Bacillus methylotrophicus DCS1: Production of Different Lipopeptide Families, In Vitro Antifungal Activity and Suppression of Fusarium Wilt in Tomato Plants.

The present work aims to quantitatively and qualitatively monitor the production of lipopeptide mixtures by Bacillus methylotrophicus DCS1 strain in Landy medium and to investigate the antifungal activities of DCS1 strain and its produced lipopeptides. The in vitro activities were tested by the direct confrontation and agar well diffusion methods, while the in vivo study was carried out in order to test the efficiency of DCS1 bacterial suspension in the control of Fusarium wilt in tomato plants. Identification of lipopeptides by mass spectrometry (LC/MSD-TOF) showed that lipopeptide isoforms produced during the first 24 h and 48 h of fermentation are identical, belonging to bacillomycin D and fengycins A and B homologues with a difference in the yield of production. After 72 h of fermentation corresponding to the end of incubation period, B. methylotrophicus DCS1 is able to produce a mixture of surfactin, pumilacidin, iturin A/mycosubtilin, iturin C1, bacillomycin D and fengycins A and B isoforms. The results of in vitro antifungal experiments suggest that B. methylotrophicus DCS1 has a significant potential as a biocontrol agent, owing to lipopeptides produced, endowed with antifungal activity against several phytopathogenic fungi. The curative treatment of tomato plants with DCS1 bacterial suspension was more effective in the protection against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) than the preventive treatment by comparing the average number of leaves remaining healthy after 30 days of each treatment and the appearance of tomato plants roots. The results indicate that B. methylotrophicus DCS1 exhibit a significant suppression of Fusarium wilt symptoms in tomato plants comparable to that of commercial fungicides and could be an alternative to chemically synthesized pesticides.

Investigation of halotolerant marine Staphylococcus sp. CO100, as a promising hydrocarbon-degrading and biosurfactant-producing bacterium, under saline conditions.

A halotolerant strain CO100 of Staphylococcus sp. was isolated from contaminated sediments taken from the fishing harbour of Sfax, Tunisia, as an efficient hydrocarbonoclastic candidate. Strain CO100 exhibited a high capacity to break down almost 72% of the aliphatic hydrocarbons contained in crude oil (1%, v/v), used as the sole carbon and energy source, after 20 days of culture, at 100 g/l NaCl, 37 °C and 180 rpm. The isolate CO100 displayed also its ability to grow on phenanthrene, fluoranthene and pyrene (100 mg/l), at 100 g/l NaCl. Moreover, the isolate CO100 showed a notable aptitude to synthesize an efficient tensioactive agent namely BS-CO100, on low-value substrates including residual frying oil and expired milk powder, thus reducing the high cost of biosurfactant production. The ESI/MS analysis designated that BS-CO100 belonged to lipopeptide class, in particular lichenysin and iturine members. Critical micelle concentrations of BS-CO100 were varying between 65 and 750 mg/l, depending on of the purity of the biosurfactant and the used carbon sources. BS-CO100 showed a high steadiness against a wide spectrum of pH (4.3-12), temperature (4-121 °C) and salinity (0-300 g/l NaCl), supporting its powerful tensioactive properties under various environmental conditions. Likewise, BS-CO100 exhibited no cytotoxic effect toward human HEK293 cells, at concentrations within 125 and 1000 µg/ml. Furthermore, the biosurfactant BS-CO100 exhibited remarkable anti-adhesive and anti-biofilm activities, being able to avoid and disrupt the biofilm formation by certain pathogenic microorganisms. In addition, BS-CO100 was found to have more potential to remove hydrocarbons from contaminated soils, compared to some chemical surfactants. In light of these promising findings, strain CO100, as well as its biosurfactant, could be successfully used in different biotechnological applications including the bioremediation of oil-polluted areas, even under saline conditions.

Antifungal and antiprotozoal green amino acid-based rhamnolipids: Mode of action, antibiofilm efficiency and selective activity against resistant Candida spp. strains and Acanthamoeba castellanii.

Nowadays, infections caused by fungi and protists constitute a serious problem for public health services. The limited number of treatment options coupled with the increasing number of resistant microorganisms makes necessary the development of new non-toxic antifungal and antiprotozoal agents. Cationic amino acid-based rhamnolipids have been recently prepared by our group and exhibited good antibacterial activity. In this work, the antifungal, antibiofilm and antiprotozoal activity of these new rhamnolipids was investigated against a collection of fluconazole-resistant strains of different Candida species and Acanthamoeba castellanii, respectively. The arginine-RLs exhibited good antifungal activity against all fluconazole-resistant Candida spp. strains tested at MICs ranging from 6.5 to 20.7 mg/L. Their mechanism of action involves alterations in the permeability of the cell membranes that provoke death by apoptosis. The Arginine based-RLs also disperse Candida biofilms at low concentrations, similar to the MICs. All RLs tested (anionic and cationic) showed antiprotozoal activity, the arginine derivatives had the best activity killing the Acanthamoeba castellanii at concentrations of 4 mg/L. Interestingly, these surfactants have a wide range of action against yeast and A. castellanii in which they do not show toxicity against keratinocytes and fibroblasts. These results indicate that these new rhamnolipids have a sufficiently wide safety margin to be considered good candidates for several pharmaceutical applications such as combating fungal resistance and microbial biofilms and the formulation of antiprotozoal drugs.

Isolation and characterization of kurstakin and surfactin isoforms produced by Enterobacter cloacae C3 strain.

In this work, the extraction, structural analysis, and identification as well as antimicrobial, anti-adhesive, and antibiofilm activities of lipopeptides produced by Enterobacter cloacae C3 strain were studied. A combination of chromatographic and spectroscopic techniques offers opportunities for a better characterization of the biosurfactant structure. Thin layer chromatography (TLC) and HPLC for amino acid composition determination are used. Efficient spectroscopic techniques have been utilized for investigations on the biochemical structure of biosurfactants, such as Fourier transform infrared (FT-IR) spectroscopy and mass spectrometry analysis. This is the first work describing the production of different isoforms belonging to kurstakin and surfactin families by E cloacae strain. Three kurstakin homologues differing by the fatty acid chain length from C10 to C12 were detected. The spectrum of lipopeptides belonging to surfactin family contains various isoforms differing by the fatty acid chain length as well as the amino acids at positions four and seven. Lipopeptide C3 extract exhibited important antibacterial activity against Gram-positive and Gram-negative bacteria, antifungal activity, and interesting anti-adhesive and disruptive properties against biofilm formation by human pathogenic bacterial strains: Salmonella typhimurium, Klebsiella pneumoniae, Staphylococcus aureus, Bacillus cereus, and Candida albicans.

Production, characterization and biotechnological potential of lipopeptide biosurfactants from a novel marine Bacillus stratosphericus strain FLU5.

This work aimed at studying the potential of a new hydrocarbonoclastic marine bacterium, Bacillus stratosphericus FLU5, to produce an efficient surface-active agent BS-FLU5. Biosurfactant production was examined on different carbon sources; using the surface tension measurement and the oil displacement test. Strain FLU5 showed its capacity to produce biosurfactants from all tested substrates, in particular the residual frying oil, which is a cheap renewable carbon source alternative, thus minimizing the high cost of producing those surfactants. MALDI-TOF MS/MS analysis confirmed the presence of lipopeptides, which are identified as members of surfactin and pumilacidin series. The critical micelle concentration (CMC) of the purified lipopeptides produced by strain FLU5 was 50 mg/l. At this concentration, the surface tension of the water was reduced from 72 to 28 mN/m. Furthermore, the crude lipopeptides showed an interesting stability against a broad range of pH, temperature and salinity. In addition, the application of BS-FLU5 in oil recovery from hydrocarbons-contaminated soil (used motor oil) showed that it was more effective on the hydrocarbon-remobilization than some tested synthetic surfactants. Interestingly, the biosurfactant BS-FLU5 showed a negligible cytotoxic effect against the mammalian cells HEK293. These results highlight the applicability of the lipopeptides BS-FLU5 in different fields, especially in environmental remediation processes.

Interaction of the Lipopeptide Biosurfactant Lichenysin with Phosphatidylcholine Model Membranes.

Lichenysins produced by Bacillus licheniformis are anionic lipopeptide biosurfactants with cytotoxic, antimicrobial, and hemolytic activities that possess enormous potential for chemical and biological applications. Through the use of physical techniques such as differential scanning calorimetry, small- and wide-angle X-ray diffraction, and Fourier-transform infrared spectroscopy as well as molecular dynamics simulations, we report on the interaction of Lichenysin with synthetic phosphatidylcholines differing in hydrocarbon chain length. Lichenysin alters the thermotropic phase behavior of phosphatidylcholines, displaying fluid-phase immiscibility and showing a preferential partitioning into fluid domains. The interlamellar repeat distance of dipalmitoylphosphatidylcholine (DPPC) is modified, affecting both the phospholipid palisade and the lipid/water interface, which also experiences a strong dehydration. Molecular dynamics confirms that Lichenysin is capable of interacting both with the hydrophobic portion of DPPC and with the polar headgroup region, which is of particular relevance to explain much of its properties. The results presented here help to establish a molecular basis for the Lichenysin-induced perturbation of model and biological membranes previously described in the literature.

Structural characterization and identification of cyclic lipopeptides produced by Bacillus methylotrophicus DCS1 strain.

Bacillus methylotrophicus DCS1 strain was isolated from diesel contaminated soil and screened for its ability to produce biosurfactants; it was found effective for the production of surface active molecules. The structural characterization of the isolated lipopeptides was studied by a variety of analytical techniques. The organic extract of DCS1 lipopeptides was fractionated by silica gel column chromatography (60Mesh). Fractions containing lipopeptides were collected and identified by tandem mass spectrometry MALDI-TOF-MS and MALDI-TOF MS2. The crude biosurfactants contains a mixture of homologous lipopeptides with molecular weights between 1016 and 1556Da. Mass spectrometry analysis of partially purified lipopeptides revealed that it contains different isoforms belonging to three families: surfactin, iturin and fengycin. To identify lipopeptides isoforms, MALDI-TOF MS2 was used and ions representing characteristic fragmentations were detected. The mass spectrometry characterization revealed the presence of four variants of surfactin lipopeptides, four variants of pumilacidin that differ according to the ß-hydroxy fatty acid chain length as well as the type of amino acid at position 7, five variants of iturin A/mycosubtilin varying in the ß-amino fatty acid chain length from C12 to C16, C16 iturin C1, five isoforms of bacillomycin D varying in the ß-amino fatty acid chain length from C14 to C18, and six fengycin isoforms that differ according to the length of the ß-hydroxy fatty acid side chain as well as the amino acid at position 6. The capacity of B. methylotrohicus DCS1 strain to produce many lipopeptides isoforms belonging to different families and having a structural diversity is a very interesting characteristic that allows them to be used in various fields of biotechnological applications.

Micellization and Antimicrobial Properties of Surface-Active Ionic Liquids Containing Cleavable Carbonate Linkages.

Imidazolium-based ionic liquids (ILs) containing cleavable carbonate linkages, 1-alkyloxycarbonyloxyethyl-3-methylimidazolium chlorides with alkyl chains of 10, 12, and 14 carbon atoms, were synthesized, and their self-assembly behavior and antimicrobial activity were investigated. Differential scanning calorimetry and polarized optical microscopy studies reveal that carbonate-functionalized ILs form stable thermotropic smectic liquid-crystalline phases over a wide range of temperature. The surface activity and aggregation behavior of these new ILs were investigated by tensiometry, conductometry, potentiometry, and spectrofluorimetry. The size of aggregates was examined by dynamic light scattering (DLS). Carbonate-functionalized ILs display a higher adsorption efficiency and a lower critical micelle concentration (cmc) than simple alkyl-chain-substituted ILs. The insertion of a carbonate ester moiety in the alkyl side chain favors adsorption at the air-water interface and micellization in the bulk solution when compared to nonfunctionalized ILs. DLS measurements show that small micellelike aggregates are spontaneously formed above the cmc. Furthermore, carbonate-functionalized ILs were examined for their antimicrobial activity against a panel of clinically relevant microorganisms. Biological activity was found to increase with hydrophobicity. The presence of a carbonate ester moiety significantly enhances the antimicrobial efficiency as compared to nonfunctionalized ILs, with the susceptibility of Staphylococcus sp. toward the action of these compounds being particularly remarkable. It has been demonstrated that the functionalization of the alkyl side chain of the imidazolium salts can not only modify the aggregation behavior but also lead to differences in both efficiency and the spectrum of antimicrobial activity of amphiphilic ILs.

Antioxidant properties, antimicrobial and anti-adhesive activities of DCS1 lipopeptides from Bacillus methylotrophicus DCS1.

BACKGROUND: The present work aims to investigate the antioxidant and antimicrobial activities as well as the potential of DCS1 lipopeptides produced by Bacillus methylotrophicus DCS1 strain at inhibition and disruption of biofilm formation. RESULTS: The produced biosurfactants were characterized as lipopeptides molecules by using thin layer chromatography (TLC) and Fourier transform infrared spectroscopy (FT-IR). The DCS1 lipopeptides were assayed for their antioxidant activity through five different tests. The scavenging effect on DPPH radicals at a concentration of 1 mg mL-1 was 80.6%. The reducing power reached a maximum value of 3.0 (OD700 nm) at 2 mg mL-1. Moreover, the DCS1 lipopeptides exhibited a strong inhibition of ß-carotene bleaching by linoleic acid assay with 80.8% at 1 mg mL-1 and showed good chelating ability and lipid peroxidation inhibition. The in vitro antimicrobial activity of DCS1 lipopeptides showed that they display significant antibacterial and antifungal activities. The anti-adhesive activity of DCS1 lipopeptides was evaluated against several pathogenic microorganisms. The lipopeptides showed excellent anti-adhesive activity, even at low concentrations, in a polystyrene surface pre-treatment against all the microorganisms tested. Further, they can disrupt performed biofilms. CONCLUSION: This study shows the potentiality of DCS1 lipopeptides as natural antioxidants, antimicrobial and/or anti-adhesive agent for several biomedical and industrial applications.

Green Catanionic Gemini Surfactant-Lichenysin Mixture: Improved Surface, Antimicrobial, and Physiological Properties.

Catanionic surfactant mixtures form a wide variety of organized assemblies and aggregates with improved physicochemical and biological properties. The green catanionic mixture NαNω-Bis(Nαcaproylarginine) α,ω-propyldiamide (C3(CA)2):Lichenysin (molar ratio 8:2) showed antimicrobial synergies against Yersinia enterocolitica, Bacillus subtilis, Escherichia coli O157:H7, and Candida albicans. Flow cytometry and viability studies indicated that this catanionic mixture increases the probability of Y. enterocolitica (38.2%) and B. subtilis (17.1%) cells entering a viable but nonculturable state. Zeta potential showed that one of the cationic charges of C3(CA)2 is neutralized by Lichenysin. An isotherm study demonstrated the formation of a stable aggregate between the two surfactants. The catanionic aggregate was able to interact with bacterial phospholipids. The lowest hemolysis (22.1 µM) was obtained with the catanionic mixture, although an irritant potential (0.70) was characterized. According to the therapeutic index, the C3(CA)2:Lichenysin mixture was the formulation least toxic to eukaryotic cells. Partial neutralization of C3(CA)2 by Lichenysin modified the mode of action that enhances the transition of bacterial cells into a viable but nonculturable state (VBNC) and improved the cell selectivity.

Lichenysin-geminal amino acid-based surfactants: Synergistic action of an unconventional antimicrobial mixture.

Recently it has been demonstrated that catanionic mixtures of oppositely charged surfactants have improved physicochemical-biological properties compared to the individual components. Isotherms of mixtures of an anionic biosurfactant (lichenysin) and a cationic aminoacid surfactant (C3(LA)2) indicate a strong interaction suggesting the formation of a new "pseudo-surfactant". The antimicrobial properties of the mixture lichenysin and C3(LA)2 M80:20, indicate a synergistic effect of the components. The mechanism of action on the bacterial envelope was assessed by flow cytometry and Transmission Electron Microscopy.

Tryptophan-containing lipopeptide antibiotics derived from polymyxin B with activity against Gram positive and Gram negative bacteria.

Resistance to all known antibiotics is a growing concern worldwide, and has renewed the interest in antimicrobial peptides, a structurally diverse class of amphipathic molecules that essentially act on the bacterial membrane. Propelled by the antimicrobial potential of this compound class, we have designed three new lipopeptides derived from polymyxin B, sp-34, sp-96 and sp-100, with potent antimicrobial activity against both Gram positive and Gram negative bacteria. The three peptides bind with high affinity to lipopolysaccharide as demonstrated by monolayer penetration and dansyl-displacement. The interaction with the cytoplasmic membrane has been elucidated by biophysical experiments with model membranes of POPG or POPE/POPG (6:4), mimicking the Gram positive and Gram negative bacterial membrane. Trp-based fluorescence experiments including steady-state, quenching, anisotropy and FRET, reveal selectivity for anionic phospholipids and deep insertion into the membrane. All three lipopeptides induce membrane fusion and leakage from anionic vesicles, a process that is favored by the presence of POPE. The molecules bind to zwitterionic POPC vesicles, a model of the eukaryotic membrane, but in a different way, with lower affinity, less penetration into the bilayer and no fusion or permeabilization of the membrane. Results in model membranes are consistent with flow cytometry experiments in Escherichia coli and Staphylococcus aureus using a membrane potential sensitive dye (bis-oxonol) and a nucleic acid dye (propidium iodide), suggesting that the mechanism of action is based on membrane binding and collapse of membrane integrity by depolarization and permeabilization.

Kinetic and Structural Aspects of the Permeabilization of Biological and Model Membranes by Lichenysin.

The various lichenysins produced by Bacillus licheniformis are anionic surfactants with interesting properties. Here it is shown that lichenysin caused hemolysis of human erythrocytes, which varied with lichenysin concentration in a sigmoidal manner. The release of K(+) from red blood cells induced by lichenysin preceded the leakage of hemoglobin, and in addition, hemolysis could be impeded by the presence of compounds in the external medium having a size larger than that of PEG 3350, indicating a colloid-osmotic mechanism for hemolysis. Lichenysin also caused permeabilization of model phospholipid membranes, which was a slow process with an initial lag period of 10-20 s observed for all lichenysin concentrations. A high cholesterol ratio in the membrane decreased the extent of leakage as compared to that of pure POPC, whereas at lower ratios the effect of cholesterol was the opposite, enhancing the extent of leakage. POPE was found to decrease the extent of leakage at all the concentrations assayed, and inclusion of DPPC resulted in a considerable increase in CF leakage extent. From this scenario it was concluded that lipid membrane composition plays a role in the target membrane selectivity of lichenysin. Molecular dynamics simulations indicated that lichenysin is well distributed along the bilayer, and Na(+) ions can penetrate inside the bilayer through the lichenysin molecules. The presence of lichenysin in the membrane increases the permeability of the membrane to hydrophilic molecules facilitating its flux across the lipid palisade. The results presented in this work contribute to understanding the molecular mechanisms that explain the biological actions of lichenysin related to biomembranes.

Purification and identification of Bacillus subtilis SPB1 lipopeptide biosurfactant exhibiting antifungal activity against Rhizoctonia bataticola and Rhizoctonia solani.

This study reports the potential of a soil bacterium, Bacillus subtilis strain SPB1, to produce lipopeptide biosurfactants. Firstly, the crude lipopeptide mixture was tested for its inhibitory activity against phytopathogenic fungi. A minimal inhibitory concentration (MIC), an inhibitory concentration at 50% (IC50%), and an inhibitory concentration at 90% (IC90%) values were determined to be 0.04, 0.012, and 0.02 mg/ml, respectively, for Rhizoctonia bataticola with a fungistatic mode of action. For Rhizoctonia solani, a MIC, an IC50%, and IC90% values were determined to be 4, 0.25, and 3.3 mg/ml, respectively, with a fungicidal mode of action. For both of the fungi, a loss of sclerotial integrity, granulation and fragmentation of hyphal mycelia, followed by hyphal shriveling and cell lysis were observed with the treatment with SPB1 biosurfactant fraction. After extraction, separation, and purification, different lipopeptide compounds were identified in the culture filtrate of strain SPB1. Mass spectroscopic analysis confirmed the presence of different lipopeptide compounds consisting of surfactin isoforms with molecular weights of 1007, 1021, and 1035 Da; iturin isoforms with molecular weights of 1028, 1042, and 1056 Da; and fengycin isoforms with molecular weights of 1432 and 1446 Da. Two new clusters of lipopeptide isoforms with molecular weights of 1410 and 1424 Da and 973 and 987 Da, respectively, were also detected. This study reported the ability of a B. subtilis strain to co-produce lipopeptide isoforms with potential use as antifungal compounds.

In Silico/In Vivo Insights into the Functional and Evolutionary Pathway of Pseudomonas aeruginosa Oleate-Diol Synthase. Discovery of a New Bacterial Di-Heme Cytochrome C Peroxidase Subfamily.

As previously reported, P. aeruginosa genes PA2077 and PA2078 code for 10S-DOX (10S-Dioxygenase) and 7,10-DS (7,10-Diol Synthase) enzymes involved in long-chain fatty acid oxygenation through the recently described oleate-diol synthase pathway. Analysis of the amino acid sequence of both enzymes revealed the presence of two heme-binding motifs (CXXCH) on each protein. Phylogenetic analysis showed the relation of both proteins to bacterial di-heme cytochrome c peroxidases (Ccps), similar to Xanthomonas sp. 35Y rubber oxidase RoxA. Structural homology modelling of PA2077 and PA2078 was achieved using RoxA (pdb 4b2n) as a template. From the 3D model obtained, presence of significant amino acid variations in the predicted heme-environment was found. Moreover, the presence of palindromic repeats located in enzyme-coding regions, acting as protein evolution elements, is reported here for the first time in P. aeruginosa genome. These observations and the constructed phylogenetic tree of the two proteins, allow the proposal of an evolutionary pathway for P. aeruginosa oleate-diol synthase operon. Taking together the in silico and in vivo results obtained we conclude that enzymes PA2077 and PA2078 are the first described members of a new subfamily of bacterial peroxidases, designated as Fatty acid-di-heme Cytochrome c peroxidases (FadCcp).

A bioinspired peptide scaffold with high antibiotic activity and low in vivo toxicity.

Bacterial resistance to almost all available antibiotics is an important public health issue. A major goal in antimicrobial drug discovery is the generation of new chemicals capable of killing pathogens with high selectivity, particularly multi-drug-resistant ones. Here we report the design, preparation and activity of new compounds based on a tunable, chemically accessible and upscalable lipopeptide scaffold amenable to suitable hit-to-lead development. Such compounds could become therapeutic candidates and future antibiotics available on the market. The compounds are cyclic, contain two D-amino acids for in vivo stability and their structures are reminiscent of other cyclic disulfide-containing peptides available on the market. The optimized compounds prove to be highly active against clinically relevant Gram-negative and Gram-positive bacteria. In vitro and in vivo tests show the low toxicity of the compounds. Their antimicrobial activity against resistant and multidrug-resistant bacteria is at the membrane level, although other targets may also be involved depending on the bacterial strain.

Rhamnolipids as emulsifying agents for essential oil formulations: antimicrobial effect against Candida albicans and methicillin-resistant Staphylococcus aureus.

This work examines the influence of essential oil composition on emulsification with rhamnolipids and their use as therapeutic antimicrobial agents against two opportunistic pathogens, methicillin-resistant Staphylococcus aureus (MRSA) and Candida albicans. Rhamnolipids, produced by Pseudomonas aeruginosa, with waste frying oil as the carbon source, were composed of eight rhamnolipid homologues. The rhamnolipid mixture was used to produce emulsions containing essential oils (EOs) of Melaleuca alternifolia, Cinnamomum verum, Origanum compactum and Lavandula angustifolia using the titration method. Ternary phase diagrams were designed to evaluate emulsion stability, which differed depending on the essential oil. The in vitro antimicrobial activity of the EOs alone and the emulsions was evaluated. The antimicrobial activity presented by the essential oils alone increased with emulsification. The surface properties of rhamnolipids contribute to the positive dispersion of EOs and thus increase their availability and antimicrobial activity against C. albicans and S. aureus. Therefore, rhamnolipid-based emulsions represent a promising approach to the development of EO delivery systems.

Self-assembly and antimicrobial activity of long-chain amide-functionalized ionic liquids in aqueous solution.

Surface active amide-functionalized ionic liquids (ILs) consisting of a long alkyl chain (C6C14) connected to a polar head group (methylimidazolium or pyridinium cation) via an amide functional group were synthesized and their thermal stability, micellar properties and antimicrobial activity in aqueous solution investigated. The incorporation of an amide group increased the thermal stability of the functionalized ionic liquids compared to simple alkyl chain substituted ionic liquids. The surface activity and aggregation behaviour in aqueous solution of amide-functionalized ionic liquids were examined by tensiometry, conductivity and spectrofluorimetry. Amide-functionalized ILs displayed surface activity and their critical micelle concentration (cmc) in aqueous media decreased with the elongation of the alkyl side chain as occurs for typical surfactants. Compared to non-functionalized ILs bearing the same alkyl chain, ionic liquids with an amide moiety possess higher surface activity (pC20) and lower cmc values. The introduction of an amide group in the hydrophobic chain close to the polar head enhances adsorption at the air/water interface and micellization which could be attributed to the H-bonding in the headgroup region. The antimicrobial activity was evaluated against a panel of representative Gram-negative and Gram-positive bacteria and fungi. Amide-functionalized ILs with more than eight carbon atoms in the side chain showed broad antimicrobial activity. Antibacterial activities were found to increase with the alkyl chain length being the C12 homologous the most effective antimicrobial agents. The introduction of an amide group enhanced significantly the antifungal activity as compared to non-functionalized ILs.

Yield and kinetic constants estimation in the production of hydroxy fatty acids from oleic acid in a bioreactor by Pseudomonas aeruginosa 42A2.

We modelled the production of hydroxy fatty acids from oleic acid by Pseudomonas aeruginosa 42A2 in a bioreactor with a non-dispersive aeration system. First, we designed an adapted wetted-wall gas-absorption column, offering a k La value of 39.9 h(-1), to enhance oxygen absorption in the culture media and prevent foam formation. Then, we analysed different kinetic models to simulate the yield coefficients and the kinetic constants in this bacterial transformation. Monod model fitting (µ max1 = 0.51 h(-1), K S1 = 1.60 C-mol l(-1), µ max2 = 0.12 h(-1), K S2 = 0.035 C-mol l(-1), and k 2 = 0.033 h(-1)) showed a good accuracy with the experimental data sets and was chosen for its simplicity. Lastly, mass balances were carried out to establish the stoichiometry of this biotransformation with the following yield coefficients, Υ X/OA, Υ X/(10S)-HPOME and Υ (10S)-HPOME/(7S10S)-HPOME of 0.172, 0.347 and 2.388 C-mol C-mol(-1), respectively.

In vitro study of the cytotoxicity and antiproliferative effects of surfactants produced by Sphingobacterium detergens.

The application of biosurfactants in the biomedical field is growing due to their antimicrobial activity, low cytotoxicity and ability to induce apoptosis in cancer cells. In the light of this therapeutic potential, as well as possible applications in cosmetics or as drug vehicles in pharmaceutical products, a new biosurfactant produced by Sphingobacterium detergens was investigated for its haemolytic activity and cytotoxic and antiproliferative effects in different cell lines. Fraction A showed 100% haemolysis in rabbit erythrocytes, but in Fraction B the rate was only 83%. When comparing cytotoxicity values (IC50) of the two fractions in model fibroblast and keratinocyte cell cultures, Fraction B was less cytotoxic, showing lower values than the reference compound SDS, indicating low skin irritability. Finally, in non-differentiated intestinal Caco-2 cultures, Fractions A and B reduced cell proliferation and induced apoptosis by 44% and 75%, respectively. According to these results, biosurfactants produced by S. detergens have potential application in cosmetic and pharmaceutical formulations.