Biomedical and therapeutic applications of biosurfactants

Microbial biosurfactants: Green alternatives and sustainable solution for augmenting pesticide remediation and management of organic waste

Pesticide pollution remains a significant environmental challenge, necessitating the exploration of sustainable alternatives. Biosurfactants are a class of unconventional surface-active chemicals that are produced by microorganisms. Biosurfactants have many applications in treating oil spills, emulsifiers, pharmaceuticals, and agriculture. Compared to chemical surfactants, they have benefits such as biodegradability, less toxicity, and a greener option because they are derived from microbes. Biosurfactants have recently been shown to have the potential to speed up pesticide cleanup. Biosurfactants are used in pesticide remediation because of their exceptional foaming ability, high selectivity, and wide range of pH, salinity, and temperature operating windows. Microbial biosurfactants emerged as potential agents for the treatment of organic waste and agricultural residue. This review unfolds the promising realm of microbial biosurfactants as green solutions for environmental sustainability, particularly in agricultural practices, with special reference to pesticide remediation. This article highlights the escalating need for eco-friendly alternatives, paving the way for discussing biosurfactants. Moreover, the articles discuss in detail various advancements in the field of rapid screening of biosurfactants, either using a conventional approach or via advanced instruments such as GC-MS, HPLC, NMR, FTIR, etc. Furthermore, the article unveils the molecular mechanisms and the microbial genes driving biosurfactant synthesis, offering insights into enhancing production efficiency. Moreover, the article explores diverse applications of microbial biosurfactants in sustainable agriculture, ranging from soil remediation to crop protection. The article also highlights the various functions of microbial biosurfactants for enhancing the decomposition and recycling of organic waste and agricultural residues, emphasizing their potential for sustainable waste management strategies. Overall, the review underscores the pivotal role of microbial biosurfactants as green alternatives for addressing pesticide pollution and advancing environmental sustainability.

Microbial lipopeptides: their pharmaceutical and biotechnological potential, applications, and way forward

As lead molecules, cyclic lipopeptides with antibacterial, antifungal, and antiviral properties have garnered a lot of attention in recent years. Because of their potential, cyclic lipopeptides have earned recognition as a significant class of antimicrobial compounds with applications in pharmacology and biotechnology. These lipopeptides, often with biosurfactant properties, are amphiphilic, consisting of a hydrophilic moiety, like a carboxyl group, peptide backbone, or carbohydrates, and a hydrophobic moiety, mostly a fatty acid. Besides, several lipopeptides also have cationic groups that play an important role in biological activities. Antimicrobial lipopeptides can be considered as possible substitutes for antibiotics that are conventional to address the current drug-resistant issues as pharmaceutical industries modify the parent antibiotic molecules to render them more effective against antibiotic-resistant bacteria and fungi, leading to the development of more resistant microbial strains. Bacillus species produce lipopeptides, which are secondary metabolites that are amphiphilic and are typically synthesized by non-ribosomal peptide synthetases (NRPSs). They have been identified as potential biocontrol agents as they exhibit a broad spectrum of antimicrobial activity. A further benefit of lipopeptides is that they can be produced and purified biotechnologically or biochemically in a sustainable manner using readily available, affordable, renewable sources without harming the environment. In this review, we discuss the biochemical and functional characterization of antifungal lipopeptides, as well as their various modes of action, method of production and purification (in brief), and potential applications as novel antibiotic agents.

Exploring the diverse applications of Carbohydrate macromolecules in food, pharmaceutical, and environmental technologies

Carbohydrates are a class of macromolecules that has significant potential across several domains, including the organisation of genetic material, provision of structural support, and facilitation of defence mechanisms against invasion. Their molecular diversity enables a vast array of essential functions, such as energy storage, immunological signalling, and the modification of food texture and consistency. Due to their rheological characteristics, solubility, sweetness, hygroscopicity, ability to prevent crystallization, flavour encapsulation, and coating capabilities, carbohydrates are useful in food products. Carbohydrates hold potential for the future of therapeutic development due to their important role in sustained drug release, drug targeting, immune antigens, and adjuvants. Bio-based packaging provides an emerging phase of materials that offer biodegradability and biocompatibility, serving as a substitute for traditional non-biodegradable polymers used as coatings on paper. Blending polyhydroxyalkanoates (PHA) with carbohydrate biopolymers, such as starch, cellulose, polylactic acid, etc., reduces the undesirable qualities of PHA, such as crystallinity and brittleness, and enhances the PHA's properties in addition to minimizing manufacturing costs. Carbohydrate-based biopolymeric nanoparticles are a viable and cost-effective way to boost agricultural yields, which is crucial for the increasing global population. The use of biopolymeric nanoparticles derived from carbohydrates is a potential and economically viable approach to enhance the quality and quantity of agricultural harvests, which is of utmost importance given the developing global population. The carbohydrate biopolymers may play in plant protection against pathogenic fungi by inhibiting spore germination and mycelial growth, may act as effective elicitors inducing the plant immune system to cope with pathogens. Furthermore, they can be utilised as carriers in controlled-release formulations of agrochemicals or other active ingredients, offering an alternative approach to conventional fungicides. It is expected that this review provides an extensive summary of the application of carbohydrates in the realms of food, pharmaceuticals, and environment.

Rhamnolipid Micelles Assist Azithromycin in Efficiently Disrupting Staphylococcus aureus Biofilms and Impeding Their Re-Formation

Introduction

Biofilm is highly resistant to antibiotics due to its heterogeneity and is implicated in over 80% of chronic infections; these refractory and relapse-prone infections pose a huge medical burden.

Methods

In this study, rhamnolipid (RHL), a biosurfactant with antibiofilm activity, was loaded with the antibiotic azithromycin (AZI) to construct a stable nanomicelle (AZI@RHL) that promotes Staphylococcus aureus (S. aureus) biofilm disruption.

Results

AZI@RHL micelles made a destruction in biofilms. The biofilm biomasses were reduced significantly by 48.2% (P<0.05), and the main components polysaccharides and proteins were reduced by 47.5% and 36.8%, respectively. These decreases were about 3.1 (15.9%), 7.3 (6.5%), and 1.9 (19.5%) times higher compared with those reported for free AZI. The disruption of biofilm structure was observed under a confocal microscope with fluorescent labeling, and 48.2% of the cells in the biofilm were killed. By contrast, the clearance rates of cells were only 20% and 17% when treated alone with blank micelles or free AZI. Biofilm formation was inhibited up to 92% in the AZI@RHL group due to effects on cell auto-aggregation and eDNA release. The rates for the other groups were significantly lower, with only 27.7% for the RHL group and 12% for the AZI group (P<0.05). The low cell survival and great formation inhibition could reduce biofilm recolonization and re-formation.

Conclusion

The antibiofilm efficacy of rhamnolipid was improved through micellar nanoparticle effects when loading azithromycin. AZI@RHL provides a one-step solution that covers biofilm disruption, bacteria inactivation, recolonization avoidance, and biofilm re-formation inhibition.

Surfactin-like lipopeptides from Bacillus clausii efficiently bind to spike glycoprotein of SARS-CoV-2

The coronavirus disease 2019 (COVID-19) rapidly spread across the globe, infecting millions and causing hundreds of deaths. It has been now around three years but still, it remained a serious threat worldwide, even after the availability of some vaccines. Bio-surfactants are known to have antiviral activities and might be a potential alternative for the treatment of SARS-CoV-2 infection. In the present study, we have isolated and purified, a surfactin-like lipopeptide produced by a probiotic bacterial strain Bacillus clausii TS. Upon purification and characterization with MALDI analysis, the molecular weight of the lipopeptide is confirmed as 1037 Da (similar to surfactin C) which is known to have antiviral activities against various enveloped viruses. Purified surfactin-like lipopeptide showed efficient binding and inhibition of SARS-CoV-2 spike (S1) protein, revealed by competitive ELISA assay. Further, we have explored the complete thermodynamics of the inhibitory binding of surfactin-like lipopeptide with S1 protein using isothermal titration calorimetric (ITC) assay. ITC results are in agreement with ELISA with a binding constant of 1.78 × 10-4 M-1. For further validation of the inhibitory binding of surfactin-like lipopeptide with S1 protein and its receptor binding domain (RBD), we performed molecular docking, dynamics, and simulation experiments. Our results suggested that surfactin could be a promising drug agent for the spike protein targeting drug development strategy against SARS-CoV-2 and other emerging variants.Communicated by Ramaswamy H. Sarma.

Microbial biosurfactants: a review of recent environmental applications

Microbial biosurfactants are low-molecular-weight surface-active compounds of high industrial interest owing to their chemical properties and stability under several environmental conditions. The chemistry of a biosurfactant and its production cost are defined by the selection of the producer microorganism, type of substrate, and purification strategy. Recently, biosurfactants have been applied to solve or contribute to solving some environmental problems, with this being their main field of application. The most referenced studies are based on the bioremediation of contaminated soils with recalcitrant pollutants, such as hydrocarbons or heavy metals. In the case of heavy metals, biosurfactants function as chelating agents owing to their binding capacity. However, the mechanism by which biosurfactants typically act in an environmental field is focused on their ability to reduce the surface tension, thus facilitating the emulsification and solubilization of certain pollutants (in-situ biostimulation and/or bioaugmentation). Moreover, despite the low toxicity of biosurfactants, they can also act as biocidal agents at certain doses, mainly at higher concentrations than their critical micellar concentration. More recently, biosurfactant production using alternative substrates, such as several types of organic waste and solid-state fermentation, has increased its applicability and research interest in a circular economy context. In this review, the most recent research publications on the use of biosurfactants in environmental applications as an alternative to conventional chemical surfactants are summarized and analyzed. Novel strategies using biosurfactants as agricultural and biocidal agents are also presented in this paper.

Nanoemulsions: Formulation, characterization, biological fate, and potential role against COVID-19 and other viral outbreaks

Viral diseases are emerging as global threats. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), that causes coronavirus disease (COVID-19), has severe global impacts. Safety, dosage, and potency of vaccines recently approved for emergency use against SARS-CoV-2 need further evaluation. There is still no effective treatment against COVID-19; therefore, safe, and effective vaccines or therapeutics against SARS-CoV-2 are urgently needed. Oil-in-water nanoemulsions (O/W NEs) are emerging as sophisticated, protective, and therapeutic platforms. Encapsulation capacity, which offers better drug pharmacokinetics, coupled with the tunable surfaces present NEs as promising tools for pharmaceutical applications. The challenges facing drug discovery, and the advancements of NEs in drug delivery demonstrate the potential of NEs against evolving diseases, like COVID-19. Here we summarize current COVID-19 knowledge and discuss the composition, stability, preparation, characterization, and biological fate of O/W NEs. We also provide insights into NE structural-functional properties that may contribute to therapeutic or preventative solutions against COVID-19.

Microbial surfactants in nanotechnology: recent trends and applications

The interest in nano-sized materials to develop novel products has increased exponentially in the last decade, together with the search for green methods for their synthesis. An alternative to contribute to a more sustainable approach is the use of microbial-derived molecules to assist nanomaterial synthesis. In this sense, biosurfactants (BSs) have emerged as eco-friendly substitutes in nano-sized materials preparation. The inherent amphiphilic and self-assembly character of BSs associated with their low eco-toxicity, biodegradability, biocompatibility, structural diversity, biological activity, and production from renewable resources are potential advantages over chemically-derived surfactants. In nanotechnology, these versatile molecules play multiple roles. In nanoparticle (NP) synthesis, they act as capping and reducing agents and they also provide self-assembly structures to encapsulation, functionalization, or templates and act as emulsifiers in nanoemulsions. Moreover, BSs can also play as active compounds owing to their intrinsic biological properties. This review presents the recent trends in the development of BS-based nanostructures and their biomedical and environmental applications. Fundamental aspects regarding their antimicrobial and anticancer activities are also discussed.

ROS-Mediated Necrosis by Glycolipid Biosurfactants on Lung, Breast, and Skin Melanoma Cells

Cancer is one of the major leading causes of death worldwide. Designing the new anticancer drugs is remained a challenging task due to ensure complexicity of cancer etiology and continuosly emerging drug resistance. Glycolipid biosurfactants are known to possess various biological activities including antimicrobial, anticancer and antiviral properties. In the present study, we sought to decipher the mechanism of action of the glycolipids (lactonic-sophorolipd, acidic-sophorolipid, glucolipid, and bolalipid) against cancer cells using lung cancer cell line (A549), breast cancer cell line (MDA-MB 231), and mouse skin melanoma cell line (B16F10). Scratch assay and fluorescence microscopy revealed that glycolipids inhibit tumorous cell migration possibly by inhibiting actin filaments. Fluorescence activated cell sorter (FACS) analysis exhibited that lactonic sophorolipid and glucolipid both induced the reactive oxygen species, altered the mitochondrial membrane potential (ΔΨ) and finally led to the cell death by necrosis. Furthermore, combinatorial effect of lactonic-sophorolipd and glucolipid demonstrated synergistic interaction on A549 cell line whereas additive effect on MDA-MB 231 and B16F10 cell lines. Our study has highlighted that lactonic-sophorolipd and glucolipid could be useful for developing new anticancer drugs either alone or in combination.

Inhibitory Effects of Lipopeptides and Glycolipids on C. albicans-Staphylococcus spp. Dual-Species Biofilms

Microbial biofilms strongly resist host immune responses and antimicrobial treatments and are frequently responsible for chronic infections in peri-implant tissues. Biosurfactants (BSs) have recently gained prominence as a new generation of anti-adhesive and antimicrobial agents with great biocompatibility and were recently suggested for coating implantable materials in order to improve their anti-biofilm properties. In this study, the anti-biofilm activity of lipopeptide AC7BS, rhamnolipid R89BS, and sophorolipid SL18 was evaluated against clinically relevant fungal/bacterial dual-species biofilms (Candida albicans, Staphylococcus aureus, Staphylococcus epidermidis) through quantitative and qualitative in vitro tests. C. albicans-S. aureus and C. albicans-S. epidermidis cultures were able to produce a dense biofilm on the surface of the polystyrene plates and on medical-grade silicone discs. All tested BSs demonstrated an effective inhibitory activity against dual-species biofilms formation in terms of total biomass, cell metabolic activity, microstructural architecture, and cell viability, up to 72 h on both these surfaces. In co-incubation conditions, in which BSs were tested in soluble form, rhamnolipid R89BS (0.05 mg/ml) was the most effective among the tested BSs against the formation of both dual-species biofilms, reducing on average 94 and 95% of biofilm biomass and metabolic activity at 72 h of incubation, respectively. Similarly, rhamnolipid R89BS silicone surface coating proved to be the most effective in inhibiting the formation of both dual-species biofilms, with average reductions of 93 and 90%, respectively. Scanning electron microscopy observations showed areas of treated surfaces that were free of microbial cells or in which thinner and less structured biofilms were present, compared to controls. The obtained results endorse the idea that coating of implant surfaces with BSs may be a promising strategy for the prevention of C. albicans-Staphylococcus spp. colonization on medical devices, and can potentially contribute to the reduction of the high economic efforts undertaken by healthcare systems for the treatment of these complex fungal-bacterial infections.

The Variety and Inscrutability of Polar Environments as a Resource of Biotechnologically Relevant Molecules

The application of an ever-increasing number of methodological approaches and tools is positively contributing to the development and yield of bioprospecting procedures. In this context, cold-adapted bacteria from polar environments are becoming more and more intriguing as valuable sources of novel biomolecules, with peculiar properties to be exploited in a number of biotechnological fields. This review aims at highlighting the biotechnological potentialities of bacteria from Arctic and Antarctic habitats, both biotic and abiotic. In addition to cold-enzymes, which have been intensively analysed, relevance is given to recent advances in the search for less investigated biomolecules, such as biosurfactants, exopolysaccharides and antibiotics.

Disinfectant-like activity of lipopeptide biosurfactant produced by Bacillus tequilensis strain SDS21

Antiseptics and disinfectants are widely applied for eliminating microorganisms. However, microorganisms dwelling in the biofilm are less susceptible and in some cases resistant to biocide treatment. The present study describes isolation and characterization of lipopeptide biosurfactant exhibiting disinfectant-like activity. Biosurfactant was produced by an endo-rhizospheric bacterium Bacillus tequilensis strain SDS21. Biosurfactant reduced the surface tension of water from 72 to 30 mN/m with CMC of 40 mg/l. The Liquid Chromatography-Mass Spectrometry analysis of biosurfactant suggested it to be a mixture of C₁₄, C₁₅, C₁₆ and C₁₇ surfactin homologues. The lipopeptide biosurfactant exhibited bactericidal activity against planktonic cells and biofilm residing sessile cells. The biosurfactant treatment eradicated more than 99% of bacterial biofilm present on polystyrene, glass and stainless steel surface. The biosurfactant retained its bactericidal and biofilm eradicating activities even after exposure to extreme conditions like high temperate and extreme pH. Unlike some of the commonly used disinfectant, biosurfactant retained its bactericidal and biofilm removing activity even in the hard water containing Mg²⁺ and Ca²⁺ ions. Thus, suggesting that biosurfactant produced by strain SDS21 can be used as a disinfectant or in disinfectant-like formulations effective against both planktonic and biofilm residing bacteria.

Production of Non-Toxic Biosurfactant – Surfactin – Through Microbial Fermentation of Biomass Hydrolysates for Industrial and Environmental Applications

The economically viable large-scale production of the pure isoforms of the surfactin biosurfactants, involving bacterial – Bacillus subtilis – fermentation of biomass hydrolysate feedstock, relies on the types of bacterial strains, optimization of the fermentation processing parameters, differences in the composition of the carbon and nitrogen in the bacterial media, and the chromatography techniques used for isolation of the isoforms. Here, we biosynthesized the surfactin isoforms in their mixture forms through fermentation of biomass hydrolysates at 2 wt.% carbohydrate content. The surfactin isoforms were assessed for their surface-active properties and toxicity. The enzyme hydrolysates considered were from switchgrass, soyhull (fiber), alfalfa, and bagasse. The isoform mixtures obtained after fermentation of the hydrolysates and, glucose as a control, were concentrated using chromatography columns, and characterized for molecular weights (MWs) and relative distribution using LCMS. The isoform mixtures, obtained in different fermenters (5- and 15-L) and, for different hydrolysates, invariably constituted 5 isoforms with MWs as 992.6, 1006.6, 1020.6, 1034.6, 1048.6, 1062.6 m/z amu, with their relative proportions as 6, 24, 35, 24, and 10 weight % respectively. The surface tension values of all these isoforms, in the absence of electrolytes and at 12 ppt salinity, were similar: 37 (pH 6.5) and 31 (pH 9.5) mN/m. Furthermore, the emulsification index values for the isoforms were also similar: Dispersant-to-Oil ratio as 1:20. The LC50 for Gulf killifish, Fundulus grandis for these surfactin isoforms ranged between 10 and 20 mg/L; a microbially-produced surfactin variant FA-Glu (Fatty acid Glutamate) was least toxic with LC50 at ∼100 mg/L. Thus, the surfactin synthesis approach adopted here suggested that pure (>95 wt.%) non-toxic isoforms of surfactin biosurfactants can be produced in the forms of their mixtures with surface-active properties similar to those of the pure forms of the surfactin isoforms.

Liposomes containing biosurfactants isolated from Lactobacillus gasseri exert antibiofilm activity against methicillin resistant Staphylococcus aureus strains

Staphylococcus aureus is the major causative agent of skin and soft tissue infections, whose prevention and treatment have become more difficult due to the emergence of antibiotic-resistant strains. In this regard, the development of an effective treatment represents a challenge that can be overcome by delivering new antibiofilm agents with appropriate nanocarriers. In this study, a biosurfactant (BS) isolated from Lactobacillus gasseri BC9 and subsequently loaded in liposomes (LP), was evaluated for its ability to prevent the development and to eradicate the biofilm of different methicillin resistant S. aureus (MRSA) strains. BS from L. gasseri BC9 was not cytotoxic and was able to prevent formation and to eradicate the biofilm of different MRSA strains. BS loaded liposomes (BS-LP) presented a mean diameter (lower than 200 nm) suitable for topical administration and a low polydispersity index (lower than 0.2) that were maintained over time for up 28 days. Notably, BS-LP showed higher ability than free BS to inhibit S. aureus biofilm formation and eradication. BS-LP were loaded in lyophilized matrices able to quickly dissolve (dissolution time lower than 5 s) upon contact with exudate, thus allowing vesicle reconstitution. In conclusion, in this work, we demonstrated the antibiofilm activity of Lactobacillus-derived BS and BS-LP against clinically relevant MRSA strains. Furthermore, the affordable production of lyophilized matrices containing BS-LP for local prevention of cutaneous infections was established.

Biosurfactant production by Trametes versicolor grown on two-phase olive mill waste in solid-state fermentation

Biosurfactants are amphiphilic compounds of microbial origin which exhibit better properties than their chemically derived counterparts. They are usually produced in submerged fermentation by different types of bacteria. However, biosurfactant production by fungi, particularly of the white-rot type, has been scarcely studied. In this work, and for the first time, we report the production of biosurfactants by the white-rot fungus Trametes versicolor, which was grown on two-phase olive mill waste (TPOMW) in a solid-state fermentation system. The effect of the composition of the culture medium on biosurfactant production was also studied. The highest biosurfactant production (373.6 ± 19.4 mg in 100 g of culture medium) was achieved with a medium containing 35% (w/w) of TPOMW, the highest concentration used, 10% of wheat bran and 55% of olive stones. Interestingly, no inhibition of biosurfactant production by TPOMW was detected within the concentration range used (5-35% w/w). The biosurfactant produced by T. versicolor was able to reduce the surface tension of an aqueous extract of the culture medium up to 34.5 ± 0.3 mN m^-1. A preliminary study of the chemical structure of the biosurfactant indicated that it contains both lipid and protein fractions. The simultaneous production of lignin-degrading enzymes was also assessed.

Fatty Acids Effect on Lipase and Biosurfactant Induction in Rhodotorula Glutinis CMGB-RG5

Fatty acids represent important substrates for obtaining microbial lipases and biosurfactants. The yeast strain CMGBRG5 was identified as Rhodotorula glutinis using the BIOLOG MicroLog System. The opacity screening tests showed that R. glutinis CMGB-RG5 was able to produce lipases in presence of 1% Tween 80 after three days of incubation. Lipase induction was estimated as cell growth in presence of Tween 80, Tween 20, olive oil and tributyrin. After 48 hours, best results were obtained in presence of butyric acid, respectively, oleic acid: 2.2 × 107 cells/ml on tributyrin and 1.0 × 107 cells/ml on olive oil. Biosurfactant production was evaluated as emulsification index (E24%). After one week, high E24 values were obtained on fried sunflower oil (53%) and olive oil (35%). Crude and concentrated biosurfactants were tested against nine Candida strains. Best antimicrobial activity was observed for [20X] biosurfactants against C. tropicalis, C. guilliermondii and C. krusei. In conclusion, R. glutinis CGB-RG5 shows high potential for using fatty acids from various sources as unique carbon substrates for synthesis of biocompounds with high economic and biotechnological value.

A. de Castilho L, Freire DMG, Barrientos L. Streptomyces luridus So3.2 from Antarctic soil as a novel producer of compounds with bioemulsification potential

The present study aimed to identify novel microbial producers of bioemulsificant compounds from Antarctic soils. Fifty-nine microbial strains were isolated from five different locations at South Shetland Islands, Antarctica, and screened for biosurfactant production by β-hemolytic activity. Strain So 3.2 was determined as bioemulsifier-producer and identified by phenotypic and molecular characterization as Streptomyces luridus. Emulsification activity, oil displacement method and drop-collapsing test were performed to evaluate the biosurfactant activity with different oils and hydrocarbons using two different culture media (Luria Bertani and Bushnell Haas in the presence of different carbon sources: glucose, glycerol, olive oil and n-Hexadecane). Cell free supernatant of Bushnell Haas culture supplemented with n-Hexadecane showed the best results for all tests. Emulsification of hydrocarbons exceeded 60%, reaching up to 90% on oil with high API grade, while displacement tests ranged from 8 cm to 4 cm in diameter according the culture media and tested oils. Our results revealed that Streptomyces luridus So3.2 is able to produce bioemulsifiers capable of emulsifying hydrocarbons and oils, which could be used in different biotechnological applications, particularly for bioremediation of environments contaminated by oil leaks.

Aquatic toxicity and biodegradability of a surfactant produced by Bacillus subtilis ICA56

In this work, the environmental compatibility of a biosurfactant produced by a Bacillus subtilis strain isolated from the soil of a Brazilian mangrove was investigated. The biosurfactant, identified as surfactin, is able to reduce surface tension (ST) to 31.5 ± 0.1 mN m^-1 and exhibits a lowcritical micelle concentration (CMC) value (0.015 ± 0.003 g L^-1). The highest crude biosurfactant concentration (224.3 ± 1.9 mg L^-1) was reached at 72 h of fermentation. Acute toxicity tests, carried out with Daphnia magna, Vibrio fischeri and Selenastrum capricornutum indicated that the toxicity of the biosurfactant is lower than that of its chemically derived counterparts. The results of the biodegradability tests demonstrated that the crude surfactin extract was degraded by both Pseudomonas putida and a mixed population from a sewage-treatment plant, in both cases the biodegradation efficiency being dependent on the initial concentration of the biosurfactant. Finally, as the biodegradation percentages obtained fall within the acceptance limits established by the Organization for Economic Co-operation and Development (Guidelines for Testing of Chemicals, OECD 301E), crude surfactin can be classified as a "readily" biodegradable compound.

Lactonic Sophorolipids Increase Tumor Burden in Apcmin+/- Mice

Sophorolipids (SL) are amphiphilic biosurfactant molecules consisting of a disaccharide sophorose with one fatty acid at the C1 position and optional acetylation at the C6’and C6” positions. They exist in a closed ring lactonic (LSL) or open acidic (ASL) structure Sophorolipids are produced in crude mixtures in economically viable amounts by the yeast Starmerella bombicola and used in a variety of consumer products. Varying levels of anti- proliferative and anti-cancer activity of crude sophorolipid mixtures are described in a number of tumor cell lines in vitro. However, significant inter-study variation exists in the composition of sophorolipid species as well as other biologically active compounds in these mixtures, which makes interpretation of in vitro and in vivo studies difficult. We produced a 96% pure C18:1 lactonic sophorolipid that dose-dependently reduces the viability of colorectal cancer, as well as normal human colonic and lung cell lines in vitro. Oral administration of vehicle-only; or lactonic sophorolipids (50 mg/kg for 70 days), to Apc^min+/- mice resulted in an increase in the number (55.5 ± 3.3 vs 70.50 ± 7.8: p < 0.05) and size (modal size 2mm vs 4mm) of intestinal polyps. Lactonic administration resulted in a systematic effect via reduced hematocrit (49.5 ± 1.0 vs 28.2 ± 2.0 vs: p<0.03) and splenomegaly (0.56 ± 0.03g vs 0.71 ± 0.04g; p<0.01) confirming exacerbation of disease progression in this model.

Sugar ester surfactants: enzymatic synthesis and applications in food industry

Sugar esters are non-ionic surfactants that can be synthesized in a single enzymatic reaction step using lipases. The stability and efficiency of lipases under unusual conditions and using non-conventional media can be significantly improved through immobilization and protein engineering. Also, the development of de novo enzymes has seen a significant increase lately under the scope of the new field of synthetic biology. Depending on the esterification degree and the nature of fatty acid and/or sugar, a range of sugar esters can be synthesized. Due to their surface activity and emulsifying capacity, sugar esters are promising for applications in food industry.

Sulfur source-mediated transcriptional regulation of the rhlABC genes involved in biosurfactants production by Pseudomonas sp. strain AK6U

Despite the nutritional significance of sulfur, its influence on biosurfactants production has not been sufficiently studied. We investigated the expression of key biosurfactants production genes, rhlABC, in cultures of Pseudomonas sp. AK6U grown with inorganic or organic sulfur sources. AK6U grew with either inorganic sulfate (MgSO₄), dibenzothiophene (DBT), or DBT-sulfone as a sole sulfur source in the presence of glucose as a carbon source. The AK6U cultures produced variable amounts of biosurfactants depending on the utilized sulfur source. Biosurfactants production profile of the DBT cultures was significantly different from that of the DBT-sulfone and inorganic sulfate cultures. The last two cultures were very similar in terms of biosurfactants productivity. Biosurfactants yield in the DBT cultures (1.3 g/L) was higher than that produced by the DBT-sulfone (0.5 g/L) and the inorganic sulfate (0.44 g/L) cultures. Moreover, the surface tension reduction in the DBT cultures (33 mN/m) was much stronger than that measured in the DBT-sulfone (58 mN/m) or inorganic sulfate (54 mN/m) cultures. RT-qPCR revealed variations in the expression levels of the rhlABC genes depending on the sulfur source. The DBT cultures had higher expression levels for the three genes as compared to the DBT-sulfone and inorganic sulfate cultures. There was no significant difference in the expression profiles between the DBT-sulfone and the MgSO₄ cultures. The increased expression of rhlC in the DBT cultures is indicative for production of higher amounts of dirhamnolipids compared to the DBT-sulfone and inorganic sulfate cultures. The gene expression results were in good agreement with the biosurfactants production yields and surface tension measurements. The sulfur source mediates a fine-tuned mechanism of transcriptional regulation of biosurfactants production genes. Our findings can have an impact on industrial production of biosurfactants and other biotechnological processes like biodesulfurization.

Biosurfactant gene clusters in eukaryotes: regulation and biotechnological potential

Biosurfactants (BSs) are a class of secondary metabolites representing a wide variety of structures that can be produced from renewable feedstock by a wide variety of micro-organisms. They have (potential) applications in the medical world, personal care sector, mining processes, food industry, cosmetics, crop protection, pharmaceuticals, bio-remediation, household detergents, paper and pulp industry, textiles, paint industries, etc. Especially glycolipid BSs like sophorolipids (SLs), rhamnolipids (RLs), mannosylerythritol lipids (MELs) and cellobioselipids (CBLs) have been described to provide significant opportunities to (partially) replace chemical surfactants. The major two factors currently limiting the penetration of BSs into the market are firstly the limited structural variety and secondly the rather high production price linked with the productivity. One of the keys to resolve the above mentioned bottlenecks can be found in the genetic engineering of natural producers. This could not only result in more efficient (economical) recombinant producers, but also in a diversification of the spectrum of available BSs as such resolving both limiting factors at once. Unraveling the genetics behind the biosynthesis of these interesting biological compounds is indispensable for the tinkering, fine tuning and rearrangement of these biological pathways with the aim of obtaining higher yields and a more extensive structural variety. Therefore, this review focuses on recent developments in the investigation of the biosynthesis, genetics and regulation of some important members of the family of the eukaryotic glycolipid BSs (MELs, CBLs and SLs). Moreover, recent biotechnological achievements and the industrial potential of engineered strains are discussed.

Production and characterization of microbial biosurfactants for potential use in oil-spill remediation

Two biosurfactants, surfactin and fatty acyl-glutamate, were produced from genetically-modified strains of Bacillus subtilis on 2% glucose and mineral salts media in shake-flasks and bioreactors. Biosurfactant synthesis ceased when the main carbohydrate source was completely depleted. Surfactin titers were ∼30-fold higher than fatty acyl-glutamate in the same medium. When bacteria were grown in large aerated bioreactors, biosurfactants mostly partitioned to the foam fraction, which was recovered. Dispersion effectiveness of surfactin and fatty acyl-glutamate was evaluated by measuring the critical micelle concentration (CMC) and dispersant-to-oil ratio (DOR). The CMC values for surfactin and fatty acyl-glutamate in double deionized distilled water were 0.015 and 0.10 g/L, respectively. However, CMC values were higher, 0.02 and 0.4 g/L for surfactin and fatty acyl-glutamate, respectively, in 12 parts per thousand Instant Ocean®[corrected].sea salt, which has been partly attributed to saline-induced conformational changes in the solvated ionic species of the biosurfactants. The DORs for surfactin and fatty acyl-glutamate were 1:96 and 1:12, respectively, in water. In Instant Ocean® solutions containing 12 ppt sea salt, these decreased to 1:30 and 1:4, respectively, suggesting reduction in oil dispersing efficiency of both surfactants in saline. Surfactant toxicities were assessed using the Gulf killifish, Fundulus grandis, which is common in estuarine habitats of the Gulf of Mexico. Surfactin was 10-fold more toxic than fatty acyl-glutamate. A commercial surfactant, sodium laurel sulfate, had intermediate toxicity. Raising the salinity from 5 to 25 ppt increased the toxicity of all three surfactants; however, the increase was the lowest for fatty acyl-glutamate.