Surfactin Concentration Research Articles

Monolayer instability of ionic surfactants at the water/air interface due to biosurfactant molecules: A molecular dynamic approach

The decomposition of monolayers prepared with anionic surfactants, sodium dodecyl sulfate (SDS), or cationic ones, dodecyltrimethylammonium bromide (DTAB), at the water/air interface was studied when biosurfactants (surfactin) are added to the films. Molecular dynamics simulations were carried out for monolayers with a fixed number of SDS or DTAB molecules and a different amount of biosurfactants to form SDS/surfactin and DTAB/surfactin mixtures. It is found that the presence of the biosurfactant modifies interfacial and structural properties of the ionic monolayers at the interface; the DTAB monolayer is distorted even for a few surfactin molecules, whereas the SDS monolayer remains steady up to a given amount of biosurfactant. In both monolayers the surface tension decreases with the number of biosurfactants, however while for the DTAB/surfactin the values seem to fluctuate, for the SDS/surfactin mixture the values decay linearly, with a discontinuity for a given surfactin concentration. The linear behaviour of the surface tension for the SDS/surfactin allows us to evaluate free energies for the monolayers and a two-dimensional equation of state. The structure of the monolayers was analyzed in terms of density profiles, order parameters, thickness of the interfaces and the data show that the DTAB/surfactin is more distorted than the SDS/surfactin by the presence of few surfactin molecules. The results indicate that SDS surfactants are more likely to form longer lasting films with fewer surfactin molecules than DTAB.

Solubilizer of bacterial origin surfactin increases the biological activity of C60 fullerene.

Currently, there exists conflicting data regarding the biological activity of unmodified fullerene C60. Various sources report its toxicity, geroprotective activity, and potential interaction with DNA. Contradictory findings regarding the toxicity of C60 may arise from the use of toxic solvents, as well as the influence of bioavailability and bioactivity on the preparation conditions of C60 suspensions. Furthermore, the microbiota of experimental animals can impact geroprotective activity results by releasing surfactants that facilitate substance penetration through the cell membrane. In this study, we selected conditions for solubilizing fullerene C60 in a solution of surfactin, a surfactant of bacterial origin, as well as in a 2% aqueous solution of TWEEN 80, employing ultrasound. Through bioluminescent analysis using lux biosensors in Escherichia coli MG1655, we observed that C60 in surfactin reduced induced genotoxic and oxidative stress. Given that surfactin enhances membrane permeability to fullerene C60, suspensions of fullerene in designated concentrations of surfactin can be regarded as a DNA protector and antioxidant, warranting further investigation as a promising component of novel drugs.

Evaluation of an external foam column for in situ product removal in aerated surfactin production processes.

In Bacillus fermentation processes, severe foam formation may occur in aerated bioreactor systems caused by surface-active lipopeptides. Although they represent interesting compounds for industrial biotechnology, their property of foaming excessively during aeration may pose challenges for bioproduction. One option to turn this obstacle into an advantage is to apply foam fractionation and thus realize in situ product removal as an initial downstream step. Here we present and evaluate a method for integrated foam fractionation. A special feature of this setup is the external foam column that operates separately in terms of, e.g., aeration rates from the bioreactor system and allows recycling of cells and media. This provides additional control points in contrast to an internal foam column or a foam trap. To demonstrate the applicability of this method, the foam column was exemplarily operated during an aerated batch process using the surfactin-producing Bacillus subtilis strain JABs24. It was also investigated how the presence of lipopeptides and bacterial cells affected functionality. As expected, the major foam formation resulted in fermentation difficulties during aerated processes, partially resulting in reactor overflow. However, an overall robust performance of the foam fractionation could be demonstrated. A maximum surfactin concentration of 7.7g/L in the foamate and enrichments of up to 4 were achieved. It was further observed that high lipopeptide enrichments were associated with low sampling flow rates of the foamate. This relation could be influenced by changing the operating parameters of the foam column. With the methodology presented here, an enrichment of biosurfactants with simultaneous retention of the production cells was possible. Since both process aeration and foam fractionation can be individually controlled and designed, this method offers the prospect of being transferred beyond aerated batch processes.

Antibacterial Activity of Surfactin and Synergistic Effect with Conventional Antibiotics Against Methicillin-Resistant Staphylococcus aureus Isolated from Patients with Diabetic Foot Ulcers.

The prevalence of diabetic foot ulcers (DFUs) is increasing, leading to a huge financial burden and human suffering. Furthermore, antibiotic resistance is an urgent problem in the realm of clinical practice. Antimicrobial peptides are an effective and feasible strategy for combating infections caused by drug-resistant bacteria. Therefore, we investigated the in vitro antimicrobial ability of the lipopeptide surfactin, either alone or in combination with conventional antibiotics, against the standard and clinical strains of Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), isolated from patients with DFUs. The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of surfactin on the selected strains were evaluated by a microbroth dilution technique. The growth curves of the selected strains with and without surfactin were measured, and transmission electron microscopy was used to observe the structure of surfactin-treated bacterial cells. The biofilm inhibitory abilities of surfactin were assessed by crystal violet staining. The antimicrobial interactions between surfactin and conventional antibiotics were established using a checkerboard assay, as well as determining the mutant prevention concentration. The inhibitory effect of surfactin on penicillinase was tested by iodometry. The MIC and MBC values of surfactin ranged from 512 to 1024 µg/mL and 1024 to 2048 µg/mL, respectively. Moreover, surfactin significantly prevented the S. aureus biofilm formation and displayed limited toxicity on human red blood cells. The synergies between surfactin and ampicillin, oxacillin, and tetracycline against S. aureus were revealed. In vitro resistance was not readily produced by surfactin. The action of surfactin may be by disrupting bacterial cell membranes and inhibiting penicillinase. Surfactin appears to be a potential option for the treatment of DFUs infected with MRSA, as it is capable of improving antimicrobial activities and can be used alone or in combination with conventional antibiotics to prevent or postpone the emergence of resistance.

Alteration in Community Dynamics of Chaetoceros curvisetus and Bacterioplankton Communities in Response to Surfactin Exposure.

The use of surfactin is a promising method to mitigate algal blooms. However, little is known about surfactin toxicity to algae and bacterioplankton. Here, we treated Chaetoceros curvisetus, the dominant species of algal blooms in the East China Sea, with 0, 0.5, 1, 2, 3, and 4 mg/L of surfactin for 96 h to investigate temporal variability. Our results showed that low concentrations of surfactin (<2 mg/L) changed the cell morphology of C. curvisetus, and higher concentrations (>3 mg/L) had lethal effects. Meanwhile, we examined the community dynamics of the free-living (FL, 0.22-5 μm) and particle-attached (PA, >5 μm) bacterioplankton of C. curvisetus in response to different surfactin concentrations and cultivation periods. Both PA and FL bacterioplankton were mainly composed of Proteobacteria, Actinobacteria, and Bacteroidetes, while FL bacterioplankton were more diverse than PA bacterioplankton. The variations of FL and PA bacterioplankton were significantly constrained by the surfactin concentration. Surfactin changed the lifestyle of some bacterioplankton from FL to PA, which mainly belonged to abundant bacterioplankton. Furthermore, we identified some surfactin-sensitive species/taxa. Our study will help enhance the ability to predict marine microbial responses under the effect of surfactin, providing a research foundation for this new harmful algal bloom mitigation method.

Experimental study on the molluscicidal activity of surfactin against Oncomelania hupensis

To evaluate the molluscicidal activity of surfactin against Oncomelania hupensis, so as to provide the experimental basis for use of Bacillus for killing O. hupensis. O. hupensis snails were collected from schistosomiasisendemic foci of Wuhu City on September 2022, and Schistosoma japonicum-infected snails were removed. Then, 60 snails were immersed in surfactin at concentrations of 2, 1, 0.5, 0.25, 0.125 mg/mL and 0.062 5 mg/mL for 24, 48, 72 hours at 26 °C, while ultrapure water-treated snails served as controls. The median lethal concentration (LC50) of surfactin against O. hupensis snails was estimated. O. hupensis snails were immersed in surfactin at a concentration of 24 h LC50 and ultrapure water, and then stained with propidium iodide (PI). The PI uptake in haemocyte was observed in O. hupensis snails using fluorescence microscopy. The mortality of O. hupensis was 5.0% following immersion in surfactin at a concentration of 0.062 5 mg/mL for 24 h, and the mortality was 100.0% following immersion in surfactin at a concentration of 2 mg/mL for 72 h, while no snail mortality was observed in the control group. There were significant differences in the mortality of O. hupensis in each surfactin treatment groups at 24 (χ2 = 180.150, P < 0.05), 48 h (χ2 = 176.786, P < 0.05) and 72 h (χ2 = 216.487, P < 0.05), respectively. The average mortality rates of O. hupensis were 38.9% (140/360), 62.2% (224/360) and 83.3% (300/360) 24, 48 h and 72 h post-immersion in surfactin, respectively (χ2 = 150.264, P < 0.05), and the 24, 48 h and 72 h LC50 values of surfactin were 0.591, 0.191 mg/mL and 0.054 mg/mL against O. hupensis snails. Fluorescence microscopy showed more numbers of haemocytes with PI uptake in 0.5 mg/mL surfactintreated O. hupensis snails than in ultrapure water-treated snails for 24 h, and there was a significant difference in the proportion of PI uptake in haemocytes between surfactin-and ultrapure water-treated snails (χ2 = 6.690, P < 0.05). Surfactin is active against O. hupensis snails, which may be associated with the alteration in the integrity of haemocyte membrane.

The effect of carbon source on the growth and lipopeptide production of Bacillus circulans

Glucose is the preferred carbon source for lipopeptide production using B. subtilis and B. amyloliquefaciens. However, glucose may not be the most cost-effective substrate for other Bacillus spp. This study compared the effect of glucose, fructose, glycerol, arabinose, maltose, xylose and lactose on biomass and lipopeptide production for s. Glycerol delivered the highest biomass concentration of 13.3 g.L−1, with glucose producing 4.3 g.L−1. Iturin, fengycin and surfactin production was higher for all evaluated carbon sources, over glucose. Fructose resulted in the highest concentration of all three lipopeptide families with iturin, fengycin and surfactin concentrations of 69.93, 111.83 and 35.45 mg.L−1 respectively. Results were compared to B. amyloliquefaciens grown on glucose, producing 108.66, 142.03 and 302.24 mg.L−1 iturin, fengycin and surfactin respectively. This study shows that glucose is not the optimal carbon source for B. circulans DSM-11. Glycerol or fructose offer a more efficient and feasible carbon source for B. circulans DSM-11 to produce biomass and lipopeptides.

Surfactin molecules with a cone-like structure promote the formation of membrane domains with negative spontaneous curvature and induce membrane invaginations

Surfactin uniquely influences lipid bilayer structure by initially inducing membrane invaginations before solubilization. In this study, we exposed DOPC giant vesicles to various surfactin concentrations at different temperatures and observed surfactin-induced membrane invaginations by using differential interference contrast and confocal laser fluorescence microscopy. These invaginations were stable at room temperature but not at higher temperatures. Surfactin molecules induce membrane nanodomains with negative spontaneous curvature and membrane invaginations despite their intrinsic conical shape and intrinsic positive curvature. Considering the experimentally observed capacity of surfactin to fluidize lipid acyl chains and induce partial dehydration of lipid headgroups, we propose that the resulting surfactin-lipid complexes exhibit a net negative spontaneous curvature. We further conducted 3D numerical Monte Carlo (MC) simulations to investigate the behaviour of vesicles containing negative curvature nanodomains within their membrane at varying temperatures. MC simulations demonstrated strong agreement with experimental results, revealing that invaginations are preferentially formed at low temperatures, while being less pronounced at elevated temperatures. Our findings go beyond the expectations of the Israelachvili molecular shape and packing concepts analysis. These concepts do not take into account the influence of specific interactions between neighboring molecules on the inherent shapes of molecules and their arrangement within curved membrane nanodomains. Our work contributes to a more comprehensive understanding of the complex factors governing vesicle morphology and membrane organization and provides insight into the role of detergent-lipid interactions in modulating vesicle morphology.

Adaptive Laboratory Evolution of Bacillus subtilis 168 for Efficient Production of Surfactin Using NH4Cl as a Nitrogen Source

Bacillus subtilis strain 168 is commonly used as a host to produce recombinant proteins and as a chassis for bio-based chemicals production. However, its preferred nitrogen source is organic nitrogen, which greatly increases production costs. In this study, adaptive laboratory evolution (ALE) was used to improve B. subtilis 168 growth using NH4Cl as the sole nitrogen source. The cell density (OD600) of a mutant strain LJ-3 was 208.7% higher than that of the original strain. We also optimized the metal ions in the medium and this resulted in a further increase in growth rate by 151.3%. Reintroduction of the sfp+ gene into strain LJ-3 led to the LJ-31 clone, which restored LJ-3’s ability to synthesize surfactin. The fermentation system was optimized (C/N, aeration, pH) in a 5 L bioreactor. Dry cell weight of 7.4 g/L and surfactin concentration of 4.1 g/L were achieved using the optimized mineral salt medium after 22 h of batch fermentation with a YP/S value of 0.082 g/g and a YP/X of 0.55 g/g. HPLC analysis identified the surfactin isoforms produced by strain LJ-31 in the synthetic medium as C13-surfactin 13.3%, C14-surfactin 44.02%, and C15-surfactin 32.79%. Hence, the variant LJ-3 isolated by ALE is a promising engineering chassis for efficient and cost-effective production of a variety of metabolites.

Preliminary Study of SurfactinProduction by Malaysian Local Isolates of Bacillus Subtilis

Surfactin is one of the most powerful lipopeptidebiosurfactants produced by various strains of Bacillus subtilis. It has exceptional surface activity, with antiviral, antibacterial, and antitumor properties. The four local isolates, which were named Bacillus subtilis1M, 3M, 7M, and 8M were provided by the School of Biosciences and Biotechnology, Faculty of Science and Technology, University of Kebangsaan, Malaysia. In this study, fermentation on shaker flasks was carried out to assess the ability of four local isolates of Bacillus subtilis strains to produce surfactin by using Cooper’s media formulation, and comparing their production with a commercial strain of Bacillus subtilis ATCC 21332, which was obtained from the American Type Culture Collection. High-Performance Liquid Chromatography (HPLC) was used for surfactin identification and surfactin concentration measurements. Results obtained show the four local isolates have the ability to produce surfactin. The Bacillus subtilis3M strain showed the highest amount of surfactin production with 117 (3) mg/L, while the Bacillus subtilis1M strain produced the lowest amount with 65 (5.4) mg/L. In addition, the production of Bacillus subtilis ATCC 21332 strain was found at 101(4) mg/L under the same fermentation conditions.

New insight into the role of oxygen supply for surfactin production in bench-scale bioreactors using induced surface aeration.

Surfactin biosurfactant produced by Bacillus sp. has been studied, because it has enormous potential in several applications in the oil and cosmetics industry. The cultivation conditions for obtaining this bioproduct, however, still require attention, as, for example, parameters related to oxygen supply and consumption. In this study, different volumetric oxygen transfer coefficient (KLa) levels (0-11.56h-1) were tested in bench-scale bioreactor for surfactin biosurfactant production by Bacillus velezensis H2O-1, using induced surface aeration. While conditions close to anaerobiosis showed insignificant production of surfactin, an intermediated KLa condition (4.24h-1) generated the best surfactin concentration (579.6mg L-1), with a volumetric productivity of 11.9mg L-1h-1. These results showed that the oxygen demand to produce surfactin is not high, being possible to use induced surface aeration strategy in bioreactors, minimizing foam formation. In addition, in all KLa conditions tested, surfactin homologues C14 and C15 had higher relative abundance. Nevertheless, the KLa parameter seems to have had minimal influence on affecting the relative abundances of surfactin homologues produced. Particularly noteworthy in this study is the possibility of producing surfactin using a low-cost and scale-up feasible aeration strategy, unlike the foam collection strategies developed in other studies to obtain this bioproduct.

Fouling Analysis in One-Stage Ultrafiltration of Precipitation-Treated Bacillus subtilis Fermentation Liquors for Biosurfactant Recovery.

Primary recovery of surfactin from precipitation-pretreated fermentation broths of Bacillus subtilis ATCC 21332 culture by one-stage dead-end and cross-flow ultrafiltration (UF) was studied. Dead-end experiments were first performed to select suitable conditions, including the amount of added ethanol-a micelle-destabilizing solvent (0-70 vol%), type (polyethersulfone, polyacrylonitrile, poly(vinylidene fluoride)) and molecular-weight cut-off (MWCO, 30-100 kDa) of the membrane in the surfactin concentration range of 0.25-1.23 g/L. Then, the cross-flow UF experiments were conducted to check the recovery performance in the ranges of feed surfactin concentration of 1.13-2.67 g/L, flow velocity of 0.025-0.05 m/s, and transmembrane pressure of 40-100 kPa. The Hermia model was also used to clarify membrane fouling mechanisms. Finally, three cleaning agents and two in situ cleaning ways (flush and back-flush) were selected to regain the permeate flux. As for the primary recovery of surfactin from the permeate in cross-flow UF, a polyethersulfone membrane with 100-kDa MWCO was suggested, and the NaOH solution at pH 11 was used for membrane flushing.

Sustainable Production of Biosurfactant from Agro-Industrial Oil Wastes by Bacillus subtilis and Its Potential Application as Antioxidant and ACE Inhibitor.

The microbial conversion of agro-industrial oil wastes into biosurfactants shows promise as a biomass refinery approach. In this study, Bacillus subtilis #309 was applied to produce surfactin using rapeseed and sunflower cakes, the most common oil processing side products in Europe. Studies of the chemical composition of the substrates were performed, to determine the feasibility of oil cakes for surfactin production. Initially, screening of proteolytic and lipolytic activity was performed to establish the capability of B. subtilis #309 for substrate utilization and hence effective surfactin production. B. subtilis #309 showed both proteolytic and lipolytic activity. The process of surfactin production was carefully analyzed by measurement of the surfactin concentration, pH, surface tension (ST) and emulsification index (E24). The maximal surfactin concentration in the sunflower and rapeseed cake medium reached 1.19 ± 0.03 and 1.45 ± 0.09 g/L, respectively. At the same time, a progressive decrease in the surface tension and increase in emulsification activity were observed. The results confirmed the occurrence of various surfactin homologues, while the surfactin C15 was the dominant one. Finally, the analysis of surfactin biological function exhibited antioxidant activity and significant angiotensin-converting enzyme (ACE)-inhibitory activity. The half-maximal inhibitory concentration (IC50) value for ACE inhibition was found to be 0.62 mg/mL for surfactin. Molecular docking of the surfactin molecule to the ACE domains confirmed its inhibitory activity against ACE. Several interactions, such as hydrophobic terms, hydrogen bonds and van der Waals interactions, were involved in the complex stabilization. To the best of our knowledge, this is the first report describing the effect of a lipopeptide biosurfactant, surfactin, produced by B. subtilis for multifunctional properties in vitro, namely the ACE-inhibitory activity and the antioxidant properties, using different assays, such as 2,2-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP). Thus, the ACE-inhibitory lipopeptide biosurfactant shows promise to be used as a natural antihypertensive agent.

Optimization of processing parameters for the improved production of surfactin from B. Subtilis using a statistical approach and demonstration of its imminent potential in cosmetic applications

Bacillus lipopeptides are promising biosurfactants that find applications in various sectors like biotechnological, cosmetics and biopharma due to their outstanding functionality like high specificity, low toxicity, and high surface activity. Among the different Bacillus species, Bacillus subtilis is well known for producing a biosurfactant surfactin. The objective of the work was to optimize the process parameters such as temperature, working volume and agitation speed that critically influence the surfactin production in batch cultivation systems using shake-flasks. Optimization of surfactin production was carried out using response surface methodology (RSM). To evaluate the significance of the processing parameters and to locate the actual optimal condition (which significantly affected the lipopeptide production) the Central Composite Design (CCD) method was used. The optimal conditions were found to be a culture volume of 250 mL (in a 500 mL conical flask), a temperature of 37˚C and an agitation speed of 250 rpm with the maximum surfactin concentration of 1.49 g/L. Results of RSM showed that the predicted response could be closely correlated with the experimentally obtained production. A kinetics study on surfactin production, substrate consumption and biomass production at optimal conditions was carried out. Overall, this study provided an efficient method for optimizing the process parameters by reducing the production cost and enhancing the production of surfactin. Partially purified surfactin based cosmetic nanoemulsion remained stable for over 100 days maintained and found to have hydrodynamic diameter of 170 and 173.9 nm and PDI of 0.178 and 0.170 on 0th and 100th day, respectively, at 28 °C. On the successful formulation of stable nanoemulsion, plant-sourced thickener, xanthan gum, was incorporated in formulating thickened cosmetic emulsion. Thickened nanoemulsion exhibited pseudoplastic behaviour and has a hydrodynamic diameter of 173.2 nm and PDI of 0.177, proving that the introduction of xanthan gum did not affect the stability.

A comparative study on surfactin production from various fruit juices for diverse applications

The ample interesting properties of lipopeptide biosurfactants- to name a few- hemolytic, antiviral, antifungal, and antibacterial properties are of significant interest to the research community. Surfactin, one of the most potent microbial surfactants, is a biosurfactant of the lipopeptide type with interesting physicochemical characteristics and biological functions. However, commercial applications of surfactin are severely constrained by its high price and limited productivity. This is primarily due to the increased production cost associated with using a chemically defined medium for cultivating the biosurfactant-producing microorganisms and the purification costs. It is crucial to highlight that despite many advancements in microbial surfactant industries, the large-scale manufacture of many biosurfactants remains economically unviable.To understand the role of substrate and carbon source in surfactin production, fruit juices rich in carbon sources (grape, pineapple, cashew apple) and pre-optimized Glucose mineral salt medium (GMSM) were compared for the production of surfactin in our study. We observed that surfactin production is high when cashew apple juice (maximum surfactin concentraiton =3.65 g/L) and grape juice (maximum surfactin concentration = 3.16 g/L) are used as the carbon sources. We believe that the results of the current study will give further impetus to the research on biosurfactants synthesis using cheaper and renewable substrates towards improving their economic viability to make a successful foray into various applications. Because of their unique properties, microbial surfactants are useful in many fields, such as environmental remediation, microbial degradation, enhanced oil recovery, drug research, food manufacturing, and more.

Surfactin-stabilized poly(D,L-lactide) nanoparticles for potential skin application

In recent years polymeric nanoparticles stabilized by biocompatible polyesters of poly(D,L-lactide) origin have been under investigation due to their favorable properties as drug nanocarriers useful for cosmetics and pharmaceutical applications. However, their design and fabrication are still limited to nonionic or polymeric stabilizers whose surface activity, toxicity, and biocompatibility may be insufficient for biological issues including transdermal applications. Therefore, there is still an ample room to look for more modern ionic biosurfactants that, apart from favorable surface properties, can ensure high biocompatibility of the system, increase the skin penetration of the active substance, and, in the future, possibly also the antimicrobial and antitumor activity of the produced nanocarrier. Accordingly, herein, we present poly(DL-lactide) nanoparticles stabilized by surfactin - a biocompatible anionic biosurfactant, for potential transdermal administration. The nanoparticles were obtained via a nanoprecipitation approach, and their physicochemical evaluation including size, surface charge, morphology, and colloidal stability was assessed. DLS measurements TEM and AFM confirmed, respectively, the obtained nanoparticles’ diameter below 200 nm as well as their morphology and shape. Electrophoretic light scattering provided negative ζ-potential of the studied nanoobjects while backscattering profiles made it possible to prove their long-term kinetic stability. In order to test the optimized nanoparticles under the surfactin concentration, cytotoxicity of the obtained systems was evaluated in vitro upon two normal human skin cell lines, i.e., HaCaT (human epidermal keratinocytes) and NHDF cells (normal human dermal fibroblasts). These studies indicated the safest concentration of the biosurfactant for nanoparticle stabilization. The skin permeability tests provided on pig ear skin proved the enhanced ability of the nanoparticles to deeper penetrate the epidermis after 5 h of the permeation test. The presented results prove that these surfactin-stabilized poly(D,L-lactide) nanoparticles are good biocompatible candidates for transdermal applications.

Formulation of a stable biocosmetic nanoemulsion using a Bacillus lipopeptide as the green-emulsifier for skin-care applications

The current work aims to formulate a stable cosmetic nanoemulsion using nature-derived ingredients such as surfactin (a lipopeptide-type biosurfactant produced by Bacillus sp) as an emulsifier, plant-based essential oil as a bioactive ingredient, and coconut oil as the base oil using high-energy ultrasonication method. To accomplish a stable nanoemulsion formulation, experiments with varying combinations of surfactin concentration, essential oil concentration, ultrasonication time, and amplitude were performed. Statistical analysis of samples, based on the responses such as visual observation, droplet size, and polydispersity index, facilitated proper segregation of best-performing samples from those of poorly performing. Nanoemulsions formulated using optimal conditions of oil-to-surfactant ratio (O/S) of 7.4:1 (%w/w), ultrasonication amplitude of 40%, and ultrasonication time of 4.5 min showed greater stability with average droplets size of 170 ± 12 nm, polydispersity index (PDI) of 0.17 ± 0.01 and zeta potential of −56 ± 0.5 mV. The nanoemulsion remained completely stable with no sign of phase separation during the test period of 200 days. Further, the performance of samples toward different stability tests such as heat treatment, centrifugation test, NaCl treatment was satisfactory. In addition, nanoemulsion exhibited significant antioxidant and antimicrobial activity toward Staphylococcus aureus. Thus, the current study demonstrates the imminent potential of surfactin as a bio-emulsifier in skin-care cosmetics.

Micelle morphology observation method of lipopeptide by negative-staining-based transmission electron microscopy

Lipopeptides, novel biosurfactants showing versatile promising applications in enhanced oil recovery, textile industry, agriculture and daily chemical products, etc., are profoundly highlighted recently. Surfactin is one of the most typical representatives of lipopetide family. The critical micelle concentration (CMC) of surfactin is as low as 10–20 mg/L. When its concentration reaches above the CMC, different micelle structure will be formed and the surface-active performances might be changed with varied micelle morphologies. Thus, observation of the changes of surfactin micellar form at different concentrations is of great significance for its new applications. But so far, the micelle structure of surfactin (and also other lipopeptide molecules) is not reported yet, and the method for effectively observing the micelle morphology is limited as well. Here, we developed a method based on transmission electron microscopy combined with negative staining to observe the morphology of surfactin micelles, with which we can clearly observe the changes of micelle morphology of surfactin (or other lipopeptides) at different concentrations. Spherical micelles only form when the concentration of surfactin is low. With the increase in concentration, rod-shaped micelles of surfactin can form. Furthermore, complex rod-shaped-micelle-layer and big ring structure will form when the concentration of surfactin is very high.

The Role of Surfactin Production by Bacillus velezensis on Colonization, Biofilm Formation on Tomato Root and Leaf Surfaces and Subsequent Protection (ISR) against Botrytis cinerea.

Many aspects regarding the role of lipopeptides (LPs) in bacterial interaction with plants are not clear yet. Of particular interest is the LP family of surfactin, immunogenic molecules involved in induced systemic resistance (ISR) and the bacterial colonization of plant surfaces. We hypothesize that the concentration of surfactin produced by a strain correlates directly with its ability to colonize and persist on different plant surfaces, which conditions its capacity to trigger ISR. We used two Bacillus velezensis strains (BBC023 and BBC047), whose antagonistic potential in vitro is practically identical, but not on plant surfaces. The surfactin production of BBC047 is 1/3 higher than that of BBC023. Population density and SEM images revealed stable biofilms of BBC047 on leaves and roots, activating ISR on both plant surfaces. Despite its lower surfactin production, strain BBC023 assembled stable biofilms on roots and activated ISR. However, on leaves only isolated, unstructured populations were observed, which could not activate ISR. Thus, the ability of a strain to effectively colonize a plant surface is not only determined through its production of surfactin. Multiple aspects, such as environmental stressors or compensation mechanisms may influence the process. Finally, the importance of surfactin lies in its impacts on biofilm formation and stable colonization, which finally enables its activity as an elicitor of ISR.

The interactions of the biosurfactant surfactin in coal flotation

Surfactin, a biosurfactant, has the potential to replace synthetic surfactants in froth flotation. This research investigates the surface interactions between surfactin and coal which determine whether surfactin has collecting or depressant characteristics on coal using electrokinetic, FTIR, and micro-flotation experiments. At concentrations of 5 mg/L, surfactin removes species on the surface of coal, especially in the alkaline pH range. At surfactin concentration of 15 mg/L adsorption of surfactin onto coal surfaces are indicated and likely to be due to hydrophobic physisorption between aliphatic groups of surfactin and the hydrophobic carbonaceous surface functional groups of coal. Hydrophobicity of coal was observed to be enhanced at pH 3,6 and 10 except the intermediate pH of 8. Micro-flotation tests showed that hydrophobicity of coal was most significantly enhanced by surfactin presence at pH 3 and 15 mg/L from 42.9% to 74%, and least impacted when surfactin concentration was 5 mg/L at a pH of 10. The collecting or depressant characteristics of surfactin on coal as a function of pH and surfactin concentration have been demonstrated for the potential use of this novel biosurfactant as a Green Chemistry substitute for synthetic surfactants.