Interaction of a bacterial monorhamnolipid secreted by Pseudomonas aeruginosa MA01 with phosphatidylcholine model membranes

Bioformulation of Bacillus proteolyticus MITWPUB1 and its biosurfactant to control the growth of phytopathogen Sclerotium rolfsii for the crop Brassica juncea var local, as a sustainable approach

Bacillus proteolyticus MITWPUB1 is a potential producer of biosurfactants (BSs), and the organism is also found to be a producer of plant growth promoting traits, such as hydrogen cyanide and indole acetic acid (IAA), and a solubilizer of phosphate. The BSs were reportedly a blend of two classes, namely glycolipids and lipopeptides, as found by thin layer chromatography and Fourier-transform infrared spectroscopy analysis. Furthermore, semi-targeted metabolite profiling via liquid chromatography mass spectroscopy revealed the presence of phospholipids, lipopeptides, polyamines, IAA derivatives, and carotenoids. The BS showed dose-dependent antagonistic activity against Sclerotium rolfsii; scanning electron microscopy showed the effects of the BS on S. rolfsii in terms of mycelial deformations and reduced branching patterns. In vitro studies showed that the application of B. proteolyticus MITWPUB1 and its biosurfactant to seeds of Brassica juncea var local enhanced the seed germination rate. However, sawdust-carrier-based bioformulation with B. proteolyticus MITWPUB1 and its BS showed increased growth parameters for B. juncea var L. This study highlights a unique bioformulation combination that controls the growth of the phytopathogen S. rolfsii and enhances the plant growth of B. juncea var L. Bacillus proteolyticus MITWPUB1 was also shown for the first time to be a prominent BS producer with the ability to control the growth of the phytopathogen S. rolfsii.

Effects of Natural Rhamnolipid Mixture on Dioleoylphosphatidylcholine Model Membrane Depending on Method of Preparation and Sterol Content

Rhamnolipids as biosurfactants have a potentially wide range of applications, for example, as "green" surfactants or components of drug delivery systems, which is associated with the features of their interaction with cell membranes. However, as noted in the literature, those kind of features have not been sufficiently studied now. This paper presents a study of the interaction of a natural mixture of rhamnolipids produced by bacteria of the rhizosphere zone of plants Pseudomonas aeruginosa with model membranes-liposomes based on dioleoylphosphatidylcholine (DOPC), depending on the method of their preparation and the content of sterols-ergosterol, cholesterol, lanosterol. Liposomes with rhamnolipids were prepared by two protocols: with film method from a mixture of DOPC and rhamnolipids; with film method from DOPC and injection of water solution of rhamnolipids. Joint analysis of the data of 31P NMR spectroscopy and ATR-FTIR spectroscopy showed that in the presence of rhamnolipids, the mobility of the head group of the DOPC phospholipid increases, the conformational disorder of the hydrophobic tail increases, and the degree of hydration of the C=O and P=O groups of the phospholipid decreases. It can be assumed that, when prepared from a mixture, rhamnolipids are incorporated into the membrane in the form of clusters and are located closer to the middle of the bilayer; while when prepared by injection, rhamnolipid molecules migrate into the membrane in the form of individual molecules and are located closer to the head part of phospholipids. The sterol composition of the model membrane also affects the interaction of rhamnolipids with the membrane. Here it is worth noting the possible presence of type of interaction between rhamnolipids and ergosterol differ from other investigated sterols, due to which rhamnolipid molecules are embedded in the area where ergosterol is located.

Biosurfactants' multifarious functional potential for sustainable agricultural practices

Increasing food demand by the ever-growing population imposes an extra burden on the agricultural and food industries. Chemical-based pesticides, fungicides, fertilizers, and high-breeding crop varieties are typically employed to enhance crop productivity. Overexploitation of chemicals and their persistence in the environment, however, has detrimental effects on soil, water, and air which consequently disturb the food chain and the ecosystem. The lower aqueous solubility and higher hydrophobicity of agrochemicals, pesticides, metals, and hydrocarbons allow them to adhere to soil particles and, therefore, continue in the environment. Chemical pesticides, viz., organophosphate, organochlorine, and carbamate, are used regularly to protect agriculture produce. Hydrophobic pollutants strongly adhered to soil particles can be solubilized or desorbed through the usage of biosurfactant/s (BSs) or BS-producing and pesticide-degrading microorganisms. Among different types of BSs, rhamnolipids (RL), surfactin, mannosylerythritol lipids (MELs), and sophorolipids (SL) have been explored extensively due to their broad-spectrum antimicrobial activities against several phytopathogens. Different isoforms of lipopeptide, viz., iturin, fengycin, and surfactin, have also been reported against phytopathogens. The key role of BSs in designing and developing biopesticide formulations is to protect crops and our environment. Various functional properties such as wetting, spreading, penetration ability, and retention period are improved in surfactant-based formulations. This review emphasizes the use of diverse types of BSs and their source microorganisms to challenge phytopathogens. Extensive efforts seem to be focused on discovering the innovative antimicrobial potential of BSs to combat phytopathogens. We discussed the effectiveness of BSs in solubilizing pesticides to reduce their toxicity and contamination effects in the soil environment. Thus, we have shed some light on the use of BSs as an alternative to chemical pesticides and other agrochemicals as sparse literature discusses their interactions with pesticides. Life cycle assessment (LCA) and life cycle sustainability analysis (LCSA) quantifying their impact on human activities/interventions are also included. Nanoencapsulation of pesticide formulations is an innovative approach in minimizing pesticide doses and ultimately reducing their direct exposures to humans and animals. Some of the established big players and new entrants in the global BS market are providing promising solutions for agricultural practices. In conclusion, a better understanding of the role of BSs in pesticide solubilization and/or degradation by microorganisms represents a valuable approach to reducing their negative impact and maintaining sustainable agricultural practices.

Deciphering the role of plant plasma membrane lipids in response to invasion patterns: how could biology and biophysics help?

Plants have to constantly face pathogen attacks. To cope with diseases, they have to detect the invading pathogen as early as possible via the sensing of conserved motifs called invasion patterns. The first step of perception occurs at the plasma membrane. While many invasion patterns are perceived by specific proteinaceous immune receptors, several studies have highlighted the influence of the lipid composition and dynamics of the plasma membrane in the sensing of invasion patterns. In this review, we summarize current knowledge on how some microbial invasion patterns could interact with the lipids of the plasma membrane, leading to a plant immune response. Depending on the invasion pattern, different mechanisms are involved. This review outlines the potential of combining biological with biophysical approaches to decipher how plasma membrane lipids are involved in the perception of microbial invasion patterns.

Carbohydrate-carbohydrate interaction drives the preferential insertion of dirhamnolipid into glycosphingolipid enriched membranes

Rhamnolipids (RLs) are among the most important biosurfactants produced by microorganisms, and have been widely investigated because of their multiple biological activities. Their action appears to depend on their structural interference with lipid membranes, therefore several studies have been performed to investigate this aspect. We studied by X-ray scattering, neutron reflectometry and molecular dynamic simulations the insertion of dirhamnolipid (diRL), the most abundant RL, in model cellular membranes made of phospholipids and glycosphingolipids. In our model systems the affinity of diRL to the membrane is highly promoted by the presence of the glycosphingolipids and molecular dynamics simulations unveil that this evidence is related to sugar-sugar attractive interactions at the membrane surface. Our results improve the understanding of the plethora of activities associated with RLs, also opening new perspectives in their selective use for pharmaceutical and cosmetics formulations. Additionally, they shed light on the still debated role of carbohydrate-carbohydrate interactions as driving force for molecular contacts at membrane surface.

Bacterial rhamnolipids and their 3-hydroxyalkanoate precursors activate Arabidopsis innate immunity through two independent mechanisms

Plant innate immunity is activated upon perception of invasion pattern molecules by plant cell-surface immune receptors. Several bacteria of the genera Pseudomonas and Burkholderia produce rhamnolipids (RLs) from l-rhamnose and (R)-3-hydroxyalkanoate precursors (HAAs). RL and HAA secretion is required to modulate bacterial surface motility, biofilm development, and thus successful colonization of hosts. Here, we show that the lipidic secretome from the opportunistic pathogen Pseudomonas aeruginosa, mainly comprising RLs and HAAs, stimulates Arabidopsis immunity. We demonstrate that HAAs are sensed by the bulb-type lectin receptor kinase LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION/S-DOMAIN-1-29 (LORE/SD1-29), which also mediates medium-chain 3-hydroxy fatty acid (mc-3-OH-FA) perception, in the plant Arabidopsis thaliana HAA sensing induces canonical immune signaling and local resistance to plant pathogenic Pseudomonas infection. By contrast, RLs trigger an atypical immune response and resistance to Pseudomonas infection independent of LORE. Thus, the glycosyl moieties of RLs, although abolishing sensing by LORE, do not impair their ability to trigger plant defense. Moreover, our results show that the immune response triggered by RLs is affected by the sphingolipid composition of the plasma membrane. In conclusion, RLs and their precursors released by bacteria can both be perceived by plants but through distinct mechanisms.

Rhamnolipids and essential oils in the control of mosquito-borne tropical diseases

The diseases transmitted by mosquito vectors are a great public health issue. Thus, effective vector control becomes the main strategy to reduce their prevalence. However, insecticide resistance has become a huge concern for the mitigation of mosquitoes; here, we propose the use of rhamnolipids in emulsion with clove oil against Aedes aegypti and Culex quinquefasciatus. The toxicity of rhamnolipids and clove oil to two species of mosquitoes transmitting tropical diseases was investigated. After 24 h, the LC₅₀ was 140 mg/L when rhamnolipids were used and 154 mg/L when clove oil was used against Aedes aegypti larvae. In the case of Culex quinquefasciatus, the LC₅₀ was 130 mg/L for rhamnolipids and 19 mg/L for clove oil. When the concentrations of the upper limits of one of the solutions (rhamnolipid or clove oil) were mixed, 100% mortality was obtained after 24 h. The bioassay of insecticidal action for solutions of rhamnolipids and clove oil in the lower limit, upper limit, and lethal concentration 50 to determine the effect on 50% of the population (KD50) achieved low results from KD50 to the upper limit compared to the other concentrations for both Aedes aegypti and Culex quinquefasciatus. The rhamnolipids and clove oil at the upper limit concentration had the greatest repellent activity against the two mosquito species. Bioassays using different concentrations of rhamnolipids revealed variations in the morphology of the intestinal epithelium (800 mg/L). A concentration of 900 mg/L led to the most severe morphological changes in the organization of the epithelium and the cells lining the intestines of these larvae. When larvae were exposed to a concentration of 1000 mg/L, the marginalization of chromatin in the nucleus of epithelial cells was very severe, indicating the onset of cell death.Key points• The toxicity of rhamnolipids and clove oil has a larvicidal, insecticidal, and repellent effect.• The combination of concentrations of these compounds enhances their action.• Different concentrations of rhamnolipids led to severe morphological changes in the organization of the epithelium and the cells and the intestines of larvae.

Interaction of an acidic sophorolipid biosurfactant with phosphatidylcholine model membranes

Sophorolipids (SLs) constitute a group of unique biosurfactants (BS) in the light of their outstanding properties, among which their antimicrobial activities stand out. SLs can exist mainly in an acidic and a lactonic form, both of which display inhibitory activity. Given the amphipathic nature of SLs it is feasible that these antimicrobial actions are the result of the perturbation of the physicochemical properties of targeted membranes. Thus, in this work we have carried out a biophysical study to unveil the molecular details of the interaction of an acidic SL with a model phospholipid membrane made of 1,2-dipalmitoy-sn-glycero-3-phosphocholine (DPPC). Using differential scanning calorimetry it was found that SL altered the phase behaviour of DPPC at low molar fractions, producing fluid phase immiscibility with the result of formation of biosurfactant-enriched domains within the phospholipid bilayer. Fourier-transform infrared spectroscopy showed that SL interacted with DPPC increasing ordering of the phospholipid acyl chain palisade and hydration of the lipid/water interface. Small angle X-ray scattering showed that SL did not modify bilayer thickness in the biologically relevant L_α fluid phase. SL was found to induce contents leakage in 1-palmitoy-2-oleoy-sn-glycero-3-phosphocholine (POPC) unilamellar liposomes, at sublytic concentrations below the cmc. This SL-induced membrane permeabilization at concentrations below the onset for membrane solubilization can be the result of the formation of laterally segregated domains, which might contribute to provide a molecular basis for the reported antimicrobial actions of SLs.

Impact of the number of rhamnose moieties of rhamnolipids on the structure, lateral organization and morphology of model biomembranes

Various studies have described remarkable biological activities and surface-active properties of rhamnolipids, leading to their proposed use in a wide range of industrial applications. Here, we report on a study of the effects of monorhamnolipid RhaC₁₀C₁₀ and dirhamnolipid RhaRhaC₁₀C₁₀ incorporation into model membranes of varying complexity, including bacterial and heterogeneous model biomembranes. For comparison, we studied the effect of HAA (C₁₀C₁₀, lacking a sugar headgroup) partitioning into these membrane systems. AFM, confocal fluorescence microscopy, DSC, and Laurdan fluorescence spectroscopy were employed to yield insights into the rhamnolipid-induced morphological changes of lipid vesicles as well as modifications of the lipid order and lateral membrane organization of the model biomembranes upon partitioning of the different rhamnolipids. The partitioning of the three rhamnolipids into phospholipid bilayers changes the phase behavior, fluidity, lateral lipid organization and morphology of the phospholipid membranes dramatically, to what extent, depends on the headgroup structure of the rhamnolipid, which affects its packing and hydrogen bonding capacity. The incorporation into giant unilamellar vesicles (GUVs) of a heterogeneous anionic raft membrane system revealed budding of domains and fission of daughter vesicles and small aggregates for all three rhamnolipids, with major destabilization of the lipid vesicles upon insertion of RhaC₁₀C₁₀, and also formation of huge GUVs upon the incorporation of RhaRhaC₁₀C₁₀. Finally, we discuss the results with regard to the role these biosurfactants play in biology and their possible impact on applications, ranging from agricultural to pharmaceutical industries.

Biosurfactants in Plant Protection Against Diseases: Rhamnolipids and Lipopeptides Case Study

Biosurfactants are amphiphilic surface-active molecules that are produced by a variety of microorganisms including fungi and bacteria. Pseudomonas, Burkholderia, and Bacillus species are known to secrete rhamnolipids and lipopeptides that are used in a wide range of industrial applications. Recently, these compounds have been studied in a context of plant-microbe interactions. This mini-review describes the direct antimicrobial activities of these compounds against plant pathogens. We also provide the current knowledge on how rhamnolipids and lipopeptides stimulate the plant immune system leading to plant resistance to phytopathogens. Given their low toxicity, high biodegradability and ecological acceptance, we discuss the possible role of these biosurfactants as alternative strategies to reduce or even replace pesticide use in agriculture.

Contributions and Limitations of Biophysical Approaches to Study of the Interactions between Amphiphilic Molecules and the Plant Plasma Membrane

Some amphiphilic molecules are able to interact with the lipid matrix of plant plasma membranes and trigger the immune response in plants. This original mode of perception is not yet fully understood and biophysical approaches could help to obtain molecular insights. In this review, we focus on such membrane-interacting molecules, and present biophysically grounded methods that are used and are particularly interesting in the investigation of this mode of perception. Rather than going into overly technical details, the aim of this review was to provide to readers with a plant biochemistry background a good overview of how biophysics can help to study molecular interactions between bioactive amphiphilic molecules and plant lipid membranes. In particular, we present the biomimetic membrane models typically used, solid-state nuclear magnetic resonance, molecular modeling, and fluorescence approaches, because they are especially suitable for this field of research. For each technique, we provide a brief description, a few case studies, and the inherent limitations, so non-specialists can gain a good grasp on how they could extend their toolbox and/or could apply new techniques to study amphiphilic bioactive compound and lipid interactions.

Design and Toxicity Evaluation of Novel Fatty Acid-Amino Acid-Based Biocompatible Surfactants

Surfactants occupy an important place owing to their wide application, but primarily compromised due to its toxicity issues. This raises the need for exploration of newer surfactants with increased biocompatibility. Novel fatty acid- and amino acid-based surfactants were prepared using standard carbodiimide chemistry. Pyrene assay was implemented to confirm the amphiphilic nature of the surfactants and to calculate their CMC (critical micellar concentration). In vitro hemolytic and cell culture study in MCF-7 and HEK cell line were done to check the in vitro biocompatibility of the developed surfactants in comparison to marketed surfactants Triton X-100 and Tween ® 80. In vivo biocompatibility test in female Swiss albino mice was carried out in comparison to marketed surfactants with respect to serum markers, organ histology, and RBC morphology. Surfactant synthesis provided more than 60% yield in all the conjugates. Pyrene assay concluded the amphiphilic nature of the surfactants with lowest CMC of 0.083% w/v in the case of stearic acid and valine conjugate. In vitro hemolytic and cell culture study depicted highest biocompatibility in vitro as compared to marketed surfactants. Similar results were obtained in in vivo biocompatibility with respect to AST (aspartate transaminase), ALT (alanine transaminase), BUN (blood urea nitrogen), and creatinine serum levels and histology of spleen, liver, and kidney in comparison to marketed surfactants Triton X-100 and Tween ® 80. The developed surfactant also depicted least RBC morphology changes in vivo. Stearic acid valine conjugate thus depicted potential for further application in formulation development replacing the commercially available surfactants.

Exploring the Dual Interaction of Natural Rhamnolipids with Plant and Fungal Biomimetic Plasma Membranes through Biophysical Studies

Rhamnolipids (RLs) are potential biocontrol agents for crop culture protection. Their mode of action has been proposed as dual, combining plant protection activation and antifungal activities. The present work focuses on the interaction of natural RLs with plant and fungi membrane models at the molecular scale. Representative models were constructed and the interaction with RLs was studied by Fourier transform infrared (FTIR) and deuterium nuclear magnetic resonance (²H NMR) spectroscopic measurements. Molecular dynamic (MD) simulations were performed to investigate RL insertion in lipid bilayers. Our results showed that the RLs fit into the membrane models and were located near the lipid phosphate group of the phospholipid bilayers, nearby phospholipid glycerol backbones. The results obtained with plant plasma membrane models suggest that the insertion of RLs inside the lipid bilayer did not significantly affect lipid dynamics. Oppositely, a clear fluidity increase of fungi membrane models was observed. This effect was related to the presence and the specific structure of ergosterol. The nature of the phytosterols could also influence the RL effect on plant plasma membrane destabilization. Subtle changes in lipid dynamics could then be linked with plant defense induction and the more drastic effects associated with fungal membrane destabilization.

Microemulsion synthesis of silver nanoparticles using biosurfactant extracted from Pseudomonas aeruginosa MKVIT3 strain and comparison of their antimicrobial and cytotoxic activities

In the present study, an efficient biosurfactant producing bacterial strain Pseudomonas aeruginosa MKVIT3 was isolated from an oil logging area in Vellore district of Tamil Nadu, India. Liquid chromatography-mass spectrometry (LC-MS/MS) analysis was performed for the identification of different congeners present in the extracted biosurfactant. The column purified biosurfactant was used to stabilise the formation of silver nanoparticles (NP) using borohydrate reduction in reverse micelles. The silver NP were characterised using UV-vis absorption spectroscopy, Powder-XRD TEM analysis and zeta potential. A comparative study of the antimicrobial activity and cytotoxic efficacy was done for the extracted purified biosurfactant and the silver NP. The LC-MS/MS analysis of the biosurfactant revealed the presence of five rhamnolipid congeners. The synthesised silver NP showed the characteristic absorption peak in UV-vis at 440 nm. Powder-XRD and TEM analysis revealed the average particle size of the NP as 17.89 ± 8.74 nm as well as their cubic structure. Zeta potential value of -30.9 mV suggested that the silver NPs are stable in the suspension. Comparative study of the antimicrobial activity revealed that the silver NP are more potent than the biosurfactant in inhibiting the growth of microbes. Cytotoxic activity revealed that the biosurfactant are more effective than the synthesised silver NP.

Interaction of curcumin with 1,2-dioctadecanoyl-sn-glycero-3-phosphocholine liposomes: Intercalation of rhamnolipids enhances membrane fluidity, permeability and stability of drug molecule

Stability of curcumin in neutral and alkaline buffer conditions has been a serious concern for its medicinal applications. We demonstrate that the stability of curucmin can be improved in 1,2-Dioctadecanoyl-sn-glycero-3-phosphocholine (DSPC) liposomes. Curcumin strongly partition into liquid crystalline phase compared to solid gel phase of DSPC liposomes. Variation of fluorescence intensity of curcumin associated with liposomes with temperature successfully determines phase transition temperature of DSPC liposomes. However, at higher molar ratio curcumin can influence phase transition temperature by intercalating into deep hydrophobic layer of liposomes and facilitating fusion of two membrane phases. Rhamnolipids (RLs) are recently being applied for various biomedical applications. Here, we have explored new insight on intercalation of rhamnolipids with DSPC liposomes. Intercalation of rhamnolipids exceptionally increases partition of curcumin into solid gel phase of DSPC liposomes, whereas this increase is moderate in liquid crystalline phase. Fluorescence quenching study establishes that permeability and fluidity of the DSPC liposomes are enhanced in the presence of RLs. Membrane permeability and fluidity can be improved further by increasing the percentage of RLs in DSPC liposomes. The phase transition temperature of DSPC liposomes decreases with increase in percentage of RLs in DSPC liposomes by encouraging fusion between solid gel and liquid crystalline phases. Intercalation of RLs is found to further boost stability of drug, curcumin, in DSPC liposomes. Thus, mixing RLs with DSPC liposomes could potentially serve as a good candidate for drug delivery application.

Rhamnolipids elicit the same cytotoxic sensitivity between cancer cell and normal cell by reducing surface tension of culture medium

Biosurfactant rhamnolipids have been claimed to show biological activities of inhibiting the proliferation of cancer cells. In this study, the cytotoxicity of rhamnolipids was examined on four cancer cells (HepG2, Caco-2, Hela, MCF-7 cells) and two normal cells (HK-2 cell, primary hepatocyte). Interestingly, both cancer cells and normal cells exhibited similar sensitivities to the addition of rhamnolipids in culture medium, and the cytotoxicity was largely attenuated by the presence of fetal bovine serum (FBS) in culture medium. In correlation of the mono-/di-rhamnolipid cytotoxicity with the surface tension of culture medium, it was found that rhamnolipids triggered cytotoxicity whenever the surface tension of culture medium decreased below 41 mN/m irrespective of the FBS content in culture medium, cell line, or rhamnolipid congener. Similarly, each chemical surfactant (Tween-80, sodium dodecyl sulfate, and sodium dodecyl benzene sulfonate) could cause cytotoxicity on HepG2 cells whenever its addition made the surface tension under 41 mN/m in culture medium with or without the presence of FBS. It seems that rhamnolipids, like chemical surfactants, exhibited cytotoxicity by reducing the surface tension of culture medium rather than by changing its specific molecular structure, which had no selection on tumor cells. This study could offer helps to correct the misleading biological activity of rhamnolipids and to avoid the possible large wastes of time and expenses on developing the applications in antitumor drugs.

Potential therapeutic applications of biosurfactants

Biosurfactants have recently emerged as promising molecules for their structural novelty, versatility, and diverse properties that are potentially useful for many therapeutic applications. Mainly due to their surface activity, these molecules interact with cell membranes of several organisms and/or with the surrounding environments, and thus can be viewed as potential cancer therapeutics or as constituents of drug delivery systems. Some types of microbial surfactants, such as lipopeptides and glycolipids, have been shown to selectively inhibit the proliferation of cancer cells and to disrupt cell membranes causing their lysis through apoptosis pathways. Moreover, biosurfactants as drug delivery vehicles offer commercially attractive and scientifically novel applications. This review covers the current state-of-the-art in biosurfactant research for therapeutic purposes, providing new directions towards the discovery and development of molecules with novel structures and diverse functions for advanced applications.