Daptomycin Pore Formation Is Restricted by Lipid Acyl Chain Composition

Defective pgsA contributes to increased membrane fluidity and cell wall thickening in Staphylococcus aureus with high-level daptomycin resistance

Daptomycin is a membrane-targeting last-resort antimicrobial therapeutic for the treatment of infections caused by methicillin- and/or vancomycin-resistant Staphylococcus aureus. In the rare event of failed daptomycin therapy, the source of resistance is often attributable to mutations directly within the membrane phospholipid biosynthetic pathway of S. aureus or in the regulatory systems that control cell envelope response and membrane homeostasis. Here we describe the structural changes to the cell envelope in a daptomycin-resistant isolate of S. aureus strain N315 that has acquired mutations in the genes most commonly reported associated with daptomycin resistance: mprF, yycG, and pgsA. In addition to the decreased phosphatidylglycerol (PG) levels that are the hallmark of daptomycin resistance, the mutant with high-level daptomycin resistance had increased branched-chain fatty acids (BCFAs) in its membrane lipids, increased membrane fluidity, and increased cell wall thickness. However, the successful utilization of isotope-labeled straight-chain fatty acids (SCFAs) in lipid synthesis suggested that the aberrant BCFA:SCFA ratio arose from upstream alteration in fatty acid synthesis rather than a structural preference in PgsA. Transcriptomics studies revealed that expression of pyruvate dehydrogenase (pdhB) was suppressed in the daptomycin-resistant isolate, which is known to increase BCFA levels. While complementation with an additional copy of pdhB had no effect, complementation of the pgsA mutation resulted in increased PG formation, reduction in cell wall thickness, restoration of normal BCFA levels, and increased daptomycin susceptibility. Collectively, these results demonstrate that pgsA contributes to daptomycin resistance through its influence on membrane fluidity and cell wall thickness, in addition to phosphatidylglycerol levels.

IMPORTANCE

The cationic lipopeptide antimicrobial daptomycin has become an essential tool for combating infections with Staphylococcus aureus that display reduced susceptibility to β-lactams or vancomycin. Since daptomycin's activity is based on interaction with the negatively charged membrane of S. aureus, routes to daptomycin-resistance occur through mutations in the lipid biosynthetic pathway surrounding phosphatidylglycerols and the regulatory systems that control cell envelope homeostasis. Therefore, there are many avenues to achieve daptomycin resistance and several different, and sometimes contradictory, phenotypes of daptomycin-resistant S. aureus, including both increased and decreased cell wall thickness and membrane fluidity. This study is significant because it demonstrates the unexpected influence of a lipid biosynthesis gene, pgsA, on membrane fluidity and cell wall thickness in S. aureus with high-level daptomycin resistance.

Defective pgsA contributes to increased membrane fluidity and cell wall thickening in S. aureus with high-level daptomycin resistance

Daptomycin is a membrane-targeting last-resort antimicrobial therapeutic for the treatment of infections caused by methicillin- and/or vancomycin-resistant Staphylococcus aureus. In the rare event of failed daptomycin therapy, the source of resistance is often attributable to mutations directly within the membrane phospholipid biosynthetic pathway of S. aureus or in the regulatory systems that control cell envelope response and membrane homeostasis. Here we describe the structural changes to the cell envelope in a daptomycin-resistant isolate of S. aureus strain N315 that has acquired mutations in the genes most commonly reported associated with daptomycin-resistance: mprF, yycG, and pgsA. In addition to the decreased phosphatidylglycerol (PG) levels that are the hallmark of daptomycin-resistance, the mutant with high-level daptomycin resistance had increased branched-chain fatty acids (BCFAs) in its membrane lipids, increased membrane fluidity, and increased cell wall thickness. However, the successful utilization of isotope-labeled straight-chain fatty acids (SCFAs) in lipid synthesis suggested that the aberrant BCFA:SCFA ratio arose from upstream alteration in fatty acid synthesis rather than a structural preference in PgsA. RT-qPCR studies revealed that expression of pyruvate dehydrogenase (pdhB) was suppressed in the daptomycin-resistant isolate, which is known to increase BCFA levels. While complementation with an additional copy of pdhB had no effect, complementation of the pgsA mutation resulted in increased PG formation, reduction in cell wall thickness, restoration of normal BCFA levels, and increased daptomycin susceptibility. Collectively, these results demonstrate that pgsA contributes to daptomycin resistance through its influence on membrane fluidity and cell wall thickness, in addition to phosphatidylglycerol levels.

Lipid-Centric Approaches in Combating Infectious Diseases: Antibacterials, Antifungals and Antivirals with Lipid-Associated Mechanisms of Action

One of the global challenges of the 21st century is the increase in mortality from infectious diseases against the backdrop of the spread of antibiotic-resistant pathogenic microorganisms. In this regard, it is worth targeting antibacterials towards the membranes of pathogens that are quite conservative and not amenable to elimination. This review is an attempt to critically analyze the possibilities of targeting antimicrobial agents towards enzymes involved in pathogen lipid biosynthesis or towards bacterial, fungal, and viral lipid membranes, to increase the permeability via pore formation and to modulate the membranes' properties in a manner that makes them incompatible with the pathogen's life cycle. This review discusses the advantages and disadvantages of each approach in the search for highly effective but nontoxic antimicrobial agents. Examples of compounds with a proven molecular mechanism of action are presented, and the types of the most promising pharmacophores for further research and the improvement of the characteristics of antibiotics are discussed. The strategies that pathogens use for survival in terms of modulating the lipid composition and physical properties of the membrane, achieving a balance between resistance to antibiotics and the ability to facilitate all necessary transport and signaling processes, are also considered.

Mechanistic insights into nanoparticle surface-bacterial membrane interactions in overcoming antibiotic resistance

Antimicrobial Resistance (AMR) raises a serious concern as it contributes to the global mortality by 5 million deaths per year. The overall impact pertaining to significant membrane changes, through broad spectrum drugs have rendered the bacteria resistant over the years. The economic expenditure due to increasing drug resistance poses a global burden on healthcare community and must be dealt with immediate effect. Nanoparticles (NP) have demonstrated inherent therapeutic potential or can serve as nanocarriers of antibiotics against multidrug resistant (MDR) pathogens. These carriers can mask the antibiotics and help evade the resistance mechanism of the bacteria. The targeted delivery can be fine-tuned through surface functionalization of Nanocarriers using aptamers, antibodies etc. This review covers various molecular mechanisms acquired by resistant bacteria towards membrane modification. Mechanistic insight on 'NP surface-bacterial membrane' interactions are crucial in deciding the role of NP as therapeutic. Finally, we highlight the potential accessible membrane targets for designing smart surface-functionalized nanocarriers which can act as bacteria-targeted robots over the existing clinically available antibiotics. As the bacterial strains around us continue to evolve into resistant versions, nanomedicine can offer promising and alternative tools in overcoming AMR.

The impact of lysyl-phosphatidylglycerol on the interaction of daptomycin with model membranes

Daptomycin is an important clinical antibiotic for which resistance is rising. Daptomycin resistant strains of S. aureus often have increased 1,2-diacyl-sn-glycero-3-[phospho-1-(3-lysyl(1-glycerol))] (lysyl-PG) and mutations to the proteins directly involved in the synthesis and translocation of lysyl-PG are implicated in resistance mechanisms. To study the interaction of daptomycin with lysyl-DMPG-containing model membranes a new stereospecific and regioselective synthesis of lysyl-DMPG was developed. Studies on model membranes containing lysyl-DMPG demonstrate that: (1) daptomycin is not significantly repelled by the cationic charge of lysyl-DMPG; (2) daptomycin binds less avidly to lysyl-DMPG compared to DMPG; (3) the presence of lysyl-DMPG does not impact the membrane bound backbone conformation of daptomycin in a significant way; (4) lysyl-DMPG increases oligomer formation; (5) lysyl-DMPG does not impact model membrane fluidity at lysyl-PG : PG ratios that are relevant to daptomycin resistance. The results of these studies suggest that increased lysyl-PG content does not confer resistance to daptomycin by altering membrane fluidity or reducing membrane affinity but may confer resistance by altering the structure of daptomycin oligomers.

Establishing the Structure-Activity Relationship between Phosphatidylglycerol and Daptomycin

Daptomycin is a clinical antibiotic used to treat serious infections caused by Gram-positive bacteria. Although there is debate about the action mechanism of daptomycin, it is known that daptomycin requires both calcium and phosphatidylglycerol (PG) to exert its antibacterial effect. Despite the importance and uniqueness of the interaction of daptomycin with PG, very little is known about this interaction or the nascent daptomycin-PG complex. In this work, we establish a structure-activity relationship between daptomycin and PG through the synthesis of PG analogues. In total, nine PGs were synthesized using a divergent approach employing phosphoramidite chemistry. The interaction between daptomycin and these PGs was studied using fluorescence, circular dichroism, and isothermal titration calorimetry. It was determined that daptomycin is highly sensitive to the modification of the headgroup of PG and both hydroxyl groups influence membrane binding, oligomerization, and backbone structure. Methylation of each hydroxyl in the headgroup suggests that the binding pocket envelops both hydroxyl groups. A PG acyl tail chain length of at least 7-8 carbons is required for stoichiometric binding at micromolar peptide concentrations. Daptomycin binds to PG having 8-carbon, linear, unsaturated acyl groups (C8PGs) at the micromolar concentration and interacts with C8PG in essentially the same manner as when the PG is incorporated into a liposome, and thus, preassembly of individual PG moieties is not a prerequisite for binding, structural transition, and oligomerization.

Lipid-mediated antimicrobial resistance: a phantom menace or a new hope?

The proposition of a post-antimicrobial era is all the more realistic with the continued rise of antimicrobial resistance. The development of new antimicrobials is failing to counter the ever-increasing rates of bacterial antimicrobial resistance. This necessitates novel antimicrobials and drug targets. The bacterial cell membrane is an essential and highly conserved cellular component in bacteria and acts as the primary barrier for entry of antimicrobials into the cell. Although previously under-exploited as an antimicrobial target, the bacterial cell membrane is attractive for the development of novel antimicrobials due to its importance in pathogen viability. Bacterial cell membranes are diverse assemblies of macromolecules built around a central lipid bilayer core. This lipid bilayer governs the overall membrane biophysical properties and function of its membrane-embedded proteins. This mini-review will outline the mechanisms by which the bacterial membrane causes and controls resistance, with a focus on alterations in the membrane lipid composition, chemical modification of constituent lipids, and the efflux of antimicrobials by membrane-embedded efflux systems. Thorough insight into the interplay between membrane-active antimicrobials and lipid-mediated resistance is needed to enable the rational development of new antimicrobials. In particular, the union of computational approaches and experimental techniques for the development of innovative and efficacious membrane-active antimicrobials is explored.

Development of Amphiphilic Coumarin Derivatives as Membrane-Active Antimicrobial Agents with Potent In Vivo Efficacy against Gram-Positive Pathogenic Bacteria

Increases in drug-resistant pathogens are becoming a serious detriment to human health. To combat pathogen infections, a new series of amphiphilic coumarin derivatives were designed and synthesized as antimicrobial agents with membrane-targeting action. We herein report a lead compound, 25, that displayed potent antibacterial activity against Gram-positive bacteria, including MRSA. Compound 25 exhibited weak hemolytic activity and low toxicity to mammalian cells and can kill Gram-positive bacteria quickly (within 0.5 h) by directly disrupting the bacterial cell membranes. Additionally, compound 25 demonstrated excellent efficacy in a murine corneal infection caused by Staphylococcus aureus. These results suggest that 25 has great potential to be a potent antimicrobial agent for treating drug-resistant Gram-positive bacterial infections.

High-speed atomic force microscopy highlights new molecular mechanism of daptomycin action

The increase in speed of the high-speed atomic force microscopy (HS-AFM) compared to that of the conventional AFM made possible the first-ever visualisation at the molecular-level of the activity of an antimicrobial peptide on a membrane. We investigated the medically prescribed but poorly understood lipopeptide Daptomycin under infection-like conditions (37 °C, bacterial lipid composition and antibiotic concentrations). We confirmed so far hypothetical models: Dap oligomerization and the existence of half pores. Moreover, we detected unknown molecular mechanisms: new mechanisms to form toroidal pores or to resist Dap action, and to unprecedently quantify the energy profile of interacting oligomers. Finally, the biological and medical relevance of the findings was ensured by a multi-scale multi-nativeness-from the molecule to the cell-correlation of molecular-level information from living bacteria (Bacillus subtilis strains) to liquid-suspended vesicles and supported-membranes using electron and optical microscopies and the lipid tension probe FliptR, where we found that the cells with a healthier state of their cell wall show smaller membrane deformations.

Physicochemical and Biological Characterization of Novel Membrane-Active Cationic Lipopeptides with Antimicrobial Properties

We have designed and synthesized new short lipopeptides composed of tetrapeptide conjugated to fatty acids with different chain lengths. The amino acid sequence of the peptide moiety included d-phenylalanine, two residues of l-2,4-diaminobutyric acid and l-leucine. To explore the possible mechanism of lipopeptide action, we have provided a physicochemical characterization of their interactions with artificial lipid membranes. For this purpose, we have used monolayers and bilayers composed of lipids representative of Gram-negative and Gram-positive bacterial membranes. Using surface pressure measurements and atomic force microscopy, we were able to monitor the changes occurring within the films upon exposure to lipopeptides. Our experiments revealed that all lipopeptides can penetrate the lipid membranes and affect their molecular ordering. The latter results in membrane thinning and fluidization. However, the effect is stronger in the lipid films mimicking Gram-positive bacterial membranes. The results of the physicochemical characterization were compared with the biological activity of lipopeptides. The effect of lipopeptides on bacterial growth was tested on several strains of bacteria. It was revealed that lipopeptides show stronger antimicrobial activity against Gram-positive bacteria. At the same time, all tested compounds display relatively low hemolytic activity.

Chemoenzymatic synthesis of daptomycin analogs active against daptomycin-resistant strains

Abstract

Daptomycin is a last resort antibiotic for the treatment of infections caused by many Gram-positive bacterial strains, including vancomycin-resistant Enterococcus (VRE) and methicillin- and vancomycin-resistant Staphylococcus aureus (MRSA and VRSA). However, the emergence of daptomycin-resistant strains of S. aureus and Enterococcus in recent years has renewed interest in synthesizing daptomycin analogs to overcome resistance mechanisms. Within this context, three aromatic prenyltransferases have been shown to accept daptomycin as a substrate, and the resulting prenylated analog was shown to be more potent against Gram-positive strains than the parent compound. Consequently, utilizing prenyltransferases to derivatize daptomycin offered an attractive alternative to traditional synthetic approaches, especially given the molecule’s structural complexity. Herein, we report exploiting the ability of prenyltransferase CdpNPT to synthesize alkyl-diversified daptomycin analogs in combination with a library of synthetic non-native alkyl-pyrophosphates. The results revealed that CdpNPT can transfer a variety of alkyl groups onto daptomycin’s tryptophan residue using the corresponding alkyl-pyrophosphates, while subsequent scaled-up reactions suggested that the enzyme can alkylate the N1, C2, C5, and C6 positions of the indole ring. In vitro antibacterial activity assays using 16 daptomycin analogs revealed that some of the analogs displayed 2–80-fold improvements in potency against MRSA, VRE, and daptomycin-resistant strains of S. aureus and Enterococcus faecalis. Thus, along with the new potent analogs, these findings have established that the regio-chemistry of alkyl substitution on the tryptophan residue can modulate daptomycin’s potency. With additional protein engineering to improve the regio-selectivity, the described method has the potential to become a powerful tool for diversifying complex indole-containing molecules.

Key points

• CdpNPT displays impressive donor promiscuity with daptomycin as the acceptor.

• CdpNPT catalyzes N1-, C2-, C5-, and C6-alkylation on daptomycin’s tryptophan residue.

• Differential alkylation of daptomycin’s tryptophan residue modulates its activity.

Electronic supplementary material

The online version of this article (10.1007/s00253-020-10790-x) contains supplementary material, which is available to authorized users.

Physicochemical Characterization of Daptomycin Interaction with Negatively Charged Lipid Membranes

Daptomycin is known as an effective antibiotic lipopeptide which shows activity against the number of Gram-positive pathogens. Its primary target is the bacterial cell membrane. However, the detailed mechanism of daptomycin action is still subject to debate. In this paper, we have investigated the interactions between lipopeptide and model lipid films composed of negatively charged phosphatidylglycerols and cardiolipin. In order to evaluate the effect of daptomycin on the molecular organization and the properties of lipid assemblies, we have used surface pressure measurements and electrochemical methods combined with atomic force microscopy, quartz crystal microbalance, and surface-enhanced infrared absorption spectroscopy. Our results indicate that daptomycin interaction with the lipid membrane is complex. It involves daptomycin aggregation and partial insertion, which in turn affect the charge distribution on both sides of the membrane and may result in a gradient of water chemical potential. The latter can drive the flux of water across the membrane.

Characterization of multimeric daptomycin bound to lipid nanodiscs formed by calcium-tolerant styrene-maleic acid copolymer

Daptomycin is a lipopeptide antibiotic that is important in the treatment of infections with Gram-positive bacteria. In the presence of calcium, daptomycin binds to phosphatidylglycerol in the bacterial cytoplasmic membrane and then forms oligomers that mediate its bactericidal effect. The structure of these bactericidal oligomers has not been elucidated. We here explore the feasibility of structural studies on the oligomer by solution-state NMR. To this end, we use nanodiscs that contain DMPC and DMPG, stabilized with a styrene-maleic acid copolymer that has been modified to minimize calcium chelation. We show that these nanodiscs bind daptomycin and induce the formation of stable oligomers under physiologically relevant conditions. The findings suggest that this membrane model is suitable for structural and functional characterization of oligomeric daptomycin, and possibly of other calcium-dependent lipopeptide antibiotics. We show that these nanodiscs bind daptomycin and induce the formation of stable oligomers, under conditions that are suitable for biomolecular NMR. The findings suggest that this membrane model is suitable for structural elucidation of oligomeric daptomycin, and possibly of other calcium-dependent lipopeptide antibiotics.

More Than a Pore: A Current Perspective on the In Vivo Mode of Action of the Lipopeptide Antibiotic Daptomycin

Daptomycin is a cyclic lipopeptide antibiotic, which was discovered in 1987 and entered the market in 2003. To date, it serves as last resort antibiotic to treat complicated skin infections, bacteremia, and right-sided endocarditis caused by Gram-positive pathogens, most prominently methicillin-resistant Staphylococcus aureus. Daptomycin was the last representative of a novel antibiotic class that was introduced to the clinic. It is also one of the few membrane-active compounds that can be applied systemically. While membrane-active antibiotics have long been limited to topical applications and were generally excluded from systemic drug development, they promise slower resistance development than many classical drugs that target single proteins. The success of daptomycin together with the emergence of more and more multi-resistant superbugs attracted renewed interest in this compound class. Studying daptomycin as a pioneering systemic membrane-active compound might help to pave the way for future membrane-targeting antibiotics. However, more than 30 years after its discovery, the exact mechanism of action of daptomycin is still debated. In particular, there is a prominent discrepancy between in vivo and in vitro studies. In this review, we discuss the current knowledge on the mechanism of daptomycin against Gram-positive bacteria and try to offer explanations for these conflicting observations.

Dynamic coupling of a hydration layer to a fluid phospholipid membrane: intermittency and multiple time-scale relaxations

Understanding the coupling of a hydration layer and a lipid membrane is crucial to gaining access to membrane dynamics and understanding its functionality towards various biological processes.

Multifunctional Pharmaceutical Effects of the Antibiotic Daptomycin

Daptomycin (DAP), a cyclic lipopeptide produced by Streptomyces roseosporus, is a novel antibiotic to clinically treat various Gram-positive pathogenic bacteria-induced infections. Although DAP has a strong broad-spectrum bactericidal effect, recently rare bacterial antibiotic resistance against DAP gradually arises. The review is to summarize the normal indications of DAP, its off-label usage against several clinical pathogen infections, the unique antibacterial mechanisms of DAP, and the combination of antibiotic therapies for highly DAP-resistant pathogens. More noticeably, rising evidences demonstrate that DAP has new potential activity of anticancer and immunomodulatory effects. So far the multifunctional pharmaceutical effects of DAP deserve to be further explored for future clinical applications.

Role of Lipid Composition, Physicochemical Interactions, and Membrane Mechanics in the Molecular Actions of Microbial Cyclic Lipopeptides

Several experimental and theoretical studies have extensively investigated the effects of a large diversity of antimicrobial peptides (AMPs) on model lipid bilayers and living cells. Many of these peptides disturb cells by forming pores in the plasma membrane that eventually lead to the cell death. The complexity of these peptide-lipid interactions is mainly related to electrostatic, hydrophobic and topological issues of these counterparts. Diverse studies have shed some light on how AMPs act on lipid bilayers composed by different phospholipids, and how mechanical properties of membranes could affect the antimicrobial effects of such compounds. On the other hand, cyclic lipopeptides (cLPs), an important class of microbial secondary metabolites, have received comparatively less attention. Due to their amphipathic structures, cLPs exhibit interesting biological activities including interactions with biofilms, anti-bacterial, anti-fungal, antiviral, and anti-tumoral properties, which deserve more investigation. Understanding how physicochemical properties of lipid bilayers contribute and determining the antagonistic activity of these secondary metabolites over a broad spectrum of microbial pathogens could establish a framework to design and select effective strategies of biological control. This implies unravelling-at the biophysical level-the complex interactions established between cLPs and lipid bilayers. This review presents, in a systematic manner, the diversity of lipidated antibiotics produced by different microorganisms, with a critical analysis of the perturbing actions that have been reported in the literature for this specific set of membrane-active lipopeptides during their interactions with model membranes and in vivo. With an overview on the mechanical properties of lipid bilayers that can be experimentally determined, we also discuss which parameters are relevant in the understanding of those perturbation effects. Finally, we expose in brief, how this knowledge can help to design novel strategies to use these biosurfactants in the agronomic and pharmaceutical industries.

Daptomycin Pore Formation and Stoichiometry Depend on Membrane Potential of Target Membrane

Daptomycin is a calcium-dependent lipodepsipeptide antibiotic clinically used to treat serious infections caused by Gram-positive pathogens. Its precise mode of action is somewhat controversial; the biggest issue is daptomycin pore formation, which we directly investigated here. We first performed a screening experiment using propidium iodide (PI) entry to Bacillus subtilis cells and chose the optimum and therapeutically relevant conditions (10 µg/ml daptomycin and 1.25 mM CaCl₂) for the subsequent analyses. Using conductance measurements on planar lipid bilayers, we show that daptomycin forms nonuniform oligomeric pores with conductance ranging from 120 pS to 14 nS. The smallest conductance unit is probably a dimer; however, tetramers and pentamers occur in the membrane most frequently. Moreover, daptomycin pore-forming activity is exponentially dependent on the applied membrane voltage. We further analyzed the membrane-permeabilizing activity in B. subtilis cells using fluorescence methods [PI and DiSC₃(5)]. Daptomycin most rapidly permeabilizes cells with high initial membrane potential and dissipates it within a few minutes. Low initial membrane potential hinders daptomycin pore formation.

Mechanistic studies on the effect of membrane lipid acyl chain composition on daptomycin pore formation

Daptomycin is a lipopeptide antibiotic that binds and permeabilizes the cell membranes of Gram-positive bacteria. Membrane permeabilization requires both calcium and phosphatidylglycerol (PG) in the target membrane, and it correlates with the formation of an oligomer that likely comprises eight subunits, which are evenly distributed between the two membrane leaflets. In both bacterial cells and model membranes, changes in the fatty acyl composition of the membrane phospholipids can prevent permeabilization. We here used liposomes to study the effect of phospholipids containing oleoyl and other fatty acyl residues on daptomycin activity, and made the following observations: (1) Oleic acid residues inhibited permeabilization when part not only of PG, but also of other phospholipids (PC or cardiolipin). (2) When included in an otherwise daptomycin-susceptible lipid mixture, even 10% of dioleoyl lipid (DOPC) can strongly inhibit permeabilization. (3) The inhibitory effect of fatty acyl residues appears to correlate more with their chain length than with unsaturation. (4) Under all conditions tested, permeabilization coincided with octamer formation, whereas tetramers were observed on membranes that were not permeabilized. Overall, our findings further support the notion that the octamer is indeed the functional transmembrane pore, and that fatty acyl residues may prevent pore formation by preventing the alignment of tetramers across the two membrane leaflets.

Comparison of the Effects of Daptomycin on Bacterial and Model Membranes

Daptomycin is a phosphatidylglycerol specific, calcium-dependent membrane-active antibiotic that has been approved for the treatment of Gram-positive infections. A recent Bacillus subtilis study found that daptomycin clustered into fluid lipid domains of bacterial membranes and the membrane binding was correlated with dislocation of peripheral membrane proteins and depolarization of membrane potential. In particular, the study disproved the existence of daptomycin ion channels. Our purpose here is to study how daptomycin interacts with lipid bilayers to understand the observed phenomena on bacterial membranes. We performed new types of experiments using aspirated giant vesicles with an ion leakage indicator, making comparisons between daptomycin and ionomycin, performing vesicle-vesicle transfers, and measuring daptomycin binding to fluid phase versus gel phase bilayers and bilayers including cholesterol. Our findings are entirely consistent with the observations for bacterial membranes. In addition, daptomycin is found to cause ion leakage through the membrane only if its concentration in the membrane is over a certain threshold. The ion leakage caused by daptomycin is transient. It occurs only when daptomycin binds the membrane for the first time; afterward, they cease to induce ion leakage. The ion leakage effect of daptomycin cannot be transferred from one membrane to another. The level of membrane binding of daptomycin is reduced in the gel phase versus the fluid phase. Cholesterol also weakens the membrane binding of daptomycin. The combination of membrane concentration threshold and differential binding is significant. This could be a reason why daptomycin discriminates between eukaryotic and prokaryotic cell membranes.