Chemical structure, surface properties and biological activities of the biosurfactant produced by Pseudomonas aeruginosa LBI from soapstock

Surface-active potential of biosurfactants produced in curd whey by Pseudomonas aeruginosa strain-PP2 and Kocuria turfanesis strain-J at extreme environmental conditions

Surface-active potential of biosurfactants produced cost-effectively in curd whey by Pseudomonas aeruginosa strain-PP2 and Kocuria turfanesis strain-J were tested using parameters viz. surface tension (ST) reduction, F(CMC) (highest dilution factor to reach critical micelle concentration) and emulsification index (EI-24) of pesticides; monocrotophos and imidacloprid at extreme environmental conditions. Results have shown that ST reduction of biosurfactants was stable at pH 2-11. High F(CMC) of the biosurfactant in the fermented whey at low pH improved emulsification of pesticides. ST marginally increased at 5% and 15% NaCl, resulting in high EI-24 and F(CMC). Over a range of temperatures 30-121 °C, ST remained low with a higher F(CMC) and EI-24 at 60 °C than at 121 and 30 °C. The biosurfactants have shown differences in their surface-active property and have marked specificity to emulsify pesticides in extreme environmental conditions.

Effect of rhamnolipids on initial attachment of bacteria on glass and octadecyltrichlorosilane-modified glass

Bacterial attachment on solid surfaces has various implications in environmental, industrial and medical applications. In this study, the effects of rhamnolipid biosurfactants on initial attachment of bacteria on hydrophilic glass and hydrophobic octadecyltrichlorosilane (OTS) modified glass were evaluated under continuous-flow conditions. The bacteria investigated were three Gram-negative species Pseudomonas aeruginosa, Pseudomonas putida, and Escherichia coli, and two Gram-positive species Staphylcoccus epidermidis and Bacillus subtilis. Rhamnolipids, at 10 and 200 mg/l, significantly reduced the attachment of all but S. epidermidis on both glass and OTS-modified glass. For S. epidermidis rhamnolipids reduced the attachment on OTS-modified glass but not on glass. Studies were further done to identify the mechanism(s) by which rhamnolipids reduced the cell attachment. The following potential properties of rhamnolipids were investigated: inhibition of microbial growth, change of cell surface hydrophobicity, easier detachment of cells already attached to substratum, and modification of substratum surface properties. Results showed that rhamnolipids were ineffective for the latter two effects. Rhamnolipids, up to 200mg/l, inhibited the growth of B. subtilis, S. epidermidis and P. aeruginosa PAO1 but not the growth of E. coli, P. putida and P. aeruginosa E0340. Also, rhamnolipids tended to increase the hydrophobicity of P. aeruginosa PAO1 and E. coli, decrease the hydrophobicity of P. putida and S. epidermidis, and have no clear effect on the hydrophobicity of B. subtillis. These trends however did not correlate with the observed trend of cell attachment reduction. The responsible mechanism(s) remained unknown.

Biological activity of glycolipids produced by microorganisms: new trends and possible therapeutic alternatives

Several biological processes in prokaryotic and eukaryotic organisms require the presence of glycolipids (biosurfactants), compounds with both hydrophilic and hydrophobic groups in their structure. They constitute the backbone of different metabolic functions and biological structures such as cell membranes. Besides being structural components, glycolipids show surface activity in the interfaces and are mainly produced by microorganisms. Interest in biosurfactants has increased considerably in recent times due to their applications in the environmental, oil, food, and pharmaceutical industries, since they have unique properties such as low toxicity, high biodegradability, environmentally friendly, foaming capacity, high selectivity and specificity at extreme temperatures, pH and salinity, as well as biological activity. All of these properties are considered advantages over other chemical surfactants, and therefore glycolipids are considered a good alternative, given the current interest on sustainable development. The present work shows a general view of bio-surfactants of microbial origin, particularly of glycolipids, referring to several studies on their biological activity that have revealed their great potential in the medical-biological field, discovering interesting possibilities for their therapeutic application in the near future.

Pseudomonas aeruginosa-derived rhamnolipids subvert the host innate immune response through manipulation of the human beta-defensin-2 expression

Pseudomonas aeruginosa is a well-known cause of infections especially in compromised patients. To neutralize this pathogen, the expression of antimicrobial factors in epithelial cells is crucial. In particular the human beta-defensin hBD-2 is especially active against P. aeruginosa. In this study, we identified rhamnolipids in P. aeruginosa culture supernatants that are able to prevent the pathogen-induced hBD-2 response in keratinocytes. The presence of rhamnolipids within the host cells and inhibition assays suggest that calcium-regulated pathways and protein kinase C activation are impaired by rhamnolipids. In consequence, the induction of hBD-2 in keratinocytes by P. aeruginosa-derived flagellin as well as the host's own hBD-2 mediator interleukin IL-1β is inhibited. Strikingly, rhamnolipids did not affect the release of the proinflammatory mediator interleukin IL-8 by flagellin. Thus, in addition to their function in establishment and persistence of P. aeruginosa infections, rhamnolipids can be engaged by P. aeruginosa for a targeted attenuation of the innate immunity to manage its survival and colonization on compromised epithelia.

Investigation of antimicrobial activity and statistical optimization of Bacillus subtilis SPB1 biosurfactant production in solid-state fermentation

During the last years, several applications of biosurfactants with medical purposes have been reported. Biosurfactants are considered relevant molecules for applications in combating many diseases. However, their use is currently extremely limited due to their high cost in relation to that of chemical surfactants. Use of inexpensive substrates can drastically decrease its production cost. Here, twelve solid substrates were screened for the production of Bacillus subtilis SPB1 biosurfactant and the maximum yield was found with millet. A Plackett-Burman design was then used to evaluate the effects of five variables (temperature, moisture, initial pH, inoculum age, and inoculum size). Statistical analyses showed that temperature, inoculum age, and moisture content had significantly positive effect on SPB1 biosurfactant production. Their values were further optimized using a central composite design and a response surface methodology. The optimal conditions of temperature, inoculum age, and moisture content obtained under the conditions of study were 37°C, 14 h, and 88%, respectively. The evaluation of the antimicrobial activity of this compound was carried out against 11 bacteria and 8 fungi. The results demonstrated that this biosurfactant exhibited an important antimicrobial activity against microorganisms with multidrug-resistant profiles. Its activity was very effective against Staphylococcus aureus, Staphylococcus xylosus, Enterococcus faecalis, Klebsiella pneumonia, and so forth.

Optimization of environmental factors for improved production of rhamnolipid biosurfactant by Pseudomonas aeruginosa RS29 on glycerol

A biosurfactant producing Pseudomonas aeruginosa RS29 (identified on the basis of 16S rDNA analysis) with good foaming and emulsification properties has been isolated from crude oil contaminated sites. Optimization of different environmental factors was carried out with an objective to achieve maximum production of biosurfactant. Production of biosurfactant was estimated in terms of surface tension reduction and emulsification (E24) index. It was recorded that the isolated strain produced highest biosurfactant after 48 h of incubation at 37.5 °C, with a pH range of 7-8 and at salinity <0.8% (w/v). Ammonium nitrate used in the experiment was the best nitrogen source for the growth of biomass of P. aeruginosa RS29. On the other hand sodium and potassium nitrate enhanced the production of biosurfactant (Surface tension, 26.3 and 26.4 mN/m and E24 index, 80 and 79% respectively). The CMC of the biosurfactant was 90 mg/l. Maximum biomass (6.30 g/l) and biosurfactant production (0.80 g/l) were recorded at an optimal C/N ratio of 12.5. Biochemical analysis and FTIR spectra confirmed that the biosurfactant was rhamnolipid in nature. GC-MS analysis revealed the presence of C(8) and C(10) fatty acid components in the purified biosurfactant.

Biosurfactant-producing bacterium, Pseudomonas aeruginosa MA01 isolated from spoiled apples: physicochemical and structural characteristics of isolated biosurfactant

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.

Evaluation antimicrobial and antiadhesive properties of the biosurfactant Lunasan produced by Candida sphaerica UCP 0995

Different groups of biosurfactants exhibit diverse properties and display a variety of physiological functions in producer microorganisms; these include enhancing the solubility of hydrophobic/water-insoluble compound, heave metal binding, bacterial pathogenesis, cell adhesion and aggregation, quorum sensing and biofilm formation. Candida sphaerica was grown in a low cost medium, consisting of distilled water supplemented with 9% refinery residue of soybean oil and 9% corn steep liquor, for 144 h at 28°C and 150 rpm. The cell-free supernatant obtained at the end of the experiments was submitted to extraction, and afterward the biosurfactant was isolated using methanol with a yield of 9 g l(-1). The critical micelle concentration of the biosurfactant was found to be 0.25 mg ml(-1) with a surface tension of 25 mN m(-1). Several concentrations of the biosurfactant (0.625-10 mg ml(-1)) were used to evaluate its antimicrobial and antiadhesive activities against a variety of microorganisms. The biosurfactant showed antimicrobial activity against Streptococcus oralis (68%), Candida albicans (57%), and Staphylococcus epidermidis(57.6%) for the highest concentration tested. Furthermore, the biosurfactant at a concentration of 10 mg ml(-1) inhibited the adhesion between 80 and 92% of Pseudomonas aeruginosa, Streptococcus agalactiae, Streptococcus sanguis12. Inhibition of adhesion with percentages near 100% occurred for the higher concentrations of biosurfactant used. Results gathered in this study point to a potential use of the biosurfactant in biomedical applications.

Flagellin delivery by Pseudomonas aeruginosa rhamnolipids induces the antimicrobial protein psoriasin in human skin

The opportunistic pathogen Pseudomonas aeruginosa can cause severe infections in patients suffering from disruption or disorder of the skin barrier as in burns, chronic wounds, and after surgery. On healthy skin P. aeruginosa causes rarely infections. To gain insight into the interaction of the ubiquitous bacterium P. aeruginosa and healthy human skin, the induction of the antimicrobial protein psoriasin by P. aeruginosa grown on an ex vivo skin model was analyzed. We show that presence of the P. aeruginosa derived biosurfactant rhamnolipid was indispensable for flagellin-induced psoriasin expression in human skin, contrary to in vitro conditions. The importance of the bacterial virulence factor flagellin as the major inducing factor of psoriasin expression in skin was demonstrated by use of a flagellin-deficient mutant. Rhamnolipid mediated shuttle across the outer skin barrier was not restricted to flagellin since rhamnolipids enable psoriasin expression by the cytokines IL-17 and IL-22 after topical application on human skin. Rhamnolipid production was detected for several clinical strains and the formation of vesicles was observed under skin physiological conditions. In conclusion we demonstrate herein that rhamnolipids enable the induction of the antimicrobial protein psoriasin by flagellin in human skin without direct contact of bacteria and responding cells. Hereby, human skin might control the microflora to prevent colonization of unwanted microbes in the earliest steps before potential pathogens can develop strategies to subvert the immune response.

Rhamnolipid biosurfactants as new players in animal and plant defense against microbes

Rhamnolipids are known as very efficient biosurfactant molecules. They are used in a wide range of industrial applications including food, cosmetics, pharmaceutical formulations and bioremediation of pollutants. The present review provides an overview of the effect of rhamnolipids in animal and plant defense responses. We describe the current knowledge on the stimulation of plant and animal immunity by these molecules, as well as on their direct antimicrobial properties. Given their ecological acceptance owing to their low toxicity and biodegradability, rhamnolipids have the potential to be useful molecules in medicine and to be part of alternative strategies in order to reduce or replace pesticides in agriculture.

Methods for investigating biosurfactants and bioemulsifiers: a review

Microorganisms produce biosurfactant (BS)/bioemulsifier (BE) with wide structural and functional diversity which consequently results in the adoption of different techniques to investigate these diverse amphiphilic molecules. This review aims to compile information on different microbial screening methods, surface active products extraction procedures, and analytical terminologies used in this field. Different methods for screening microbial culture broth or cell biomass for surface active compounds production are also presented and their possible advantages and disadvantages highlighted. In addition, the most common methods for purification, detection, and structure determination for a wide range of BS and BE are introduced. Simple techniques such as precipitation using acetone, ammonium sulphate, solvent extraction, ultrafiltration, ion exchange, dialysis, ultrafiltration, lyophilization, isoelectric focusing (IEF), and thin layer chromatography (TLC) are described. Other more elaborate techniques including high pressure liquid chromatography (HPLC), infra red (IR), gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance (NMR), and fast atom bombardment mass spectroscopy (FAB-MS), protein digestion and amino acid sequencing are also elucidated. Various experimental strategies including static light scattering and hydrodynamic characterization for micelles have been discussed. A combination of various analytical methods are often essential in this area of research and a numbers of trials and errors to isolate, purify and characterize various surface active agents are required. This review introduces the various methodologies that are indispensable for studying biosurfactants and bioemulsifiers.

Rhamnolipids: diversity of structures, microbial origins and roles

Rhamnolipids are glycolipidic biosurfactants produced by various bacterial species. They were initially found as exoproducts of the opportunistic pathogen Pseudomonas aeruginosa and described as a mixture of four congeners: alpha-L-rhamnopyranosyl-alpha-L-rhamnopyranosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate (Rha-Rha-C(10)-C(10)), alpha-L-rhamnopyranosyl-alpha-L-rhamnopyranosyl-beta-hydroxydecanoate (Rha-Rha-C(10)), as well as their mono-rhamnolipid congeners Rha-C(10)-C(10) and Rha-C(10). The development of more sensitive analytical techniques has lead to the further discovery of a wide diversity of rhamnolipid congeners and homologues (about 60) that are produced at different concentrations by various Pseudomonas species and by bacteria belonging to other families, classes, or even phyla. For example, various Burkholderia species have been shown to produce rhamnolipids that have longer alkyl chains than those produced by P. aeruginosa. In P. aeruginosa, three genes, carried on two distinct operons, code for the enzymes responsible for the final steps of rhamnolipid synthesis: one operon carries the rhlAB genes and the other rhlC. Genes highly similar to rhlA, rhlB, and rhlC have also been found in various Burkholderia species but grouped within one putative operon, and they have been shown to be required for rhamnolipid production as well. The exact physiological function of these secondary metabolites is still unclear. Most identified activities are derived from the surface activity, wetting ability, detergency, and other amphipathic-related properties of these molecules. Indeed, rhamnolipids promote the uptake and biodegradation of poorly soluble substrates, act as immune modulators and virulence factors, have antimicrobial activities, and are involved in surface motility and in bacterial biofilm development.

Microbial biosurfactants production, applications and future potential

Microorganisms synthesise a wide range of surface-active compounds (SAC), generally called biosurfactants. These compounds are mainly classified according to their molecular weight, physico-chemical properties and mode of action. The low-molecular-weight SACs or biosurfactants reduce the surface tension at the air/water interfaces and the interfacial tension at oil/water interfaces, whereas the high-molecular-weight SACs, also called bioemulsifiers, are more effective in stabilising oil-in-water emulsions. Biosurfactants are attracting much interest due to their potential advantages over their synthetic counterparts in many fields spanning environmental, food, biomedical, and other industrial applications. Their large-scale application and production, however, are currently limited by the high cost of production and by limited understanding of their interactions with cells and with the abiotic environment. In this paper, we review the current knowledge and the latest advances in biosurfactant applications and the biotechnological strategies being developed for improving production processes and future potential.

Glycerol as substrate for the production of biosurfactant by Pseudomonas aeruginosa UCP0992

In this work the influence of the carbon source concentration, of the type and concentration of the nitrogen source and of the cultivation conditions (temperature, aeration and agitation speed) in mineral medium formulated with glycerol was studied for biosurfactant production by Pseudomonas aeruginosa UCP0992. The kinetics of microorganism growth and biosurfactant production have been described for the medium supplemented with 3% glycerol and 0.6% NaNO(3), at 28 degrees C during 120 h under 200 rpm, showing a growth-associated production. The isolated biosurfactant corresponded to a concentration of 8.0 g/l after 96 h. The medium surface tension was reduced to 27.4 mN/m and the emulsification index of hexadecane reached 75-80% after 72 h. A CMC of 700 mg/l and an interfacial tension against hexadecane of 2 mN/m were obtained. The biosurfactant showed stability when submitted at 90 degrees C during 2 h, and thermal (4-120 degrees C) and pH (4-12) stability regarding the surface tension reduction and the emulsification capacity of vegetable oils and hydrocarbons, and tolerance under high salt concentrations (2-10%). The biosurfactant was characterized as a group of rhamnolipids with anionic nature. The crude biosurfactant did not show toxicity against the microcrustacean Artemia salina and the cabbage (Brassica oleracea), while the isolated biosurfactant showed toxicity against the microcrustacean at the CMC. The application of the biosurfactant in diesel recovery from sand was demonstrated by removal percentiles above 85%. The results obtained in this work are noteworthy for possible biosurfactant production from glycerol with potential of application in the environment.

Effects of rhamnolipids from Pseudomonas aeruginosa DS10-129 on luminescent bacteria: toxicity and modulation of cadmium bioavailability

In this study, the mixture of mono- and di-rhamnolipids produced by Pseudomonas aeruginosa DS10-129 was characterized for its toxicity and modulatory effects on Cd availability to different bacteria. Gram-negative naturally bioluminescent Vibrio fischeri and recombinant bioluminescent Pseudomonas fluorescens, P. aeruginosa, Escherichia coli, and Gram-positive Bacillus subtilis were used as model organisms. Rhamnolipids reduced the bioluminescence of these bacteria in less than a second of exposure even in relatively low concentrations (30-min EC(50) 45-167 mg l(-1)). Toxicity of Cd to Gram-negative bacteria (30-min EC(50) values 0.16 mg l(-1) for E. coli, 0.96 mg l(-1) for P. fluorescens, and 4.4 mg l(-1) for V. fischeri) was remarkably (up to 10-fold) reduced in the presence of 50 mg l(-1) rhamnolipids. Interestingly, the toxicity of Cd to Gram-positive B. subtilis (30-min EC(50) value 0.49 mg l(-1)) was not affected by rhamnolipids. Rhamnolipids had an effect on desorption of Cd from soil: 40 mg l(-1) rhamnolipids increased the water-extracted fraction of Cd twice compared with untreated control. However, this additionally desorbed fraction of Cd remained bound with rhamnolipids and was not available to bacteria. Hence, in carefully chosen concentrations (still effectively complexing heavy metals but not yet toxic to soil bacteria), rhamnolipids could be applied in remediation of polluted areas.

Antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20

AIMS

The aim of this study was to determine the antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20 against several micro-organisms, including Gram-positive and Gram-negative bacteria, yeasts and filamentous fungi.

METHODS AND RESULTS

Antimicrobial and antiadhesive activities were determined using the microdilution method in 96-well culture plates. The biosurfactant showed antimicrobial activity against all the micro-organisms assayed, and for twelve of the eighteen micro-organisms (including the pathogenic Candida albicans, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus agalactiae), the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were achieved for biosurfactant concentrations between 25 and 50 mg ml(-1). Furthermore, the biosurfactant showed antiadhesive activity against most of the micro-organisms evaluated.

CONCLUSIONS

As far as we know, this is the first compilation of data on antimicrobial and antiadhesive activities of biosurfactants obtained from lactobacilli against such a broad group of micro-organisms. Although the antiadhesive activity of biosurfactants isolated from lactic acid bacteria has been widely reported, their antimicrobial activity is quite unusual and has been described only in a few strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained in this study regarding the antimicrobial and antiadhesive properties of this biosurfactant opens future prospects for its use against micro-organisms responsible for diseases and infections in the urinary, vaginal and gastrointestinal tracts, as well as in the skin, making it a suitable alternative to conventional antibiotics.

Biomedical and therapeutic applications of biosurfactants

During the last years, several applications of biosurfactants with medical purposes have been reported. Biosurfactants are considered relevant molecules for applications in combating many diseases and as therapeutic agents due to their antibacterial, antifungal and antiviral activities. Furthermore, their role as anti-adhesive agents against several pathogens illustrate their utility as suitable anti-adhesive coating agents for medical insertional materials leading to a reduction of a large number of hospital infections without the use of synthetic drugs and chemicals. Biomedical and therapeutic perspectives of biosurfactants applications are presented and discussed in this chapter.

Isolation and functional characterization of a biosurfactant produced by Lactobacillus paracasei

In this study, the crude biosurfactant produced by a Lactobacillus paracasei strain isolated in a Portuguese dairy industry was characterized. The minimum surface tension (41.8mN/m) and the critical micelle concentration (2.5mg/ml) obtained were found to be similar to the values previously reported for biosurfactants isolated from other lactobacilli. The biosurfactant was found to be stable to pH changes over a range from 6 to 10, being more effective at pH 7, and showed no loss of surface activity after incubation at 60 degrees C for 120h. Although the biosurfactant chemical composition has not been determined yet, a fraction was isolated through acidic precipitation, which exhibited higher surface activity as compared with the crude biosurfactant. Furthermore, this isolated biosurfactant showed antimicrobial and anti-adhesive activities against several pathogenic microorganisms. In addition, L. paracasei exhibited a strong autoaggregating phenotype, which was maintained after washing and resuspending the cells in PBS, meaning that this attribute must be related to cell surface components and not to excreted factors. The autoaggregation ability exhibited by this strain, together with the antimicrobial and anti-adhesive properties observed for this biosurfactant opens the possibility for its use as an effective probiotic strain.

Comparison between waste frying oil and paraffin as carbon source in the production of biodemulsifier by Dietzia sp. S-JS-1

In order to lower the production cost, waste frying oils were used in the biosynthesis of demulsifier by Dietzia sp. S-JS-1, which was isolated from petroleum contaminated soil. After 7 days of cultivation, the biomass concentration of the most suitable waste frying oil (WFO II) culture reached 3.78 g/L, which was 2.4 times the concentration of paraffin culture. The biodemulsifier produced with WFO II culture broke the emulsions more efficiently than that produced with paraffin culture, given the same volume ratio of carbon source in the culture medium and the same cultivation conditions. It achieved 88.3% of oil separation ratio in W/O emulsion and 76.4% of water separation ratio in O/W emulsion within 5 h. With the aid of thin layer chromatography (TLC) and Fourier transform infrared (FTIR) spectrometry, biodemulsifiers produced from both paraffin and WFO II were identified as a mixture of lipopeptide homologues. The subtle variation in the distribution of these homologues and high biomass concentration of WFO II cultures may account for the afore-mentioned good demulsification performance.

Characterization of rhamnolipids produced by a Pseudomonas aeruginosa mutant strain grown on waste oils

Pseudomonas aeruginosa EBN-8 mutant rhamnolipids produced on waste oils were investigated using normal-phase thin layer chromatography and fast atom bombardment mass spectrometry. Negative ion mode mass spectra yielded [M - H](-) ions and their fragment ions, which gave some indications on the sequence of rhamnolipid biosynthesis. Five rhamnolipid homologs [viz. RC(10)C(10) (m/z 503), RC(12)C(10) or RC(10)C(12) (531), RRC(10)C(8) or RRC(8)C(10) (621), RRC(10)C(10) (649) and RRC(12)C(10) or RRC(10)C(12) (677)] were detected in four rhamnolipid combinations under the different carbon sources. The prevalence of rhamnolipids was confirmed by Fourier transform infrared and one-dimensional proton nuclear magnetic resonance. We also observed some correlations between the tensioactive characteristics and structural chemistry of the rhamnolipid surfactants.

Bacterial biosurfactant in enhancing solubility and metabolism of petroleum hydrocarbons

Biosurfactant can make hydrocarbon complexes more mobile with the potential use in oil recovery, pumping of crude oil and in bioremediation of crude oil contaminant. In the investigation, bacterial isolates capable of utilizing poly-cyclic aromatic hydrocarbons like phenanthrene, pyrene and fluorene were used. A gradual decrease of the supplemented hydrocarbons in the culture medium was observed with corresponding increase in bacterial biomass and protein. The medium having the combined application of fluorine and phenanthrene caused better biosurfactant production (0.45 g l(-1)) and (0.38 g l(-1)) by Pseudomonas aeruginosa strains MTCC7815 and MTCC7814. The biosurfactant from MTCC7815 (41.0 microg ml(-1)) and MTCC7812 (26 microg ml(-1)) exhibited higher solubilization of pyrene; whereas, MTCC8165 caused higher solubilization of phenanthrene; and that of MTCC7812 (24.45 microg ml(-1)) and MTCC8163 (24.49 microg ml(-1)) caused more solubilzation of fluorene. Higher solubilization of pyrene and fluorene by the biosurfactant of MTCC7815 and MTCC7812, respectively enhanced their metabolism causing sustained growth. Biosurfactants were found to be lipopeptide and protein-starch-lipid complex in nature and they could reduce the surface tension of pure water (72 m Nm(-1)) to 35 m Nm(-1). The critical micelle concentration (CMC) was also lower than the chemical surfactant sodium dodecyl sulphate (SDS). They differed in quantity and structure. The predominant rhamnolipids present in biosurfactants were Rha-C(8)-C(10) and Rha-C(10)-C(8).

Structure and applications of a rhamnolipid surfactant produced in soybean oil waste

Soybean oil soapstock was utilized as an alternative carbon source for the production of rhamnolipids by Pseudomonas aeruginosa LBI strain. The chemical composition and properties of the rhamnolipid mixture obtained were determined to define its potential applications. The chemical characterization of the rhamnolipid has revealed the presence of ten different homologues. The monorhamnolipid RhaC10C1) and the dirhamnolipid Rha2C10C10 were the main components of the mixture that showed predominance of 44% and 29%, respectively, after 144-h of cultivation. The biosurfactant was able to form stable emulsions with several hydrocarbons and showed excellent emulsification for soybean oil and chicken fat (100%). The rhamnolipid removed 67% of crude oil present in sand samples and presented antimicrobial activity against Bacillus cereus and Mucor miehei at 64 microg/mL and inhibition of Neurospora crassa, Staphylococcus aureus, and Micrococcus luteus at 256 microg/mL. The results demonstrated that the rhamnolipid produced in soybean oil soapstock can be useful in environmental and food industry applications.

Natural surfactants used in cosmetics: glycolipids

Cosmetic surfactant performs detergency, wetting, emulsifying, solubilizing, dispersing and foaming effects. Adverse reactions of chemical synthesis surfactant have an effect on environment and humans, particularly severe in long term. Biodegradability, low toxicity and ecological acceptability which are the benefits of naturally derived surfactant that promises cosmetic safety are, therefore, highly on demand. Biosurfactant producible from microorganisms exhibiting potential surface properties suitable for cosmetic applications especially incorporate with their biological activities. Sophorolipids, rhamnolipids and mannosylerythritol lipids are the most widely used glycolipids biosurfactant in cosmetics. Literatures and patents relevant to these three glycolipids reviewed were emphasizing on the cosmetic applications including personal care products presenting the cosmetic efficiency, efficacy and economy benefits of glycolipids biosurfactant.

Aggregation of the naturally occurring lipopeptide, surfactin, at interfaces and in solution: an unusual type of surfactant?

Neutron reflectometry has been used to study the structure of the biosurfactant, surfactin, at the air/water and at the hydrophobic solid/water interfaces. Three different deuterated surfactins were produced from the Bacillus subtilis strain: one perdeuterated, one with the four leucines perdeuterated, and one with everything except the four leucines perdeuterated. The neutron reflectivity profiles of these three samples in null reflecting water and in D20 with a seventh profile of the protonated surfactin in D2O were measured at pH 7.5. This combination of different isotopic compositions made it possible to deduce the distribution of each type of labeled fragment in the surfactin. Surfactin is found to adopt a ball-like structure with a thickness of 14 +/- A and an area per molecule of 147 +/- 5 A2. This makes it more like a hydrophobic nanoparticle, whose solubility in water is maintained only by its charge, than a conventional surfactant. This is probably what makes it surface-active at such low concentrations and what contributes to its forming very compact surface layers that are more dense than observed for most conventional amphiphiles. The reflectivity data were fitted by a model in which the structure of surfactin was divided into three fragments: the four leucines taken as a group, the hydrocarbon chain, and a hydrophilic group containing the two negative charges. An analysis of the reflectivity gave the following separations between fragments, where zero corresponds to the Gibbs plane for zero water adsorption: chain-water 7 A, hydrophile-water 1 A, and leucines-water 6.5 A, all +/- 1 A. The overall structure of the layer appears to be identical at a hydrophobic octadecyltrichlorosilane-coated silicon surface where the thickness of the surfactin layer is 15 +/- 1 A and the area per molecule is 145 +/- 5 A2. Finally, the structure of surfactin micelles has been examined by means of small-angle neutron scattering. The aggregation number was found to be unusually small at 20 +/- 5. The structure of the micelle is of the core-shell type with the hydrocarbon chain and the four hydrophobic leucines forming the core of the micelle.