Dynamic and equilibrium surface tensions of surfactin aqueous solutions

Effect of Fluid-Rock Interactions on In Situ Bacterial Alteration of Interfacial Properties and Wettability of CO2-Brine-Mineral Systems for Geologic Carbon Storage

This study explored the feasibility of biosurfactant amendment in modifying the interfacial characteristics of carbon dioxide (CO₂) with rock minerals under high-pressure conditions for GCS. In particular, while varying the CO₂ phase and the rock mineral, we quantitatively examined the production of biosurfactants by Bacillus subtilis and their effects on interfacial tension (IFT) and wettability in CO₂-brine-mineral systems. The results demonstrated that surfactin produced by B. subtilis caused the reduction of CO₂-brine IFT and modified the wettability of both quartz and calcite minerals to be more CO₂-wet. The production yield of surfactin was substantially greater with the calcite mineral than with the quartz mineral. The calcite played the role of a pH buffer, consistently maintaining the brine pH above 6. By contrast, an acidic condition in CO₂-brine-quartz systems caused the precipitation of surfactin, and hence surfactin lost its ability as a surface-active agent. Meanwhile, the CO₂-driven mineral dissolution and precipitation in CO₂-brine-calcite systems under a non-equilibrium system altered the solid substrates, produced surface roughness, and caused contact angle variations. These results provide unique experimental data on biosurfactant-mediated interfacial properties and wettability in GCS-relevant conditions, which support the exploitation of in situ biosurfactant production for biosurfactant-aided CO₂ injection.

Synthesis of Quaternary Ammonium Salts Based on Diketopyrrolopyrroles Skeletons and Their Applications in Copper Electroplating

A series of DPP derivatives bearing quaternary ammonium salt centers with different lengths of carbon chains have been designed and synthesized. Their inhibition actions on copper electroplating were first investigated. A total of four diketopyrrolopyrrole (DPP) derivatives showed different inhibition capabilities on copper electroplating. To investigate interactions between metal surface and additives, we used quantum chemical calculations. Static and dynamic surface tension of four DPP derivatives had been measured, and the results showed DPP-10C (1c) with a faster-decreasing rate of dynamic surface tension among the four derivatives, which indicated higher adsorption rate of additive on the cathode surface and gives rise to stronger inhibiting effect of copper electrodeposition. Then, DPP-10C (1c) as the representative additive, was selected for the systematic study of the leveling influence during microvia filling through comprehensive electroplating tests. In addition, field-emission scanning electron microscope images and X-ray diffraction results showed the surface morphology, which indicated that addition of DPP derivative (1c) could lead a fine copper deposit and cause the preferential orientations of copper deposits to change from [220] to [111], which happened in particular at higher concentrations.

Towards the development of an effective in vivo wound healing agent from Bacillus sp. derived biosurfactant using Catla catla fish fat

The aim of the present study was to investigate the excisional wound healing activity of a biosurfactant isolated fromBacillus stratosphericussp.

Bacillus subtilis alters the proportion of major membrane phospholipids in response to surfactin exposure

Surfactin, an anionic lipopeptide produced by Bacillus subtilis, is an antimicrobial that targets the cytoplasmic membrane. Nowadays it appears increasingly apparent that the mechanism of resistance against these types of antibiotics consists of target site modification. This prompted us to investigate whether the surfactin non-producing strain B. subtilis 168 changes its membrane composition in response to a sublethal surfactin concentration. Here we show that the exposure of B. subtilis to surfactin at concentrations of 350 and 650 μg/ml (designated as SF350 and SF650, respectively) leads to a concentration-dependent growth arrest followed by regrowth with an altered growth rate. Analysis of the membrane lipid composition revealed modifications both in the polar head group and the fatty acid region. The presence of either surfactin concentration resulted in a reduction in the content of the major membrane phospholipid phosphatidylglycerol (PG) and increase in phosphatidylethanolamine (PE), which was accompanied by elevated levels of phosphatidic acid (PA) in SF350 cultures. The fatty acid analysis of SF350 cells showed a marked increase in non-branched high-melting fatty acids, which lowered the fluidity of the membrane interior measured as the steady-state fluorescence anisotropy of DPH. The liposome leakage of carboxyfluorescein-loaded vesicles resembling the phospholipid composition of surfactin-adapted cells showed that the susceptibility to surfactin-induced leakage is strongly reduced when the PG/PE ratio decreases and/or PA is included in the target bilayer. We concluded that the modifications of the phospholipid content of B. subtilis cells might provide a self-tolerance of the membrane active surfactin.

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.

The dynamic surface tension of atmospheric aerosol surfactants reveals new aspects of cloud activation

The activation of aerosol particles into cloud droplets in the Earth’s atmosphere is both a key process for the climate budget and a main source of uncertainty. Its investigation is facing major experimental challenges, as no technique can measure the main driving parameters, the Raoult’s term and surface tension, σ, for sub-micron atmospheric particles. In addition, the surfactant fraction of atmospheric aerosols could not be isolated until recently. Here we present the first dynamic investigation of the total surfactant fraction of atmospheric aerosols, evidencing adsorption barriers that limit their gradient (partitioning) in particles and should enhance their cloud-forming efficiency compared with current models. The results also show that the equilibration time of surfactants in sub-micron atmospheric particles should be beyond the detection of most on-line instruments. Such instrumental and theoretical shortcomings would be consistent with atmospheric and laboratory observations and could have limited the understanding of cloud activation until now.

The formation of cloud droplets from aerosol particles in the atmosphere is difficult to comprehend experimentally and theoretically. Here, the authors measure the dynamic surface tension of atmospheric aerosols and evidence previously overlooked processes, likely to improve this understanding.

Polydiacetylene-based high-throughput screen for surfactin producing strains of Bacillus subtilis

Although traditional mutation is still an attractive approach for strain improvement, it is tedious, time-consuming, and inefficient to screen for surfactin producing strains. To overcome this, we developed a high-throughput screening method for surfactin producing mutants by applying polydiacetylene (PDA) vesicles as sensors with visible chromatic change from blue to red, detected as colorimetric response (CR%) signal, which can even semi-quantify the yields of surfactin. Bacillus subtilis 723 was used as parent strain and multiply mutated with atmospheric and room temperature plasma (ARTP). Mutants were cultured in MicroFlask by Duetz (24 square deepwell plates, Applikon Biotechnology) and surfactin titers were tested in 96-well plates with PDA vesicles. Mutants with surfactin titers above150 mg/L (CR% value above 26%) were selected as high-yield strains and further quantified by HPLC. By integrating MicroFlask cultivation and the PDA vesicles detection, we screened 27,000 mutants and found 37 high-yield strains. From these, one mutant produced 473.6 mg/L surfactin (including 353.1 mg/L C15 surfactin), which was 5.4-fold than that of the parent strain. This method is efficient, cost-effective and provides wider application in screening for various surfactants.

Optimization for the production of surfactin with a new synergistic antifungal activity

Background

Two of our long term efforts are to discover compounds with synergistic antifungal activity from metabolites of marine derived microbes and to optimize the production of the interesting compounds produced by microorganisms. In this respect, new applications or mechanisms of already known compounds with a high production yield could be continually identified. Surfactin is a well-known lipopeptide biosurfactant with a broad spectrum of antimicrobial and antiviral activity; however, there is less knowledge on surfactin’s antifungal activity. In this study, we investigated the synergistic antifungal activity of C₁₅-surfactin and the optimization of its production by the response surface method.

Methodology/Principal Findings

Using a synergistic antifungal screening model, we found that the combination of C₁₅-surfactin and ketoconazole (KTC) showed synergistic antifungal effect on Candida albicans SC5314 when the concentrations of C₁₅-surfactin and KTC were 6.25 µg/mL and 0.004 µg/mL, respectively. These concentrations were lower than their own efficient antifungal concentrations, which are >100 µg/mL and 0.016 µg/mL, respectively. The production of C₁₅-surfactin from Bacillus amyloliquefaciens was optimized by the response surface methodology in shaker flask cultivation. The Plackett-Burman design found sucrose, ammonium nitrate and NaH₂PO₄.2H₂O to have significant effects on C₁₅-surfactin production. The optimum values of the tested variables were 21.17 g/L sucrose, 2.50 g/L ammonium nitrate and 11.56 g/L NaH₂PO₄·2H₂O. A production of 134.2 mg/L, which were in agreement with the prediction, was observed in a verification experiment. In comparison to the production of original level (88.6 mg/L), a 1.52-fold increase had been obtained.

Conclusion/Significance

This work first found that C₁₅-surfactin was an efficient synergistic antifungal agent, and demonstrated that response surface methodology was an effective method to improve the production of C₁₅-surfactin.

Monolayer properties of uronic acid bicatenary derivatives at the air-water interface: effect of hydroxyl group stereochemistry evidenced by experimental and computational approaches

By screening uronic acid-based surfactant interfacial properties, the effect of the hydroxyl group stereochemistry (OH-4) on the conformation of bicatenary (disubstituted) derivatives at the air-water interface has been evidenced by experimental and computational approaches. Physical and optical properties of a monolayer characterized by Langmuir film balance, Brewster angle microscopy, and ellipsometry at 20 °C reveal that the derivative of glucuronate (C(14/14)-GlcA) forms a more expanded monolayer, and shows a transition state under compression, in the opposite to that of galacturonate (C(14/14)-GalA). Both films are very mechanically resistant (compression modulus > 300 mN m(-1)) and stable (collapse pressure exceeding 60 mN m(-1)), while that of C(14/14)-GalA exhibits a very high compression modulus up to 600 mN m(-1) like films in the solid state. Computational approaches provide single and assembly molecular models that corroborate the molecule expansion degree and interactions data from experimental results. Differences in the molecular conformation and film behaviours of uronic acid bicatenary derivatives at the air-water interface are attributed to the intra-H-bonding formation, which is more favourable with an OH-4 in the axial (C(14/14)-GalA) than in the equatorial position (C(14/14)-GlcA).

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.

Isolation and characterization of a C12-lipopeptide produced by Bacillus subtilis HSO 121

A new lipopeptide with C12 fatty acid has been isolated from the cell broth of Bacillus subtilis HSO121 by chromatographic methods, which is believed to be the homologue of lipopeptides. The fatty acid portion was methylated and analyzed by GC/MS, ESI Q-TOF MS and 1H-NMR. The peptide portion, of which the amino acid composition was obtained by HPLC combined with a phenyl isothiocyanate (PITC) derivatization methods, was analyzed by ESI Q-TOF MS. Comparing the obtained results with surfactin C13 showed that the new lipopeptide has a peptide moiety similar to that of surfactin and the difference exists in the fatty acid portion, which is an iso-C12 beta-hydroxy fatty acid. The critical micelle concentration (CMC) of this new homologue is estimated to be 6.27 x 10(-5) mol/l in 10 mmol/l phosphate buffer solution (PBS, pH 8.0) at 30 degrees C, and the surface tension at CMC (gamma CMC) achieved is as little as 27.71 mN/m. The hemolytic activities of the C12-lipopeptide on 2% human erythrocytes showed a HC50 of 26.5 micromol/l.

The biologically important surfactin lipopeptide induces nanoripples in supported lipid bilayers

Under specific conditions, lipid membranes form ripple phases with intriguing nanoscale undulations. Here, we show using in situ atomic force microscopy (AFM) that the biologically important surfactin lipopeptide induces nanoripples of 30 nm periodicity in dipalmitoyl phosphatidylcholine (DPPC) bilayers at 25 degrees (i.e. well below the pretransition temperature of DPPC). Whereas most undulations formed the classical straight orientation with characteristic angle changes of 120 degrees , some of them also displayed unusual circular orientations. Strikingly, ripple structures were formed at 15% surfactin but were rarely or never observed at 5 and 30% surfactin, emphasizing the important role played by the surfactin concentration. Theoretical simulations corroborated the AFM data by revealing the formation of stable surfactin/lipid assemblies with positive curvature.

Penetration of surfactin into phospholipid monolayers: nanoscale interfacial organization

Atomic force microscopy (AFM) combined with surface pressure-area isotherms were used to probe the interfacial behavior of phospholipid monolayers following penetration of surfactin, a cyclic lipopeptide produced by Bacillus subtilis strains. Prior to penetration experiments, interfacial behavior of different surfactin molecules (cyclic surfactins with three different aliphatic chain lengths--S13, S14, and S15--and a linear surfactin obtained by chemical cleavage of the cycle of the surfactin S15) has been investigated. A more hydrophobic aliphatic chain induces greater surface-active properties of the lipopeptide. The opening of the peptide ring reduces the surface activity. The effect of phospholipid acyl chain length (dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine- (DPPC), and distearoylphosphatidylcholine) and phospholipid polar head (DPPC, dipalmitoylphosphatidylethanolamine and dipalmitoylphosphatidylserine) on monolayer penetration properties of the surfactin S15 has been explored. Results showed that while the lipid monolayer thickness and the presence of electrostatic repulsions from the interfacial film do not significantly influence surfactin insertion, these parameters strongly modulate the ability of the surfactin to alter the nanoscale organization of the lipid films. We also probed the effect of surfactin structure (influence of the aliphatic chain length and of the cyclic structure of the peptide ring) on the behavior of DPPC monolayers. AFM images and isotherms showed that surfactin penetration is promoted by longer lipopeptide chain length and a cyclic polar head. This indicates that hydrophobic interactions are of main importance for the penetration power of surfactin molecules.

Hemolytic activity of new linear surfactin analogs in relation to their physico-chemical properties

New linear analogs of surfactin have been synthesized. Their physico-chemical parameters were determined. The results indicate that these linear products show surface activities although they are lowered compared to those of cyclic compounds. The hemolytic activities have also been assayed. In contrast with cyclic surfactins, no significant hemolysis occurs for the linear products in the range of concentrations tested. Moreover, a protective effect against Triton X-100 induced hemolysis has been highlighted for linear surfactins. The concentration at which this protective effect happens is correlated directly to the CMC, and inversely to the acyl chain length of the product. In a hypotonic medium, analogs having a long acyl chain tend to increase the hemolysis, meanwhile the product with the shortest chain tends to decrease it.

Nanoscale properties of mixed fengycin/ceramide monolayers explored using atomic force microscopy

To gain insight into the interactions between fengycin and skin membrane lipids, mixed fengycin/ceramide monolayers were investigated using atomic force microscopy (AFM) (monolayers supported on mica) and surface pressure-area isotherms (monolayers at the air-water interface). AFM topographic images revealed phase separation in mixed monolayers prepared at 20 degrees C/pH 2 and composed of 0.25 and 0.5 fengycin molar ratios, in the form of two-dimensional (2-D) hexagonal crystalline domains of ceramide surrounded by a fengycin-enriched fluid phase. Surface pressure-area isotherms as well as friction and adhesion AFM images confirmed that the two phases had different molecular orientations: while ceramide formed a highly ordered phase with crystalline chain packing, fengycin exhibited a disordered fluid phase with the peptide ring lying horizontally on the substrate. Increasing the temperature and pH to values corresponding to the skin parameters, i.e., 37 degrees C/pH 5, was found to dramatically affect the film organization. At low fengycin molar ratio (0.25), the hexagonal ceramide domains transformed into round domains, while at higher ratio (0.5) these were shown to melt into a continuous fengycin/ceramide fluid phase. These observations were directly supported by the thermodynamic analysis (deviation from the additivity rule, excess of free energy) of the monolayer properties at the air-water interface. Accordingly, this study demonstrates that both the environmental conditions (temperature, pH) and fengycin concentration influence the molecular organization of mixed fengycin/ceramide monolayers. We believe that the ability to modulate the formation of 2-D domains in the skin membrane may be an important biological function of fengycin, which should be increasingly investigated in future pharmacological research.