuits, which enable complex and sophisticated regulation. In this review, I introduce what types of proteins have been used for translational regulation, how to combine them, and how to design effective gene circuits.

Natural diversity provides a broad spectrum of cyanobacteriochrome-based diguanylate cyclases

Cyanobacteriochromes (CBCRs) are spectrally diverse photosensors from cyanobacteria distantly related to phytochromes that exploit photoisomerization of linear tetrapyrrole (bilin) chromophores to regulate associated signaling output domains. Unlike phytochromes, a single CBCR domain is sufficient for photoperception. CBCR domains that regulate the production or degradation of cyclic nucleotide second messengers are becoming increasingly well characterized. Cyclic di-guanosine monophosphate (c-di-GMP) is a widespread small-molecule regulator of bacterial motility, developmental transitions, and biofilm formation whose biosynthesis is regulated by CBCRs coupled to GGDEF (diguanylate cyclase) output domains. In this study, we compare the properties of diverse CBCR-GGDEF proteins with those of synthetic CBCR-GGDEF chimeras. Our investigation shows that natural diversity generates promising candidates for robust, broad spectrum optogenetic applications in live cells. Since light quality is constantly changing during plant development as upper leaves begin to shade lower leaves-affecting elongation growth, initiation of flowering, and responses to pathogens, these studies presage application of CBCR-GGDEF sensors to regulate orthogonal, c-di-GMP-regulated circuits in agronomically important plants for robust mitigation of such deleterious responses under natural growing conditions in the field.

Sensory perception in bacterial cyclic diguanylate signal transduction

Cyclic diguanylate (c-di-GMP) signal transduction systems provide bacteria with the ability to sense changing cell status or environmental conditions and then execute suitable physiological and social behaviors in response. In this review, we provide a comprehensive census of the stimuli and receptors that are linked to the modulation of intracellular c-di-GMP. Emerging evidence indicates that c-di-GMP networks sense light, surfaces, energy, redox potential, respiratory electron acceptors, temperature, and structurally diverse biotic and abiotic chemicals. Bioinformatic analysis of sensory domains in diguanylate cyclases and c-di-GMP-specific phosphodiesterases as well as the receptor complexes associated with them reveals that these functions are linked to a diverse repertoire of protein domain families. We describe the principles of stimulus perception learned from studying these modular sensory devices, illustrate how they are assembled in varied combinations with output domains, and summarize a system for classifying these sensor proteins based on their complexity. Biological information processing via c-di-GMP signal transduction not only is fundamental to bacterial survival in dynamic environments but also is being used to engineer gene expression circuitry and synthetic proteins with à la carte biochemical functionalities.

A guide to the optogenetic regulation of endogenous molecules

Genetically encoded tools for the regulation of endogenous molecules (RNA, DNA elements and protein) are needed to study and control biological processes with minimal interference caused by protein overexpression and overactivation of signaling pathways. Here we focus on light-controlled optogenetic tools (OTs) that allow spatiotemporally precise regulation of gene expression and protein function. To control endogenous molecules, OTs combine light-sensing modules from natural photoreceptors with specific protein or nucleic acid binders. We discuss OT designs and group OTs according to the principles of their regulation. We outline characteristics of OT performance, discuss considerations for their use in vivo and review available OTs and their applications in cells and in vivo. Finally, we provide a brief outlook on the development of OTs.

Constructing Smartphone-Controlled Optogenetic Switches in Mammalian Cells

With the increasing indispensable role of smartphones in our daily lives, the mobile health care system coupled with embedded physical sensors and modern communication technologies make it an attractive technology for enabling the remote monitoring of an individual's health. Using a multidisciplinary design principle coupled with smart electronics, software, and optogenetics, the investigators constructed smartphone-controlled optogenetic switches to enable the ultraremote-control transgene expression. A custom-designed SmartController system was programmed to process wireless signals from smartphones, enabling the regulation of therapeutic outputs production by optically engineered cells via a far-red light (FRL)-responsive optogenetic interface. In the present study, the investigators describe the details of the protocols for constructing smartphone-controlled optogenetic switches, including the rational design of an FRL-triggered transgene expression circuit, the procedure for cell culture and transfection, the implementation of the smartphone-controlled far-red light-emitting diode (LED) module, and the reporter detection assay.

Roadmap on emerging concepts in the physical biology of bacterial biofilms: from surface sensing to community formation

Bacterial biofilms are communities of bacteria that exist as aggregates that can adhere to surfaces or be free-standing. This complex, social mode of cellular organization is fundamental to the physiology of microbes and often exhibits surprising behavior. Bacterial biofilms are more than the sum of their parts: single-cell behavior has a complex relation to collective community behavior, in a manner perhaps cognate to the complex relation between atomic physics and condensed matter physics. Biofilm microbiology is a relatively young field by biology standards, but it has already attracted intense attention from physicists. Sometimes, this attention takes the form of seeing biofilms as inspiration for new physics. In this roadmap, we highlight the work of those who have taken the opposite strategy: we highlight the work of physicists and physical scientists who use physics to engage fundamental concepts in bacterial biofilm microbiology, including adhesion, sensing, motility, signaling, memory, energy flow, community formation and cooperativity. These contributions are juxtaposed with microbiologists who have made recent important discoveries on bacterial biofilms using state-of-the-art physical methods. The contributions to this roadmap exemplify how well physics and biology can be combined to achieve a new synthesis, rather than just a division of labor.

Single-component near-infrared optogenetic systems for gene transcription regulation

Near-infrared (NIR) optogenetic systems for transcription regulation are in high demand because NIR light exhibits low phototoxicity, low scattering, and allows combining with probes of visible range. However, available NIR optogenetic systems consist of several protein components of large size and multidomain structure. Here, we engineer single-component NIR systems consisting of evolved photosensory core module of Idiomarina sp. bacterial phytochrome, named iLight, which are smaller and packable in adeno-associated virus. We characterize iLight in vitro and in gene transcription repression in bacterial and gene transcription activation in mammalian cells. Bacterial iLight system shows 115-fold repression of protein production. Comparing to multi-component NIR systems, mammalian iLight system exhibits higher activation of 65-fold in cells and faster 6-fold activation in deep tissues of mice. Neurons transduced with viral-encoded iLight system exhibit 50-fold induction of fluorescent reporter. NIR light-induced neuronal expression of green-light-activatable CheRiff channelrhodopsin causes 20-fold increase of photocurrent and demonstrates efficient spectral multiplexing.

Current near-IR optogenetic systems to regulate transcription consist of a number of large protein components. Here the authors report a smaller single-component near-IR system, iLight, developed from a bacterial phytochrome that they use to control gene transcription in bacterial and mammalian cells.

An Engineered Biliverdin-Compatible Cyanobacteriochrome Enables a Unique Ultrafast Reversible Photoswitching Pathway

Cyanobacteriochromes (CBCRs) are promising optogenetic tools for their diverse absorption properties with a single compact cofactor-binding domain. We previously uncovered the ultrafast reversible photoswitching dynamics of a red/green photoreceptor AnPixJg2, which binds phycocyanobilin (PCB) that is unavailable in mammalian cells. Biliverdin (BV) is a mammalian cofactor with a similar structure to PCB but exhibits redder absorption. To improve the AnPixJg2 feasibility in mammalian applications, AnPixJg2_BV4 with only four mutations has been engineered to incorporate BV. Herein, we implemented femtosecond transient absorption (fs-TA) and ground state femtosecond stimulated Raman spectroscopy (GS-FSRS) to uncover transient electronic dynamics on molecular time scales and key structural motions responsible for the photoconversion of AnPixJg2_BV4 with PCB (Bpcb) and BV (Bbv) cofactors in comparison with the parent AnPixJg2 (Apcb). Bpcb adopts the same photoconversion scheme as Apcb, while BV4 mutations create a less bulky environment around the cofactor D ring that promotes a faster twist. The engineered Bbv employs a reversible clockwise/counterclockwise photoswitching that requires a two-step twist on ~5 and 35 picosecond (ps) time scales. The primary forward P_fr → P_o transition displays equal amplitude weights between the two processes before reaching a conical intersection. In contrast, the primary reverse P_o → P_fr transition shows a 2:1 weight ratio of the ~35 ps over 5 ps component, implying notable changes to the D-ring-twisting pathway. Moreover, we performed pre-resonance GS-FSRS and quantum calculations to identify the Bbv vibrational marker bands at ~659,797, and 1225 cm^-1. These modes reveal a stronger H-bonding network around the BV cofactor A ring with BV4 mutations, corroborating the D-ring-dominant reversible photoswitching pathway in the excited state. Implementation of BV4 mutations in other PCB-binding GAF domains like AnPixJg4, AM1_1870g3, and NpF2164g5 could promote similar efficient reversible photoswitching for more directional bioimaging and optogenetic applications, and inspire other bioengineering advances.

Impact of amino acid substitutions on the behavior of a photoactivatable near infrared fluorescent protein PAiRFP1

A photoactivatable near-infrared fluorescent protein (NIR-FP) PAiRFP1 has been developed by 15 amino acid substitutions in its nonfluorescent template Agp2. In our previous communication, we investigated the role of three amino acids in PHY domain distal from BV molecule. The impact of the twelve amino acids in GAF domain, especially five residues near BV-binding pocket is unclear. In this paper, PCR based reverse mutagenesis, spectroscopic methods, molecular modelling and simulations have been employed to explore the roles of these substitutions during the molecular evolution of PAiRFP1. It was found that the residue L163 is important for protein folding in PAiRFP1. The residues F244 and C280 exerted remarkable effects on molar extinction coefficient, NIR fluorescence quantum yield, molecular brightness, fluorescence fold, and dark recovery rate. The residues F244 and V276 modulate the maximum absorption and emission peak position. The reverse mutant L168M exhibited a higher fluorescence fold than PAiRFP1. Additionally, the reverse mutants V203A, V294E, S218G and D127G possessed better spectral properties than PAiRFP1. This study is important for the rational design of a better BphP-based photoactivatable NIR-FPs.

Steering Molecular Activity with Optogenetics: Recent Advances and Perspectives

Optogenetics utilizes photosensitive proteins to manipulate the localization and interaction of molecules in living cells. Because light can be rapidly switched and conveniently confined to the sub-micrometer scale, optogenetics allows for controlling cellular events with an unprecedented resolution in time and space. The past decade has witnessed an enormous progress in the field of optogenetics within the biological sciences. The ever-increasing amount of optogenetic tools, however, can overwhelm the selection of appropriate optogenetic strategies. Considering that each optogenetic tool may have a distinct mode of action, a comparative analysis of the current optogenetic toolbox can promote the further use of optogenetics, especially by researchers new to this field. This review provides such a compilation that highlights the spatiotemporal accuracy of current optogenetic systems. Recent advances of optogenetics in live cells and animal models are summarized, the emerging work that interlinks optogenetics with other research fields is presented, and exciting clinical and industrial efforts to employ optogenetic strategy toward disease intervention are reported.

Transient electronic and vibrational signatures during reversible photoswitching of a cyanobacteriochrome photoreceptor

Cyanobacteriochromes (CBCRs) are an emerging class of photoreceptors that are distant relatives of the phytochromes family. Unlike phytochromes, CBCRs have gained popularity in optogenetics due to their highly diverse spectral properties spanning the UV to near-IR region and only needing a single compact binding domain. AnPixJg2 is a CBCR that can reversibly photoswitch between its red-absorbing (^15ZP_r) and green-absorbing (^15EP_g) forms of the phycocyanobilin (PCB) cofactor. To reveal primary events of photoconversion, we implemented femtosecond transient absorption spectroscopy with a homemade LED box and a miniature peristaltic pump flow cell to track transient electronic responses of the photoexcited AnPixJg2 on molecular time scales. The 525 nm laser-induced P_g-to-P_r reverse conversion exhibits a ~3 ps excited-state lifetime before reaching the conical intersection (CI) and undergoing further relaxation on the 30 ps time scale to generate a long-lived Lumi-G ground state intermediate en route to P_r. The 650 nm laser-induced P_r-to-P_g forward conversion is less efficient than reverse conversion, showing a longer-lived excited state which requires two steps with ~13 and 217 ps time constants to enter the CI region. Furthermore, using a tunable ps Raman pump with broadband Raman probe on both the Stokes and anti-Stokes sides, we collected the pre-resonance ground-state femtosecond stimulated Raman spectroscopy (GS-FSRS) data with mode assignments aided by quantum calculations. Key vibrational marker bands at ~850, 1050, 1615, and 1649 cm^-1 of the P_r conformer exhibit a notable blueshift to those of the P_g conformer inside AnPixJg2, reflecting the PCB chromophore terminal D (major) and A (minor) ring twist along the primary photoswitching reaction coordinate. This integrated ultrafast spectroscopy and computational platform has the potential to elucidate photochemistry and photophysics of more CBCRs and photoactive proteins in general, providing the highly desirable mechanistic insights to facilitate the rational design of functional molecular sensors and devices.

Approach for in vivo delivery of CRISPR/Cas system: a recent update and future prospect

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) system provides a groundbreaking genetic technology that allows scientists to modify genes by targeting specific genomic sites. Due to the relative simplicity and versatility of the CRISPR/Cas system, it has been extensively applied in human genetic research as well as in agricultural applications, such as improving crops. Since the gene editing activity of the CRISPR/Cas system largely depends on the efficiency of introducing the system into cells or tissues, an efficient and specific delivery system is critical for applying CRISPR/Cas technology. However, there are still some hurdles remaining for the translatability of CRISPR/Cas system. In this review, we summarized the approaches used for the delivery of the CRISPR/Cas system in mammals, plants, and aquacultures. We further discussed the aspects of delivery that can be improved to elevate the potential for CRISPR/Cas translatability.

Going virtual: a report from the sixth Young Microbiologists Symposium on 'Microbe Signalling, Organisation and Pathogenesis'

The sixth Young Microbiologists Symposium on 'Microbe Signalling, Organisation and Pathogenesis' was scheduled to be held at the University of Southampton, UK, in late August 2020. However, due to the health and safety guidelines and travel restrictions as a response to the COVID-19 pandemic, the symposium was transitioned to a virtual format, a change embraced enthusiastically as the meeting attracted over 200 microbiologists from 40 countries. The event allowed junior scientists to present their work to a broad audience and was supported by the European Molecular Biology Organization, the Federation of European Microbiological Societies, the Society of Applied Microbiology, the Biochemical Society, the Microbiology Society and the National Biofilms Innovation Centre. Sessions covered recent advances in all areas of microbiology including: Secretion and transport across membranes, Gene regulation and signalling, Host-microbe interactions, and Microbial communities and biofilm formation. This report focuses on several of the highlights and exciting developments communicated during the talks and poster presentations.

Synthetic Biological Approaches for Optogenetics and Tools for Transcriptional Light-Control in Bacteria

Light has become established as a tool not only to visualize and investigate but also to steer biological systems. This review starts by discussing the unique features that make light such an effective control input in biology. It then gives an overview of how light-control came to progress, starting with photoactivatable compounds and leading up to current genetic implementations using optogenetic approaches. The review then zooms in on optogenetics, focusing on photosensitive proteins, which form the basis for optogenetic engineering using synthetic biological approaches. As the regulation of transcription provides a highly versatile means for steering diverse biological functions, the focus of this review then shifts to transcriptional light regulators, which are presented in the biotechnologically highly relevant model organism Escherichia coli.

Two-photon conversion of a bacterial phytochrome

In nature, sensory photoreceptors underlie diverse spatiotemporally precise and generally reversible biological responses to light. Photoreceptors also serve as genetically encoded agents in optogenetics to control by light organismal state and behavior. Phytochromes represent a superfamily of photoreceptors that transition between states absorbing red light (Pr) and far-red light (Pfr), thus expanding the spectral range of optogenetics to the near-infrared range. Although light of these colors exhibits superior penetration of soft tissue, the transmission through bone and skull is poor. To overcome this fundamental challenge, we explore the activation of a bacterial phytochrome by a femtosecond laser emitting in the 1 μm wavelength range. Quantum chemical calculations predict that bacterial phytochromes possess substantial two-photon absorption cross sections. In line with this notion, we demonstrate that the photoreversible Pr ↔ Pfr conversion is driven by two-photon absorption at wavelengths between 1170 and 1450 nm. The Pfr yield was highest for wavelengths between 1170 and 1280 nm and rapidly plummeted beyond 1300 nm. By combining two-photon activation with bacterial phytochromes, we lay the foundation for enhanced spatial resolution in optogenetics and unprecedented penetration through bone, skull, and soft tissue.

Phytochromes and Cyanobacteriochromes: Photoreceptor Molecules Incorporating a Linear Tetrapyrrole Chromophore

In this chapter, we summarize the molecular mechanisms of the linear tetrapyrrole-binding photoreceptors, phytochromes, and cyanobacteriochromes. We especially focus on the color-tuning mechanisms and conformational changes during the photoconversion process. Furthermore, we introduce current status of development of the optogenetic tools based on these molecules. Huge repertoire of these photoreceptors with diverse spectral properties would contribute to development of multiplex optogenetic regulation. Among them, the photoreceptors incorporating the biliverdin IXα chromophore is advantageous for in vivo optogenetics because this is intrinsic in the mammalian cells, and absorbs far-red light penetrating into deep mammalian tissues.

Optogenetic control of gut bacterial metabolism to promote longevity

Gut microbial metabolism is associated with host longevity. However, because it requires direct manipulation of microbial metabolism in situ, establishing a causal link between these two processes remains challenging. We demonstrate an optogenetic method to control gene expression and metabolite production from bacteria residing in the host gut. We genetically engineer an Escherichia coli strain that secretes colanic acid (CA) under the quantitative control of light. Using this optogenetically-controlled strain to induce CA production directly in the Caenorhabditis elegans gut, we reveal the local effect of CA in protecting intestinal mitochondria from stress-induced hyper-fragmentation. We also demonstrate that the lifespan-extending effect of this strain is positively correlated with the intensity of green light, indicating a dose-dependent CA benefit on the host. Thus, optogenetics can be used to achieve quantitative and temporal control of gut bacterial metabolism in order to reveal its local and systemic effects on host health and aging.

Carbon Atoms Speaking Out: How the Geometric Sensitivity of 13C Chemical Shifts Leads to Understanding the Colour Tuning of Phycocyanobilin in Cph1 and AnPixJ

We present a combined quantum mechanics/molecular mechanics (QM/MM) molecular dynamics-statistical approach for the interpretation of nuclear magnetic resonance (NMR) chemical shift patterns in phycocyanobilin (PCB). These were originally associated with colour tuning upon photoproduct formation in red/green-absorbing cyanobacteriochrome AnPixJg2 and red/far-red-absorbing phytochrome Cph1Δ2. We pursue an indirect approach without computation of the absorption frequencies since the molecular geometry of cofactor and protein are not accurately known. Instead, we resort to a heuristic determination of the conjugation length in PCB through the experimental NMR chemical shift patterns, supported by quantum chemical calculations. We have found a characteristic correlation pattern of 13C chemical shifts to specific bond orders within the π-conjugated system, which rests on the relative position of carbon atoms with respect to electron-withdrawing groups and the polarisation of covalent bonds. We propose the inversion of this regioselective relationship using multivariate statistics and to apply it to the known experimental NMR chemical shifts in order to predict changes in the bond alternation pattern. Therefrom the extent of electronic conjugation, and eventually the change in absorption frequency, can be derived. In the process, the consultation of explicit mesomeric formulae plays an important role to qualitatively account for possible conjugation scenarios of the chromophore. While we are able to consistently associate the NMR chemical shifts with hypsochromic and bathochromic shifts in the Pg and Pfr, our approach represents an alternative method to increase the explanatory power of NMR spectroscopic data in proteins.

Bringing Light into Cell-Free Expression

Cell-free systems, as part of the synthetic biology field, have become a critical platform in biological studies. However, there is a lack of research into developing a switch for a dynamical control of the transcriptional and translational process. The optogenetic tool has been widely proven as an ideal control switch for protein synthesis due to its nontoxicity and excellent time-space conversion. Hence, in this study, a blue light-regulated two-component system named YF1/FixJ was incorporated into an Escherichia coli-based cell-free system to control protein synthesis. The corresponding cell-free system successfully achieved a 5-fold dynamic protein expression by blue light repression and 3-fold dynamic expression by blue light activation. With the aim of expanding the applications of cell-free synthetic biology, the cell-free blue light-sensing system was used to perform imaging, light-controlled antibody synthesis, and light-triggered artificial cell assembly. This study can provide a guide for further research into the field of cell-free optical sensing. Moreover, it will also promote the development of cell-free synthetic biology and optogenetics through applying the cell-free optical sensing system to synthetic biology education, biopharmaceutical research, and artificial cell construction.

A non-invasive far-red light-induced split-Cre recombinase system for controllable genome engineering in mice

The Cre-loxP recombination system is a powerful tool for genetic manipulation. However, there are widely recognized limitations with chemically inducible Cre-loxP systems, and the UV and blue-light induced systems have phototoxicity and minimal capacity for deep tissue penetration. Here, we develop a far-red light-induced split Cre-loxP system (FISC system) based on a bacteriophytochrome optogenetic system and split-Cre recombinase, enabling optogenetical regulation of genome engineering in vivo solely by utilizing a far-red light (FRL). The FISC system exhibits low background and no detectable photocytotoxicity, while offering efficient FRL-induced DNA recombination. Our in vivo studies showcase the strong organ-penetration capacity of FISC system, markedly outperforming two blue-light-based Cre systems for recombination induction in the liver. Demonstrating its strong clinical relevance, we successfully deploy a FISC system using adeno-associated virus (AAV) delivery. Thus, the FISC system expands the optogenetic toolbox for DNA recombination to achieve spatiotemporally controlled, non-invasive genome engineering in living systems.

Current light-inducible Cre-loxP systems have minimal capacity for deep tissue penetration. Here, the authors present a far-red light-induced split Cre-loxP system for in vivo genome engineering.

Light-powered Escherichia coli cell division for chemical production

Cell division can perturb the metabolic performance of industrial microbes. The C period of cell division starts from the initiation to the termination of DNA replication, whereas the D period is the bacterial division process. Here, we first shorten the C and D periods of E. coli by controlling the expression of the ribonucleotide reductase NrdAB and division proteins FtsZA through blue light and near-infrared light activation, respectively. It increases the specific surface area to 3.7 μm⁻¹ and acetoin titer to 67.2 g·L⁻¹. Next, we prolong the C and D periods of E. coli by regulating the expression of the ribonucleotide reductase NrdA and division protein inhibitor SulA through blue light activation-repression and near-infrared (NIR) light activation, respectively. It improves the cell volume to 52.6 μm³ and poly(lactate-co-3-hydroxybutyrate) titer to 14.31 g·L⁻¹. Thus, the optogenetic-based cell division regulation strategy can improve the efficiency of microbial cell factories.

Manipulation of genes controlling microbial shapes can affect bio-production. Here, the authors employ an optogenetic method to realize dynamic morphological engineering of E. coli replication and division and show the increased production of acetoin and poly(lactate-co-3-hydroxybutyrate).

Controlling biofilms using synthetic biology approaches

Bacterial biofilms are formed by the complex but ordered regulation of intra- or inter-cellular communication, environmentally responsive gene expression, and secretion of extracellular polymeric substances. Given the robust nature of biofilms due to the non-growing nature of biofilm bacteria and the physical barrier provided by the extracellular matrix, eradicating biofilms is a very difficult task to accomplish with conventional antibiotic or disinfectant treatments. Synthetic biology holds substantial promise for controlling biofilms by improving and expanding existing biological tools, introducing novel functions to the system, and re-conceptualizing gene regulation. This review summarizes synthetic biology approaches used to eradicate biofilms via protein engineering of biofilm-related enzymes, utilization of synthetic genetic circuits, and the development of functional living agents. Synthetic biology also enables beneficial applications of biofilms through the production of biomaterials and patterning biofilms with specific temporal and spatial structures. Advances in synthetic biology will add novel biofilm functionalities for future therapeutic, biomanufacturing, and environmental applications.

Genetic manipulation of cyclic nucleotide signaling during hippocampal neuroplasticity and memory formation

Decades of research have underscored the importance of cyclic nucleotide signaling in memory formation and synaptic plasticity. In recent years, several new genetic techniques have expanded the neuroscience toolbox, allowing researchers to measure and modulate cyclic nucleotide gradients with high spatiotemporal resolution. Here, we will provide an overview of studies using genetic approaches to interrogate the role cyclic nucleotide signaling plays in hippocampus-dependent memory processes and synaptic plasticity. Particular attention is given to genetic techniques that measure real-time changes in cyclic nucleotide levels as well as newly-developed genetic strategies to transiently manipulate cyclic nucleotide signaling in a subcellular compartment-specific manner with high temporal resolution.

Bioengineered smart bacterial carriers for combinational targeted therapy of solid tumours

Despite many endeavours for the development of new anticancer drugs, effective therapy of solid tumours remains a challenging issue. The current cancer chemotherapies may associate with two important limitations, including the lack/trivial specificity of treatment modalities towards diseased cells/tissues resulting in undesired side effects, and the emergence of drug-resistance mechanisms by tumour cells causing the failure of the treatment. Much attention, therefore, has currently been paid to develop smart and highly specific anticancer agents with maximal therapeutic impacts and minimal side effects. Among various strategies used to target cancer cells, bacteria-based cancer therapies (BCTs) have been validated as potential gene/drug delivery carriers, which can also be engineered to be used in diagnosis processes. They can be devised to selectively target the tumour microenvironment (TME), within which they may preferentially proliferate in the necrotic and anaerobic parts - often inaccessible to other therapeutics. BCTs are capable to sense and respond to the environmental signals, upon which they are considered as smart microrobots applicable in the controlled delivery of therapeutic agents to the TME. In this review, we aimed to provide comprehensive insights into the potentials of the bioengineered bacteria as smart and targeted bio-carriers and discuss their applications in cancer therapy.

Phytochrome evolution in 3D: deletion, duplication, and diversification

Canonical plant phytochromes are master regulators of photomorphogenesis and the shade avoidance response. They are also part of a widespread superfamily of photoreceptors with diverse spectral and biochemical properties. Plant phytochromes belong to a clade including other phytochromes from glaucophyte, prasinophyte, and streptophyte algae (all members of the Archaeplastida) and those from cryptophyte algae. This is consistent with recent analyses supporting the existence of an AC (Archaeplastida + Cryptista) clade. AC phytochromes have been proposed to arise from ancestral cyanobacterial genes via endosymbiotic gene transfer (EGT), but most recent studies instead support multiple horizontal gene transfer (HGT) events to generate extant eukaryotic phytochromes. In principle, this scenario would be compared to the emerging understanding of early events in eukaryotic evolution to generate a coherent picture. Unfortunately, there is currently a major discrepancy between the evolution of phytochromes and the evolution of eukaryotes; phytochrome evolution is thus not a solved problem. We therefore examine phytochrome evolution in a broader context. Within this context, we can identify three important themes in phytochrome evolution: deletion, duplication, and diversification. These themes drive phytochrome evolution as organisms evolve in response to environmental challenges.

Role of cyclic nucleotides and their downstream signaling cascades in memory function: Being at the right time at the right spot

A plethora of studies indicate the important role of cAMP and cGMP cascades in neuronal plasticity and memory function. As a result, altered cyclic nucleotide signaling has been implicated in the pathophysiology of mnemonic dysfunction encountered in several diseases. In the present review we provide a wide overview of studies regarding the involvement of cyclic nucleotides, as well as their upstream and downstream molecules, in physiological and pathological mnemonic processes. Next, we discuss the regulation of the intracellular concentration of cyclic nucleotides via phosphodiesterases, the enzymes that degrade cAMP and/or cGMP, and via A-kinase-anchoring proteins that refine signal compartmentalization of cAMP signaling. We also provide an overview of the available data pointing to the existence of specific time windows in cyclic nucleotide signaling during neuroplasticity and memory formation and the significance to target these specific time phases for improving memory formation. Finally, we highlight the importance of emerging imaging tools like Förster resonance energy transfer imaging and optogenetics in detecting, measuring and manipulating the action of cyclic nucleotide signaling cascades.

Optogenetics and CRISPR: A New Relationship Built to Last

Since the breakthrough discoveries that CRISPR-Cas9 nucleases can be easily programmed and employed to induce targeted double-strand breaks in mammalian cells, the gene editing field has grown exponentially. Today, CRISPR technologies based on engineered class II CRISPR effectors facilitate targeted modification of genes and RNA transcripts. Moreover, catalytically impaired CRISPR-Cas variants can be employed as programmable DNA binding domains and used to recruit effector proteins, such as transcriptional regulators, epigenetic modifiers or base-modifying enzymes, to selected genomic loci. The juxtaposition of CRISPR and optogenetics enables spatiotemporally confined and highly dynamic genome perturbations in living cells and animals and holds unprecedented potential for biology and biomedicine.Here, we provide an overview of the state-of-the-art methods for light-control of CRISPR effectors. We will detail the plethora of exciting applications enabled by these systems, including spatially confined genome editing, timed activation of endogenous genes, as well as remote control of chromatin-chromatin interactions. Finally, we will discuss limitations of current optogenetic CRISPR tools and point out routes for future innovation in this emerging field.

Optogenetic Modulation of a Catalytic Biofilm for the Biotransformation of Indole into Tryptophan

In green chemical synthesis, biofilms as biocatalysts have shown great promise. Efficient biofilm-mediated biocatalysis requires the modulation of biofilm formation. Optogenetic tools are ideal to control biofilms because light is noninvasive, easily controllable, and cost-efficient. In this study, a gene circuit responsive to near-infrared (NIR) light was used to modulate the cellular level of bis-(3'-5') cyclic dimeric guanosine monophosphate (c-di-GMP), a central regulator of the prokaryote biofilm lifestyle, which allowed the regulation of biofilm formation by using NIR light. The engineered biofilm was applied to catalyze the biotransformation of indole into tryptophan in submerged biofilm reactors and NIR-light-enhanced biofilm formation resulted in an approximately 30 % increase in tryptophan yield, which demonstrates the feasibility of the application of light to modulate the formation and performance of catalytic biofilms for chemical production. The c-di-GMP-targeted optogenetic approach to modulate catalytic biofilms showcases applications for biofilm-mediated biocatalysis.

Optogenetic Medicine: Synthetic Therapeutic Solutions Precision-Guided by Light

Gene- and cell-based therapies are well recognized as central pillars of next-generation medicine, but controllability remains a critical issue for clinical applications. In this context, optogenetics is opening up exciting new opportunities for precision-guided medicine by using illumination with light of appropriate intensity and wavelength as a trigger signal to achieve pinpoint spatiotemporal control of cellular activities, such as transgene expression. In this review, we highlight recent advances in optogenetics, focusing on devices for biomedical applications. We introduce the construction and applications of optogenetic-based biomedical tools to treat neurological diseases, diabetes, heart diseases, and cancer, as well as bioelectronic implants that combine light-interfaced electronic devices and optogenetic systems into portable personalized precision bioelectronic medical tools. Optogenetics-based technology promises the capability to achieve traceless, remotely controlled precision dosing of an enormous range of therapeutic outputs. Finally, we discuss the prospects for optogenetic medicine, as well as some emerging challenges.

Inducible asymmetric cell division and cell differentiation in a bacterium

Multicellular organisms achieve greater complexity through cell divisions that generate different cell types. We engineered a simple genetic circuit that induces asymmetric cell division and subsequent cell differentiation in Escherichia coli. The circuit involves a scaffolding protein, PopZ, that is stably maintained at a single cell pole over multiple asymmetric cell divisions. PopZ was functionalized to degrade the signaling molecule, c-di-GMP. By regulating synthesis of functionalized PopZ via small molecules or light, we can chemically or optogenetically control the relative abundance of two distinct cell types, characterized by either low or high c-di-GMP levels. Differences in c-di-GMP levels can be transformed into genetically programmable differences in protein complex assembly or gene expression, which in turn produce differential behavior or biosynthetic activities. This study shows emergence of complex biological phenomena from a simple genetic circuit and adds programmable bacterial cell differentiation to the genetic toolbox of synthetic biology and biotechnology.