Solution three-dimensional structure of surfactin: a cyclic lipopeptide studied by 1H-NMR, distance geometry, and molecular dynamics

A mini-review: mechanism of antimicrobial action and application of surfactin

Surfactin, an antibacterial lipopeptide produced by different strains of Bacillus subtilis, is a powerful biosurfactant. It also has multiple biological activities including antiviral, anti-mycoplasma and antiprotozoal activities, in addition to the broad-spectrum antimicrobial activities against Gram-positive bacteria, Gram-negative bacteria and fungi. Surfactin may be one of the promising alternatives to antibiotics. Surfactin's chemical structure and physicochemical properties are briefly discussed in this mini-review. Surfactin's antibacterial mechanism is mainly outlined as follows: (1) attacking pathogenic bacteria's cell membrane, causing cell membrane disintegration or osmotic pressure imbalance; (2) inhibiting pathogenic bacteria's protein synthesis, preventing cell reproduction; (3) inhibiting pathogenic bacteria's enzyme activity, affecting normal cell metabolism. This provides basis for the further research and application of surfactin. Finally, the application of surfactin in food and its prospect are summarized in brief.

Discovery of Surfactins as Inhibitors of MicroRNA Processing Using Cat-ELCCA

MicroRNAs (miRNAs) are a family of small noncoding RNAs that regulate gene expression. Due to their important activity in the fine-tuning of protein translation, abnormal expression of miRNAs has been linked to many human diseases, making the targeting of miRNAs attractive as a novel therapeutic strategy. Accordingly, researchers have been heavily engaged in the discovery of small molecule modulators of miRNAs. With an interest in the identification of new chemical space for targeting miRNAs, we developed a high-throughput screening (HTS) technology, catalytic enzyme-linked click chemistry assay (cat-ELCCA), aimed at the discovery of small molecule ligands for pre-miR-21, a miRNA that is frequently overexpressed in human cancers. From our HTS campaign, we found that natural products, a source of many impactful human medicines, may be a promising source of potential pre-miR-21-selective maturation inhibitors. Herein we describe our first efforts in natural product inhibitor discovery leading to the identification of a depsipeptide class of natural products as RNA-binding inhibitors of Dicer-mediated miRNA processing.

Surfactin isoforms isolated from a mushroom derived Bacillus halotolerans DMG-7-2

A new iso-C₁₄ [Val², Val⁷] surfactin isoform (1) together with eight known ones (2-9), was isolated from the culture of a mushroom derived bacterium, Bacillus halotolerans DMG-7-2. The structures of them were mainly elucidated by NMR and MS data, and the NMR data of 5 also was reported for the first time. The absolute configuration of 1 was determined by Marfey's analysis (for amino acid residues) and the ¹³C NMR calculation of the two plausible epimers of 1 (for fatty acid). Compounds 1-9 showed moderate cytotoxicity against two human cancer cell lines (A549, MCF-7) and mice microglial BV2 cells, the IC₅₀ values ranged from 8.91 to 33.00 µM, and the IC₅₀ values of the positive control 5-FU were 99.94, 71.49 and 0.12 µM, respectively.

A Coarse-Grained Model for Microbial Lipopeptide Surfactin and Its Application in Self-Assembly

Biosurfactants exhibit outstanding interfacial properties and unique biological activities that fairly related to their self-assembly in solutions and at interfaces. Computational simulations provide structural details of biosurfactant aggregates at the molecular level relevant to thermodynamic properties, but the understanding of kinetics of self-assembly remains limited due to lower simulation efficiency. In this work, a coarse-grained model has been developed for microbial lipopeptide surfactin, and surfactin monolayer at the octane/water interface and micelle in aqueous solution were studied using molecular dynamics simulations. Interaction parameters were optimized and validated by comparing with results obtained from experiments and atomistic molecular dynamics simulations. In particular, self-assembly of surfactin in aqueous solution was studied using the optimized parameters. Results showed that coarse-grained simulations well reproduced structural properties of surfactin monolayer and micelle and the molecular behavior such as surfactin orientation and conformation. Self-assembly features of surfactin in different stages have been captured, and the aggregation numbers of dominant clusters were in accordance with experimental data. This report suggested that the present coarse-grained model and interaction parameters allowed surfactin simulations over longer timescales and larger systems, which provide insights into characterizing both the kinetics of surfactin self-assembly and the adsorption of surfactin onto varying interfaces.

Toxicity and applications of surfactin for health and environmental biotechnology

Characterized as one of the most potent biosurfactants, surfactin is a cyclic lipopeptide synthesized by several strains of Bacillus genus. The aim of this review was to present the physicochemical and structural properties of surfactin and to demonstrate advances and applications of this biosurfactant for health and environmental biotechnology. Further, this review also focused on toxicological effects of surfactin on in vivo and in in vitro systems. The hydrophobic nature of surfactin enables interaction with membrane-bound phospholipids and indicates the ability of the molecule to act as a new weapon with respect to therapeutic and environmental properties. Seeking to avoid environmental contamination produced by widespread use of synthetic surfactants, surfactin emerges as a biological control agent against pathogen species owing to its antibacterial and antiviral properties. In addition, the mosquitocidal activity of surfactin was suggested as new strategy to control disease vectors. The current findings warrant future research to assess the toxicity of surfactin to enable an optimizing anticancer therapy and to seek refined methodologies, including nanotechnology techniques, to allow for an improved delivery of the biogenic molecule on target cells.

Surface Activity and Ca2+-Dependent Aggregation Property of Lichenysin Produced by Bacillus licheniformis NBRC 104464

Bacillus licheniformis NBRC 104464 produces a cyclic lipopeptide different from surfactin. After we performed liquid chromatography fractionation and purification, we used structural analyses to identify the cyclic lipopeptide as lichenysin. Surface tension measurements of lichenysin sodium salt in water yielded a critical micelle concentration (CMC) of 1.0×10^-5 M. The surface tension at the CMC was 28.9 mN/m. Comparative analysis of Ca²⁺-influenced micellar aggregation of lichenysin and surfactin revealed that the formation rate of the lichenysin-Ca²⁺ complex aggregate remained low up to a [Ca²⁺]/[lichenysin] molar ratio of 80, whereas the surfactin-Ca²⁺ complex formed micellar aggregates at the same molar ratio. Further excessive addition of Ca²⁺ to the micellar solution of lichenysin induced higher turbidity than surfactin.

Molecular Dynamics Simulation of Protein Biosurfactants

Surfaces and interfaces are ubiquitous in nature and are involved in many biological processes. Due to this, natural organisms have evolved a number of methods to control interfacial and surface properties. Many of these methods involve the use of specialised protein biosurfactants, which due to the competing demands of high surface activity, biocompatibility, and low solution aggregation may take structures that differ from the traditional head–tail structure of small molecule surfactants. As well as their biological functions, these proteins have also attracted interest for industrial applications, in areas including food technology, surface modification, and drug delivery. To understand the biological functions and technological applications of protein biosurfactants, it is necessary to have a molecular level description of their behaviour, in particular at surfaces and interfaces, for which molecular simulation is well suited to investigate. In this review, we will give an overview of simulation studies of a number of examples of protein biosurfactants (hydrophobins, surfactin, and ranaspumin). We will also outline some of the key challenges and future directions for molecular simulation in the investigation of protein biosurfactants and how this can help guide future developments.

Insight into the Selectivity and Mechanism of Surfactin Containing Multiple Dissociated Carboxyls with 1-Bromoacetylpyrene in Fluorescent Derivatization

Fluorescent derivatization of the carboxyls in surfactin peptide rings is an effective way to improve the sensitivity of trace detection of surfactin, but very little is known about the reaction selectivity of surfactin containing multiple carboxyls in derivatization. In this paper, the reaction selectivity in fluorescent derivatization of a surfactin containing two carboxyls in its peptide ring with 1-bromoacetylpyrene and the catalysis role in the reactions were investigated using electrospray ionization mass spectrometry and tandem mass spectrometry. It showed that only one carboxyl was labeled with 1-bromoacetylpyrene in derivatization reactions, and the connection of the Asp residue with 1-bromoacetylpyrene was confirmed. It also showed that triethylamine as a catalyst was connected with surfactin to liberate more nucleophilic groups beneficial to promote the derivatization rate. This would contribute to better understanding the mechanism of derivatization of surfactin and its analogues with 1-bromoacetylpyrene, and with other fluorescent labeling reagents.

An Electrospray Ionization Mass Spectrometry Study on the "In Vacuo" Hetero-Oligomers Formed by the Antimicrobial Peptides, Surfactin and Gramicidin S

It was previously observed that the lipopeptide surfactants in surfactin (Srf) have an antagonistic action towards the highly potent antimicrobial cyclodecapeptide, gramicidin S (GS). This study reports on some of the molecular aspects of the antagonism as investigated through complementary electrospray ionization mass spectrometry techniques. We were able to detect stable 1:1 and 2:1 hetero-oligomers in a mixture of surfactin and gramicidin S. The noncovalent interaction between GS and Srf, with the proposed equilibrium: GS~Srf↔GS+Srf correlated to apparent K _d values of 6-9 μM in gas-phase and 1 μM in aqueous solution. The apparent K _d values decreased with a longer incubation time and indicated a slow oligomerization equilibrium. Furthermore, the low μM K _d^app values of GS~Srf↔GS+Srf fell within the biological concentration range and related to the 2- to 3-fold increase in [GS] needed for bacterial growth inhibition in the presence of Srf. Competition studies indicated that neither Na⁺ nor Ca²⁺ had a major effect on the stability of preformed heterodimers and that GS in fact out-competed Ca²⁺ and Na⁺ from Srf. Traveling wave ion mobility mass spectrometry revealed near symmetrical peaks of the heterodimers correlating to a compact dimer conformation that depend on specific interactions. Collision-induced dissociation studies indicated that the peptide interaction is most probably between one Orn residue in GS and the Asp residue, but not the Glu residue in Srf. We propose that flanking hydrophobic residues in both peptides stabilize the antagonistic and inactive peptide hetero-oligomers and shield the specific polar interactions in an aqueous environment. Graphical Abstract ᅟ.

Molecular Characteristics and Biological Functions of Surface-Active and Surfactant Proteins

Many critical biological processes take place at hydrophobic:hydrophilic interfaces, and a wide range of organisms produce surface-active proteins and peptides that reduce surface and interfacial tension and mediate growth and development at these boundaries. Microorganisms produce both small lipid-associated peptides and amphipathic proteins that allow growth across water:air boundaries, attachment to surfaces, predation, and improved bioavailability of hydrophobic substrates. Higher-order organisms produce surface-active proteins with a wide variety of functions, including the provision of protective foam environments for vulnerable reproductive stages, evaporative cooling, and gas exchange across airway membranes. In general, the biological functions supported by these diverse polypeptides require them to have an amphipathic nature, and this is achieved by a diverse range of molecular structures, with some proteins undergoing significant conformational change or intermolecular association to generate the structures that are surface active.

A multicomponent macrocyclization strategy to natural product-like cyclic lipopeptides: synthesis and anticancer evaluation of surfactin and mycosubtilin analogues

Two birds in one shot: oligopeptides can be cyclized and lipidated in one step with multicomponent reactions.

Interaction of a biosurfactant, Surfactin with a cationic Gemini surfactant in aqueous solution

The interaction between biosurfactant Surfactin and cationic Gemini surfactant ethanediyl-1,3-bis(dodecyldimethylammonium bromide) (abbreviated as 12-3-12) was investigated using turbidity, surface tension, dynamic light scattering (DLS) and small angle neutron scattering (SANS). Analysis of critical micelle concentration (CMC) values in Surfactin/12-3-12 mixture indicates that there is synergism in formation of mixed Surfactin/12-3-12 micelles. Although Surfactin and 12-3-12 are oppositely charged in phosphate buffer solution (PBS, pH7.4), there are no precipitates observed at the concentrations below the CMC of Surfactin/12-3-12 system. However, at the concentration above CMC value, the Surfactin/12-3-12 mixture is severely turbid with high 12-3-12 content. DLS and SANS measurements follow the size and shape changes of mixed Surfactin/12-3-12 aggregates from small spherical micelles via elongated aggregates to large bulk complexes with increasing fraction of Gemini surfactant.

Deconvolving molecular signatures of interactions between microbial colonies

Motivation: The interactions between microbial colonies through chemical signaling are not well understood. A microbial colony can use different molecules to inhibit or accelerate the growth of other colonies. A better understanding of the molecules involved in these interactions could lead to advancements in health and medicine. Imaging mass spectrometry (IMS) applied to co-cultured microbial communities aims to capture the spatial characteristics of the colonies’ molecular fingerprints. These data are high-dimensional and require computational analysis methods to interpret.

Results: Here, we present a dictionary learning method that deconvolves spectra of different molecules from IMS data. We call this method MOLecular Dictionary Learning (MOLDL). Unlike standard dictionary learning methods which assume Gaussian-distributed data, our method uses the Poisson distribution to capture the count nature of the mass spectrometry data. Also, our method incorporates universally applicable information on common ion types of molecules in MALDI mass spectrometry. This greatly reduces model parameterization and increases deconvolution accuracy by eliminating spurious solutions. Moreover, our method leverages the spatial nature of IMS data by assuming that nearby locations share similar abundances, thus avoiding overfitting to noise. Tests on simulated datasets show that this method has good performance in recovering molecule dictionaries. We also tested our method on real data measured on a microbial community composed of two species. We confirmed through follow-up validation experiments that our method recovered true and complete signatures of molecules. These results indicate that our method can discover molecules in IMS data reliably, and hence can help advance the study of interaction of microbial colonies.

Availability and implementation: The code used in this paper is available at: https://github.com/frizfealer/IMS_project.

Contact:vjojic@cs.unc.edu

Supplementary information:Supplementary data are available at Bioinformatics online.

Surfactin at the Water/Air Interface and in Solution

The lipopeptide surfactin produced by certain strains of Bacillus subtillis is a potent biosurfactant with high amphiphilicity and a strong tendency for self-aggregation. Surfactin possesses a number of valuable biological properties such as antiviral, antibacterial, antifungal, and hemolytic activities. Owing to these properties, in addition to the general advantages of biosurfactants over synthetic surfactants, surfactin has potential biotechnological and biomedical applications. Here, the aggregation properties of surfactin in solution together with its behavior at the water/air interface were studied using classical molecular dynamics simulations (MD) at three different pH values. Validation of the MD structural data was performed by comparing neutron reflectivity and volume fraction profiles computed from the simulations with their experimental counterparts. Analysis of the MD trajectories supported conclusions about the distribution, conformations, and interactions of surfactin in solution and at the water-air interface. Considering altogether, the work presented provides atomistic models for the rationalization of some of the structural and dynamic characteristics as well as the modes of action of surfactin at different pH values.

Chemical structure, property and potential applications of biosurfactants produced by Bacillus subtilis in petroleum recovery and spill mitigation

Lipopeptides produced by microorganisms are one of the five major classes of biosurfactants known and they have received much attention from scientific and industrial communities due to their powerful interfacial and biological activities as well as environmentally friendly characteristics. Microbially produced lipopeptides are a series of chemical structural analogues of different families and, among them, 26 families covering about 90 lipopeptide compounds have been reported in the last two decades. This paper reviews the chemical structural characteristics and molecular behaviors of surfactin, one of the representative lipopeptides of the 26 families. In particular, two novel surfactin molecules isolated from cell-free cultures of Bacillus subtilis HSO121 are presented. Surfactins exhibit strong self-assembly ability to form sphere-like micelles and larger aggregates at very low concentrations. The amphipathic and surface properties of surfactins are related to the existence of the minor polar and major hydrophobic domains in the three 3-D conformations. In addition, the application potential of surfactin in bioremediation of oil spills and oil contaminants, and microbial enhanced oil recovery are discussed.

Additive and synergistic membrane permeabilization by antimicrobial (lipo)peptides and detergents

Certain antibiotic peptides are thought to permeabilize membranes of pathogens by effects that are also observed for simple detergents, such as membrane thinning and disordering, asymmetric bilayer expansion, toroidal pore formation, and micellization. Here we test the hypothesis that such peptides act additively with detergents when applied in parallel. Additivity is defined analogously to a fractional inhibitory concentration index of unity, and the extent and mechanism of leakage is measured by the fluorescence lifetime-based vesicle leakage assay using calcein-loaded vesicles. Good additivity was found for the concerted action of magainin 2, the fungicidal lipopeptide class of surfactins from Bacillus subtilis QST713, and the detergent octyl glucoside, respectively, with the detergent C12EO8. Synergistic or superadditive action was observed for fengycins from B. subtilis, as well as the detergent CHAPS, when combined with C12EO8. The results illustrate two mechanisms of synergistic action: First, maximal leakage requires an optimum degree of heterogeneity in the system that may be achieved by mixing a graded with an all-or-none permeabilizer. (The optimal perturbation should be focused to certain defect structures, yet not to the extent that some vesicles are not affected at all.) Second, a cosurfactant may enhance the bioavailability of a poorly soluble peptide. The results are important for understanding the concerted action of membrane-permeabilizing compounds in biology as well as for optimizing formulations of such antimicrobials for medical applications or crop protection.

Substrate dependent in vitro antifungal activity of Bacillus sp strain AR2

Background

Biosurfactants are a structurally diverse group of secondary metabolites with lots of potential to serve mankind. Depending upon the structure and composition they may exhibit properties that make them suitable for a particular application. Structural and compositional diversity of biosurfactant is unambiguously substrate dependent. The present study investigates the qualitative and quantitative effect of different water soluble carbon source on the biosurfactant produced by Bacillus amylofaciens strain AR2.

Results

Strain AR2 produced lipopeptide type biosurfactant while growing on water soluble carbon sources. Maximum biosurfactant production was observed in the sucrose supplemented minimal salt medium (MSM). Strain AR2 exhibited carbon source dependent surface tension reduction in the range of 30-37 mN/m, critical micelle concentration (CMC) in the range 80-110 mg/l and emulsification index (EI₂₄ kerosene) in the range of 32-66%. In dextrose, sucrose and glycerol supplemented MSM, strain AR2 produced lipopeptides as a mixture of surfactin, iturin and fengycin. However, in the presence of maltose, lactose and sorbitol only iturin was produced. This substrate dependent compositional variation in the lipopeptides significantly influenced antifungal activity. Lipopeptides produced by strain AR2 while growing on sucrose and dextrose based MSM was observed to be most efficient as an antifungal agent.

Conclusions

These results suggest that carbon source provided for the growth and biosurfactant production not only influences the yield but also the type of biosurfactant. Sucrose is the most suitable carbon source for production of lipopeptide biosurfactant with antifungal activity.

Insights into the interactions among Surfactin, betaines, and PAM: surface tension, small-angle neutron scattering, and small-angle X-ray scattering study

The interactions among neutral polymer polyacrylamide (PAM) and the biosurfactant Surfactin and four betaines, N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SDDAB), N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (STDAB), N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SHDAB), and N-dodecyl-N,N-dimethyl-2-ammonio-acetate (C12BE), in phosphate buffer solution (PBS) have been studied by surface tension measurements, small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and rheological experiments. It has been confirmed that the length of alkyl chain is a key parameter of interaction between betaines and PAM. Differences in scattering contrast between X-ray and neutrons for surfactants and PAM molecules provide the opportunity to separately follow the changes of structure of PAM and surfactant aggregates. At concentrations of betaines higher than CMC (critical micelle concentration) and C2 (CMC of surfactant with the presence of polymer), spherical micelles are formed in betaines and betaines/PAM solutions. Transition from spherical to rod-like aggregates (micelles) has been observed in solutions of Surfactin and Surfactin/SDDAB (αSurfactin = 0.67 (molar fraction)) with addition of 0.8 wt % of PAM. The conformation change of PAM molecules only can be observed for Surfactin/SDDAB/PAM system. Viscosity values follow the structural changes suggested from scattering measurements i.e., gradually increases for mixtures PAM → Surfactin/PAM → Surfactin/SDDAB/PAM in PBS.

Self-assembly of surfactin in aqueous solution: role of divalent counterions

Myriad applications of surfactin in environmental and biomedical field prompt understanding the self-assembly behaviour of surfactin in aqueous solution as well as its interaction with counterions. Effect of four divalent counterions namely, Ni(2+), Zn(2+), Cd(2+), and Ca(2+) on the self-assembly of the surfactin, a biosurfactant isolated from Bacillus subtilis YB7 is studied by fluorescence spectroscopy, dynamic light scattering, optical and electron microscopic studies. The critical micelle concentration (CMC) and aggregation number (Nagg) of surfactin are 96.76 ± 15.49 μM and 101.12 ± 2.53, respectively. The degree of counterion association increases as its ionic radius decreases. Ni(2+) exhibits the highest and Ca(2+) the least degree of counterion association. Addition of counterion reduces the size of the microstructures, aggregation number (Nagg) and zeta potential. The reduction in the zeta potential indicates the neutralization of the negative charges on the electrical double layer of the microstructures. Differential interference contrast (DIC) and transmission electron microscopic (TEM) images of surfactin show the presence of vesicles and large aggregates including giant vesicles. On the addition of Ca(2+), fusion of vesicles into large aggregates is predominantly observed. Ni(2+) induces the transition of large spherical vesicles into small spherical, worm-like vesicles and multicompartment-like structures (vesosome). Such structures are the evidences for metal ion coordinated intervesicular interactions. This study reveals that the self-assembly process of surfactin can be controlled by the addition of metal ions according to the requirements.

Application of the Gibbs equation to the adsorption of nonionic surfactants and polymers at the air-water interface: comparison with surface excesses determined directly using neutron reflectivity

Four recent papers by Menger et al. have questioned methods of analysis of surface tension (ST) data that use the Gibbs equation to obtain the surface excess (Γ) of a surfactant at the air-water interface. There have been two responses which challenge the assertions of Menger et al. and a response from Menger et al. We use directly determined values of Γ from a range of neutron reflectometry (NR) data to examine some of the issues that are relevant to these seven papers. We show that there is excellent agreement between NR measurements and careful ST analyses for a wide range of nonionic adsorbents, including surfactants and polymers. The reason it is possible to obtain good agreement near the critical micelle concentration (CMC) is that nonionic surfactants generally seem to saturate the surface before the CMC is reached and this makes it relatively easy to determine the limiting slope (and hence Γ) of the ST-log(concentration) plot at the CMC. Furthermore, there is also generally good agreement between ST and NR over the whole range of concentrations below the CMC until depletion effects become important. Depletion effects are shown to become important at higher concentrations than expected, which brings them into the range of many experiments, including techniques other than ST and NR. This is illustrated with new measurements on the biosurfactant surfactin. The agreement between ST and NR outside the depletion range can be regarded as a mutual validation of the two methods, especially as it is demonstrated independently of any model adsorption isotherms. In the normal experimental situation NR is less vulnerable to depletion than ST and we show how NR and a single ST measurement can be used to determine the hitherto undetermined CMC of the nonionic surfactant C18E12, which is found to be 1.3 × 10(-6) M.

Kinetic modeling of esterification reaction of surfactin-C₁₅ in methanol solution

Surfactin in methanol solution with acid would be spontaneously esterified into the mono- or dimethyl ester surfactin even at a temperature as low as 4 °C because there were two free carboxyl groups in the peptide loop of surfactin. Using trifluoroacetic acid as the catalyst, the esterification and the contents change in surfactin-C(15), mono- and dimethyl ester surfactin-C(15) with time were investigated at 4, 25, and 45 °C, respectively. The kinetic model was established for prediction of the esterification degree under experimental conditions. At 4, 25, and 45 °C, more than 10 % of the surfactin-C(15) in methanol solution in the presence of 0.05 % trifluoroacetic acid was changed into the esterified surfactin-C(15) after 37.6, 14.1, and 7.4 h, respectively. The maximum of intermediate of the mono-methyl ester surfactin-C(15) was observed at 4, 25, and 45 °C after 25, 10, and 5 days, respectively. Our results indicated that the time for preparation should be strictly controlled to avoid an unexpected esterification of surfactin during its storage and experimental treatment, and the kinetic results could be adopted as the reference condition for preparation of monomethyl ester surfactin-C(15).

Direct surfactin-gramicidin S antagonism supports detoxification in mixed producer cultures of Bacillus subtilis and Aneurinibacillus migulanus

Antibiotic production as a defence mechanism is a characteristic of a wide variety of organisms. In natural evolutionary adaptation, cellular events such as sporulation, biofilm formation and resistance to antibiotics enable some micro-organisms to survive environmental and antibiotic stress conditions. The two antimicrobial cyclic peptides in this study, gramicidin S (GS) from Aneurinibacillus migulanus and the lipopeptide surfactin (Srf) from Bacillus subtilis, have been shown to affect both membrane and intercellular components of target organisms. Many functions, other than that of antimicrobial activity, have been assigned to Srf. We present evidence that an additional function may exist for Srf, namely that of a detoxifying agent that protects its producer from the lytic activity of GS. We observed that Srf producers were more resistant to GS and could be co-cultured with the GS producer. Furthermore, exogenous Srf antagonized the activity of GS against both Srf-producing and non-producing bacterial strains. A molecular interaction between the anionic Srf and the cationic GS was observed with circular dichroism and electrospray MS. Our results indicate that the formation of an inactive complex between GS and Srf supports resistance towards GS, with the anionic Srf forming a chemical barrier to protect its producer. This direct detoxification combined with the induction of protective stress responses in B. subtilis by Srf confers resistance toward GS from A. migulanus and allows survival in mixed cultures.

Temperature influence on the structure and interfacial properties of surfactin micelle: a molecular dynamics simulation study

Surfactin is an efficient biosurfactant excreted by different strains of Bacillus subtilis. Our study provides a molecular view of the temperature dependence of the structure and the interfacial properties of un-ionized surfactin micelles. The overall size and shape, the surface area, the radial density distribution of the micelles, the conformation of the hydrocarbon chain, and the intramolecular/intermolecular hydrogen bonds formed in surfactin molecules were investigated. The micelles were mostly in sphere shapes, and the radii of surfactin micelle were estimated to be around 2.2 nm. The peptide rings occupied most of the surface of the micelles. Small amounts of β-turn and γ-turn structures were found in the conformations of the peptide rings. When the temperature increased, the shape of the peptide rings became planar; the solvent accessible surface area decreased as temperature dehydration occurred. At 343 K some hydrocarbon chains reversed their orientation (flip-flopped). In addition, the stability of the hydrogen bond interactions in the micelles decreases with the increasing temperature.

Enzymatic resistance to the lipopeptide surfactin as identified through imaging mass spectrometry of bacterial competition

Many species of bacteria secrete natural products that inhibit the growth or development of competing species. In turn, competitors may develop or acquire resistance to antagonistic molecules. Few studies have investigated the interplay of these countervailing forces in direct competition between two species. We have used an imaging mass spectrometry (IMS) approach to track metabolites exchanged between Bacillus subtilis and Streptomyces sp. Mg1 cultured together. Surfactin is a cyclic lipopeptide produced by B. subtilis that inhibits the formation of aerial hyphae by streptomycetes. IMS analysis exposed an addition of 18 mass units to surfactin in the agar proximal to Streptomyces sp. Mg1 but not other streptomycetes tested. The spatially resolved change in the mass of surfactin indicated hydrolysis of the molecule. We observed that the aerial growth of Streptomyces sp. Mg1 was resistant to inhibition by surfactin, which suggests that hydrolysis was a mechanism of resistance. To identify possible enzymes from Streptomyces sp. Mg1 with surfactin hydrolase activity, we isolated secreted proteins and identified candidates by mass spectrometry. We purified one candidate enzyme that hydrolyzed surfactin in vitro. We tested the role of this enzyme in surfactin resistance by deleting the corresponding gene from the S. Mg1 genome. We observed that aerial growth by the ΔsfhA mutant strain was now sensitive to surfactin. Our results identify an enzyme that hydrolyzes surfactin and confers resistance to aerial growth inhibition, which demonstrates the effective use of an IMS approach to track natural product modifications during interspecies competition.

Importance of the long-chain fatty acid beta-hydroxylating cytochrome P450 enzyme YbdT for lipopeptide biosynthesis in Bacillus subtilis strain OKB105

Bacillus species produce extracellular, surface-active lipopeptides such as surfactin that have wide applications in industry and medicine. The steps involved in the synthesis of 3-hydroxyacyl-coenzyme A (CoA) substrates needed for surfactin biosynthesis are not understood. Cell-free extracts of Bacillus subtilis strain OKB105 synthesized lipopeptide biosurfactants in presence of l-amino acids, myristic acid, coenzyme A, ATP, and H₂O₂, which suggested that 3-hydroxylation occurs prior to CoA ligation of the long chain fatty acids (LCFAs). We hypothesized that YbdT, a cytochrome P450 enzyme known to beta-hydroxylate LCFAs, functions to form 3-hydroxy fatty acids for lipopeptide biosynthesis. An in-frame mutation of ybdT was constructed and the resulting mutant strain (NHY1) produced predominantly non-hydroxylated lipopeptide with diminished biosurfactant and beta-hemolytic activities. Mass spectrometry showed that 95.6% of the fatty acids in the NHY1 biosurfactant were non-hydroxylated compared to only ∼61% in the OKB105 biosurfactant. Cell-free extracts of the NHY1 synthesized surfactin containing 3-hydroxymyristic acid from 3-hydroxymyristoyl-CoA at a specific activity similar to that of the wild type (17 ± 2 versus 17.4 ± 6 ng biosurfactant min⁻¹·ng·protein⁻¹, respectively). These results showed that the mutation did not affect any function needed to synthesize surfactin once the 3-hydroxyacyl-CoA substrate was formed and that YbdT functions to supply 3-hydroxy fatty acid for surfactin biosynthesis. The fact that YbdT is a peroxidase could explain why biosurfactant production is rarely observed in anaerobically grown Bacillus species. Manipulation of LCFA specificity of YbdT could provide a new route to produce biosurfactants with activities tailored to specific functions.

Flexible loops of thread-like micelles are formed upon interaction of L-alpha-dimyristoyl-phosphatidylcholine with the biosurfactant surfactin as revealed by cryo-electron tomography

Vesicles of L-alpha-dimyristoyl-phosphatidylcholine (DMPC) are known to disintegrate upon treatment with surfactin, a lipoheptapeptide biosurfactant from Bacillus subtilis OKB 105, as was observed by static light scattering (SLS) and cryo-transmission electron microscopy (cryo-TEM) recently. The lysis of DMPC bilayers occurs strongly dependent on the surfactin concentration according to a three-stage model. Unilamellar DMPC vesicles are disrupted to form sheet-like lamellar intermediates at a moderate surfactant concentration, but undergo a transition towards smaller particles of unknown structure at a higher surfactant concentration according to earlier neutron scattering experiments. Here we present direct structural evidence from cryo-electron tomography data that thread-like micelles with a uniform diameter of 6.5 nm are organized into loops of different sizes at a surfactin concentration of > 15 mol%.

Lipopeptides in cosmetics

Lipopeptides are biosurfactants extensively used in cosmetics. The consumption of cosmetics containing lipopeptides is increasing as a result of the exceptional surface properties and diverse biological activities of lipopeptides which facilitate a vast number of applications not only in the pharmaceutics industry which includes cosmetics but also in the food industry. Cosmetics containing lipopeptides are available in various dosage forms according to their beneficial surface properties, which include anti-wrinkle and moisturizing activities and cleansing cosmetics. The microbial production of lipopeptides particularly those with biological and surface activities applicable to cosmetics are summarized based on appropriate studies and patents up to the year 2008 to manage the information and sufficiently review the data.