Bacterial Redox Potential Powers Controlled Radical Polymerization

Microbe-material hybrids for therapeutic applications

As natural living substances, microorganisms have emerged as useful resources in medicine for creating microbe-material hybrids ranging from nano to macro dimensions. The engineering of microbe-involved nanomedicine capitalizes on the distinctive physiological attributes of microbes, particularly their intrinsic "living" properties such as hypoxia tendency and oxygen production capabilities. Exploiting these remarkable characteristics in combination with other functional materials or molecules enables synergistic enhancements that hold tremendous promise for improved drug delivery, site-specific therapy, and enhanced monitoring of treatment outcomes, presenting substantial opportunities for amplifying the efficacy of disease treatments. This comprehensive review outlines the microorganisms and microbial derivatives used in biomedicine and their specific advantages for therapeutic application. In addition, we delineate the fundamental strategies and mechanisms employed for constructing microbe-material hybrids. The diverse biomedical applications of the constructed microbe-material hybrids, encompassing bioimaging, anti-tumor, anti-bacteria, anti-inflammation and other diseases therapy are exhaustively illustrated. We also discuss the current challenges and prospects associated with the clinical translation of microbe-material hybrid platforms. Therefore, the unique versatility and potential exhibited by microbe-material hybrids position them as promising candidates for the development of next-generation nanomedicine and biomaterials with unique theranostic properties and functionalities.

Harnessing in vivo synthesis of bioactive multiarylmethanes in Escherichia coli via oxygen-mediated free radical reaction induced by simple phenols

BACKGROUND

Xanthenes and multi-aryl carbon core containing compounds represent different types of complex and condensed architectures that have impressive wide range of pharmacological, industrial and synthetic applications. Moreover, indoles as building blocks were only found in naturally occurring metabolites with di-aryl carbon cores and in chemically synthesized tri-aryl carbon core containing compounds. Up to date, rare xanthenes with indole bearing multicaryl carbon core have been reported in natural or synthetic products. The underlying mechanism of fluorescein-like arthrocolins with tetra-arylmethyl core were synthesized in an engineered Escherichia coli fed with toluquinol remained unclear.

RESULTS

In this study, the Keio collection of single gene knockout strains of 3901 mutants of E. coli BW25113, together with 14 distinct E. coli strains, was applied to explore the origins of endogenous building blocks and the biogenesis for arthrocolin assemblage. Deficiency in bacterial respiratory and aromatic compound degradation genes ubiX, cydB, sucA and ssuE inhibited the mutant growth fed with toluquinol. Metabolomics of the cultures of 3897 mutants revealed that only disruption of tnaA involving in transforming tryptophan to indole, resulted in absence of arthrocolins. Further media optimization, thermal cell killing and cell free analysis indicated that a non-enzyme reaction was involved in the arthrocolin biosynthesis in E. coli. Evaluation of redox potentials and free radicals suggested that an oxygen-mediated free radical reaction was responsible for arthrocolins formation in E. coli. Regulation of oxygen combined with distinct phenol derivatives as inducer, 31 arylmethyl core containing metabolites including 13 new and 8 biological active, were isolated and characterized. Among them, novel arthrocolins with p-hydroxylbenzene ring from tyrosine were achieved through large scale of aerobic fermentation and elucidated x-ray diffraction analysis. Moreover, most of the known compounds in this study were for the first time synthesized in a microbe instead of chemical synthesis. Through feeding the rat with toluquinol after colonizing the intestines of rat with E. coli, arthrocolins also appeared in the rat blood.

CONCLUSION

Our findings provide a mechanistic insight into in vivo synthesis of complex and condensed arthrocolins induced by simple phenols and exploits a quinol based method to generate endogenous aromatic building blocks, as well as a methylidene unit, for the bacteria-facilitated synthesis of multiarylmethanes.

Aerobic mechanochemical reversible-deactivation radical polymerization

Polymer materials suffer mechano-oxidative deterioration or degradation in the presence of molecular oxygen and mechanical forces. In contrast, aerobic biological activities combined with mechanical stimulus promote tissue regeneration and repair in various organs. A synthetic approach in which molecular oxygen and mechanical energy synergistically initiate polymerization will afford similar robustness in polymeric materials. Herein, aerobic mechanochemical reversible-deactivation radical polymerization was developed by the design of an organic mechano-labile initiator which converts oxygen into activators in response to ball milling, enabling the reaction to proceed in the air with low-energy input, operative simplicity, and the avoidance of potentially harmful organic solvents. In addition, this approach not only complements the existing methods to access well-defined polymers but also has been successfully employed for the controlled polymerization of (meth)acrylates, styrenic monomers and solid acrylamides as well as the synthesis of polymer/perovskite hybrids without solvent at room temperature which are inaccessible by other means.

A Supramolecular Naphthalene Diimide Radical Anion with Efficient NIR-II Photothermal Conversion for E. coli-Responsive Photothermal Therapy

We report a supramolecular naphthalene diimide (NDI) radical anion with efficient NIR-II photothermal conversion for E. coli-responsive photothermal therapy. The supramolecular radical anion (NDI-2CB[7])⋅- , which is obtained from the E. coli-induced in situ reduction of NDI-2CB[7] neutral complex, formed by the host-guest interaction between an NDI derivative and cucurbit[7]uril (CB[7]), exhibits unexpectedly strong NIR-II absorption and remarkable photothermal conversion capacity in aqueous solution. The NIR-II absorption is caused by the self-assembly of NDI radical anions to form supramolecular dimer radicals in aqueous solution, which is supported by theoretically predicted spectra. The (NDI-2CB[7])⋅- demonstrates excellent NIR-II photothermal antimicrobial activity (>99 %). This work provides a new approach for constructing NIR-II photothermal agents and non-contact treatments for bacterial infections.

Gut microbes involvement in gastrointestinal cancers through redox regulation

Gastrointestinal (GI) cancers are among the most common and lethal cancers worldwide. GI microbes play an important role in the occurrence and development of GI cancers. The common mechanisms by which GI microbes may lead to the occurrence and development of cancer include the instability of the microbial internal environment, secretion of cancer-related metabolites, and destabilization of the GI mucosal barrier. In recent years, many studies have found that the relationship between GI microbes and the development of cancer is closely associated with the GI redox level. Redox instability associated with GI microbes may induce oxidative stress, DNA damage, cumulative gene mutation, protein dysfunction and abnormal lipid metabolism in GI cells. Redox-related metabolites of GI microbes, such as short-chain fatty acids, hydrogen sulfide and nitric oxide, which are involved in cancer, may also influence GI redox levels. This paper reviews the redox reactions of GI cells regulated by microorganisms and their metabolites, as well as redox reactions in the cancer-related GI microbes themselves. This study provides a new perspective for the prevention and treatment of GI cancers.

Tyrosine residues initiated photopolymerization in living organisms

Towards intracellular engineering of living organisms, the development of new biocompatible polymerization system applicable for an intrinsically non-natural macromolecules synthesis for modulating living organism function/behavior is a key step. Herein, we find that the tyrosine residues in the cofactor-free proteins can be employed to mediate controlled radical polymerization under 405 nm light. A proton-coupled electron transfer (PCET) mechanism between the excited-state TyrOH* residue in proteins and the monomer or the chain transfer agent is confirmed. By using Tyr-containing proteins, a wide range of well-defined polymers are successfully generated. Especially, the developed photopolymerization system shows good biocompatibility, which can achieve in-situ extracellular polymerization from the surface of yeast cells for agglutination/anti-agglutination functional manipulation or intracellular polymerization inside yeast cells, respectively. Besides providing a universal aqueous photopolymerization system, this study should contribute a new way to generate various non-natural polymers in vitro or in vivo to engineer living organism functions and behaviours.

Polymerization in living organisms

Vital biomacromolecules, such as RNA, DNA, polysaccharides and proteins, are synthesized inside cells via the polymerization of small biomolecules to support and multiply life. The study of polymerization reactions in living organisms is an emerging field in which the high diversity and efficiency of chemistry as well as the flexibility and ingeniousness of physiological environment are incisively and vividly embodied. Efforts have been made to design and develop in situ intra/extracellular polymerization reactions. Many important research areas, including cell surface engineering, biocompatible polymerization, cell behavior regulation, living cell imaging, targeted bacteriostasis and precise tumor therapy, have witnessed the elegant demeanour of polymerization reactions in living organisms. In this review, recent advances in polymerization in living organisms are summarized and presented according to different polymerization methods. The inspiration from biomacromolecule synthesis in nature highlights the feasibility and uniqueness of triggering living polymerization for cell-based biological applications. A series of examples of polymerization reactions in living organisms are discussed, along with their designs, mechanisms of action, and corresponding applications. The current challenges and prospects in this lifeful field are also proposed.

Engineered Living Materials For Sustainability

Recent advances in synthetic biology and materials science have given rise to a new form of materials, namely engineered living materials (ELMs), which are composed of living matter or cell communities embedded in self-regenerating matrices of their own or artificial scaffolds. Like natural materials such as bone, wood, and skin, ELMs, which possess the functional capabilities of living organisms, can grow, self-organize, and self-repair when needed. They also spontaneously perform programmed biological functions upon sensing external cues. Currently, ELMs show promise for green energy production, bioremediation, disease treatment, and fabricating advanced smart materials. This review first introduces the dynamic features of natural living systems and their potential for developing novel materials. We then summarize the recent research progress on living materials and emerging design strategies from both synthetic biology and materials science perspectives. Finally, we discuss the positive impacts of living materials on promoting sustainability and key future research directions.

Cucurbit[10]uril-based supramolecular radicals: Powerful arms to kill facultative anaerobic bacteria

Two water-soluble supramolecular complexes (CB[10]⊃PSA and CB[10]⊃TPE-cyc) are constructed based on the host-guest interaction between cucurbit[10]uril (CB[10]) and perylene diimide derivative (PSA) or tetracationic cyclophane (TPE-cyc). Attributing to the matched redox potential, both supramolecular complexes can be specifically reduced into corresponding supramolecular radical cations or anions by facultative anaerobic E. coli. Benefiting from the strong near-infrared (NIR) absorption, CB[10]⊃PSA radical anions and CB[10]⊃TPE-cyc radical cations act as efficient NIR photosensitizers and perform an excellent antimicrobial activity (close to 100%) via PTT. In addition, the biocompatibility of TPE-cyc is notably improved under the protection of CB[10], guaranteeing its biosafety for in vivo application. CB[10]⊃PSA radical anions and CB[10]⊃TPE-cyc radical cations are in situ generated in the E. coli-infected abscess of mice and effectively inhibit the bacterial infection without obvious system toxicity. It is anticipated that this supramolecular strategy may pave a new way for the selective bacteria inhibition to regulate the balance of different bacterial flora.

In Situ Polymerization of Aniline Derivative in Vivo for NIR-II Phototheranostics of Tumor

Natural biopolymers can be controllably in situ synthesized in organisms and play important roles in biological activities. Inspired by this, the manipulation of in situ biosynthesis of functional polymers in vivo will be an important way to obtain materials for meeting biological requirements. Herein, in situ biosynthesis of functional conjugated polymer at the tumor site was achieved via the utilization of specific tumor microenvironment (TME) characteristics for the first time. Specially, a water-soluble aniline dimer derivative (N-(3-sulfopropyl) p-aminodiphenylamine, SPA) was artfully in situ polymerized into polySPA (PSPA) nanoparticles at the tumor site, which was activated via the catalysis of hydrogen peroxide (H₂O₂) overexpressed in TME to produce hydroxyl radical (•OH) by coinjected horseradish peroxidase (HRP). Benefiting from outstanding near-infrared (NIR)-II absorption of PSPA, the in situ polymerization process can be validly monitored by photoacoustic (PA) signal at the NIR-II region. Meanwhile, in situ polymerization would induce the size of polymeric materials from small to large, improving the distribution and retention of PSPA at the tumor site. On the combination of NIR-II absorption of PSPA and the size variation induced by polymerization, such polymerization can be applied for tumor-specific NIR-II light mediated PA image and photothermal inhibition of tumors, enhancing the precision and efficacy of tumor phototheranostics. Therefore, the present work opens the way to manipulate TME-activated in situ biosynthesis of functional conjugated polymer at the tumor site for overcoming formidable challenges in tumor theranostics.

Antibacterial Nanomaterials: Mechanisms, Impacts on Antimicrobial Resistance and Design Principles

Antimicrobial resistance (AMR) is one of the biggest threats to the environment and health. AMR rapidly invalidates conventional antibiotics, and antimicrobial nanomaterials have been increasingly explored as alternatives. Interestingly, several antimicrobial nanomaterials show AMR-independent antimicrobial effects without detectable new resistance and have therefore been suggested to prevent AMR evolution. In contrast, some are found to trigger the evolution of AMR. Given these seemingly conflicting findings, a timely discussion of the two faces of antimicrobial nanomaterials is urgently needed. This review systematically compares the killing mechanisms and structure-activity relationships of antibiotics and antimicrobial nanomaterials. We then focus on nano-microbe interactions to elucidate the impacts of molecular initiating events on AMR evolution. Finally, we provide an outlook on future antimicrobial nanomaterials and propose design principles for the prevention of AMR evolution.

Tinware-Inspired Aerobic Surface-Initiated Controlled Radical Polymerization (SI-Sn0CRP) for Biocompatible Surface Engineering

Surface anchored polymer brushes prepared by surface-initiated controlled radical polymerization (SI-CRP) have raised considerable interest in biomaterials and bioengineering. However, undesired residues of noxious transition metal catalysts critically restrain their widespread biomedical applications. Herein, we present a robust and biocompatible surface-initiated controlled radical polymerization catalyzed by a Sn(0) sheet (SI-Sn⁰CRP) under ambient conditions. Through this approach, microliter volumes of vinyl monomers with diverse functions (heterocyclic, ionic, hydrophilic, and hydrophobic) could be efficiently converted to homogeneous polymer brushes. The excellent controllability of SI-Sn⁰CRP strategy is further demonstrated by the exquisite fabrication of predetermined block and patterned polymer brushes through chain extension and photolithography, respectively. Additionally, in virtue of intrinsic biocompatibility of Sn, the resultant polymer brushes present transcendent affinity toward blood and cell, in marked contrast to those of copper-based approaches. This strategy could provide an avenue for the controllable fabrication of biocompatible polymer brushes toward biological applications.

Bacteria-mediated in situ polymerization of peptide-modified acrylamide for enhancing antimicrobial activity

Bacteria-mediated reactions can utilize the natural activities of bacteria to produce bioactive products. Here, bacteria-mediated polymerization of the acrylamide-functionalized peptide Trp-Arg-Lys (Am-WRK) afforded an antibacterial polymer, PAm-WRK, which simulates the cationic and hydrophobic structures of antimicrobial peptides. Facultative anaerobes with strong reductive abilities exhibited better reactivity and achieved selective antibacterial effects through non-covalent interactions with bacterial membranes. This bacteria-mediated synthesis of AMP-mimic polymers provides a new strategy for overcoming bacterial resistance and for the in situ generation of bioactive functional materials.

Oxygen-Tolerant RAFT Polymerization Initiated by Living Bacteria

Living organisms can synthesize a wide range of macromolecules from a small set of natural building blocks, yet there is potential for even greater materials diversity by exploiting biochemical processes to convert unnatural feedstocks into new abiotic polymers. Ultimately, the synthesis of these polymers in situ might aid the coupling of organisms with synthetic matrices, and the generation of biohybrids or engineered living materials. The key step in biohybrid materials preparation is to harness the relevant biological pathways to produce synthetic polymers with predictable molar masses and defined architectures under ambient conditions. Accordingly, we report an aqueous, oxygen-tolerant RAFT polymerization platform based on a modified Fenton reaction, which is initiated by Cupriavidus metallidurans CH34, a bacterial species with iron-reducing capabilities. We show the synthesis of a range of water-soluble polymers under normoxic conditions, with control over the molar mass distribution, and also the production of block copolymer nanoparticles via polymerization-induced self-assembly. Finally, we highlight the benefits of using a bacterial initiation system by recycling the cells for multiple polymerizations. Overall, our method represents a highly versatile approach to producing well-defined polymeric materials within a hybrid natural-synthetic polymerization platform and in engineered living materials with properties beyond those of biotic macromolecules.

A Bacteria-Responsive Porphyrin for Adaptable Photodynamic/Photothermal Therapy

We report a cationic porphyrin 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphyrin (TMPyP) that can respond to specific bacteria, followed by adaptable photodynamic/photothermal therapy processes. TMPyP could be reduced to phlorin by facultative anaerobes with a strong reducing ability such as E. coli and S. typhimurium in hypoxic environments, possessing strong NIR absorption and remarkable photothermal conversion capacity, thus demonstrating excellent antimicrobial activity (>99 %) by photothermal therapy. While in an aerobic environment with aerobic bacteria, TMPyP functioned as a typical photosensitizer that killed bacteria effectively (>99.9 %) by photodynamic therapy. By forming a host-guest complex with cucurbit[7]uril, the biocompatibility of TMPyP significantly improved. This kind of bacteria-responsive porphyrin shows specificity and adaptivity in antimicrobial treatment and holds potential in non-invasive treatments of bacterial infections.

Electrogenic Bacteria Promise New Opportunities for Powering, Sensing, and Synthesizing

Considerable research efforts into the promises of electrogenic bacteria and the commercial opportunities they present are attempting to identify potential feasible applications. Metabolic electrons from the bacteria enable electricity generation sufficient to power portable or small-scale applications, while the quantifiable electric signal in a miniaturized device platform can be sensitive enough to monitor and respond to changes in environmental conditions. Nanomaterials produced by the electrogenic bacteria can offer an innovative bottom-up biosynthetic approach to synergize bacterial electron transfer and create an effective coupling at the cell-electrode interface. Furthermore, electrogenic bacteria can revolutionize the field of bioelectronics by effectively interfacing electronics with microbes through extracellular electron transfer. Here, these new directions for the electrogenic bacteria and their recent integration with micro- and nanosystems are comprehensively discussed with specific attention toward distinct applications in the field of powering, sensing, and synthesizing. Furthermore, challenges of individual applications and strategies toward potential solutions are provided to offer valuable guidelines for practical implementation. Finally, the perspective and view on how the use of electrogenic bacteria can hold immeasurable promise for the development of future electronics and their applications are presented.

Polymer Grafting to Polydopamine Free Radicals for Universal Surface Functionalization

Modifying surfaces using free radical polymerization (FRP) offers a means to incorporate the diverse physicochemical properties of vinyl polymers onto new materials. Here, we harness the universal surface attachment of polydopamine (PDA) to "prime" a range of different surfaces for free radical polymer attachment, including glass, cotton, paper, sponge, and stainless steel. We show that the intrinsic free radical species present in PDA can serve as an anchor point for subsequent attachment of propagating vinyl polymer macroradicals through radical-radical coupling. Leveraging a straightforward, twofold soak-wash protocol, FRP over the PDA-functionalized surfaces results in covalent polymer attachment on both porous and nonporous substrates, imparting new properties to the functionalized materials, including enhanced hydrophobicity, fluorescence, or temperature responsiveness. Our strategy is then extended to covalently incorporate PDA nanoparticles into organo-/hydrogels via radical cross-linking, yielding tunable PDA-polymer composite networks. The propensity of PDA free radicals to quench FRP is studied using in situ ¹H nuclear magnetic resonance and electron paramagnetic resonance spectroscopy, revealing a surface area-dependent macroradical scavenging mechanism that underpins PDA-polymer conjugation. By combining the arbitrary surface attachment of PDA with the broad physicochemical properties of vinyl polymers, our strategy provides a straightforward route for imparting unlimited new functionality to practically any surface.

Cytochrome C catalyzed oxygen tolerant atom-transfer radical polymerization

Atom-transfer radical polymerization (ATRP) is a well-known technique for controlled polymer synthesis. However, the ATRP usually employed toxic heavy metal ionas as the catalyst and was susceptible to molecular oxygen, which made it should be conducted under strictly anoxic condition. Conducting ATRP under ambient and biocompatible conditions is the major challenge. In this study, cytochrome C was explored as an efficient biocatalyst for ATRP under biocompatible conditions. The cytochrome C catalyzed ATRP showed a relatively low polymer dispersity index of 1.19. More interestingly, the cytochrome C catalyzed ATRP showed superior oxygen resistance as it could be performed under aerobic conditions with high dissolved oxygen level. Further analysis suggested that the Fe(II) embed in the cytochrome C might serve as the catalytic center and methyl radical was responsible for the ATRP catalysis. This work explored new biocompatible catalyst for aerobic ATRP, which might open new dimension for practical ATRP and application of cytochrome C protein.

Extracellular Electron Transfer Enables Cellular Control of Cu(I)-Catalyzed Alkyne-Azide Cycloaddition

Extracellular electron transfer (EET) is an anaerobic respiration process that couples carbon oxidation to the reduction of metal species. In the presence of a suitable metal catalyst, EET allows for cellular metabolism to control a variety of synthetic transformations. Here, we report the use of EET from the electroactive bacterium Shewanella oneidensis for metabolic and genetic control over Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC). CuAAC conversion under anaerobic and aerobic conditions was dependent on live, actively respiring S. oneidensis cells. The reaction progress and kinetics were manipulated by tailoring the central carbon metabolism. Similarly, EET-CuAAC activity was dependent on specific EET pathways that could be regulated via inducible expression of EET-relevant proteins: MtrC, MtrA, and CymA. EET-driven CuAAC exhibited modularity and robustness in the ligand and substrate scope. Furthermore, the living nature of this system could be exploited to perform multiple reaction cycles without regeneration, something inaccessible to traditional chemical reductants. Finally, S. oneidensis enabled bioorthogonal CuAAC membrane labeling on live mammalian cells without affecting cell viability, suggesting that S. oneidensis can act as a dynamically tunable biocatalyst in complex environments. In summary, our results demonstrate how EET can expand the reaction scope available to living systems by enabling cellular control of CuAAC.

Effect of cell culture media on photopolymerizations

Radical polymerization is one of the most widely used methods for the synthesis of polymeric materials for biomedical applications, such as drug delivery, 3D cell culture, and regenerative medicine. Among radical polymerization reactions, thiol-ene click chemistry has shown excellent orthogonality in diverse reaction conditions. However, our preliminary investigations revealed that it fails in cell culture environment. Herein, we investigate the mechanisms by which cell culture media interfere with radical photoreactions. Three different models including free radical linear photopolymerization (N,N-dimethylacrylamide photopolymerization), free radical photohydrogelation (poly(ethylene glycol) diacrylate photohydrogelation), and thiol-ene photohydrogelation (4-arm poly(ethylene glycol)-norbornene thiol-ene photohydrogelation) were investigated. We showed that common cell culture media ingredients can interfere with radical polymerization by two different pathways; namely, radical chain transfer and radical scavenging effects. Thiol-ene photoclick hydrogelation was seriously affected by cell culture media especially under the alkaline conditions of many of them, due to the impact of deprotonation of the thiol reactant. We intend these findings to serve as a reference guide to researchers employing free radical-based molecular synthesis in cell culture settings. The nonbenign impact of media components, pH, and concentration should provide a cue for future studies that aim to prepare well-defined polymeric materials in the presence of cell culture media.

Interfacing non-enzymatic catalysis with living microorganisms

Interfacing non-enzymatic catalysis with cellular metabolism is emerging as a powerful approach to produce a range of high value small molecules and polymers. In this review, we highlight recent examples from this promising young field. Specifically, we discuss demonstrations of living cells mediating redox processes for biopolymer production, interfacing solar-light driven chemistry with microbial metabolism, and intra- and extracellular non-enzymatic catalysis to generate high value molecules. This review highlights the vast potential of this nascent field to bridge the two disciplines of synthetic chemistry and synthetic biology for a sustainable chemical industry.