Characterization of biosurfactant produced in response to petroleum crude oil stress by Bacillus sp. WD22 in marine environment.

Bacillus sp. WD22, previously isolated from refinery effluent, degraded 71% of C8 hydrocarbons present in 1.0% v/v PCO in seawater (control medium), which reduced to 16.3%, on addition of yeast extract. The bacteria produced a biosurfactant in both media, whose surface was observed to be amorphous in nature under FESEM-EDAX analysis. The biosurfactant was characterized as a linear surfactin by LCMS and FT-IR analysis. The critical micelle concentration was observed as 50 mg/L and 60 mg/L at which the surface tension of water was reduced to 30 mN/m. Purified biosurfactant could emulsify petroleum-based oils and vegetable oils effectively and was stable at all tested conditions of pH, salinity and temperature up to 80 °C. The biosurfactant production was found to be mixed growth associated in control medium, while it was strictly growth associated in medium with yeast extract as studied by the Leudeking-Piret model.

A General Approach on Surfactants Use and Properties in Drug Delivery Systems.

Surfactants are amphiphilic molecules of great interest in the pharmaceutical field which are used in combination with other adjuvants to solubilize poorly soluble drugs, improve their dissolution profile, promote permeation, improve drug delivery, enhance stabilization, among other characteristics. Literature shows that surfactants are included in several pharmaceutical compositions: tablets, solid dispersions, emulsions, microemulsions, nanoemulsions, liposomes and niosomes. This review aims to elucidate the different classes of surfactants based on their charges (cationic, anionic, nonionic, zwitterionic, and dimeric), the micelles formation process, and how surfactant molecules geometry can affect this phenomenon. Moreover, current studies regarding the benefits of surfactants in the development of formulations are presented. Finally, a discussion on how charges and chain length of surfactants can affect the stratum corneum epithelial cells leading to increased permeation or skin irritability is reported.

A Source of Systematic Errors in the Determination of Critical Micelle Concentration and Micellization Enthalpy by Graphical Methods in Isothermal Titration Calorimetry.

Isothermal titration calorimetry is frequently employed to determine the critical micelle concentration and the micellization enthalpy of surfactants in terms of geometrical characteristics of the titration curves. Previously we have shown theoretically that even for an infinitesimal injection, the heat per titrant mol depends on the stock solution concentration. In this work, we explore experimentally the influence of the stock solution concentration on the geometrical characteristics of the titration curve and its effect in determining the critical micelle concentration and the micellization enthalpy of surfactants. The systematic study of this phenomenology involves a great number of measurements at different temperatures with several repetitions carried out using a robotic calorimeter. As surfactant hexadecyltrimethylamonium bromide was used. The magnitude and shape of the heat titration depend on the stock solution concentration. As a consequence, the inflexion-point, break-point, and step-height decrease until a limiting value. A qualitative analysis suggests that the limiting value depends only on substance. This work shows that graphical methods could not be suitable for the calculation of the critical micelle concentration and micellization enthalpy because the magnitude and shape of the titration curve depend on the stock solution concentration. Micellar properties should be calculated by the application of theoretical models as in the ligand-binding studies.

A Comparative Study of the Antimicrobial and Structural Properties of Short Peptides and Lipopeptides Containing a Repetitive Motif KLFK.

BACKGROUND: In the last years, Antimicrobial Peptides (AMPs) and lipopeptides have received attention as promising candidates to treat infections caused by resistant microorganisms. OBJECTIVE: The main objective of this study was to investigate the effect of repetitive KLFK motifs and the attachment of aliphatic acids to the N-terminus of (KLFK)n peptides on therapeutic properties. METHODS: Minimal inhibitory concentration against Gram (+) and (-) bacteria and yeast of synthetic compounds were determined by broth microtiter dilution method, and the toxicity was evaluated by hemolysis assay. Membrane-peptide interaction studies were performed with model phospholipid membranes mimicking those of bacterial and mammalian cells by Fluorescence Spectroscopy. The secondary structure in solution and membranes was determined by Circular Dichroism. RESULTS: Our results showed that the resulting compounds have inhibitory activity against bacteria and fungi. The (KLFK)3 peptide showed the highest therapeutic index against bacterial and yeast strains, and the (KLFK)2 peptide conjugated with octanoic acid was the most active against yeasts. All the lipopeptides containing long-chain fatty acids (C14 or longer) were highly hemolytic at low concentrations. The antimicrobial activity of (KLFK)2 and (KLFK)3 lipopeptides was mainly associated with improved stability of the amphipathic secondary structure, which showed high contributions of α-helix in dipalmitoylphosphatidylglycerol (DPPG) vesicles. CONCLUSION: The repetition of the KLFK sequence and the conjugation with lipid tails allowed obtained compounds with high antimicrobial activity and low toxicity, becoming good candidates for treating infectious diseases.

Surfactant chain length and concentration influence on the interfacial tension of two immiscible model liquids: a coarse-grained approach.

The interfacial tension between immiscible liquids is studied as a function of a model linear surfactant length and concentration using coarse-grained, dissipative particle dynamics numerical simulations. The adsorption isotherms obtained from the simulations are found to be in agreement with Langmuir's model. The reduction of the interfacial tension with increasing surfactant concentration is found to display some common characteristics for all the values of chain length modeled, with our predictions being in agreement with Szyszkowski's equation. Lastly, the critical micelle concentration is predicted for all surfactant lengths, finding exponentially decaying behavior, in agreement with Kleven's model. It is argued that these findings can be helpful guiding tools in the interpretation of available experiments and in the design of new ones with new surfactants and polymers.

New glycolipid biosurfactants produced by the yeast strain Wickerhamomyces anomalus CCMA 0358.

In this work, biosurfactant production by several yeast strains was evaluated using different culture media. The best results were obtained with the strain Wickerhamomyces anomalus CCMA 0358 growing in a culture medium containing glucose (1g/L) and olive oil (20g/L) as carbon sources. This strain produced 2.6g of biosurfactant per liter after 24h of growth. The crude biosurfactant reduced the surface tension of water to values around 31mN/m, and its critical micelle concentration was 0.9mg/mL. This biosurfactant was characterized through mass spectrometry (MS), and nuclear magnetic resonance (NMR) as a mixture of two different glycolipids, comprising a sugar moiety linked to one or three molecules of oleic acid. To the best of our knowledge, these biosurfactants are structurally different from those previously reported. Furthermore, the crude biosurfactant exhibited antimicrobial activity against several microorganisms, including the pathogens Candida albicans, Escherichia coli, Staphylococcus epidermidis and Streptococcus agalactiae, which opens the possibility for its use in several biomedical applications.

Biological and structural effects of the conjugation of an antimicrobial decapeptide with saturated, unsaturated, methoxylated and branched fatty acids.

The increasing bacterial resistance against conventional antibiotics has led to the search for new antimicrobial drugs with different modes of action. Cationic antimicrobial peptides (AMPs) and lipopeptides are promising candidates to treat infections because they act on bacterial membranes causing rapid destruction of sensitive bacteria. In this study, a decapeptide named A2 (IKQVKKLFKK) was conjugated at the N-terminus with saturated, unsaturated, methoxylated and methyl -branched fatty acids of different chain lengths (C8 - C20), the antimicrobial and structural properties of the lipopeptides being then investigated. The attachment of the fatty acid chain significantly improved the antimicrobial activity of A2 against bacteria, and so, endowed it with moderated antifungal activity against yeast strains belonging to genus Candida. Lipopeptides containing hydrocarbon chain lengths between C8 and C14 were the best antibacterial compounds (MIC = 0.7 to 5.8 µM), while the most active compounds against yeast were A2 conjugated with methoxylated and enoic fatty acids (11.1 to 83.3 µM). The improvement in antimicrobial activity was mainly related to the amphipathic secondary structure adopted by A2 lipopeptides in the presence of vesicles that mimic bacterial membranes. Peptide conjugation with long hydrocarbon chains (C12 or more), regardless of their structure, significantly increased toxicity towards eukaryotic cells, resulting in a loss of selectivity. These findings suggest that A2-derived lipopeptides are potential good candidates for the treatment of infectious diseases caused by bacteria and opportunistic pathogenic yeast belonging to genus Candida. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Biosurfactants: Multifunctional Biomolecules of the 21st Century.

In the era of global industrialisation, the exploration of natural resources has served as a source of experimentation for science and advanced technologies, giving rise to the manufacturing of products with high aggregate value in the world market, such as biosurfactants. Biosurfactants are amphiphilic microbial molecules with hydrophilic and hydrophobic moieties that partition at liquid/liquid, liquid/gas or liquid/solid interfaces. Such characteristics allow these biomolecules to play a key role in emulsification, foam formation, detergency and dispersal, which are desirable qualities in different industries. Biosurfactant production is considered one of the key technologies for development in the 21st century. Besides exerting a strong positive impact on the main global problems, biosurfactant production has considerable importance to the implantation of sustainable industrial processes, such as the use of renewable resources and "green" products. Biodegradability and low toxicity have led to the intensification of scientific studies on a wide range of industrial applications for biosurfactants in the field of bioremediation as well as the petroleum, food processing, health, chemical, agricultural and cosmetic industries. In this paper, we offer an extensive review regarding knowledge accumulated over the years and advances achieved in the incorporation of biomolecules in different industries.

Miltefosine and BODIPY-labeled alkylphosphocholine with leishmanicidal activity: Aggregation properties and interaction with model membranes.

Miltefosine (hexadecylphosphocholine, MT) afforded successful oral treatment against human visceral and cutaneous leishmaniasis. Knowledge of MT aggregation in aqueous solutions and of its interaction with lipid membranes is important to understand pharmacokinetics, bioavailability and antiparasitic effects. Methods based on surface tension and fluorescence spectroscopy gave the value of 50µM for critical micelle concentration (CMC) in buffered water solution, and the value is influenced by salt content. Interaction between MT and lipid vesicles was monitored by fluorescence and the drug promotes only minor changes in the surface of the vesicles. At MT concentration below CMC, modifications in probe fluorescence are due to disordering effects promoted by the drug in the bilayer. Above the CMC, MT promoted large modifications in the vesicles as a whole, resulting in mixed aggregates containing lipids, drug and probe. Effects are less evident above thermal phase transition when the bilayer is in less ordered state.

Solubilization of human erythrocyte membranes by ASB detergents

Understanding the membrane solubilization process and finding effective solubilizing agents are crucial challenges in biochemical research. Here we report results on the interaction of the novel linear alkylamido propyl dimethyl amino propanosulfonate detergents, ASB-14 and ASB-16, with human erythrocyte membranes. An estimation of the critical micelle concentration of these zwitterionic detergents (ASB-14 = 100 µM and ASB-16 = 10 µM) was obtained using electron paramagnetic resonance. The amount of proteins and cholesterol solubilized from erythrocytes by these detergents was then determined. The hemolytic activities of the ASB detergents were assayed and the detergent/lipid molar ratios for the onset of hemolysis (Re sat) and total lysis (Re sol) were calculated, allowing the determination of the membrane binding constants (Kb). ASB-14 presented lower membrane affinity (Kb = 7050 M-1) than ASB-16 (Kb = 15610 M-1). The amount of proteins and cholesterol solubilized by both ASB detergents was higher while Re sat values (0.22 and 0.08 detergent/lipid for ASB-14 and ASB-16, respectively) were smaller than those observed with the classic detergents CHAPS and Triton X-100. These results reveal that, besides their well-known use as membrane protein solubilizers to enhance the resolution of two dimensional electrophoresis/mass spectrometry, ASB-14 and ASB-16 are strong hemolytic agents. We propose that the physicochemical properties of ASB detergents determine their membrane disruption efficiency and can help to explain the improvement in the solubilization of membrane proteins, as reported in the literature.