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This work presents a biophysical study on the interactions of a monorhamnolipid (monoRL) produced by Pseudomonas aeruginosa MA01 with model dielaidoylphosphatidylethanolamine (DEPE) membranes. Incorporation of monoRL into DEPE shifts the onset temperature of the Lβ-to-Lα and the Lα-to-HII phase transitions toward lower values. Incorporation of monoRL into DEPE indicates the coexistence of lamellar and hexagonal-HII phases in rhamnolipid-containing samples at 60°C, at which pure DEPE is lamellar. Thus, both techniques show that monoRL facilitates formation of the hexagonal-HII phase in DEPE, i.e. it destabilizes the bilayer organization. The phase diagram for the phospholipid component indicates a near-ideal behavior, with better miscibility of monoRL into DEPE in the fluid phase than in the gel phase. The various vibrational mode bands of the acyl chains of DEPE were studied by FTIR spectroscopy, focusing on the CH2 symmetric stretching mode. Incorporation of monoRL into DEPE shifts the frequency of this band to higher wavenumbers, at temperatures both below and above the main gel to liquid-crystalline phase transition. Examination of the CO stretching band of DEPE indicates that monoRL/DEPE interactions result in an overall dehydration effect on the polar headgroup of DEPE. These results are discussed in light of the possible role of rhamnolipids as bilayer stabilizers/destabilizers during cell membrane fluctuation events., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Given the increasing interest in the characterization of new biosurfactants, in this work we have carried out a physicochemical study of a monorhamnolipid (monoRL) produced by Pseudomonas aeruginosa MA01 in aqueous media. The detailed knowledge of the physicochemical properties of these monoRL biosurfactant is of importance for the validation of this particular P. aeruginosa strain as a useful biosurfactant producer. A pKa value for monoRL of 5.9 was consistently obtained, as well as the indication that the presence of one or two rhamnose rings does not have a notorious influence on the pKa of the carboxyl group. The critical micelle concentration (cmc) of the negatively charged monoRL is dependent on the ionic strength, whereas that of the protonated form is not, whereas the charge of the polar head of monoRL has little effect on the surface area. Dynamic light scattering showed that in the vicinity of the cmc structures with an average diameter of 50 nm are present, whereas at concentrations well above the cmc the size increases to about 200 nm. Taken together our results show that monoRL presents a monomer-to-micelle transition, which depends on pH and ionic strength, similar to that described before for the diRL species. However the formation of lamellar vesicles described for diRL at pH 7.4, was not observed here. Molecular dynamics (MD) simulations yielded a similar value for the lateral diffusion coefficient of protonated anionic monoRL, indicating that the negative charge does not affect biosurfactant mobility in the monolayer surface. The radial distribution function value is slightly higher for the protonated monoRL; therefore the number of molecules located at a particular distance is somehow higher in the case of the protonated form. On the other hand, it is clearly obtained that the carboxylate group of the anionic form moves more inside the aqueous phase as compared to the carboxyl group of the protonated form. The results obtained correspond to the expected behaviour for a biosurfactant molecule in relation to the dependence of protonation state and micelle formation, and therefore the molecular dynamics simulation appears to describe properly our molecular systems., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A potent biosurfactant-producing bacterial strain isolated from spoiled apples was identified by 16S rRNA as Pseudomonas aeruginosa MA01. Compositional analysis revealed that the extracted biosurfactant was composed of high percentages of lipid (66%, w/w) and carbohydrate (32%, w/w). The surface tension of pure water decreased gradually with increasing biosurfactant concentration to 32.5 mN m(-1) with critical micelle concentration (CMC) value of 10.1 mg L(-1). The Fourier transform infrared spectrum of extracted biosurfactant confirmed the glycolipid nature of this natural product. Response surface methodology (RSM) was employed to optimize the biosynthesis medium for the production of MA01 biosurfactant. Nineteen carbon sources and 11 nitrogen sources were examined, with soybean oil and sodium nitrate being the most effective carbon and nitrogen sources on biosurfactant production, respectively. Among the organic nitrogen sources examined, yeast extract was necessary as a complementary nitrogen source for high production yield. Biosurfactant production at the optimum value of fermentation processing factor (15.68 g/L) was 29.5% higher than the biosurfactant concentration obtained before the RSM optimization (12.1 g/L). A central composite design algorithm was used to optimize the levels of key medium components, and it was concluded that two stages of optimization using RSM could increase biosurfactant production by 1.46 times, as compared to the values obtained before optimization.

This work presents a biophysical study on the interactions of a monorhamnolipid (monoRL) produced by Pseudomonas aeruginosa MA01 with model phosphatidylcholine membranes. The molecular characterization of the biological activities, including the modulation of phospholipid membranes structure, of this monoRL biosurfactant is of importance for the validation of this particular Pseudomonas aeruginosa strain as a useful biosurfactant producer. The marked amphiphilic structure of monoRL is expected to result in strong interactions with the phospholipid constituents of membrane bilayers. Incorporation of monoRL into DMPC completely abolished the pretransition, and the main gel to liquid-crystalline phase transition was progressively broadened and shifted to lower temperatures, as observed by differential scanning calorimetry. Partial phase diagrams for DPPC and DSPC indicated near-ideal behavior. However, the DMPC diagram indicated fluid phase immiscibility. X-ray diffraction showed and apparent increase in d-value for DPPC containing monoRL, which might be the result of an effective increase in the bilayer thickness, or in the thickness of the hydration layer between bilayers. FTIR indicated that interaction of monoRL with the phospholipid acyl chains did not result in a large additional disordering of the acyl chain region of the fluid bilayer. Analysis of the C=O stretching band of DPPC indicated an important effect of monoRL on the interfacial region of phosphatidylcholine bilayers, which might contribute to explain some of the biological activities of this glycolipid., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

An extensive investigation was conducted to isolate indigenous bacterial strains with outstanding performance for biosurfactant production from different types of spoiled fruits, food-related products and food processing industries. An isolate was selected from 800 by the highest biosurfactant yield in soybean oil medium and it was identified by 16S rRNA and the two most relevant hypervariable regions of this gene; V3 and V6 as Pseudomonas aeruginosa MA01. The isolate was able to produce 12 g/l of a glycolipid-type biosurfactant and generally less efficient to emulsify vegetable oils compared to hydrocarbons and could emulsify corn and coconut oils more than 50%. However, emulsification index (E(24)) of different hydrocarbons including hexane, toluene, xylene, brake oil, kerosene and hexadecane was between 55.8% and 100%. The surface tension of pure water decreased gradually with increasing biosurfactant concentration to 32.5 mNm(-1) with critical micelle concentration (CMC) value of 10.1mg/l. Among all carbon substrates examined, vegetable oils were the most effective on biosurfactant production. Two glycolipid fractions were purified from the biosurfactant crude extracts, and FTIR and ES-MS were used to determine the structure of these compounds. The analysis indicated the presence of three major monorhamnolipid species: R(1)C(10)C(10), R(1)C(10)C(12:1), and R(1)C(10)C(12); as well as another three major dirhamnolipid species: R(2)C(10)C(10), R(2)C(10)C(12:1), and R(2)C(10)C(12). The strain sweep experiment for measuring the linear viscoelastic of biosurfactant showed that typical behavior characteristics of a weak viscoelastic gel, with storage modulus greater than loss modulus at all frequencies examined, both showing some frequency dependence., (Copyright © 2011 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Rhamnolipid (RL) is a surfactant biosynthesized by Pseudomonas aeruginosa strains. The RL feasibility as a high-efficient emulsifier in increasing the physical stability of sesame oil (SO)-based beverage emulsions formed by the ultrasound-assisted emulsification process was studied. The concentration of SO (2.02%–6.98% wt/wt), and RL (0.49%–1.51% wt/wt) was adequately optimized based on the analysis of physical stability, turbidity loss rate (TLR), size index, density, and viscosity characteristics using the central composite rotatable design-response surface methodology. The overall optimum region to attain the highest stability (92.64%), viscosity ratio (0.338), and density (1.017 g/cm³), and the lowest TLR (0.216 Ǻ/day) and size index (0.240) based on the adequate second-order polynomial models (R² = 0.956–0.991) was obtained at the combined level of 2.75% (wt/wt) SO and 0.662% (wt/wt) RL. No significant difference between the observed and predicted values fitted to secondorder polynomial models was found. RL as an efficient biosurfactant can stabilize food-grade emulsion systems. [ABSTRACT FROM AUTHOR]

Abstract: In this work, surface activity and frothability of rhamnolipid biosurfactant produced by a Pseudomonas aeruginosa MA01 were studied and compared with conventional flotation frothers, i.e. methyl isobutyl carbinol (MIBC), pine oil, Dowfroth-250 (DF-250), and Aerofroth-65 (A-65). FTIR and ES-MS analysis indicated that the product contained two types of commonly found rhamnolipids: l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (RL-1) and l-rhamnosyl l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (RL-2). Surface tension measurements showed that the rhamnolipid product reduces surface tension more effectively than frothers due to higher molecular weight and the presence of multiple oxygenated groups in its structure, producing more viscous liquid film, which was confirmed with film elasticity calculations. Both surface tension and elasticity values followed the order: rhamnolipid>A-65>DF-250>pine oil>MIBC. Frothability of the tested surfactants gave the order: rhamnolipid>A-65>DF-250>MIBC>pine oil. [Copyright &y& Elsevier]