Chemical and Physical Characterization of Interfacial-Active Lipids from Rhodococcus erythropolis Grown on n -Alkanes

An Insightful Overview of Microbial Biosurfactant: A Promising Next-Generation Biomolecule for Sustainable Future

Microbial biosurfactant is an emerging vital biomolecule of the 21st century. They are amphiphilic compounds produced by microorganisms and possess unique properties to reduce surface tension activity. The use of microbial surfactants spans most of the industrial fields due to their biodegradability, less toxicity, being environmentally safe, and being synthesized from renewable sources. These would be highly efficient eco-friendly alternatives to petroleum-derived surfactants that would open up new approaches to research on the production of biosurfactants. In the upcoming era, biobased surfactants will become a dominating multifunctional compound in the world market. Research on biosurfactants ranges from the search for novel microorganisms that can produce new molecules, structural and physiochemical characterization of biosurfactants, and fermentation process for enhanced large-scale productivity and green applications. The main goal of this review is to provide an overview of the recent state of knowledge and trends about microbially derived surfactants, various aspects of biosurfactant production, definition, properties, characteristics, diverse advances, and applications. This would lead a long way in the production of biosurfactants as globally successful biomolecules of the current century.

Biodesulfurization of organosulfur compounds by a trehalose biosurfactant producing Gordonia sp. isolated from crude oil contaminated soil

Certain factors hinder the commercialization of biodesulfurization process, including low substrate-specificity of the currently reported desulfurizing bacteria and restricted mass transfer of organic-sulfur compounds in biphasic systems. These obstacles must be addressed to clean organic-sulfur rich petro-fuels that pose serious environmental and health challenges. In current study, a dibenzothiophene desulfurizing strain, Gordonia rubripertincta W3S5 (source: oil contaminated soil) was systematically evaluated for its potential to remove sulfur from individual compounds and mixture of organic-sulfur compounds. Metabolic and genetic analyses confirmed that strain W3S5 desulfurized dibenzothiophene to 2-hydroxybiphenyl, suggesting that it follows the sulfur specific 4 S pathway. Furthermore, this strain demonstrated the ability to produce trehalose biosurfactants (with an EI24 of 53%) in the presence of dibenzothiophene, as confirmed by TLC and FTIR analyses. Various genome annotation tools, such as ClassicRAST, BlastKOALA, BV-BRC, and NCBI-PGAP, predicted the presence of otsA, otsB, treY, treZ, treP, and Trehalose-monomycolate lipid synthesis genes in the genomic pool of strain W3S5, confirming the existence of the OtsAB, TreYZ, and TreP pathways. Overall, these results underscore the potential of strain W3S5 as a valuable candidate for enhancing desulfurization efficiency and addressing the mass transfer challenges essential for achieving a scaled-up scenario.

A comprehensive review of biosurfactant production and its uses in the pharmaceutical industry

Biosurfactants are naturally occurring, surface-active chemicals generated by microorganisms and have attracted interest recently because of their numerous industrial uses. Compared to their chemical equivalents, they exhibit qualities that include lower toxic levels, increased biodegradable properties, and unique physiochemical properties. Due to these traits, biosurfactants have become attractive substitutes for synthetic surfactants in the pharmaceutical industry. In-depth research has been done in the last few decades, demonstrating their vast use in various industries. This review article includes a thorough description of the various types of biosurfactants and their production processes. The production process discussed here is from oil-contaminated waste, agro-industrial waste, dairy, and sugar industry waste, and also how biosurfactants can be produced from animal fat. Various purification methods such as ultrafiltration, liquid-liquid extraction, acid precipitation, foam fraction, and adsorption are required to acquire a purified product, which is necessary in the pharmaceutical industry, are also discussed here. Alternative ways for large-scale production of biosurfactants using different statistical experimental designs such as CCD, ANN, and RSM are described here. Several uses of biosurfactants, including drug delivery systems, antibacterial and antifungal agents, wound healing, and cancer therapy, are discussed. Additionally, in this review, the future challenges and aspects of biosurfactant utilization in the pharmaceutical industry and how to overcome them are also discussed.

A review on biosurfactant producing bacteria for remediation of petroleum contaminated soils

The discharge of potentially toxic petroleum hydrocarbons into the environment has been a matter of concern, as these organic pollutants accumulate in many ecosystems due to their hydrophobicity and low bioavailability. Petroleum hydrocarbons are neurotoxic and carcinogenic organic pollutants, extremely harmful to human and environmental health. Traditional treatment methods for removing hydrocarbons from polluted areas, including various mechanical and chemical strategies, are ineffective and costly. However, many indigenous microorganisms in soil and water can utilise hydrocarbon compounds as sources of carbon and energy and hence, can be employed to degrade hydrocarbon contaminants. Therefore, bioremediation using bacteria that degrade petroleum hydrocarbons is commonly viewed as an environmentally acceptable and effective method. The efficacy of bioremediation can be boosted further by using potential biosurfactant-producing microorganisms, as biosurfactants reduce surface tension, promote emulsification and micelle formation, making hydrocarbons bio-available for microbial breakdown. Further, introducing nanoparticles can improve the solubility of hydrophobic hydrocarbons as well as microbial synthesis of biosurfactants, hence establishing a favourable environment for microbial breakdown of these chemicals. The review provides insights into the role of microbes in the bioremediation of soils contaminated with petroleum hydrocarbons and emphasises the significance of biosurfactants and potential biosurfactant-producing bacteria. The review partly focusses on how nanotechnology is being employed in different critical bioremediation processes.

Isolation and chemical characterization of the biosurfactant produced by Gordonia sp. IITR100

Biosurfactants are amphipathic molecules produced from microorganisms. There are relatively few species known where the detailed chemical characterization of biosurfactant has been reported. Here, we report isolation and chemical characterization of the biosurfactant produced by a biodesulfurizing bacterium Gordonia sp. IITR100. Biosurfactant production was determined by performing oil spreading, drop-collapse, Emulsion index (E24), and Bacterial adhesion to hydrocarbons (BATH) assay. The biosurfactant was identified as a glycolipid by LCMS and GCMS analysis. The chemical structure was further confirmed by performing FTIR and NMR of the extracted biosurfactant. The emulsion formed by the biosurfactant was found to be stable between temperatures of 4°C to 30°C, pH of 6 to 10 and salt concentrations up to 2%. It was successful in reducing the surface tension of the aqueous media from 61.06 mN/m to 36.82 mN/m. The biosurfactant produced can be used in petroleum, detergents, soaps, the food and beverage industry and the healthcare industry.

Biosurfactants: Potential Agents for Controlling Cellular Communication, Motility, and Antagonism

Biosurfactants are surface-active molecules produced by microorganisms, either on the cell surface or secreted extracellularly. They form a thin film on the surface of microorganisms and help in their detachment or attachment to other cell surfaces. They are involved in regulating the motility of bacteria and quorum sensing. Here, we describe the various types of biosurfactants produced by microorganisms and their role in controlling motility, antagonism, virulence, and cellular communication.

Microbial biosurfactants: A broad analysis of properties, applications, biosynthesis, and techno-economical assessment of rhamnolipid production

Biosurfactants are surface-active molecules originated from renewable resources, which are produced by microbial fermentation or chemical/enzymatic catalysis. These molecules present important advantages as compared to petrochemical surfactants, given their resistance to extreme conditions, biodegradability, specificity, and environmental compatibility. Besides that, the high production costs hinder its commercialization. In this way, this article aimed to analyze microbial biosurfactants production, focusing on the optimization of metabolic pathways and production processes, to identify key aspects and provide alternatives to allow a cost-effective production at industrial scale. This was achieved by a broad analysis of biosurfactants properties, applications, and biosynthetic pathways (in terms of yield, cofactors, and energy), in addition to an assessment of production-associated costs. As a result of the present extensive data survey and analysis, key production aspects are disclosed. The metabolic pathway yield analysis demonstrated that production of biosurfactants can be significantly improved (highest theoretical yield was 0.47 g_{biosurfactant} /g_substrate ) by the use of biomolecular engineering techniques to generate optimized synthetic pathways. With an alternative proposed pathway for surfactin, yield was improved and imbalance in cofactors and ATP was reduced. Analysis of productive costs indicated that to make rhamnolipids commercial production feasible, the main efforts should focus on lowering substrate costs as well as the identification of energy-efficient unit operations to lower electricity cost, since these parameters accounted for 19.36 and 78.22%, respectively, of the production costs. The data generated by this analysis highlight the need for multidisciplinary collaboration to make rhamnolipids economically feasible, including biomolecular engineering and process intensification.

Biosurfactants as a Novel Additive in Pharmaceutical Formulations: Current Trends and Future Implications

BACKGROUND

Surfactants are an important category of additives that are used widely in most of the formulations as solubilizers, stabilizers, and emulsifiers. Current drug delivery systems comprise of numerous synthetic surfactants (such as Cremophor EL, polysorbate 80, Transcutol-P), which are associated with several side effects though used in many formulations. Therefore, to attenuate the problems associated with conventional surfactants, a new generation of surface-active agents is obtained from the metabolites of fungi, yeast, and bacteria, which are termed as biosurfactants.

OBJECTIVES

In this article, we critically analyze the different types of biosurfactants, their origin along with their chemical and physical properties, advantages, drawbacks, regulatory status, and detailed pharmaceutical applications.

METHODS

243 papers were reviewed and included in this review.

RESULTS

Briefly, Biosurfactants are classified as glycolipids, rhamnolipids, sophorolipids, trehalolipids, surfactin, lipopeptides & lipoproteins, lichenysin, fatty acids, phospholipids, and polymeric biosurfactants. These are amphiphilic biomolecules with lipophilic and hydrophilic ends and are used as drug delivery vehicles (foaming, solubilizer, detergent, and emulsifier) in the pharmaceutical industry. Despite additives, they have some biological activity as well (anti-cancer, anti-viral, anti-microbial, P-gp inhibition, etc.). These biomolecules possess better safety profiles and are biocompatible, biodegradable, and specific at different temperatures.

CONCLUSION

Biosurfactants exhibit good biomedicine and additive properties that can be used in developing novel drug delivery systems. However, more research should be driven due to the lack of comprehensive toxicity testing and high production cost which limits their use.

Biotechnology of Rhodococcus for the production of valuable compounds

Bacteria belonging to Rhodococcus genus represent ideal candidates for microbial biotechnology applications because of their metabolic versatility, ability to degrade a wide range of organic compounds, and resistance to various stress conditions, such as metal toxicity, desiccation, and high concentration of organic solvents. Rhodococcus spp. strains have also peculiar biosynthetic activities that contribute to their strong persistence in harsh and contaminated environments and provide them a competitive advantage over other microorganisms. This review is focused on the metabolic features of Rhodococcus genus and their potential use in biotechnology strategies for the production of compounds with environmental, industrial, and medical relevance such as biosurfactants, bioflocculants, carotenoids, triacylglycerols, polyhydroxyalkanoate, siderophores, antimicrobials, and metal-based nanostructures. These biosynthetic capacities can also be exploited to obtain high value-added products from low-cost substrates (industrial wastes and contaminants), offering the possibility to efficiently recover valuable resources and providing possible waste disposal solutions. Rhodococcus spp. strains have also recently been pointed out as a source of novel bioactive molecules highlighting the need to extend the knowledge on biosynthetic capacities of members of this genus and their potential utilization in the framework of bioeconomy. KEY POINTS: • Rhodococcus possesses promising biosynthetic and bioconversion capacities. • Rhodococcus bioconversion capacities can provide waste disposal solutions. • Rhodococcus bioproducts have environmental, industrial, and medical relevance. Graphical abstract.

Microbial Biosurfactants as Key Multifunctional Ingredients for Sustainable Cosmetics

A polar head and an apolar tail chemically characterize surfactants, they show different properties and are categorized by different factors such as head charge and molecular weight. They work by reducing the surface tension between oil and water phases to facilitate the formation of one homogeneous mixture. In this respect, they represent unavoidable ingredients, their main application is in the production of detergents, one of if not the most important categories of cosmetics. Their role is very important, it should be remembered that it was precisely soaps and hygiene that defeated the main infectious diseases at the beginning of the last century. Due to their positive environmental impact, the potential uses of microbial sourced surfactants are actively investigated. These compounds are produced with different mechanisms by microorganisms in the aims to defend themselves from external threats, to improve the mobility in the environment, etc. In the cosmetic field, biosurfactants, restricted in the present work to those described above, can carry high advantages, in comparison to traditional surfactants, especially in the field of sustainable and safer approaches. Besiede this, costs still remain an obsatcle to their diffusion; in this regard, exploration of possible multifunctional actions could help to contain application costs. To highlight their features and possible multifunctional role, on the light of specific biological profiles yet underestimated, we have approached the present review work.

Marine Biosurfactants: Biosynthesis, Structural Diversity and Biotechnological Applications

Biosurfactants are amphiphilic secondary metabolites produced by microorganisms. Marine bacteria have recently emerged as a rich source for these natural products which exhibit surface-active properties, making them useful for diverse applications such as detergents, wetting and foaming agents, solubilisers, emulsifiers and dispersants. Although precise structural data are often lacking, the already available information deduced from biochemical analyses and genome sequences of marine microbes indicates a high structural diversity including a broad spectrum of fatty acid derivatives, lipoamino acids, lipopeptides and glycolipids. This review aims to summarise biosyntheses and structures with an emphasis on low molecular weight biosurfactants produced by marine microorganisms and describes various biotechnological applications with special emphasis on their role in the bioremediation of oil-contaminated environments. Furthermore, novel exploitation strategies are suggested in an attempt to extend the existing biosurfactant portfolio.

Screening, isolation and characterization of biosurfactant producing Bacillus subtilis strain ANSKLAB03

Biosurfactants are surface-active compounds produced by a wide range of microorganisms. They have both hydrophobic and hydrophilic domains and can decrease the surface tension and the interfacial tension of growth medium. Biosurfactants have different chemical structures like-lipopeptides, glycolipids, neutral lipids and fatty acids. They are biodegradable non-toxic biomolecules that show strong emulsification of hydrophobic compounds. They have the ability to form stable emulsions. The low water-solubility of these compounds restricts their availability to microorganisms. Surfactants secreted by microbes enhance the bioavailability of such hydrophobic compounds for bioremediation. Therefore, biosurfactant-enhanced solubility of pollutants has prospective applications in bioremediation. Biosurfactants are useful in a variety of industrial processes, and are also of vital importance to the microbes in adhesion, emulsification, and bioavailability, desorption and defense strategy. Therefore, it is of interest to identify biosurfuctantproducing strain of bacteria from brackish water. The microbial samples were isolated from the Chilika Lake, odisha, India and were tested for its biosurfactant property by various biochemical methods. 16S rRNA was sequenced using Sanger dideoxy sequencing method to characterize the biosurfuctant producing strain. The new Bacillus subtilis strain ANSKLAB03 isolated from 40 samples was deposited in GenBank with accession number KU523257.

Lipids of Dietzia sp. A14101. Part II: A study of the dynamics of the release of surface active compounds by Dietzia sp. A14101 into the medium

Dietzia sp. A14101 isolated from an oil reservoir model column was found to induce a strong decrease of the interfacial tension (IFT) in hydrocarbon-water mixtures in the presence of the intact bacterial cells (Kowalewski et al., 2005). The strain was shown to be able to degrade a wide range of hydrocarbon substrates (Bødtker et al., 2009). Further studies showed that the surface-active compounds tentatively identified as glycolipids were produced by Dietzia sp. A14101 on non- and water-immiscible -hydrocarbon substrates, Part I (Hvidsten et al., 2017). The results suggested that biosurfactant (BS) was a mixture of several isomers. The study presented here is aimed to investigate whether BS are secreted into the aqueous medium, and if so, then at which phase of the culture growth and in which amounts - the dynamics of the BS release in incubations on water-immiscible hydrocarbons. Two methods of BS extraction from the medium were attempted and compared: a liquid-liquid extraction (LLE) and precipitation by acid. For qualitative and semi-quantitative assessment, gas chromatography-mass spectrometry (GC/MS), thin-layer chromatography (TLC), liquid chromatography-mass spectrometry (LC-MS), surface tension measurements (SFT), emulsification (E₂₄) and oil-spreading tests were employed. The results indicated that BS only partially were secreted into the medium. Detectable amounts of glycolipids in media were first identified during the exponential growth phase. However, only a slight decrease of SFT was observed in the cell-free medium. The emulsification index values of the sampled material were lower than those reported for related strains. The results suggested that most of the BS produced by Dietzia sp. A14101 remains cell-bound during the culture development in a batch mode and only a narrow range of the BS isomers can be detected in small amounts in media.

A comprehensive multi-omics approach uncovers adaptations for growth and survival of Pseudomonas aeruginosa on n-alkanes

Background

Examination of complex biological systems has long been achieved through methodical investigation of the system’s individual components. While informative, this strategy often leads to inappropriate conclusions about the system as a whole. With the advent of high-throughput “omic” technologies, however, researchers can now simultaneously analyze an entire system at the level of molecule (DNA, RNA, protein, metabolite) and process (transcription, translation, enzyme catalysis). This strategy reduces the likelihood of improper conclusions, provides a framework for elucidation of genotype-phenotype relationships, and brings finer resolution to comparative genomic experiments. Here, we apply a multi-omic approach to analyze the gene expression profiles of two closely related Pseudomonas aeruginosa strains grown in n-alkanes or glycerol.

Results

The environmental P. aeruginosa isolate ATCC 33988 consumed medium-length (C₁₀–C₁₆) n-alkanes more rapidly than the laboratory strain PAO1, despite high genome sequence identity (average nucleotide identity >99%). Our data shows that ATCC 33988 induces a characteristic set of genes at the transcriptional, translational and post-translational levels during growth on alkanes, many of which differ from those expressed by PAO1. Of particular interest was the lack of expression from the rhl operon of the quorum sensing (QS) system, resulting in no measurable rhamnolipid production by ATCC 33988. Further examination showed that ATCC 33988 lacked the entire lasI/lasR arm of the QS response. Instead of promoting expression of QS genes, ATCC 33988 up-regulates a small subset of its genome, including operons responsible for specific alkaline proteases and sphingosine metabolism.

Conclusion

This work represents the first time results from RNA-seq, microarray, ribosome footprinting, proteomics, and small molecule LC-MS experiments have been integrated to compare gene expression in bacteria. Together, these data provide insights as to why strain ATCC 33988 is better adapted for growth and survival on n-alkanes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3708-4) contains supplementary material, which is available to authorized users.

High molecular weight bioemulsifiers, main properties and potential environmental and biomedical applications

High molecular weight bioemulsifiers are amphipathic polysaccharides, proteins, lipopolysaccharides, lipoproteins, or complex mixtures of these biopolymers, produced by a wide variety of microorganisms. They are characterized by highly structural diversity and have the ability to decrease the surface and interfacial tension at the surface and interface respectively and/or emulsify hydrophobic compounds. Emulsan, fatty acids, phospholipids, neutral lipids, exopolysaccharides, vesicles and fimbriae are among the most popular high molecular weight bioemulsifiers. They have great physic-chemical properties like tolerance to extreme conditions of pH, temperature and salinity, low toxicity and biodegradability. Owing their emulsion forming and breaking capacities, solubilization, mobilization and dispersion activities and their viscosity reduction activity; they possess great environmental application as enhancer of hydrocarbon biodegradation and for microbial enhanced oil recovery. Besides, they are applied in biomedical fields for their antimicrobial and anti-adhesive activities and involvement in immune responses.

Immobilization of R. erythropolis in alginate-based artificial cells for simulated plaque degradation in aqueous media

Cholesterol degradation rates of free and immobilized Rhodococcus erythropolis (ATCC # 25544) were studied utilizing the bacterium's cholesterol oxidase enzyme pathway to degrade cholesterol in an aqueous simulated non-calcified plaque solution. An L16 (4(5)) Taguchi design was used to minimize the glycolipid bio-surfactant by-product in the growth medium, to improve bacterial viability in the immobilized state. As an expected outcome of miniaturization, there is a significant difference between the atomized (d = 850 ± 50 μm) and inkjet-bioprinted (d = 32 ± 5 μm) lumped kinetic degradation rates after 48 h (p = 0.029, α = 0.05) per ml of jetted alginate. Based on a biphasic cholesterol degradation model, at an initial bacterial cell density of Nlow = 4.53 × 10(8)/ml, for an initial cholesterol concentration of 3 mg/ml, the percentage mass of metabolite degraded is 37.0% ± 0.42%, 57.8% ± 0.04% and 65.1% ± 0.01% for the free, atomized and inkjet immobilized bacteria, respectively.

Structural definition of trehalose 6-monomycolates and trehalose 6,6'-dimycolates from the pathogen Rhodococcus equi by multiple-stage linear ion-trap mass spectrometry with electrospray ionization

The cell wall of the pathogenic bacterium Rhodococcus equi (R. equi) contains abundant trehalose monomycolate (TMM) and trehalose dimycolate (TDM), the glycolipids bearing mycolic acids. Here, we describe multiple-stage (MS(n)) linear ion-trap (LIT) mass spectrometric approaches toward structural characterization of TMM and TDM desorbed as [M + Alk](+) (Alk = Na, Li) and as [M + X](-) (X = CH(3)CO(2), HCO(2)) ions by electrospray ionization (ESI). Upon MS(n) (n=2, 3, 4) on the [M + Alk](+) or the [M + X](-) adduct ions of TMM and TDM, abundant structurally informative fragment ions are readily available, permitting fast assignment of the length of the meromycolate chain and of the α-branch on the mycolyl residues. In this way, structures of TMM and TDM isolated from pathogenic R. equi strain 103 can be determined. Our results indicate that the major TMM and TDM molecules possess 6, and/or 6'-mycolyl groups that consist of mainly C14 and C16 α-branches with meromycolate branches ranging from C18 to C28, similar to the structures of the unbound mycolic acids found in the cell envelope. Up to 60 isobaric isomers varying in chain length of the α-branch and of the meromycolate backbone were observed for some of the TDM species in the mixture. This mass spectrometric approach provides a direct method that affords identification of various TMM and TDM isomers in a mixture of which the complexity of this lipid class has not been previously reported using other analytical methods.

Adsorption of sophorolipid biosurfactants on their own and mixed with sodium dodecyl benzene sulfonate, at the air/water interface

The adsorption of the lactonic (LS) and acidic (AS) forms of sophorolipid and their mixtures with the anionic surfactant sodium dodecyl benzene sulfonate (LAS) has been measured at the air/water interface by neutron reflectivity, NR. The AS and LS sophorolipids adsorb with Langmuir-like adsorption isotherms. The more hydrophobic LS is more surface active than the AS, with a lower critical micellar concentration, CMC, and stronger surface adsorption, with an area/molecule ∼70 Å(2) compared with 85 Å(2) for the AS. The acidic sophorolipid shows a maximum in its adsorption at the CMC which appears to be associated with a mixture of different isomeric forms. The binary LS/AS and LS/LAS mixtures show a strong surface partitioning in favor of the more surface active and hydrophobic LS component but are nevertheless consistent with ideal mixing at the interface. In contrast, the surface composition of the AS/LAS mixture is much closer to the solution composition, but the surface mixing is nonideal and can be accounted for by regular solution theory, RST. In the AS/LS/LAS ternary mixtures, the surface adsorption is dominated by the sophorolipid, and especially the LS component, in a way that is not consistent with the observations for the binary mixtures. The extreme partitioning in favor of the sophorolipid for the LAS/LS/AS (1:2) mixtures is attributed to a reduction in the packing constraints at the surface due to the AS component. Measurements of the surface structure reveal a compact monolayer for LS and a narrow solvent region for LS, LS/AS, and LS/LAS mixtures, consistent with the more hydrophobic nature of the LS component. The results highlight the importance of the relative packing constraints on the adsorption of multicomponent mixtures, and the impact of the lactonic form of the sophorolipid on the adsorption of the sophorolipid/LAS mixtures.

Solution self-assembly of the sophorolipid biosurfactant and its mixture with anionic surfactant sodium dodecyl benzene sulfonate

The self-assembly in aqueous solution of the acidic (AS) and lactonic (LS) forms of the sophorolipid biosurfactant, their mixtures, and their mixtures with anionic surfactant sodium dodecyl benzene sulfonate, LAS, has been studied using predominantly small-angle neutron scattering, SANS, at relatively low surfactant concentrations of <30 mM. The more hydrophobic lactonic sophorolipid forms small unilamellar vesicles at low surfactant concentrations, in the concentration range of 0.2 to 3 mM, and transforms via a larger unilamellar vesicle structure at 7 mM to a disordered dilute phase of tubules at higher concentrations, 10 to 30 mM. In marked contrast, the acidic sophorolipid is predominantly in the form of small globular micelles in the concentration range of 0.5 to 30 mM, with a lower concentration of larger, more planar aggregates (lamellar or vesicular) in coexistence. In mixtures of AS and LS, over the same concentration range, the micellar structure associated with the AS sophorolipid dominates the mixed-phase behavior. In mixtures of anionic surfactant LAS with the AS sophorolipid, the globular micellar structure dominates over the entire composition and concentration range studied. In contrast, mixtures of LAS with the LS sophorolipid exhibit a rich evolution in phase behavior with solution composition and concentration. At low surfactant concentrations, the small unilamellar vesicle structure present for LS-rich solution compositions evolves into a globular micelle structure as the solution becomes richer in LAS. At higher surfactant concentrations, the disordered lamellar structure present for LS-rich compositions transforms to small vesicle/lamellar coexistence, to lamellar/micellar coexistence, to micellar/lamellar coexistence, and ultimately to a pure micellar phase as the solution becomes richer in LAS. The AS sophorolipid surfactant exhibits self-assembly properties similar to those of most other weakly ionic or nonionic surfactants that have relatively large headgroups. However, the more hydrophobic nature of the lactonic sophorolipid results in a more complex and unusual evolution in phase behavior with concentration and with concentration and composition when mixed with anionic surfactant LAS.

Biosurfactant-mediated biodegradation of straight and methyl-branched alkanes by Pseudomonas aeruginosa ATCC 55925

Accidental oil spills and waste disposal are important sources for environmental pollution. We investigated the biodegradation of alkanes by Pseudomonas aeruginosa ATCC 55925 in relation to a rhamnolipid surfactant produced by the same bacterial strain. Results showed that the linear C11-C21 compounds in a heating oil sample degraded from 6% to 100%, whereas the iso-alkanes tended to be recalcitrant unless they were exposed to the biosurfactant; under such condition total biodegradation was achieved. Only the biodegradation of the commercial C12-C19 alkanes could be demonstrated, ranging from 23% to 100%, depending on the experimental conditions. Pristane (a C19 branched alkane) only biodegraded when present alone with the biosurfactant and when included in an artificial mixture even without the biosurfactant. In all cases the biosurfactant significantly enhanced biodegradation. The electron scanning microscopy showed that cells depicted several adaptations to growth on hydrocarbons, such as biopolymeric spheres with embedded cells distributed over different layers on the spherical surfaces and cells linked to each other by extracellular appendages. Electron transmission microscopy revealed transparent inclusions, which were associated with hydrocarbon based-culture cells. These patterns of hydrocarbon biodegradation and cell adaptations depended on the substrate bioavailability, type and length of hydrocarbon.

Production of a Biosurfactant from Torulopsis bombicola

Two types of carbon sources-carbohydrate and vegetable oil-are necessary to obtain large yields of biosurfactant from Torulopsis bombicola ATCC 22214. Most of the surfactant is produced in the late exponential phase of growth. It is possible to grow the yeast on a single carbon source and then add the other type of substrate, after the exponential growth phase, and cause a burst of surfactant production. This product is a mixture of glycolipids. The maximum yield is 70 g liter, or 35% of the weight of the substrate used. An economic comparison demonstrated that this biosurfactant could be produced significantly more cheaply than any of the previously reported microbial surfactants.

Formation and identification of interfacial-active glycolipids from resting microbial cells

Resting cells of Arthrobacter sp. strain DSM2567 incubated in the presence of various mono-, di-, or trisaccharides biosynthesized different glycolipids. All eight glycolipids, containing the corresponding carbohydrate moiety and one, two, or three alpha-branched beta-hydroxy fatty acids, were produced when mannose, glucose, cellobiose, maltose, and maltotriose were used as carbon sources in a simple phosphate buffer. The structures of the compounds were elucidated by means of H and C nuclear magnetic resonance spectroscopy and by chemical ionization mass spectroscopy. In high-salinity solution, the substances showed different surfactant properties. Cellobiose and maltose monocorynomycolates reduced the interfacial tension from 42 to 1 mN/m at critical micelle concentrations below 20 mg/liter.

Preliminary characterization of biosurfactants produced by microorganisms isolated from refinery wastewaters

Some bacterial strains isolated from refinery wastewaters were identified as Pseudomonas aeruginosa RWI, Pseudomonas putida RWII, Pseudomonas fluorescens RWIII and Burkholderia cepacia RWIV, and the biosurfactants produced by these strains were coded as BS-I, BS-II, BS-III and BS-IV, respectively. The bacterial strains were characterized by the following biochemical methods: Gram stain, oxidase activity, indol, lactose and growth at 42 degrees C. Biosurfactant production was evaluated by: emulsification activity, surface tension measurement and critical micelle concentration. Chemical characterization of the biosurfactants was done by: FTIR and analysis of carbohydrate, protein and lipid content. The biosurfactants showed good emulsification activity against different hydrocarbon sources. The initial surface tension of culture broth was determined as 67.3 mN/m, and production of BS-I, BS-II, BS-III and BS-IV lowered this value to 35.9, 49.2, 51.6 and 45.7 mN/m, respectively. The critical micelle concentration of the biosurfactants was found to be in the range 10-50 mg/L. From the results of this study it was observed that the refinery wastewaters are a suitable source for isolation of biosurfactant-producing bacteria, but are not a substrate for biosurfactant production.

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).