Spatiotemporal dynamics of the proton motive force on single bacterial cells.

Electrochemical gradients across biological membranes are vital for cellular bioenergetics. In bacteria, the proton motive force (PMF) drives essential processes like adenosine triphosphate production and motility. Traditionally viewed as temporally and spatially stable, recent research reveals a dynamic PMF behavior at both single-cell and community levels. Moreover, the observed lateral segregation of respiratory complexes could suggest a spatial heterogeneity of the PMF. Using a light-activated proton pump and detecting the activity of the bacterial flagellar motor, we perturb and probe the PMF of single cells. Spatially homogeneous PMF perturbations reveal millisecond-scale temporal dynamics and an asymmetrical capacitive response. Localized perturbations show a rapid lateral PMF homogenization, faster than proton diffusion, akin to the electrotonic potential spread observed in passive neurons, explained by cable theory. These observations imply a global coupling between PMF sources and consumers along the membrane, precluding sustained PMF spatial heterogeneity but allowing for rapid temporal changes.

Development of novel indole-quinoline hybrid molecules targeting bacterial proton motive force.

AIMS: This study aimed to develop an editable structural scaffold for improving drug development, including pharmacokinetics and pharmacodynamics of antibiotics by using synthetic compounds derived from a (hetero)aryl-quinoline hybrid scaffold. METHODS AND RESULTS: In this study, 18 CF3-substituted (hetero)aryl-quinoline hybrid molecules were examined for their potential antibacterial activity against Staphylococcus aureus by determining minimal inhibitory concentrations. These 18 synthetic compounds represent modifications to key regions of the quinoline N-oxide scaffold, enabling us to conduct a structure-activity relationship analysis for antibacterial potency. Among the compounds, 3 m exhibited potency against with both methicillin resistant S. aureus strains, as well as other Gram-positive bacteria, including Enterococcus faecalis and Bacillus subtilis. We demonstrated that 3 m disrupted the bacterial proton motive force (PMF) through monitoring the PMF and conducting the molecular dynamics simulations. Furthermore, we show that this mechanism of action, disrupting PMF, is challenging for S. aureus to overcome. We also validated this PMF inhibition mechanism of 3 m in an Acinetobacter baumannii strain with weaken lipopolysaccharides. Additionally, in Gram-negative bacteria, we demonstrated that 3 m exhibited a synergistic effect with colistin that disrupts the outer membrane of Gram-negative bacteria. CONCLUSIONS: Our approach to developing editable synthetic novel antibacterials underscores the utility of CF3-substituted (hetero)aryl-quinoline scaffold for designing compounds targeting the bacterial proton motive force, and for further drug development, including pharmacokinetics and pharmacodynamics.

The effect of in vitro simulated colonic pH gradients on microbial activity and metabolite production using common prebiotics as substrates.

BACKGROUND: The interplay between gut microbiota (GM) and the metabolization of dietary components leading to the production of short-chain fatty acids (SCFAs) is affected by a range of factors including colonic pH and carbohydrate source. However, there is still only limited knowledge on how the GM activity and metabolite production in the gastrointestinal tract could be influenced by pH and the pH gradient increases along the colon. RESULTS: Here we investigate the effect of pH gradients corresponding to levels typically found in the colon on GM composition and metabolite production using substrates inulin, lactose, galactooligosaccharides (GOS), and fructooligosaccharide (FOS) in an in vitro colon setup. We investigated 3 different pH regimes (low, 5.2 increasing to 6.4; medium, 5.6 increasing to 6.8 and high, 6.0 increasing to 7.2) for each fecal inoculum and found that colonic pH gradients significantly influenced in vitro simulated GM structure, but the influence of fecal donor and substrate was more pronounced. Low pH regimes strongly influenced GM with the decreased relative abundance of Bacteroides spp. and increased Bifidobacterium spp. Higher in vitro simulated colonic pH promoted the production of SCFAs in a donor- and substrate-dependent manner. The butyrate producer Butyricimonas was enriched at higher pH conditions, where also butyrate production was increased for inulin. The relative abundance of Phascolarctobacterium, Bacteroides, and Rikenellaceae also increased at higher colonic pH, which was accompanied by increased production of propionate with GOS and FOS as substrates. CONCLUSIONS: Together, our results show that colonic substrates such as dietary fibres influence GM composition and metabolite production, not only by being selectively utilized by specific microbes, but also because of their SCFA production, which in turn also influences colonic pH and overall GM composition and activity. Our work provides details about the effect of the gradients of rising pH from the proximal to distal colon on fermenting dietary substrates in vitro and highlights the importance of considering pH in GM research.

Macromolecular condensation organizes nucleolar sub-phases to set up a pH gradient.

Nucleoli are multicomponent condensates defined by coexisting sub-phases. We identified distinct intrinsically disordered regions (IDRs), including acidic (D/E) tracts and K-blocks interspersed by E-rich regions, as defining features of nucleolar proteins. We show that the localization preferences of nucleolar proteins are determined by their IDRs and the types of RNA or DNA binding domains they encompass. In vitro reconstitutions and studies in cells showed how condensation, which combines binding and complex coacervation of nucleolar components, contributes to nucleolar organization. D/E tracts of nucleolar proteins contribute to lowering the pH of co-condensates formed with nucleolar RNAs in vitro. In cells, this sets up a pH gradient between nucleoli and the nucleoplasm. By contrast, juxta-nucleolar bodies, which have different macromolecular compositions, featuring protein IDRs with very different charge profiles, have pH values that are equivalent to or higher than the nucleoplasm. Our findings show that distinct compositional specificities generate distinct physicochemical properties for condensates.

Regulation of metabolism and proton motive force generation during mixed carbon fermentation by an Escherichia coli strain lacking the FOF1-ATPase.

Proton FOF1-ATPase is the key enzyme in E. coli under fermentative conditions. In this study the role of E. coli proton ATPase in the µ and formation of metabolic pathways during the fermentation of mixture of glucose, glycerol and formate using the DK8 (lacking FOF1) mutant strain was investigated. It was shown that the contribution of FOF1-ATPase in the specific growth rate was ∼45 %. Formate was not taken up in the DK8 strain during the initial hours of the growth. The utilization rates of glucose and glycerol were unchanged in DK8, however, the production of succinate, lactate and ethanol was decreased causing a reduction of the redox state up to -450 mV. Moreover, the contribution of FOF1-ATPase in the interplay between H+ and H2 cycles was described depending on the bacterial growth phase and main utilizing substrate. Besides, the H2 production rate in the DK8 strain was decreased by ∼60 % at 20 h and was absent at 72 h. Δp was decreased from -157 ± 4.8 mV to -140 ± 4.2 mV at 20 h and from -195 ± 5.9 mV to -148 ± 4.4 mV at 72 h, compared to WT. Taken together it can be concluded that during fermentation of mixed carbon sources metabolic cross talk between FOF1-ATPase-TrkA-Hyd-Fdh-H is taking place for maintaining the cell energy balance via regulation proton motive force.

Intoxication of antibiotic persisters by host RNS inactivates their efflux machinery during infection.

The host environment is of critical importance for antibiotic efficacy. By impacting bacterial machineries, stresses encountered by pathogens during infection promote the formation of phenotypic variants that are transiently insensitive to the action of antibiotics. It is assumed that these recalcitrant bacteria-termed persisters-contribute to antibiotic treatment failure and relapsing infections. Recently, we demonstrated that host reactive nitrogen species (RNS) transiently protect persisters against the action of ß-lactam antibiotics by delaying their regrowth within host cells. Here, we discovered that RNS intoxication of persisters also collaterally sensitizing them to fluoroquinolones during infection, explaining the higher efficiency of fluoroquinolones against intramacrophage Salmonella. By reducing bacterial respiration and the proton-motive force, RNS inactivate the AcrAB efflux machinery of persisters, facilitating the accumulation of fluoroquinolones intracellularly. Our work shows that target inactivity is not the sole reason for Salmonella persisters to withstand antibiotics during infection, with active efflux being a major contributor to survival. Thus, understanding how the host environment impacts persister physiology is critical to optimize antibiotics efficacy during infection.

Transmembrane pH gradient imaging in rodent glioma models.

A unique feature of the tumor microenvironment is extracellular acidosis in relation to intracellular milieu. Metabolic reprogramming in tumors results in overproduction of H+ ions (and lactate), which are extruded from the cells to support tumor survival and progression. As a result, the transmembrane pH gradient (ΔpH), representing the difference between intracellular pH (pHi) and extracellular pH (pHe), is posited to be larger in tumors compared with normal tissue. Controlling the transmembrane pH difference has promise as a potential therapeutic target in cancer as it plays an important role in regulating drug delivery into cells. The current study shows successful development of an MRI/MRSI-based technique that provides ΔpH imaging at submillimeter resolution. We applied this technique to image ΔpH in rat brains with RG2 and U87 gliomas, as well as in mouse brains with GL261 gliomas. pHi was measured with Amine and Amide Concentration-Independent Detection (AACID), while pHe was measured with Biosensor Imaging of Redundant Deviation in Shifts (BIRDS). The results indicate that pHi was slightly higher in tumors (7.40-7.43 in rats, 7.39-7.47 in mice) compared with normal brain (7.30-7.38 in rats, 7.32-7.36 in mice), while pHe was significantly lower in tumors (6.62-6.76 in rats, 6.74-6.84 in mice) compared with normal tissue (7.17-7.22 in rats, 7.20-7.21 in mice). As a result, ΔpH was higher in tumors (0.64-0.81 in rats, 0.62-0.65 in mice) compared with normal brain (0.13-0.16 in rats, 0.13-0.16 in mice). This work establishes an MRI/MRSI-based platform for ΔpH imaging at submillimeter resolution in gliomas.

Elevated proton motive force is a tetracycline resistance mechanism that leads to the sensitivity to gentamicin in Edwardsiella tarda.

Tetracycline is a commonly used human and veterinary antibiotic that is mostly discharged into environment and thereby tetracycline-resistant bacteria are widely isolated. To combat these resistant bacteria, further understanding for tetracycline resistance mechanisms is needed. Here, GC-MS based untargeted metabolomics with biochemistry and molecular biology techniques was used to explore tetracycline resistance mechanisms of Edwardsiella tarda. Tetracycline-resistant E. tarda (LTB4-RTET ) exhibited a globally repressed metabolism against elevated proton motive force (PMF) as the most characteristic feature. The elevated PMF contributed to the resistance, which was supported by the three results: (i) viability was decreased with increasing PMF inhibitor carbonylcyanide-3-chlorophenylhydrazone; (ii) survival is related to PMF regulated by pH; (iii) LTB4-RTET were sensitive to gentamicin, an antibiotic that is dependent upon PMF to kill bacteria. Meanwhile, gentamicin-resistant E. tarda with low PMF are sensitive to tetracycline is also demonstrated. These results together indicate that the combination of tetracycline with gentamycin will effectively kill both gentamycin and tetracycline resistant bacteria. Therefore, the present study reveals a PMF-enhanced tetracycline resistance mechanism in LTB4-RTET and provides an effective approach to combat resistant bacteria.

Molecular Genetic Dissection of the Regulatory Network of Proton Motive Force in Chloroplasts.

The proton motive force (pmf) generated across the thylakoid membrane rotates the Fo-ring of ATP synthase in chloroplasts. The pmf comprises two components: membrane potential (∆Ψ) and proton concentration gradient (∆pH). Acidification of the thylakoid lumen resulting from ∆pH downregulates electron transport in the cytochrome b6f complex. This process, known as photosynthetic control, is crucial for protecting photosystem I (PSI) from photodamage in response to fluctuating light. To optimize the balance between efficient photosynthesis and photoprotection, it is necessary to regulate pmf. Cyclic electron transport around PSI and pseudo-cyclic electron transport involving flavodiiron proteins contribute to the modulation of pmf magnitude. By manipulating the ratio between the two components of pmf, it is possible to modify the extent of photosynthetic control without affecting the pmf size. This adjustment can be achieved by regulating the movement of ions (such as K+ and Cl-) across the thylakoid membrane. Since ATP synthase is the primary consumer of pmf in chloroplasts, its activity must be precisely regulated to accommodate other mechanisms involved in pmf optimization. Although fragments of information about each regulatory process have been accumulated, a comprehensive understanding of their interactions is lacking. Here, I summarize current knowledge of the network for pmf regulation, mainly based on genetic studies.

A hairpin-contained i-motif guided DNA nanoantenna for sensitive and specific sensing of tumor extracellular pH gradients.

Antenna, as a converter, could receive and convert signals from the outside world flexibly. Inspired by the behavior of antennas receiving external signals, we developed a pH-stimulated and aptamer-anchored Y-shaped DNA nanoantenna (termed pH-Apt-YNA) for sensitive and specific sensing of tumor extracellular pH gradients. The nanoantenna consisted of three functional nucleic acid sequences, an I-strand, Apt-Y-R and Y-L-G, where the I-strand endowed the DNA nanoantenna with the ability to receive and convert signals, the Apt-Y-R containing an aptamer fragment gave the DNA nanoantenna the ability to specifically anchor target tumor cells, and the complementarity of Y-L-G with the other two sequences ensured the stability of the DNA nanoantenna. Initially, the DNA nanoantenna was in a "silent" state, and rhodamine green was close to BHQ2, leading to suppressed signal emission. When the DNA nanoantenna anchored on the surface of target cancer cells through the aptamer recognition domain, the I-strand tended to fold into a hairpin-contained i-motif tetramer structure owing to the extracellular low pH stimuli, resulting in the DNA nanoantenna changing into an "active" state. In the meantime, rhodamine green moved far away from BHQ2, resulting in a strong signal output. The results demonstrate that the pH-Apt-YNA presents a sensitive pH sensing capacity within a narrow pH range of 6.2-7.4 and exhibits excellent specificity for the imaging of target cancer cell extracellular pH. Based on these advantages, we therefore anticipate that our facile design of the DNA nanoantenna with sensitive responsiveness provides a new way and great promise in the application of sensing pH-related physiological and pathological processes.

Responses of root characteristics and nitrogen absorption and assimilation to different pH gradients of winter wheat at seedling stage.

Nitrogen (N) and rhizosphere pH are the two main factors restricting the growth of winter wheat (Triticum aestivum L.) in North China Plain. Soil nutrient availability is affected by soil acidity and alkalinity. In order to understand the effect of rhizosphere pH value on wheat nitrogen metabolism and the response of wheat growth to pH value at seedling stage, winter wheat varieties 'Aikang 58' (AK58) and 'Bainong 4199' (BN4199) were tested in hydroponics under three pH treatments (pH = 4.0, 6.5, and 9.0). The results showed that the accumulation of dry matter in root and above ground under pH 4.0 and pH 9.0 treatments was lower than that under pH 6.5 treatments, and the root/shoot ratio increased with the increase of pH value. Regardless of pH value, 'BN4199' had higher root dry weight, root length, root surface area, root activity and root tip than 'AK58'. Therefore, wheat that is tolerant to extreme pH is able to adapt to the acid-base environment by changing root characteristics. At pH 4.0, the net H+ outflow rate of wheat roots was significantly lower than that of the control group, and the net NO3- flux of wheat roots was also low. The net H+ outflow occurred at pH 6.5 and 9.0, and at the same time, the net NO3- flux of roots also increased, and both increased with the increase of pH. The activity of nitrate reductase (NR) in stem of pH 9.0 treatment was significantly higher than that of other treatments, while the activity of glutamine synthetase (GS) in root and stem of pH 6.5 treatment was significantly higher than that of other treatments. Under pH 4.0 and pH 9.0 treatments, the activities of NR and GS in 'BN4199' were higher than those in 'AK58', The root respiration of 'BN4199' was significantly higher than that of 'AK58' under pH 4.0 and pH 9.0 treatment, and 'BN4199' had higher NO3- net flux, key enzyme activity of root nitrogen metabolism and root respiration. Therefore, we believe that 'BN4199' has strong resistance ability to extreme pH stress, and high root/shoot ratio and strong root respiration can be used as important indicators for wheat variety screening adapted to the alkaline environment at the seedling stage.

Bacterial genome size and gene functional diversity negatively correlate with taxonomic diversity along a pH gradient.

Bacterial gene repertoires reflect adaptive strategies, contribute to ecosystem functioning and are limited by genome size. However, gene functional diversity does not necessarily correlate with taxonomic diversity because average genome size may vary by community. Here, we analyse gene functional diversity (by shotgun metagenomics) and taxonomic diversity (by 16S rRNA gene amplicon sequencing) to investigate soil bacterial communities along a natural pH gradient in 12 tropical, subtropical, and temperate forests. We find that bacterial average genome size and gene functional diversity decrease, whereas taxonomic diversity increases, as soil pH rises from acid to neutral; as a result, bacterial taxonomic and functional diversity are negatively correlated. The gene repertoire of acid-adapted oligotrophs is enriched in functions of signal transduction, cell motility, secretion system, and degradation of complex compounds, while that of neutral pH-adapted copiotrophs is enriched in functions of energy metabolism and membrane transport. Our results indicate that a mismatch between taxonomic and functional diversity can arise when environmental factors (such as pH) select for adaptive strategies that affect genome size distributions.

Antibody sequence-based prediction of pH gradient elution in multimodal chromatography.

Multimodal chromatography has emerged as a promising technique for antibody purification, owing to its capacity to selectively capture and separate target molecules. However, the optimization of chromatography parameters remains a challenge due to the intricate nature of protein-ligand interactions. To tackle this issue, efficient predictive tools are essential for the development and optimization of multimodal chromatography processes. In this study, we introduce a methodology that predicts the elution behavior of antibodies in multimodal chromatography based on their amino acid sequences. We analyzed a total of 64 full-length antibodies, including IgG1, IgG4, and IgG-like multispecific formats, which were eluted using linear pH gradients from pH 9.0 to 4.0 on the anionic mixed-mode resin Capto adhere. Homology models were constructed, and 1312 antibody-specific physicochemical descriptors were calculated for each molecule. Our analysis identified six key structural features of the multimodal antibody interaction, which were correlated with the elution behavior, emphasizing the antibody variable region. The results show that our methodology can predict pH gradient elution for a diverse range of antibodies and antibody formats, with a test set R² of 0.898. The developed model can inform process development by predicting initial conditions for multimodal elution, thereby reducing trial and error during process optimization. Furthermore, the model holds the potential to enable an in silico manufacturability assessment by screening target antibodies that adhere to standardized purification conditions. In conclusion, this study highlights the feasibility of using structure-based prediction to enhance antibody purification in the biopharmaceutical industry. This approach can lead to more efficient and cost-effective process development while increasing process understanding.

pH gradients guide ADF/cofilin isoforms in pollen tubes.

In a recent study, Wang et al. (https://doi.org/10.1083/jcb.202206074) demonstrate that subtle differences between two ADF/cofilin isoforms allow fine spatial regulation of the actin cytoskeleton in pollen tubes. This article illustrates how two similar proteins have progressively evolved to adapt their localization and activity according to the cellular environment.

A real-time analysis of protein transport via the twin arginine translocation pathway in response to different components of the protonmotive force.

The twin arginine translocation (Tat) pathway transports folded protein across the cytoplasmic membrane in bacteria, archaea, and across the thylakoid membrane in plants as well as the inner membrane in some mitochondria. In plant chloroplasts, the Tat pathway utilizes the protonmotive force (PMF) to drive protein translocation. However, in bacteria, it has been shown that Tat transport depends only on the transmembrane electrical potential (Δψ) component of PMF in vitro. To investigate the comprehensive PMF requirement in Escherichia coli, we have developed the first real-time assay to monitor Tat transport utilizing the NanoLuc Binary Technology in E. coli spheroplasts. This luminescence assay allows for continuous monitoring of Tat transport with high-resolution, making it possible to observe subtle changes in transport in response to different treatments. By applying the NanoLuc assay, we report that, under acidic conditions (pH = 6.3), ΔpH, in addition to Δψ, contributes energetically to Tat transport in vivo in E. coli spheroplasts. These results provide novel insight into the mechanism of energy utilization by the Tat pathway.

Model of membrane deformations driven by a surface pH gradient.

Many cellular organelles are membrane-bound structures with complex membrane composition and shape. Their shapes have been observed to depend on the metabolic state of the organelle and the mechanisms that couple biochemical pathways and membrane shape are still actively investigated. Here, we study a model coupling inhomogeneities in the lipid composition and membrane geometry via a generalized Helfrich free energy. We derive the resulting stress tensor, the Green's function for a tubular membrane, and compute the phase diagram of the induced deformations. We then apply this model to study the deformation of mitochondria cristae described as membrane tubes supporting a pH gradient at its surface. This gradient in turn controls the lipid composition of the membrane via the protonation or deprotonation of cardiolipins, which are acid-based lipids known to be crucial for mitochondria shape and functioning. Our model predicts the appearance of tube deformations resembling the observed shape changes of cristea when submitted to a proton gradient.

Differential sensitivity of ADF isovariants to a pH gradient promotes pollen tube growth.

The actin cytoskeleton is one of the targets of the pH gradient in tip-growing cells, but how cytosolic pH regulates the actin cytoskeleton remains largely unknown. We here demonstrate that Arabidopsis ADF7 and ADF10 function optimally at different pH levels when disassembling actin filaments. This differential pH sensitivity allows ADF7 and ADF10 to respond to the cytosolic pH gradient to regulate actin dynamics in pollen tubes. ADF7 is an unusual actin-depolymerizing factor with a low optimum pH in in vitro actin depolymerization assays. ADF7 plays a dominant role in promoting actin turnover at the pollen tube apex. ADF10 has a typically high optimum pH in in vitro assays and plays a dominant role in regulating the turnover and organization of subapical actin filaments. Thus, functional specification and cooperation of ADF isovariants with different pH sensitivities enable the coordination of the actin cytoskeleton with the cytosolic pH gradient to support pollen tube growth.

SPI-1 virulence gene expression modulates motility of Salmonella Typhimurium in a proton motive force- and adhesins-dependent manner.

Both the bacterial flagellum and the evolutionary related injectisome encoded on the Salmonella pathogenicity island 1 (SPI-1) play crucial roles during the infection cycle of Salmonella species. The interplay of both is highlighted by the complex cross-regulation that includes transcriptional control of the flagellar master regulatory operon flhDC by HilD, the master regulator of SPI-1 gene expression. Contrary to the HilD-dependent activation of flagellar gene expression, we report here that activation of HilD resulted in a dramatic loss of motility, which was dependent on the presence of SPI-1. Single cell analyses revealed that HilD-activation triggers a SPI-1-dependent induction of the stringent response and a substantial decrease in proton motive force (PMF), while flagellation remains unaffected. We further found that HilD activation enhances the adhesion of Salmonella to epithelial cells. A transcriptome analysis revealed a simultaneous upregulation of several adhesin systems, which, when overproduced, phenocopied the HilD-induced motility defect. We propose a model where the SPI-1-dependent depletion of the PMF and the upregulation of adhesins upon HilD-activation enable flagellated Salmonella to rapidly modulate their motility during infection, thereby enabling efficient adhesion to host cells and delivery of effector proteins.

Bacterial proton motive force as an unprecedented target to control antimicrobial resistance.

Novel antibacterial therapies are urgently required to tackle the increasing number of multidrug-resistant pathogens. Identification of new antimicrobial targets is critical to avoid possible cross-resistance issues. Bacterial proton motive force (PMF), an energetic pathway located on the bacterial membrane, crucially regulates various biological possesses such as adenosine triphosphate synthesis, active transport of molecules, and rotation of bacterial flagella. Nevertheless, the potential of bacterial PMF as an antibacterial target remains largely unexplored. The PMF generally comprises electric potential (ΔΨ) and transmembrane proton gradient (ΔpH). In this review, we present an overview of bacterial PMF, including its functions and characterizations, highlighting the representative antimicrobial agents that specifically target either ΔΨ or ΔpH. At the same time, we also discuss the adjuvant potential of bacterial PMF-targeting compounds. Lastly, we highlight the value of PMF disruptors in preventing the transmission of antibiotic resistance genes. These findings suggest that bacterial PMF represents an unprecedented target, providing a comprehensive approach to controlling antimicrobial resistance.

Armeniaspirol analogues disrupt the electrical potential (ΔΨ) of the proton motive force.

The armeniaspirol family of natural product antibiotics have been shown to inhibit the ATP-dependent proteases ClpXP and ClpYQ and disrupt membrane potential through shuttling of protons across the membrane. Herein we investigate their ability to disrupt the proton motive force (PMF). We show, using a voltage sensitive, that armeniaspiols disrupt the electrical membrane potential (ΔΨ) component of the PMF and not the transmembrane proton gradient (ΔpH). Using checkerboard assays, we confirm this by showing antagonism, with kanamycin, an antibiotic that required ΔΨ for penetration. By evaluating the antibiotic activity and disruption of the PMF by sixteen armeniaspirol analogs, we find that disruption of the PMF is necessary but not sufficient for antibiotic activity. Analogs that are potent disruptors of the PMF without possessing the ability to inhibit ClpXP and ClpYQ are not potent antibiotics. Thus we propose that the armeniaspirols utilize a dual mechanism of action where they disrupt PMF and inhibit the ATP-dependent proteases ClpXP and ClpYQ. This type of dual mechanism has been observed in other natural product-based antibiotics, most notably chelocardin.