Electrically induced bacterial membrane-potential dynamics correspond to cellular proliferation capacity

Anti-MRSA mechanism of spirostane saponin in Rohdea pachynema F.T.Wang & tang

ETHNOPHARMACOLOGY RELEVANCE

Rohdea pachynema F.T.Wang & Tang (R. pachynema), is a traditional folk medicine used for the treatment of stomach pain, stomach ulcers, bruises, and skin infections in China. Some of the diseases may relate to microbial infections in traditional applications. However few reports on its antimicrobial properties and bioactive components.

AIM OF THE STUDY

To identify its bioactive constituents against methicillin-resistant Staphylococcus aureus (MRSA) in vitro and in vivo, and its mechanism.

MATERIALS AND METHODS

The anti-MRSA ingredient 6α-O-[β-D-xylopyranosyl-(1 → 3)-β-D-quinovopyranosyl]-(25S)-5α-spirostan-3β-ol (XQS) was obtained from R. pachynema by phytochemical isolation. Subsequently, XQS underwent screening using the broth microdilution method and growth inhibition curves to assess its antibacterial activity. The mechanism of XQS was evaluated by multigeneration induction, biofilm resistance assay, scanning electron microscopy, transmission electron microscopy, and metabolomics. Additionally, a mouse skin infection model was established in vivo.

RESULTS

26 compounds were identified from the R. pachynema, in which anti-MRSA spirostane saponin (XQS) was reported for the first time with a minimum inhibitory concentration (MIC) of 8 μg/mL. XQS might bind to peptidoglycan (PGN) of the cell wall, phosphatidylglycerol (PG), and phosphatidylethanolamine (PE) of the cell membrane, then destroying the cell wall and the cell membrane, resulting in reduced membrane fluidity and membrane depolarization. Furthermore, XQS affected MRSA lipid metabolism, amino acid metabolism, and ABC transporters by metabolomics analysis, which targeted cell walls and membranes causing less susceptibility to drug resistance. Furthermore, XQS (8 mg/kg) recovered skin wounds in mice infected by MRSA effectively, superior to vancomycin (8 mg/kg).

CONCLUSIONS

XQS showed anti-MRSA bioactivity in vitro and in vivo, and its mechanism association with cell walls and membranes was reported for the first, which supported the traditional uses of R. pachynema and explained its sensitivity to MRSA.

Comparative physiological and transcriptomic analysis of sono-biochemical control over post-acidification of Lactobacillus delbrueckii subsp. bulgaricus

Thermosonication (UT) prestress treatments combining with varied fermentation patterns has been revealed as an effective method to regulate post-acidification as exerted by Lactobacillus delbrueckii subsp. bulgaricus (L. delbrueckii), but sono-biochemical controlling mechanisms remain elusive. This study employed physiological and transcriptomic analysis to explore the response mechanism of L. delbrueckii to UT-induced microstress (600 W, 33 kHz, 10 min). UT stress-induced inhibition of acidification of L. delbrueckii during (post)-fermentation was first confirmed, relying on the UT process parameters such as stress exposure duration and UT power. The significantly enhanced membrane permeability in cells treated by 600 W for 10 min than the microbes stressed by 420 W for 20 min suggested the higher dependence of UT-derived stresses on the treatment durations, relative to the ultrasonic powers. In addition, ultrasonication treatment-induced changes in cell membrane integrity enhanced and/or disrupted permeability of L. delbrueckii, resulting in an imbalance in intracellular conditions associated with corresponding alterations in metabolic behaviors and fermentation efficiencies. UT-prestressed inoculum exhibited a 21.46% decrease in the membrane potential during the lag phase compared to untreated samples, with an intracellular pH of 5.68 ± 0.12, attributed to the lower activities of H+-ATPase and lactate dehydrogenase due to UT stress pretreatments. Comparative transcriptomic analysis revealed that UT prestress influenced the genes related to glycolysis, pyruvate metabolism, fatty acid synthesis, and ABC transport. The genes encoding 3-oxoacyl-[acyl-carrier-protein] reductases I, II, and III, CoA carboxylase, lactate dehydrogenase, pyruvate oxidase, glucose-6-phosphate isomerase, and glycerol-3-phosphate dehydrogenase were downregulated, thus identifying the relevance of the UT microstresses-downregulated absorption and utilization of carbohydrates with the attenuated fatty acid production and energy metabolisms. These findings could contribute to provide a better understanding of the inactivated effects on the post-acidification of L. delbrueckii by ultrasonic pretreatments, thus providing theoretical basis for the targeted optimization of acidification inhibition efficiencies for yogurt products during chilled preservation processes.

Programming mammalian cell behaviors by physical cues

In recent decades, the field of synthetic biology has witnessed remarkable progress, driving advances in both research and practical applications. One pivotal area of development involves the design of transgene switches capable of precisely regulating specified outputs and controlling cell behaviors in response to physical cues, which encompass light, magnetic fields, temperature, mechanical forces, ultrasound, and electricity. In this review, we delve into the cutting-edge progress made in the field of physically controlled protein expression in engineered mammalian cells, exploring the diverse genetic tools and synthetic strategies available for engineering targeting cells to sense these physical cues and generate the desired outputs accordingly. We discuss the precision and efficiency limitations inherent in these tools, while also highlighting their immense potential for therapeutic applications.

Mixed species biofilm: Structure, challenge and its intricate involvement in hospital associated infections

Hospital associated infections or healthcare associated infections (HAIs) are a major threat to healthcare and medical management, mostly because of their recalcitrant nature. The primary cause of these HAIs is bacterial associations, especially the interspecies interactions. In interspecies interactions, more than one species co-exists in a common platform of extracellular polymeric substances (EPS), establishing a strong interspecies crosstalk and thereby lead to the formation of mixed species biofilms. In this process, the internal microenvironment and the surrounding EPS matrix of the biofilms ensure the protection of the microorganisms and allow them to survive under antagonistic conditions. The communications between the biofilm members as well as the interactions between the bacterial cells and the matrix polymers, also aid in the rigidity of the biofilm structure and allow the microorganisms to evade both the host immune response and a wide range of anti-microbials. Therefore, to design a treatment protocol for HAIs is difficult and it has become a growing point of concern. This review therefore first aims to discuss the role of microenvironment, molecular structure, cell-cell communication, and metabolism of mixed species biofilms in manifestation of HAIs. In addition, we discuss the electrochemical properties of mixed-species biofilms and their mechanism in developing drug resistance. Then we focus on the most dreaded bacterial HAI including oral and gut multi-species infections, catheter-associated urinary tract infections, surgical site infections, and ventilator-associated pneumonia. Further, we highlight the challenges to eradication of the mixed species biofilms and the current and prospective future strategies for the treatment of mixed species-associated HAI. Together, the review presents a comprehensive understanding of mixed species biofilm-mediated infections in clinical scenario, and summarizes the current challenge and prospect of therapeutic strategies against HAI.

Interaction of anionic Fe3O4 nanoparticles with lipid vesicles: a review on deformation and poration under various conditions

This review focuses on the deformation and poration of lipid vesicles caused by the interaction of anionic magnetite nanoparticles (MNPs). Effects of various factors, such as surface charge density, salt and sugar concentrations in buffer, membrane cholesterol content, polymer-grafted phospholipid, and membrane potential have been discussed for the interaction of MNPs with lipid vesicles. To quantify these effects on the vesicles, compactness, fraction of deformation and poration, dynamics of membrane permeation, and kinetics of membrane permeation have been critically evaluated. The review explores the potential advancements as well as future directions of the research field in the biomedical application of MNPs.

Membrane potential dynamics unveil the promise of bioelectrical antimicrobial susceptibility Testing (BeAST) for anti-fungal screening

Membrane potential is a useful marker for antimicrobial susceptibility testing (AST) due to its fundamental roles in cell function. However, the difficulties associated with measuring the membrane potential in microbes restrict its broad application. In this study, we present bioelectrical AST (BeAST) using the model fungus Saccharomyces cerevisiae. Using fluorescent indicators [DiBAC4(3), ThT, and TMRM], we measured plasma and mitochondrial membrane-potential dynamics upon electric stimulation. We find that a 2.5 second electric stimulation induces hyperpolarization of plasma membrane lasting 20 minutes in vital S. cerevisiae, but depolarization in inhibited cells. The numerical simulation of FitzHugh-Nagumo model successfully recapitulates vitality-dependent dynamics. The model also suggests that the magnitude of plasma-membrane potential dynamics (PMD) correlates with the degree of inhibition. To test this prediction and to examine if BeAST can be used for assessing novel anti-fungal compounds, we treat cells with biogenic silver nanoparticles (bioAgNPs) synthesized using orange fruit flavonoids and Fusarium oxysporum. Comparing BeAST with optical density assay alongside various stressors, we show that PMD correlates with the magnitude of growth inhibitions. These results suggest that BeAST holds promise for screening anti-fungal compounds, offering a valuable approach to tackling antimicrobial resistance.

IMPORTANCE

Rapid assessment of the efficacy of antimicrobials is important for optimizing treatments, avoiding misuse and facilitating the screening of new antimicrobials. The need for rapid antimicrobial susceptibility testing (AST) is growing with the rise of antimicrobial resistance. Here, we present bioelectrical AST (BeAST). Combining time-lapse microscopy and mathematical modeling, we show that electrically induced membrane potential dynamics of yeast cells correspond to the strength of growth inhibition. Furthermore, we demonstrate the utility of BeAST for assessing antimicrobial activities of novel compounds using biogenic silver nanoparticles.

Towards optical measurements of membrane potential values in Bacillus subtilis using fluorescence lifetime

Membrane potential (MP) changes can provide a simple readout of bacterial functional and metabolic state or stress levels. While several optical methods exist for measuring fast changes in MP in excitable cells, there is a dearth of such methods for absolute and precise measurements of steady-state membrane potentials (MPs) in bacterial cells. Conventional electrode-based methods for the measurement of MP are not suitable for calibrating optical methods in small bacterial cells. While optical measurement based on Nernstian indicators have been successfully used, they do not provide absolute or precise quantification of MP or its changes. We present a novel, calibrated MP recording approach to address this gap. In this study, we used a fluorescence lifetime-based approach to obtain a single-cell resolved distribution of the membrane potential and its changes upon extracellular chemical perturbation in a population of bacterial cells for the first time. Our method is based on (i) a unique VoltageFluor (VF) optical transducer, whose fluorescence lifetime varies as a function of MP via photoinduced electron transfer (PeT) and (ii) a quantitative phasor-FLIM analysis for high-throughput readout. This method allows MP changes to be easily visualized, recorded and quantified. By artificially modulating potassium concentration gradients across the membrane using an ionophore, we have obtained a Bacillus subtilis-specific MP versus VF lifetime calibration and estimated the MP for unperturbed B. subtilis cells to be -65 mV and that for chemically depolarized cells as -14 mV. We observed a population level MP heterogeneity of ~6-10 mV indicating a considerable degree of diversity of physiological and metabolic states among individual cells. Our work paves the way for deeper insights into bacterial electrophysiology and bioelectricity research.

Label-free, non-contact determination of resting membrane potential using dielectrophoresis

Measurement of cellular resting membrane potential (RMP) is important in understanding ion channels and their role in regulation of cell function across a wide range of cell types. However, methods available for the measurement of RMP (including patch clamp, microelectrodes, and potential-sensitive fluorophores) are expensive, slow, open to operator bias, and often result in cell destruction. We present non-contact, label-free membrane potential estimation which uses dielectrophoresis to determine the cytoplasm conductivity slope as a function of medium conductivity. By comparing this to patch clamp data available in the literature, we have demonstratet the accuracy of this approach using seven different cell types, including primary suspension cells (red blood cells, platelets), cultured suspension cells (THP-1), primary adherent cells (chondrocytes, human umbilical mesenchymal stem cells), and adherent (HeLa) and suspension (Jurkat) cancer cell lines. Analysis of the effect of ion channel inhibitors suggests the effects of pharmaceutical agents (TEA on HeLa; DMSO and neuraminidase on red blood cells) can also be measured. Comparison with published values of membrane potential suggest that the differences between our estimates and values recorded by patch clamp are accurate to within published margins of error. The method is low-cost, non-destructive, operator-independent and label-free, and has previously been shown to allow cells to be recovered after measurement.

Electrochemical biofilter enhances performance of volatile organic compounds abatement

An electrochemical biofilter (EBF) was developed for enhancing the removal of volatile organic compounds (VOCs) through current. The removal efficiency (RE) of toluene exhibited a notable increase of 15% while the biomass growth rate exhibited a corresponding decline of 46% under an optimal current intensity of 50 mA. Meanwhile, the efficacy of the EBF system was markedly enhanced upon the removal of n-hexane, styrene, dichloromethane, and diisobutylene. The results indicated that there was an 11% to 49% increase in RE and a 0% to 64% reduction in biomass growth rates under the influence of the current. The current stimulation inhibited the accumulation of microorganisms, thereby alleviating biofilm clogging. The relative abundance of gram-positive phyla, including Firmicutes and Actinobacteria, increased by 15% and 23%, respectively, while the traditionally dominant genera within the Proteobacteria phylum, such as Rhodococcus and Dokdonella, exhibited a decline. In addition, the presence of hydrogen peroxide, free chlorine, and superoxides in the leachate indicated that the oxidative reaction increased in EBF system. This study provides an attractive pathway for current stimulation to enhance degradation of VOCs and alleviate biofilm clogging.

Bacterial Electrophysiology

Bacterial ion fluxes are involved in the generation of energy, transport, and motility. As such, bacterial electrophysiology is fundamentally important for the bacterial life cycle, but it is often neglected and consequently, by and large, not understood. Arguably, the two main reasons for this are the complexity of measuring relevant variables in small cells with a cell envelope that contains the cell wall and the fact that, in a unicellular organism, relevant variables become intertwined in a nontrivial manner. To help give bacterial electrophysiology studies a firm footing, in this review, we go back to basics. We look first at the biophysics of bacterial membrane potential, and then at the approaches and models developed mostly for the study of neurons and eukaryotic mitochondria. We discuss their applicability to bacterial cells. Finally, we connect bacterial membrane potential with other relevant (electro)physiological variables and summarize methods that can be used to both measure and influence bacterial electrophysiology.

From the Microbiome to the Electrome: Implications for the Microbiota-Gut-Brain Axis

The gut microbiome plays a fundamental role in metabolism, as well as the immune and nervous systems. Microbial imbalance (dysbiosis) can contribute to subsequent physical and mental pathologies. As such, interest has been growing in the microbiota-gut-brain brain axis and the bioelectrical communication that could exist between bacterial and nervous cells. The aim of this study was to investigate the bioelectrical profile (electrome) of two bacterial species characteristic of the gut microbiome: a Proteobacteria Gram-negative bacillus Escherichia coli (E. coli), and a Firmicutes Gram-positive coccus Enterococcus faecalis (E. faecalis). We analyzed both bacterial strains to (i) validate the fluorescent probe bis-(1,3-dibutylbarbituric acid) trimethine oxonol, DiBAC4(3), as a reliable reporter of the changes in membrane potential (Vmem) for both bacteria; (ii) assess the evolution of the bioelectric profile throughout the growth of both strains; (iii) investigate the effects of two neural-type stimuli on Vmem changes: the excitatory neurotransmitter glutamate (Glu) and the inhibitory neurotransmitter γ-aminobutyric acid (GABA); (iv) examine the impact of the bioelectrical changes induced by neurotransmitters on bacterial growth, viability, and cultivability using absorbance, live/dead fluorescent probes, and viable counts, respectively. Our findings reveal distinct bioelectrical profiles characteristic of each bacterial species and growth phase. Importantly, neural-type stimuli induce Vmem changes without affecting bacterial growth, viability, or cultivability, suggesting a specific bioelectrical response in bacterial cells to neurotransmitter cues. These results contribute to understanding the bacterial response to external stimuli, with potential implications for modulating bacterial bioelectricity as a novel therapeutic target.

Microbial inactivation of pressure spray combined with high-voltage electrospray and its application in honey raspberry juice

Pressure spray combined with high-voltage electrospray (PS-ES) has garnered considerable interest as a novel, non-thermal approach for microbial inactivation and preservation of liquid food. This study compared PS-ES with heat treatment (HT) to understand its inactivation mechanism against E. coli and S. aureus in a simulated system. Microbial activity, cell permeability, membrane integrity, membrane potential, and cell membrane structure were assessed. Furthermore, the impact of PS-ES treatment on microbial activity and flavor in honey raspberry juice, was examined. The changes in microbial growth and color during storage were also discussed. The experimental findings revealed that PS-ES treatment effectively reduced the number of E. coli and S. aureus by 1.99 and 1.83 log colony-forming units (CFU/mL). Additionally, it disrupted the integrity of bacterial cell membranes increasing their permeability, which led to the release of cellular proteins and nucleic acids. PS-ES treatment lowered the membrane potential and altered the structure of bacterial proteins. Application of PS-ES in honey raspberry juice reduced bacterial counts from 4.48 log CFU/mL to 1.99 log CFU/mL, with less flavor deterioration compared to HT treatment. After 30 days of storage at 4 °C and room temperature, PS-ES effectively controlled the growth of microorganisms in raspberry juice and maintained the color of the juice.

Electrical Impedance Spectroscopy with Bacterial Biofilms: Neuronal-like Behavior

Negative capacitance at low frequencies for spiking neurons was first demonstrated in 1941 (K. S. Cole) by using extracellular electrodes. The phenomenon subsequently was explained by using the Hodgkin-Huxley model and is due to the activity of voltage-gated potassium ion channels. We show that Escherichia coli (E. coli) biofilms exhibit significant stable negative capacitances at low frequencies when they experience a small DC bias voltage in electrical impedance spectroscopy experiments. Using a frequency domain Hodgkin-Huxley model, we characterize the conditions for the emergence of this feature and demonstrate that the negative capacitance exists only in biofilms containing living cells. Furthermore, we establish the importance of the voltage-gated potassium ion channel, Kch, using knock-down mutants. The experiments provide further evidence for voltage-gated ion channels in E. coli and a new, low-cost method to probe biofilm electrophysiology, e.g., to understand the efficacy of antibiotics. We expect that the majority of bacterial biofilms will demonstrate negative capacitances.

What happens to Bifidobacterium adolescentis and Bifidobacterium longum ssp. longum in an experimental environment with eukaryotic cells?

BACKGROUND

The impact of probiotic strains on host health is widely known. The available studies on the interaction between bacteria and the host are focused on the changes induced by bacteria in the host mainly. The studies determining the changes that occurred in the bacteria cells are in the minority. Within this paper, we determined what happens to the selected Bifidobacterium adolescentis and Bifidobacterium longum ssp. longum in an experimental environment with the intestinal epithelial layer. For this purpose, we tested the bacteria cells' viability, redox activity, membrane potential and enzymatic activity in different environments, including CaCo-2/HT-29 co-culture, cell culture medium, presence of inflammatory inductor (TNF-α) and oxygen.

RESULTS

We indicated that the external milieu impacts the viability and vitality of bacteria. Bifidobacterium adolescentis decrease the size of the live population in the cell culture medium with and without TNF-α (p < 0.001 and p < 0.01 respectively). In contrast, Bifidobacterium longum ssp. longum significantly increased survivability in contact with the eukaryotic cells and cell culture medium (p < 0.001). Bifidobacterium adolescentis showed significant changes in membrane potential, which was decreased in the presence of eukaryotic cells (p < 0.01), eukaryotic cells in an inflammatory state (p < 0.01), cell culture medium (p < 0.01) and cell culture medium with TNF-α (p < 0.05). In contrast, Bifidobacterium longum ssp. longum did not modulate membrane potential. Instead, bacteria significantly decreased the redox activity in response to milieus such as eukaryotic cells presence, inflamed eukaryotic cells as well as the culture medium (p < 0.001). The redox activity was significantly different in the cells culture medium vs the presence of eukaryotic cells (p < 0.001). The ability to β-galactosidase production was different for selected strains: Bifidobacterium longum ssp. longum indicated 91.5% of positive cells, whereas Bifidobacterium adolescentis 4.34% only. Both strains significantly reduced the enzyme production in contact with the eukaryotic milieu but not in the cell culture media.

CONCLUSION

The environmental-induced changes may shape the probiotic properties of bacterial strains. It seems that the knowledge of the sensitivity of bacteria to the external environment may help to select the most promising probiotic strains, reduce research costs, and contribute to greater reproducibility of the obtained probiotic effects.

Chickpea-Derived Modified Antimicrobial Peptides KTA and KTR Inactivate Staphylococcus aureus via Disrupting Cell Membrane and Interfering with Peptidoglycan Synthesis

The widespread bacterial contamination caused by foodborne pathogens has continuously driven the development of advanced and potent food antimicrobial agents. In this study, two novel antimicrobial peptides (AMPs) named KTA and KTR were obtained by modifying a natural AMP, Leg2, from chickpea storage protein legumin hydrolysates. They were further predicted to be stable hydrophobic cationic AMPs of α-helical structure with no hemolytic toxicity by several online servers. Moreover, the AMPs exerted superior antibacterial activity against two representative Staphylococcus aureus strains thanks to the increased hydrophobicity and positive charge, with minimum inhibition concentration value (4.74-7.41 μM) significantly lower than that of Leg2 (>1158.70 μM). Further, this study sought to elucidate the specific antimicrobial mechanism against Gram-positive bacteria. It was found that the electrostatic interactions of the AMPs with peptidoglycan were vital for peptide activity in combating Gram-positive bacteria. Subsequently, the cell membrane of S. aureus cells was irreversibly disrupted by increasing permeability and impairing membrane components, which led to the massive release of intracellular substances and eventual cell death. Overall, this work demonstrated that KTA and KTR were active against Gram-positive bacteria via peptidoglycan targeting and membrane-disruptive mechanisms and paved the way for expanding their application potential to alleviate food contamination.

A membrane targeted multifunctional cationic nanoparticle conjugated fusogenic nanoemulsion (CFusoN): induced membrane depolarization and lipid solubilization to accelerate the killing of Staphylococcus aureus

Bacterial infections caused by Staphylococcus aureus are one of the growing concerns for human health care management globally. Antibiotic-associated adverse effects and the emergence of bacterial resistant strains necessitate the development of an alternative yet effective approach. Nanoemulsion-based therapy has emerged as a potential therapeutic strategy to combat bacterial infestation. Herein, we designed a cationic metal nanoparticle-conjugated fusogenic nanoemulsion (CFusoN) as a lipid solubilizing nanovesicle for the effective treatment of S. aureus infection with a killing efficiency of 99.999%. The cationic nanoparticle-conjugated nanoemulsion (viz. NECNP) (24.4 ± 2.9 mV) electrostatically bound with the negatively charged bacterial cell membrane (-10.2 ± 3.7 mV) causing alteration of the bacterial surface charge. The fluorometric and flow cytometry studies confirmed the bacterial membrane depolarization and altered cell membrane permeability leading to cell death. The atomic force microscopic studies further demonstrated the damage of the cellular ultrastructure, while the transmission electron microscopic image and membrane lipid solubilization analysis depicted the solubilization of the bacterial membrane lipid bilayer along with the leakage of the intracellular contents. The cell membrane fatty acid analysis revealed that the methyl esters of palmitic acid, stearic acid and octadecadienoic acid isomers were solubilized after the treatment of S. aureus with CFusoN. The bactericidal killing efficiency of CFusoN is proposed to occur through the synergistic efficacy of the targeted attachment of CNP to the bacterial cells along with the lipid solubilization property of NE. Interestingly, NECNP didn't elicit any in vitro hemolytic activity or cytotoxicity against red blood cells (RBCs) and L929 fibroblast cells, respectively, at its bactericidal concentration. Furthermore, a porcine skin wound infection model exhibited the enhanced wound cleansing potency of CFusoN in comparison to the commercially available wound cleansers. The obtained antibacterial activity, biocompatibility and skin wound disinfection efficacy of the NECNP demonstrated the formulation of a cell targeted CFusoN as a promising translatable strategy to combat bacterial infection.

Klebsiella pneumoniae DedA family proteins have redundant roles in divalent cation homeostasis and resistance to phagocytosis

The DedA superfamily is a highly conserved family of membrane proteins. Deletion of Escherichia coli yqjA and yghB, encoding related DedA family proteins, results in sensitivity to elevated temperature, antibiotics, and alkaline pH. The human pathogen Klebsiella pneumoniae possesses genes encoding DedA family proteins with >90% amino acid identity to E. coli YqjA and YghB. We hypothesized that the deletion of K. pneumoniae yqjA and yghB will impact its physiology and may reduce its virulence. The K. pneumoniae ΔyqjA ΔyghB mutant (strain VT101) displayed a growth defect at 42°C and alkaline pH sensitivity, not unlike its E. coli counterpart. However, VT101 retained mostly wild-type resistance to antibiotics. We found VT101 was sensitive to the chelating agent EDTA, the anionic detergent SDS, and agents capable of alkalizing the bacterial cytoplasm such as bicarbonate or chloroquine. We could restore growth at alkaline pH and at elevated temperature by addition of 0.5-2 mM Ca2+ or Mg2+ to the culture media. VT101 displayed a slower uptake of calcium, which was dependent upon calcium channel activity. VT201, with similar deletions as VT101 but derived from a virulent K. pneumoniae strain, was highly susceptible to phagocytosis by alveolar macrophages and displayed a defect in the production of capsule. These findings suggest divalent cation homeostasis and virulence are interlinked by common functions of the DedA family.IMPORTANCEKlebsiella pneumoniae is a dangerous human pathogen. The DedA protein family is found in all bacteria and is a membrane transporter often required for virulence and antibiotic resistance. K. pneumoniae possesses homologs of E. coli YqjA and YghB, with 60% amino acid identity and redundant functions, which we have previously shown to be required for tolerance to biocides and alkaline pH. A K. pneumoniae strain lacking yqjA and yghB was found to be sensitive to alkaline pH, elevated temperature, and EDTA/SDS and displayed a defect in calcium uptake. Sensitivity to these conditions was reversed by addition of calcium or magnesium to the growth medium. Introduction of ΔyqjA and ΔyghB mutations into virulent K. pneumoniae resulted in the loss of capsule, increased phagocytosis by macrophages, and a partial loss of virulence. These results show that targeting the Klebsiella DedA family results in impaired divalent cation transport and, in turn, loss of virulence.

Excite the unexcitable: engineering cells and redox signaling for targeted bioelectronic control

The ever-growing influence of technology in our lives has led to an increasing interest in the development of smart electronic devices to interrogate and control biological systems. Recently, redox-mediated electrogenetics introduced a novel avenue that enables direct bioelectronic control at the genetic level. In this review, we discuss recent advances in methodologies for bioelectronic control, ranging from electrical stimulation to engineering efforts that allow traditionally unexcitable cells to be electrically 'programmable.' Alongside ion-transport signaling, we suggest redox as a route for rational engineering because it is a native form of electronic communication in biology. Using redox as a common language allows the interfacing of electronics and biology. This newfound connection opens a gateway of possibilities for next-generation bioelectronic tools.

Ultrasonically functionalized chitosan-gallic acid films inactivate Staphylococcus aureus through envelope-disruption under UVA light exposure

The significant threat of foodborne pathogens contamination has continuously promoted the development of efficient antimicrobial food packaging materials. Here, an antimicrobial film was prepared with gallic acid-grafted-chitosan (CS/GA) that obtained by a two-step ultrasound method. The resultant films exhibited good transparency, improved UV barrier performance, and enhanced mechanical strength. Specifically, with the grafting of 1.2 % GA, the UV blocking ability of CS/GA film at 400 nm was significantly increased by 19.7 % and the tensile strength was nearly two times higher than that of CS film. Moreover, the CS/GA films exhibited an inspiring photoactivated bactericidal ability under 400 nm UVA light irradiation that eradicated almost 99.9 % of Staphylococcus aureus (S. aureus) cells within 60 min. To gain more insights into the antibacterial mechanism, the treated S. aureus cells were further investigated by visualizing bacterial ultrastructure and analyzing membrane properties. The results pointed to the peptidoglycan layer as the primary action target when bacteria come into contact with CS/GA films. Afterward, the intracellular oxidative lesions, disrupted bacterial integrity, and disordered membrane functional properties collectively resulted in eventual cell death. The findings revealed the unique peptidoglycan targeting and membrane disruptive mechanisms of CS/GA films, confirming the application values in controlling foodborne pathogens.

Thioflavin T indicates mitochondrial membrane potential in mammalian cells

The fluorescent benzothiazole dye thioflavin T (ThT) is widely used as a marker for protein aggregates, most commonly in the context of neurodegenerative disease research and diagnosis. Recently, this same dye was shown to indicate membrane potential in bacteria due to its cationic nature. This finding prompted a question whether ThT fluorescence is linked to the membrane potential in mammalian cells, which would be important for appropriate utilization of ThT in research and diagnosis. Here, we show that ThT localizes into the mitochondria of HeLa cells in a membrane-potential-dependent manner. Specifically, ThT colocalized in cells with the mitochondrial membrane potential indicator tetramethylrhodamine methyl ester (TMRM) and gave similar temporal responses as TMRM to treatment with a protonophore, carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP). Additionally, we found that presence of ThT together with exposure to blue light (λ = 405 nm), but neither factor alone, caused depolarization of mitochondrial membrane potential. This additive effect of the concentration and blue light was recapitulated by a mathematical model implementing the potential-dependent distribution of ThT and its effect on mitochondrial membrane potential through photosensitization. These results show that ThT can act as a mitochondrial membrane potential indicator in mammalian cells, when used at low concentrations and with low blue light exposure. However, it causes dissipation of the mitochondrial membrane potential depending additively on its concentrations and blue light exposure. This conclusion motivates a re-evaluation of ThT's use at micromolar range in live-cell analyses and indicates that this dye can enable future studies on the potential connections between mitochondrial membrane potential dynamics and protein aggregation.

Conformation Dependent Architectures of Assembled Antimicrobial Peptides with Enhanced Antimicrobial Ability

Antimicrobial peptides (AMPs) are a developing class of natural and synthetic oligopeptides with host defense mechanisms against a broad spectrum of microorganisms. With in-depth research on the structural conformations of AMPs, synthesis or modification of peptides has shown great potential in effectively obtaining new therapeutic agents with improved physicochemical and biological properties. Notably, AMPs with self-assembled properties have gradually become a hot research topic for various biomedical applications. Compared to monomeric peptides, these peptides can exist in diverse forms (e.g., nanoparticles, nanorods, and nanofibers) and possess several advantages, such as high stability, good biocompatibility, and potent biological functions, after forming aggregates under specific conditions. In particular, the stability and antibacterial property of these AMPs can be modulated by rationally regulating the peptide sequences to promote self-assembly, leading to the reconstruction of molecular structure and spatial orientation while introducing some peptide fragments into the scaffolds. In this work, four self-assembled AMPs are developed, and the relationship between their chemical structures and antibacterial activity is explored extensively through different experiments. Importantly, the evaluation of antibacterial performance in both in vitro and in vivo studies has provided a general guide for using self-assembled AMPs in subsequent treatments for combating bacterial infections.

Thioflavin-T does not report on electrochemical potential and memory of dormant or germinating bacterial spores

IMPORTANCE

Bacillus and Clostridium spores cause food spoilage and disease because of spores' dormancy and resistance to microbicides. However, when spores "come back to life" in germination, their resistance properties are lost. Thus, understanding the mechanisms of spore germination could facilitate the development of "germinate to eradicate" strategies. One germination feature is the memory of a pulsed germinant stimulus leading to greater germination following a second pulse. Recent observations of increases in spore binding of the potentiometric dye thioflavin-T early in their germination of spores led to the suggestion that increasing electrochemical potential is how spores "remember" germinant pulses. However, new work finds no increased thioflavin-T binding in the physiological germination of Coatless spores or of intact spores germinating with dodecylamine, even though spore memory is seen in both cases. Thus, using thioflavin-T uptake by germinating spores to assess the involvement of electrochemical potential in memory of germinant exposure, as suggested recently, is questionable.

The Use of Thioflavin T for the Estimation and Measurement of the Plasma Membrane Electric Potential Difference in Different Yeast Strains

The use of the cationic, dye thioflavin T (ThT), to estimate the electric plasma membrane potential difference (PMP) via the fluorescence changes and to obtain its actual values from the accumulation of the dye, considering important correction factors by its binding to the internal components of the cell, was described previously for baker's yeast. However, it was considered important to explore whether the method developed could be applied to other yeast strains. Alternative ways to estimate the PMP by using flow cytometry and a multi-well plate reader are also presented here. The methods were tested with other strains of Saccharomyces cerevisiae (W303-1A and FY833), as well as with non-conventional yeasts: Debaryomyces hansenii, Candida albicans, Meyerozyma guilliermondii, and Rhodotorula mucilaginosa. Results of the estimation of the PMP via the fluorescence changes under different conditions were adequate with all strains. Consistent results were also obtained with several mutants of the main monovalent transporters, validating ThT as a monitor for PMP estimation.

Increase in anionic Fe3O4 nanoparticle-induced membrane poration and vesicle deformation due to membrane potential - an experimental study

The membrane potential plays a significant role in various cellular processes while interacting with membrane active agents. So far, all the investigations of the interaction of nanoparticles (NPs) with lipid vesicles have been performed in the absence of membrane potential. In this study, the anionic magnetite NP-induced poration along with deformation of cell-mimetic giant unilamellar vesicles (GUVs) has been studied in the presence of various membrane potentials. Lipids 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and channel forming protein gramicidin A (GrA) are used to synthesize the DOPG/DOPC/GrA-GUVs. The static and dynamic nature of GUVs is investigated using phase contrast fluorescent microscopy. The presence of GrA in the membrane decreases the leakage constant of the encapsulating fluorescent probe (calcein) in the absence of membrane potential. With the increase of negative membrane potential, the leakage shifts from a single exponential to two exponential functions, obtaining two leakage constants. The leakage became faster at the initial stage, and at the final stage, it became slower with the increase in negative membrane potential. Both the fraction of poration and deformation increase with the increase of negative membrane potential. These results suggested that the membrane potential enhances the NP-induced poration along with the deformation of DOPG/DOPC/GrA-GUVs. The increase of the binding constant in the NPs with membrane potential is one of the important factors for increasing membrane permeation and vesicle deformation.

Multifunctional Gold-Silver-Carbon Quantum Dots Nano-Hybrid Composite: Advancing Antibacterial Wound Healing and Cell Proliferation

The urgent need for innovative materials that effectively eliminate bacteria while promoting cell growth to accelerate wound healing has led to the exploration of new options, as current antimicrobial nanoparticles often exhibit high cytotoxicity, which hinders wound closure. In this study, a nano-hybrid composite, named gold-silver-carbon quantum dots (AuAg-CDs), was prepared by embedding gold and silver nanoclusters into carbon dots. The AuAg-CDs nano-hybrid composite demonstrates remarkable biocompatibility, displays potent antibacterial activity, and possesses a unique capability to promote cell proliferation. By physically disrupting bacterial membranes and promoting mammalian cell proliferation, this composite emerges as a highly promising material for wound healing applications. The underlying mechanism of the multifunctional AuAg-CDs was investigated through comprehensive analyses encompassing cell morphology, bacterial membrane potential, levels of reactive oxygen species (ROS), and adenosine triphosphate (ATP) production in both bacterial and mammalian cells. Additionally, AuAg-CDs were incorporated into alginate to create a hydrogel wound dressing, which underwent evaluation using animal models. The results underscore the remarkable potential of the AuAg-CDs wound dressing in facilitating the proliferation of wound fibroblasts and combating bacterial infections. The significance of designing multifunctional nanomaterials to address the challenges associated with pathogenic bacterial infections and regenerative medicine is highlighted by this study, paving the way for future advancements in these fields.

Bioelectrical State of Bacteria Is Linked to Growth Dynamics and Response to Neurotransmitters: Perspectives for the Investigation of the Microbiota-Brain Axis

Inter-cellular communication is mediated by a sum of biochemical, biophysical, and bioelectrical signals. This might occur not only between cells belonging to the same tissue and/or animal species but also between cells that are, from an evolutionary point of view, far away. The possibility that bioelectrical communication takes place between bacteria and nerve cells has opened exciting perspectives in the study of the gut microbiota-brain axis. The aim of this paper is (i) to establish a reliable method for the assessment of the bioelectrical state of two bacterial strains: Bacillus subtilis (B. subtilis) and Limosilactobacillus reuteri (L. reuteri); (ii) to monitor the bacterial bioelectrical profile throughout its growth dynamics; and (iii) to evaluate the effects of two neurotransmitters (glutamate and γ-aminobutyric acid-GABA) on the bioelectrical signature of bacteria. Our results show that membrane potential (Vmem) and the proliferative capacity of the population are functionally linked in B. subtilis in each phase of the cell cycle. Remarkably, we demonstrate that bacteria respond to neural signals by changing Vmem properties. Finally, we show that Vmem changes in response to neural stimuli are present also in a microbiota-related strain L. reuteri. Our proof-of-principle data reveal a new methodological approach for the better understanding of the relation between bacteria and the brain, with a special focus on gut microbiota. Likewise, this approach will open exciting perspectives in the study of the inter-cellular mechanisms which regulate the bi-directional communication between bacteria and neurons and, ultimately, for designing gut microbiota-brain axis-targeted treatments for neuropsychiatric diseases.

Super Antibacterial Capacity and Cell Envelope-Disruptive Mechanism of Ultrasonically Grafted N-Halamine PBAT/PBF Films against Escherichia coli

Antibacterial materials are urgently needed to combat bacterial contamination, growth, or attachment on contact surfaces, as bacterial infections remain a public health crisis worldwide. Here, a novel ultrasound-assisted method is utilized for the first time to fabricate oxidative chlorine-loaded AH@PBAT/PBF-Cl films with more superior grafting efficiency and rechargeable antibacterial effect than those from conventional techniques. The films remarkably inactivate 99.9999% Escherichia coli and Staphylococcus aureus cells, inducing noticeable cell deformations and mechanical instability. The specific antibacterial mechanism against E. coli used as a model organism is unveiled using several cell envelope structural and functional analyses combined with proteomics, peptidoglycomics, and fluorescence probe techniques. Film treatment partially neutralizes the bacterial surface charge, induces oxidative stress and cytoskeleton deformity, alters membrane properties, and disrupts the expression of key proteins involved in the synthesis and transport of the lipopolysaccharide and peptidoglycan, indicating the cell envelope as the primary target. The films specifically target lipopolysaccharides, resulting in structural impairment of the polysaccharide and lipid A components, and inhibit peptidoglycan precursor synthesis. Together, these lead to metabolic disorders, membrane dysfunction, structural collapse, and eventual death. Given the films' antibacterial effects via the disruption of key cell envelope components, they can potentially combat a wide range of bacteria. These findings lay a theoretical basis for developing efficient antibacterial materials for food safety or biomedical applications.

Baicalein Resensitizes Multidrug-Resistant Gram-Negative Pathogens to Doxycycline

As multidrug-resistant pathogens emerge and spread rapidly, novel antibiotics urgently need to be discovered. With a dwindling antibiotic pipeline, antibiotic adjuvants might be used to revitalize existing antibiotics. In recent decades, traditional Chinese medicine has occupied an essential position in adjuvants of antibiotics. This study found that baicalein potentiates doxycycline against multidrug-resistant Gram-negative pathogens. Mechanism studies have shown that baicalein causes membrane disruption by attaching to phospholipids on the Gram-negative bacterial cytoplasmic membrane and lipopolysaccharides on the outer membrane. This process facilitates the entry of doxycycline into bacteria. Through collaborative strategies, baicalein can also increase the production of reactive oxygen species and inhibit the activities of multidrug efflux pumps and biofilm formation to potentiate antibiotic efficacy. Additionally, baicalein attenuates the lipopolysaccharide-induced inflammatory response in vitro. Finally, baicalein can significantly improve doxycycline efficacy in mouse lung infection models. The present study showed that baicalein might be considered a lead compound, and it should be further optimized and developed as an adjuvant that helps combat antibiotic resistance. IMPORTANCE Doxycycline is an important broad-spectrum tetracycline antibiotic used for treating multiple human infections, but its resistance rates are recently rising globally. Thus, new agents capable of boosting the effectiveness of doxycycline need to be discovered. In this study, it was found that baicalein potentiates doxycycline against multidrug-resistant Gram-negative pathogens in vitro and in vivo. Due to its low cytotoxicity and resistance, the combination of baicalein and doxycycline provides a valuable clinical reference for selecting more effective therapeutic strategies for treating infections caused by multidrug-resistant Gram-negative clinical isolates.

Microwave-Excited, Antibacterial Core-Shell BaSO4/BaTi5O11@PPy Heterostructures for Rapid Treatment of S. aureus-Infected Osteomyelitis

Owing to its deep penetration capability, microwave (MW) therapy has emerged as a promising method to eradicate deep-seated acute bone infection diseases such as osteomyelitis. However, the MW thermal effect still needs to be enhanced to achieve rapid and efficient treatment of deep focal infected areas. In this work, the multi-interfacial core-shell structure barium sulfate/barium polytitanates@polypyrrole (BaSO₄/BaTi₅O₁₁@PPy) was prepared, which exhibited enhanced MW thermal response via the well-designed multi-interfacial structure. To be specific, BaSO₄/BaTi₅O₁₁@PPy achieved rapid temperature increases in a short period and efficient clearance of Staphylococcus aureus (S. aureus) infections under MW irradiation. After 15 min MW irradiation, the antibacterial efficacy of BaSO₄/BaTi₅O₁₁@PPy can reach up to 99.61 ± 0.22%. Their desirable thermal production capabilities originated from enhanced dielectric loss including multiple interfacial polarization and conductivity loss. Additionally, in vitro analysis illuminated that the underlying antimicrobial mechanism was attributed to the noticeable MW thermal effect and changes in energy metabolic pathways on bacterial membrane instigated by BaSO₄/BaTi₅O₁₁@PPy under MW irradiation. Considering remarkable antibacterial efficiency and acceptable biosafety, we envision that it has significant value in broadening the pool of desirable candidates to fight against S. aureus-infected osteomyelitis. STATEMENT OF SIGNIFICANCE: : The treatment of deep bacterial infection remains challenging due to the ineffectiveness of antibiotic treatment and the susceptibility to bacterial resistance. Microwave (MW) thermal therapy (MTT) is a promising approach with remarkable penetration to centrally heat up the infected area. This study proposes to utilize the core-shell structure BaSO₄/BaTi₅O₁₁@PPy as an MW absorber to achieve localized heating under MW radiation for MTT. In vitro experiments demonstrated that the disrupted bacterial membrane is primarily due to the localized high temperature and interrupted electron transfer chain. As a consequence, its antibacterial rate is as high as 99.61% under MW irradiation. It is shown that the BaSO₄/BaTi₅O₁₁@PPy is a promising candidate for eliminating bacterial infection in deep-seated tissues.

Passive Recording of Bioelectrical Signals from Non-Excitable Cells by Fluorescent Mirroring

Bioelectrical variations trigger different cell responses, including migration, mitosis, and mutation. At the tissue level, these actions result in phenomena such as wound healing, proliferation, and pathogenesis. Monitoring these mechanisms dynamically is highly desirable in diagnostics and drug testing. However, existing technologies are invasive: either they require physical access to the intracellular compartments, or they imply direct contact with the cellular medium. Here, we present a novel approach for the passive recording of electrical signals from non-excitable cells adhering to 3D microelectrodes, based on optical mirroring. Preliminary results yielded a fluorescence intensity output increase of the 5,8% in the presence of a HEK-293 cell on the electrode compared to bare microelectrodes. At present, this technology may be employed to evaluate cell-substrate adhesion and monitor cell proliferation. Further refinements could allow extrapolating quantitative data on surface charges and resting potential to investigate the electrical phenomena involved in cell migration and cancer progression.

Bioelectricity in Developmental Patterning and Size Control: Evidence and Genetically Encoded Tools in the Zebrafish Model

Developmental patterning is essential for regulating cellular events such as axial patterning, segmentation, tissue formation, and organ size determination during embryogenesis. Understanding the patterning mechanisms remains a central challenge and fundamental interest in developmental biology. Ion-channel-regulated bioelectric signals have emerged as a player of the patterning mechanism, which may interact with morphogens. Evidence from multiple model organisms reveals the roles of bioelectricity in embryonic development, regeneration, and cancers. The Zebrafish model is the second most used vertebrate model, next to the mouse model. The zebrafish model has great potential for elucidating the functions of bioelectricity due to many advantages such as external development, transparent early embryogenesis, and tractable genetics. Here, we review genetic evidence from zebrafish mutants with fin-size and pigment changes related to ion channels and bioelectricity. In addition, we review the cell membrane voltage reporting and chemogenetic tools that have already been used or have great potential to be implemented in zebrafish models. Finally, new perspectives and opportunities for bioelectricity research with zebrafish are discussed.

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.

Living electronics: A catalogue of engineered living electronic components

Biology leverages a range of electrical phenomena to extract and store energy, control molecular reactions and enable multicellular communication. Microbes, in particular, have evolved genetically encoded machinery enabling them to utilize the abundant redox-active molecules and minerals available on Earth, which in turn drive global-scale biogeochemical cycles. Recently, the microbial machinery enabling these redox reactions have been leveraged for interfacing cells and biomolecules with electrical circuits for biotechnological applications. Synthetic biology is allowing for the use of these machinery as components of engineered living materials with tuneable electrical properties. Herein, we review the state of such living electronic components including wires, capacitors, transistors, diodes, optoelectronic components, spin filters, sensors, logic processors, bioactuators, information storage media and methods for assembling these components into living electronic circuits.

Advances in pulsed electric stimuli as a physical method for treating liquid foods

There is a need for alternative technologies that can deliver safe and nutritious foods at lower costs as compared to conventional processes. Pulsed electric field (PEF) technology has been utilised for a plethora of different applications in the life and physical sciences, such as gene/drug delivery in medicine and extraction of bioactive compounds in food science and technology. PEF technology for treating liquid foods involves engineering principles to develop the equipment, and quantitative biochemistry and microbiology techniques to validate the process. There are numerous challenges to address for its application in liquid foods such as the 5-log pathogen reduction target in food safety, maintaining the food quality, and scale up of this physical approach for industrial integration. Here, we present the engineering principles associated with pulsed electric fields, related inactivation models of microorganisms, electroporation and electropermeabilization theory, to increase the quality and safety of liquid foods; including water, milk, beer, wine, fruit juices, cider, and liquid eggs. Ultimately, we discuss the outlook of the field and emphasise research gaps.

Collective polarization dynamics in bacterial colonies signify the occurrence of distinct subpopulations

Membrane potential in bacterial systems has been shown to be dynamic and tightly related to survivability at the single-cell level. However, little is known about spatiotemporal patterns of membrane potential in bacterial colonies and biofilms. Here, we discovered a transition from uncorrelated to collective dynamics within colonies formed by the human pathogen Neisseria gonorrhoeae. In freshly assembled colonies, polarization is heterogeneous with instances of transient and uncorrelated hyper- or depolarization of individual cells. As colonies reach a critical size, the polarization behavior transitions to collective dynamics: A hyperpolarized shell forms at the center, travels radially outward, and halts several micrometers from the colony periphery. Once the shell has passed, we detect an influx of potassium correlated with depolarization. Transient hyperpolarization also demarks the transition from volume to surface growth. By combining simulations and the use of an alternative electron acceptor for the respiratory chain, we provide strong evidence that local oxygen gradients shape the collective polarization dynamics. Finally, we show that within the hyperpolarized shell, tolerance against aminoglycoside antibiotics increases. These findings highlight that the polarization pattern can signify the differentiation into distinct subpopulations with different growth rates and antibiotic tolerance.

Sensitive bacterial Vm sensors revealed the excitability of bacterial Vm and its role in antibiotic tolerance

As an important free energy source, the membrane voltage (V_m) regulates many essential physiological processes in bacteria. However, in comparison with eukaryotic cells, knowledge of bacterial electrophysiology is very limited. Here, we developed a set of novel genetically encoded bacterial V_m sensors which allow single-cell recording of bacterial V_m dynamics in live cells with high temporal resolution. Using these new sensors, we reveal the electrically "excitable" and "resting" states of bacterial cells dependent on their metabolic status. In the electrically excitable state, frequent hyperpolarization spikes in bacterial V_m are observed, which are regulated by Na⁺/K⁺ ratio of the medium and facilitate increased antibiotic tolerance. In the electrically resting state, bacterial V_m displays significant cell-to-cell heterogeneity and is linked to the cell fate after antibiotic treatment. Our findings demonstrate the potential of our newly developed voltage sensors to reveal the underpinning connections between bacterial V_m and antibiotic tolerance.

An Enzymatic Antibiotic Adjuvant Modulates the Infectious Microenvironment to Overcome Antimicrobial Resistance of Pathogens

The emergence and evolution of antimicrobial resistance (AMR) pose a significant challenge to the current arsenal to fight infection. Antibiotic adjuvants represent an appealing tactic for tackling the AMR of pathogens, however, their practical applications are greatly constrained by the harsh infectious microenvironment. Herein, it is found that silver nanoclusters (Ag NCs) can possess tunable enzymatic activities to modulate infectious microenvironments. Based on this finding, an enzymatic nanoadjuvant (EnzNA) self-assembled from Ag NCs, which is inert under neutral physiological conditions but can readily disassemble into isolated Ag NCs exhibiting biofilm destructive oxidase-mimetic activity in the acidic biofilm microenvironment, is developed. Once internalized into the neutral cytoplasm of bacteria, Ag NCs switch to reveal the thiol oxidase-mimetic activity to suppress ribosomal biogenesis for AMR reversal and evolution inhibition of pathogens. Consequently, EnzNAs revitalize various existing antibiotics against methicillin-resistant Staphylococcus aureus, and potentiate the antibiotic efficacy against biofilm-mediated skin infection and lethal lung infection in mice. These findings highlight the capability of enzyme-mimetic nanomaterials to modulate the infectious microenvironment and potentiate antibiotics, providing a paradigm shift for anti-infection therapy.

TrkA serves as a virulence modulator in Porphyromonas gingivalis by maintaining heme acquisition and pathogenesis

Periodontitis is an inflammatory disease of the supporting tissues of the teeth, with polymicrobial infection serving as the major pathogenic factor. As a periodontitis-related keystone pathogen, Porphyromonas gingivalis can orchestrate polymicrobial biofilm skewing into dysbiosis. Some metatranscriptomic studies have suggested that modulation of potassium ion uptake might serve as a signal enhancing microbiota nososymbiocity and periodontitis progression. Although the relationship between potassium transport and virulence has been elucidated in some bacteria, less is mentioned about the periodontitis-related pathogen. Herein, we centered on the virulence modulation potential of TrkA, the potassium uptake regulatory protein of P. gingivalis, and uncovered TrkA as the modulator in the heme acquisition process and in maintaining optimal pathogenicity in an experimental murine model of periodontitis. Hemagglutination and hemolytic activities were attenuated in the case of trkA gene loss, and the entire transcriptomic profiling revealed that the trkA gene can control the expression of genes in relation to electron transport chain activity and translation, as well as some transcriptional factors, including cdhR, the regulator of the heme uptake system hmuYR. Collectively, these results link the heme acquisition process to the potassium transporter, providing new insights into the role of potassium ion in P. gingivalis pathogenesis.

Bactericidal Activity of Carvacrol against Streptococcus pyogenes Involves Alteration of Membrane Fluidity and Integrity through Interaction with Membrane Phospholipids

Background: Carvacrol, a mono-terpenoid phenol found in herbs, such as oregano and thyme, has excellent antibacterial properties against Streptococcus pyogenes. However, its mechanism of bactericidal activity on S. pyogenes has not been elucidated. Objectives: This study investigated the bactericidal mechanism of carvacrol using three strains of S. pyogenes. Methods: Flow cytometry (FCM) experiments were conducted to determine carvacrol’s membrane permeabilization and cytoplasmic membrane depolarization activities. Protoplasts of S. pyogenes were used to investigate carvacrol’s effects on the membrane, followed by gel electrophoresis. The carvacrol-treated protoplasts were examined by transmission electron microscopy (TEM) to observe ultrastructural morphological changes. The fluidity of the cell membrane was measured by steady-state fluorescence anisotropy. Thin-layer chromatographic (TLC) profiling was conducted to study the affinity of carvacrol for membrane phospholipids. Results: Increased membrane permeability and decreased membrane potential from FCM and electron microscopy observations revealed that carvacrol killed the bacteria primarily by disrupting membrane integrity, leading to whole-cell lysis. Ultra-structural morphological changes in the membrane induced by carvacrol over a short period were confirmed using the S. pyogenes protoplast and membrane isolate models in vitro. In addition, changes in the other biophysical properties of the bacterial membrane, including concentration- and time-dependent increased fluidity, were observed. TLC experiments showed that carvacrol preferentially interacts with membrane phosphatidylglycerol (P.G.), phosphatidylethanolamine (P.E.), and cardiolipins (CL). Conclusions: Carvacrol exhibited rapid bactericidal action against S. pyogenes by disrupting the bacterial membrane and increasing permeability, possibly due to affinity with specific membrane phospholipids, such as P.E., P.G., and CL. Therefore, the bactericidal concentration of carvacrol (250 µg/mL) could be used to develop safe and efficacious natural health products for managing streptococcal pharyngitis or therapeutic applications.

Hardware, Software, and Wetware Codesign Environment for Synthetic Biology

Synthetic biology is the process of forward engineering living systems. These systems can be used to produce biobased materials, agriculture, medicine, and energy. One approach to designing these systems is to employ techniques from the design of embedded electronics. These techniques include abstraction, standards, modularity, automated design, and formal semantic models of computation. Together, these elements form the foundation of "biodesign automation," where software, robotics, and microfluidic devices combine to create exciting biological systems of the future. This paper describes a "hardware, software, wetware" codesign vision where software tools can be made to act as "genetic compilers" that transform high-level specifications into engineered "genetic circuits" (wetware). This is followed by a process where automation equipment, well-defined experimental workflows, and microfluidic devices are explicitly designed to house, execute, and test these circuits (hardware). These systems can be used as either massively parallel experimental platforms or distributed bioremediation and biosensing devices. Next, scheduling and control algorithms (software) manage these systems' actual execution and data analysis tasks. A distinguishing feature of this approach is how all three of these aspects (hardware, software, and wetware) may be derived from the same basic specification in parallel and generated to fulfill specific cost, performance, and structural requirements.

A guide for membrane potential measurements in Gram-negative bacteria using voltage-sensitive dyes

Transmembrane potential is one of the main bioenergetic parameters of bacterial cells, and is directly involved in energizing key cellular processes such as transport, ATP synthesis and motility. The most common approach to measure membrane potential levels is through use of voltage-sensitive fluorescent dyes. Such dyes either accumulate or are excluded from the cell in a voltage-dependent manner, which can be followed by means of fluorescence microscopy, flow cytometry, or fluorometry. Since the cell's ability to maintain transmembrane potential relies upon low and selective membrane ion conductivity, voltage-sensitive dyes are also highly sensitive reporters for the activity of membrane-targeting antibacterials. However, the presence of an additional membrane layer in Gram-negative (diderm) bacteria complicates their use significantly. In this paper, we provide guidance on how membrane potential and its changes can be monitored reliably in Gram-negatives using the voltage-sensitive dye 3,3'-dipropylthiadicarbocyanine iodide [DiSC₃(5)]. We also discuss the confounding effects caused by the presence of the outer membrane, or by measurements performed in buffers rather than growth medium. We hope that the discussed methods and protocols provide an easily accessible basis for the use of voltage-sensitive dyes in Gram-negative organisms, and raise awareness of potential experimental pitfalls associated with their use.

Bioremediation potential of hexavalent chromium-resistant Arthrobacter globiformis 151B: study of the uptake of cesium and other alkali ions

Cesium (Cs⁺) enters environments largely because of global release into the environment from weapons testing and accidents such as Fukushima Daiichi and Chernobyl nuclear waste. Even at low concentrations, Cs⁺ is highly toxic to ecological receptors because of its physicochemical similarity to macronutrient potassium (K⁺). We investigated the uptake and accumulation of Cs⁺ by Arthrobacter globiformis strain 151B in reference to three similar alkali metal cations rubidium (Rb⁺), sodium (Na⁺), and potassium (K⁺). The impact of hexavalent chromium (Cr⁺⁶) as a co-contaminant was also evaluated. A. globiformis 151B accumulated Cs⁺ and Cr⁶⁺ in a time-dependent fashion. In contrast, the uptake and accumulation of Rb⁺ did not exhibit any trends. An exposure to Cs⁺, Rb⁺, and Cr⁺⁶ triggered a drastic increase in K⁺ and Na⁺ uptake by the bacterial cells. That was followed by the efflux of K⁺ and Na⁺, suggesting a Cs⁺ "substitution." Two-dimensional gel-electrophoresis of bacterial cell proteomes with the following mass-spectrometry of differentially expressed bands revealed that incubation of bacterial cells with Cs⁺ induced changes in the expression of proteins involved in the maintenance of cellular homeostasis and reactive oxygen species removal. The ability of A. globiformis 151B to mediate the uptake and accumulation of cesium and hexavalent chromium suggests that it possesses wide-range bioremediation potential.

Measurement of the low-frequency charge noise of bacteria

Bacteria meticulously regulate their intracellular ion concentrations and create ionic concentration gradients across the bacterial membrane. These ionic concentration gradients provide free energy for many cellular processes and are maintained by transmembrane transport. Given the physical dimensions of a bacterium and the stochasticity in transmembrane transport, intracellular ion concentrations and hence the charge state of a bacterium are bound to fluctuate. Here we investigate the charge noise of hundreds of nonmotile bacteria by combining electrical measurement techniques from condensed matter physics with microfluidics. In our experiments, bacteria in a microchannel generate charge density fluctuations in the embedding electrolyte due to random influx and efflux of ions. Detected as electrical resistance noise, these charge density fluctuations display a power spectral density proportional to 1/f^{2} for frequencies 0.05Hz≤f≤1Hz. Fits to a simple noise model suggest that the steady-state charge of a bacterium fluctuates by ±1.30×10^{6}e(e≈1.60×10^{-19}C), indicating that bacterial ion homeostasis is highly dynamic and dominated by strong charge noise. The rms charge noise can then be used to estimate the fluctuations in the membrane potential; however, the estimates are unreliable due to our limited understanding of the intracellular concentration gradients.

Magnetoelectric Polymer Membrane-Based Electrical Microenvironment with Magnetically Controlled Antibacterial Activity

The "hard to clean" parts of food processing devices (e.g., the corners of pipes) are difficult to disinfect. This challenge might be overcome through the application of a positive electrical environment. However, the chemical modification of a material surface is complex and difficult. In this work, we developed a smart electroactive Tb_xDy_1-xFe alloy/poly(vinylidene fluoride-trifluoroethylene) (TD/P(VDF-TrFE)) magnetoelectric coating to endow stainless steel with the function of a smart adjustable electrical environment, which was realized by the introduction of a magnetic field of various intensities (0-1800 Oe). An antibacterial assay showed that the polarized coating@stainless steel (P-CS) exhibited antibacterial effects, with the highest antibacterial effect observed at 1800 Oe. Furthermore, in this study, we have, for the first time, explored the antibacterial mechanism of TD/P(VDF-TrFE)-assisted electrical stimulation based on the bacterial intracellular reactive oxygen species (ROS) level, cell respiratory chain, and membrane potential. The results showed that a microelectric field was formed on the P-CS sample in an aqueous solution, which not only generated ROS on the cathode surface but also caused H⁺ consumption in the electrochemical gradient of the bacterial membrane, leading to OH^- production and inhibition of adenosine triphosphate (ATP) synthesis. In addition, the electric field also induced hyperpolarization of the membrane potential in Escherichia coli cells via a K⁺ efflux, thus inducing rearrangement of the outer membrane. In conclusion, an adjustable surface potential was established through the introduction of magnetoelectric polymer coatings, which endowed stainless steel with magnetically controlled antibacterial effects.

Localized electrical stimulation triggers cell-type-specific proliferation in biofilms

Biological systems ranging from bacteria to mammals utilize electrochemical signaling. Although artificial electrochemical signals have been utilized to characterize neural tissue responses, the effects of such stimuli on non-neural systems remain unclear. To pursue this question, we developed an experimental platform that combines a microfluidic chip with a multielectrode array (MiCMA) to enable localized electrochemical stimulation of bacterial biofilms. The device also allows for the simultaneous measurement of the physiological response within the biofilm with single-cell resolution. We find that the stimulation of an electrode locally changes the ratio of the two major cell types comprising Bacillus subtilis biofilms, namely motile and extracellular-matrix-producing cells. Specifically, stimulation promotes the proliferation of motile cells but not matrix cells, even though these two cell types are genetically identical and reside in the same microenvironment. Our work thus reveals that an electronic interface can selectively target bacterial cell types, enabling the control of biofilm composition and development.

Technological Approach to Mind Everywhere: An Experimentally-Grounded Framework for Understanding Diverse Bodies and Minds

Synthetic biology and bioengineering provide the opportunity to create novel embodied cognitive systems (otherwise known as minds) in a very wide variety of chimeric architectures combining evolved and designed material and software. These advances are disrupting familiar concepts in the philosophy of mind, and require new ways of thinking about and comparing truly diverse intelligences, whose composition and origin are not like any of the available natural model species. In this Perspective, I introduce TAME-Technological Approach to Mind Everywhere-a framework for understanding and manipulating cognition in unconventional substrates. TAME formalizes a non-binary (continuous), empirically-based approach to strongly embodied agency. TAME provides a natural way to think about animal sentience as an instance of collective intelligence of cell groups, arising from dynamics that manifest in similar ways in numerous other substrates. When applied to regenerating/developmental systems, TAME suggests a perspective on morphogenesis as an example of basal cognition. The deep symmetry between problem-solving in anatomical, physiological, transcriptional, and 3D (traditional behavioral) spaces drives specific hypotheses by which cognitive capacities can increase during evolution. An important medium exploited by evolution for joining active subunits into greater agents is developmental bioelectricity, implemented by pre-neural use of ion channels and gap junctions to scale up cell-level feedback loops into anatomical homeostasis. This architecture of multi-scale competency of biological systems has important implications for plasticity of bodies and minds, greatly potentiating evolvability. Considering classical and recent data from the perspectives of computational science, evolutionary biology, and basal cognition, reveals a rich research program with many implications for cognitive science, evolutionary biology, regenerative medicine, and artificial intelligence.

Re-sensitization of mcr carrying multidrug resistant bacteria to colistin by silver

Superbugs carrying a mobile colistin resistance gene (mcr) are jeopardizing the clinical efficacy of the last-line antibiotic colistin. The development of MCR inhibitors is urgently required to cope with antibiotic-resistance emergencies. Here, we show that silver (Ag⁺) fully restores the susceptibility of mcr-1–carrying superbugs against colistin both in vitro and in vivo. We found an unprecedented tetra-silver center in the active-site pocket of MCR-1 through the substitution of the essential Zn²⁺ ions in the intact enzyme, leading to the prevention of substrate binding (i.e. the dysfunction of MCR-1 in transferring phosphorylethanolamine to lipid A). Importantly, the ability of Ag⁺ to suppress resistance evolution extends the lifespan of currently used antibiotics, providing a strategy to treat infections by mcr-positive bacteria.

Colistin is considered the last-line antimicrobial for the treatment of multidrug-resistant gram-negative bacterial infections. The emergence and spread of superbugs carrying the mobile colistin resistance gene (mcr) have become the most serious and urgent threat to healthcare. Here, we discover that silver (Ag⁺), including silver nanoparticles, could restore colistin efficacy against mcr-positive bacteria. We show that Ag⁺ inhibits the activity of the MCR-1 enzyme via substitution of Zn²⁺ in the active site. Unexpectedly, a tetra-silver center was found in the active-site pocket of MCR-1 as revealed by the X-ray structure of the Ag-bound MCR-1, resulting in the prevention of substrate binding. Moreover, Ag⁺ effectively slows down the development of higher-level resistance and reduces mutation frequency. Importantly, the combined use of Ag⁺ at a low concentration with colistin could relieve dermonecrotic lesions and reduce the bacterial load of mice infected with mcr-1–carrying pathogens. This study depicts a mechanism of Ag⁺ inhibition of MCR enzymes and demonstrates the potentials of Ag⁺ as broad-spectrum inhibitors for the treatment of mcr-positive bacterial infection in combination with colistin.

Co3 O4 Nanowires Capable of Discharging Low Voltage Electricity Showing Potent Antibacterial Activity for Treatment of Bacterial Skin Infection

Overuse of antibiotics has led to multidrug resistance in bacteria, posing a tremendous challenge to the healthcare system. There is an urgent need to explore unconventional strategies to overcome this issue. Herein, for the first time, we report a capacitive Co₃ O₄ nanowire (NW) electrode coated on flexible carbon cloth, which is capable of eliminating bacteria while discharging, for the treatment of skin infection. Benefiting from the unique NW-like morphology, the Co₃ O₄ NW electrode with increased active sites and enhanced capacitive property exhibits a prominent antibacterial effect against both Gram-positive and Gram-negative bacteria after charging at a low voltage of 2 V for 30 min. Furthermore, the electrode is demonstrated to be recharged for multiple antibacterial treatment cycles without significant change of antibacterial activity, allowing for practical use in a non-clinical setting. More importantly, this Co₃ O₄ NW electrode is capable of damaging bacterial cell membrane and inducing the accumulation of intracellular reactive oxygen species without impairing viability of skin keratinocytes. In a mouse model of bacterial skin infection, the Co₃ O₄ electrode shows significant therapeutic efficacy by eradicating colonized bacteria, thus accelerating the healing process of infected wounds. This nanostructured capacitive electrode provides an antibiotic-free, rechargeable, and wearable approach to treat bacterial skin infection.