Tuning cell surface charge in E. coli with conjugated oligoelectrolytes

Supramolecular Switch for the Regulation of Antibacterial Efficacy of Near-Infrared Photosensitizer

The global antibiotic resistance crisis has drawn attention to the development of treatment methods less prone to inducing drug resistance, such as antimicrobial photodynamic therapy (aPDT). However, there is an increasing demand for new photosensitizers capable of efficiently absorbing in the near-infrared (NIR) region, enabling antibacterial treatment in deeper sites. Additionally, advanced strategies need to be developed to avert drug resistance stemming from prolonged exposure. Herein, we have designed a conjugated oligoelectrolyte, namely TTQAd, with a donor-acceptor-donor (D-A-D) backbone, enabling the generation of reactive oxygen species (ROS) under NIR light irradiation, and cationic adamantaneammonium groups on the side chains, enabling the host-guest interaction with curcubit[7]uril (CB7). Due to the amphiphilic nature of TTQAd, it could spontaneously form nanoassemblies in aqueous solution. Upon CB7 treatment, the positive charge of the cationic adamantaneammonium group was largely shielded by CB7, leading to a further aggregation of the nanoassemblies and a reduced antibacterial efficacy of TTQAd. Subsequent treatment with competitor guests enables the release of TTQAd and restores its antibacterial effect. The reversible supramolecular switch for regulating the antibacterial effect offers the potential for the controlled release of active photosensitizers, thereby showing promise in preventing the emergence of drug-resistant bacteria.

Membrane Targeted Azobenzene Drives Optical Modulation of Bacterial Membrane Potential

Recent studies have shown that bacterial membrane potential is dynamic and plays signaling roles. Yet, little is still known about the mechanisms of membrane potential dynamics regulation-owing to a scarcity of appropriate research tools. Optical modulation of bacterial membrane potential could fill this gap and provide a new approach for studying and controlling bacterial physiology and electrical signaling. Here, the authors show that a membrane-targeted azobenzene (Ziapin2) can be used to photo-modulate the membrane potential in cells of the Gram-positive bacterium Bacillus subtilis. It is found that upon exposure to blue-green light (λ = 470 nm), isomerization of Ziapin2 in the bacteria membrane induces hyperpolarization of the potential. To investigate the origin of this phenomenon, ion-channel-deletion strains and ion channel blockers are examined. The authors found that in presence of the chloride channel blocker idanyloxyacetic acid-94 (IAA-94) or in absence of KtrAB potassium transporter, the hyperpolarization response is attenuated. These results reveal that the Ziapin2 isomerization can induce ion channel opening in the bacterial membrane and suggest that Ziapin2 can be used for studying and controlling bacterial electrical signaling. This new optical tool could contribute to better understand various microbial phenomena, such as biofilm electric signaling and antimicrobial resistance.

Membrane-intercalating conjugated oligoelectrolytes

By acting as effective biomimetics of the lipid bilayers, membrane-intercalating conjugated oligoelectrolytes (MICOEs) can spontaneously insert themselves into both synthetic lipid bilayers and biological membranes. The modular and intentional molecular design of MICOEs enable a range of applications, such as bioproduction, biocatalysis, biosensing, and therapeutics. This tutorial review provides a structural evolution of MICOEs, which originated from the broader class of conjugated molecules, and analyses the drivers behind this evolutionary process. Various representative applications of MICOEs, accompanied by insights into their molecular design principles, will be reviewed separately. Perspectives on the current challenges and opportunities in research on MICOEs will be discussed at the end of the review to highlight their potential as unconventional and value-added materials for biological systems.

A self-powered and drug-free diabetic wound healing patch breaking hyperglycemia and low H2O2 limitations and precisely sterilizing driven by electricity

Accelerating diabetes-related chronic wound healing is a long-sought-after goal in diabetes management. However, therapeutic strategies based on antibiotics or catalysts still face great challenges to break the limitations of antimicrobial resistance, low H2O2 and the blocking effect of bacterial biofilms on antibiotic/catalyst penetration. Herein, we reported a glucose biofuel cell-powered and drug-free antibacterial patch, which consisted of an MAF-7 protected glucose oxidase/horseradish peroxidase anode and a horseradish peroxidase cathode, for treating diabetic wounds. This self-powered patch could take high blood glucose as fuel to generate electricity and abundant reactive oxygen species (ROS) in situ, synergistically regulating local hyperglycemia and breaking the limitations of insufficient ROS caused by low H2O2 levels. In particular, the electric field created by the GBFC could drive the negatively charged bacteria to adhere firmly to the electrode surface. As a result, the ROS produced in situ on the electrodes was localized to the bacteria, realizing precise sterilization. In vivo experiments confirmed that this self-powered patch enabled the wounds on diabetic mice to take a mere 10 days to eliminate inflammation and form mature skin with new hair follicles, demonstrating its great potential in treating bacteria-infected diabetic wounds.

Allelic variation of Escherichia coli outer membrane protein A: Impact on cell surface properties, stress tolerance and allele distribution

Outer membrane protein A (OmpA) is one of the most abundant outer membrane proteins of Gram-negative bacteria and is known to have patterns of sequence variations at certain amino acids-allelic variation-in Escherichia coli. Here we subjected seven exemplar OmpA alleles expressed in a K-12 (MG1655) ΔompA background to further characterization. These alleles were observed to significantly impact cell surface charge (zeta potential), cell surface hydrophobicity, biofilm formation, sensitivity to killing by neutrophil elastase, and specific growth rate at 42°C and in the presence of acetate, demonstrating that OmpA is an attractive target for engineering cell surface properties and industrial phenotypes. It was also observed that cell surface charge and biofilm formation both significantly correlate with cell surface hydrophobicity, a cell property that is increasingly intriguing for bioproduction. While there was poor alignment between the observed experimental values relative to the known sequence variation, differences in hydrophobicity and biofilm formation did correspond to the identity of residue 203 (N vs T), located within the proposed dimerization domain. The relative abundance of the (I, δ) allele was increased in extraintestinal pathogenic E. coli (ExPEC) isolates relative to environmental isolates, with a corresponding decrease in (I, α) alleles in ExPEC relative to environmental isolates. The (I, α) and (I, δ) alleles differ at positions 203 and 251. Variations in distribution were also observed among ExPEC types and phylotypes. Thus, OmpA allelic variation and its influence on OmpA function warrant further investigation.

Improved membrane permeability with cetyltrimethylammonium bromide (CTAB) addition for enhanced bidirectional transport of substrate and electron shuttles

The effects of membrane permeability on extracellular electron transfer (EET) and performance of microbial fuel cell (MFC) need to be explored. In this work, cetyltrimethylammonium bromide (CTAB) was chosen to enhance the current generation and bidirectional transport of substrate and electron shuttles by tailoring the cell membrane permeability. Specifically, the peak currents of biofilms treated with CTAB especially at 200 μM were obviously higher than the control biofilm with no CTAB, and the riboflavin mediated electron transfer was promoted prominently. Biomass and viability analyses showed that an appropriate concentration of CTAB had almost no adverse effect on the cell viability of biofilm and could increase the biomass of biofilm. Measurements of the extracellular activity of alkaline phosphatase and UV-vis absorption confirmed the increased membrane permeability and the promoted efficiency of substrates transported into cells. This contribution paves the key step for facilitating EET process by adjusting membrane permeability through CTAB or other surfactants addition.

Current Progress of Interfacing Organic Semiconducting Materials with Bacteria

Microbial bioelectronics require interfacing microorganisms with electrodes. The resulting abiotic/biotic platforms provide the basis of a range of technologies, including energy conversion and diagnostic assays. Organic semiconductors (OSCs) provide a unique strategy to modulate the interfaces between microbial systems and external electrodes, thereby improving the performance of these incipient technologies. In this review, we explore recent progress in the field on how OSCs, and related materials capable of charge transport, are being used within the context of microbial systems, and more specifically bacteria. We begin by examining the electrochemical communication modes in bacteria and the biological basis for charge transport. Different types of synthetic organic materials that have been designed and synthesized for interfacing and interrogating bacteria are discussed next, followed by the most commonly used characterization techniques for evaluating transport in microbial, synthetic, and hybrid systems. A range of applications is subsequently examined, including biological sensors and energy conversion systems. The review concludes by summarizing what has been accomplished so far and suggests future design approaches for OSC bioelectronics materials and technologies that hybridize characteristic properties of microbial and OSC systems.

Photoswitchable Conjugated Oligoelectrolytes for a Light-Induced Change of Membrane Morphology

The synthesis of a new conjugated oligoelectrolyte (COE), namely DSAzB, is described, which contains a conjugated core bearing a diazene moiety in the center of its electronically delocalized structure. Similar to structurally related phenylenevinylene-based COEs, DSAzB readily intercalates into model and natural lipid bilayer membranes. Photoinduced isomerization transforms the linear trans COE into a bent or C-shape form. It is thereby possible to introduce DSAzB into the bilayer of a cell and disrupt its integrity by irradiation with light. This leads to controlled permeabilization of membranes, as demonstrated by the release of calcein from DMPG/DMPC vesicles and by propidium iodide influx experiments on S. epidermidis. Both experiments support that the permeabilization is selective for the light stimulus, highly efficient, and repeatable. Target-selective and photoinduced actions demonstrated by DSAzB may have broad applications in biocatalysis and related biotechnologies.

Cationic π-Conjugated Polyelectrolyte Shows Antimicrobial Activity by Causing Lipid Loss and Lowering Elastic Modulus of Bacteria

Cationic, π-conjugated oligo-/polyelectrolytes (CCOEs/CCPEs) have shown great potential as antimicrobial materials to fight against antibiotic resistance. In this work, we treated wild-type and ampicillin-resistant (amp-resistant) Escherichia coli (E. coli) with a promising cationic, π-conjugated polyelectrolyte (P1) with a phenylene-based backbone and investigated the resulting morphological, mechanical, and compositional changes of the outer membrane of bacteria in great detail. The cationic quaternary amine groups of P1 led to electrostatic interactions with negatively charged moieties within the outer membrane of bacteria. Using atomic force microscopy (AFM), high-resolution transmission electron microscopy (TEM), we showed that due to this treatment, the bacterial outer membrane became rougher, decreased in stiffness/elastic modulus (AFM nanoindentation), formed blebs, and released vesicles near the cells. These evidences, in addition to increased staining of the P1-treated cell membrane by lipophilic dye Nile Red (confocal laser scanning microscopy (CLSM)), suggested loosening/disruption of packing of the outer cell envelope and release and exposure of lipid-based components. Lipidomics and fatty acid analysis confirmed a significant loss of phosphate-based outer membrane lipids and fatty acids, some of which are critically needed to maintain cell wall integrity and mechanical strength. Lipidomics and UV-vis analysis also confirmed that the extracellular vesicles released upon treatment (AFM) are composed of lipids and cationic P1. Such surface alterations (vesicle/bleb formation) and release of lipids/fatty acids upon treatment were effective enough to inhibit further growth of E. coli cells without completely disintegrating the cells and have been known as a defense mechanism of the cells against cationic antimicrobial agents.

Biodegradable Polymer Theranostic Fluorescent Nanoprobe for Direct Visualization and Quantitative Determination of Antimicrobial Activity

We report a biodegradable fluorescent theranostic nanoprobe design strategy for simultaneous visualization and quantitative determination of antibacterial activity for the treatment of bacterial infections. Cationic-charged polycaprolactone (PCL) was tailor-made through ring-opening polymerization methodology, and it was self-assembled into well-defined tiny 5.0 ± 0.1 nm aqueous nanoparticles (NPs) having a zeta potential of +45 mV. Excellent bactericidal activity at 10.0 ng/mL concentration was accomplished in Gram-negative bacterium Escherichia coli (E. coli) while maintaining their nonhemolytic nature in mice red blood cells (RBC) and their nontoxic trend in wild-type mouse embryonic fibroblast cells with a selectivity index of >10⁴. Electron microscopic studies are evident of the E. coli membrane disruption mechanism by the cationic NP with respect to their high selectivity for antibacterial activity. Anionic biomarker 8-hydroxy-pyrene-1,3,6-trisulfonic acid (HPTS) was loaded in the cationic PCL NP via electrostatic interaction to yield a new fluorescent theranostic nanoprobe to accomplish both therapeutics and diagnostics together in a single nanosystem. The theranostic NP was readily degradable by a bacteria-secreted lipase enzyme as well as by lysosomal esterase enzymes at the intracellular compartments in <12 h and support their suitability for biomedical application. In the absence of bactericidal activity, the theranostic nanoprobe functions exclusively as a biomarker to exhibit strong green-fluorescent signals in live E. coli. Once it became active, the theranostic probe induces membrane disruption on E. coli, which enabled the costaining of nuclei by red fluorescent propidium iodide. As a result, live and dead bacteria could be visualized via green and orange signals (merging of red+green), respectively, during the course of the antibacterial activity by the theranostic probe. This has enabled the development of a new image-based fluorescence assay to directly visualize and quantitatively estimate the real-time antibacterial activity. Time-dependent bactericidal activity was coupled with selective photoexcitation in a confocal microscope to demonstrate the proof-of-concept of the working principle of a theranostic probe in E. coli. This new theranostic nanoprobe creates a new platform for the simultaneous probing and treating of bacterial infections in a single nanodesign, which is very useful for a long-term impact in healthcare applications.

Evaluating the Photodynamic Biocidal Activity and Investigating the Mechanism of Thiazolium Cyanine Dyes

In order to develop ideal photosensitizers for photodynamic therapy (PDT), a thiazolium group was introduced in cyanine dyes to possess the advantages of intense absorption in the visible region and anti-microbial activity. We evaluated the anti-bacterial activity of the three thiazolium cyanine dyes against Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria) in vitro. This is the first time that such kinds of cyanine dyes are applied in the photodynamic antibiotic area. Cyanines display excellent anti-bacterial activity to S. aureus and E. coli exposed to white light irradiation, and the corresponding light-induced biocidal efficacy of cyanines increased with irradiation time and concentration. At the same time, there was no observation of dark anti-bacterial abilities. Especially, cyanines show low cell cytotoxicity and excellent biocompatibility. These results suggest that thiazolium cyanine could work as a photosensitizer in PDT with great promise and broad applications for killing bacteria. Mechanistic studies suggest that the reactive oxygen species (ROS) is the vital factor for combating bacteria exposure to white light conditions, whereas it is not the only determining factor of the biocidal activity. The interaction of the cyanine to the cell membrane also plays a critical role in killing bacteria, which has exhibited a synergic effect of electrostatic and hydrophobic interactions. It influences the cell uptake and the membrane perturbation activity of the cyanines, which indirectly affects the biocidal activity.

Mechanistic Understanding of the Interactions of Cationic Conjugated Oligo- and Polyelectrolytes with Wild-type and Ampicillin-resistant Escherichia coli

An in-depth understanding of cell-drug binding modes and action mechanisms can potentially guide the future design of novel drugs and antimicrobial materials and help to combat antibiotic resistance. Light-harvesting π-conjugated molecules have been demonstrated for their antimicrobial effects, but their impact on bacterial outer cell envelope needs to be studied in detail. Here, we synthesized poly(phenylene) based model cationic conjugated oligo- (2QA-CCOE, 4QA-CCOE) and polyelectrolytes (CCPE), and systematically explored their interactions with the outer cell membrane of wild-type and ampicillin (amp)-resistant Gram-negative bacteria, Escherichia coli (E. coli). Incubation of the E. coli cells in CCOE/CCPE solution inhibited the subsequent bacterial growth in LB media. About 99% growth inhibition was achieved if amp-resistant E. coli was treated for ~3-5 min, 1 h and 6 h with 100 μM of CCPE, 4QA-CCOE, and 2QA-CCOE solutions, respectively. Interestingly, these CCPE and CCOEs inhibited the growth of both wild-type and amp-resistant E. coli to a similar extent. A large surface charge reversal of bacteria upon treatment with CCPE suggested the formation of a coating of CCPE on the outer surface of bacteria; while a low reversal of bacterial surface charge suggested intercalation of CCOEs within the lipid bilayer of bacteria.

A perylene-based membrane intercalating conjugated oligoelectrolyte with efficient photodynamic antimicrobial activity

A perylene probe PC4 acts as a membrane intercalating antimicrobial agent and a fluorescent microbial cell death marker.

Functionalized 2D nanomaterials with switchable binding to investigate graphene-bacteria interactions

Graphene and its derivatives have recently attracted much attention for sensing and deactivating pathogens. However, the mechanism of multivalent interactions at the graphene-pathogen interface is not fully understood. Since different physicochemical parameters of graphene play a role at this interface, control over graphene's structure is necessary to study the mechanism of these interactions. In this work, different graphene derivatives and also zwitterionic graphene nanomaterials (ZGNMs) were synthesized with defined exposure, in terms of polymer coverage and functionality, and isoelectric points. Then, the switchable interactions of these nanomaterials with E. coli and Bacillus cereus were investigated to study the validity of the generally proposed "trapping" and "nano-knives" mechanisms for inactivating bacteria by graphene derivatives. It was found that the antibacterial activity of graphene derivatives strongly depends on the accessible area, i.e. edges and basal plane of sheets and tightness of their agglomerations. Our data clearly confirm the authenticity of "trapping" and "nano-knives" mechanisms for the antibacterial activity of graphene sheets.

Interactions of a paracyclophane-based conjugated oligoelectrolyte with biological membranes

We report a non-planar conjugated oligoelectrolyte as a membrane permeabilizing material and its membrane interactions compared to the linear analog.

Hollow Au loaded with kanamycin for pharmacological and laser-triggered photothermal sterilization

Anti-E. coli-conjugated and kanamycin-loaded hAuNPs (hAuNPs-anti-E. coli-kana) were prepared for sterilization.

Nanoshell Assembly for Magnet-Responsive Oil-Degrading Bacteria

The modified polyelectrolyte-magnetite nanocoating was applied to functionalize the cell walls of oil decomposing bacteria Alcanivorax borkumensis. Cationic coacervate of poly(allylamine) and 20 nm iron oxide nanoparticles allowed for a rapid single-step encapsulation process exploiting electrostatic interaction with bacteria surfaces. The bacteria were covered with rough 70-100-nm-thick shells of magnetite loosely bound to the surface through polycations. This encapsulation allowed for external manipulations of A. borkumensis with magnetic field, as demonstrated by magnetically facilitated cell displacement on the agar substrate. Magnetic coating was naturally removed after multiple cell proliferations providing next generations of the cell in the native nonmagnetic form. The discharged biosurfactant vesicles indicating the bacterial functionality (150 ± 50 nm lipid micelles) were visualized with atomic force microscopy in the bacterial biofilms.

Membrane permeabilization by conjugated oligoelectrolytes accelerates whole-cell catalysis

Conjugated oligoelectrolytes (COE) increase outer membrane permeability inEscherichia coli,improve transport of small molecules through the cell envelope and thus accelerate whole-cell catalysis.