Sophorolipid Mixture Research Articles

Production of new antimicrobial palm oil-derived sophorolipids by the yeast Starmerella riodocensis sp. nov. against Candida albicans hyphal and biofilm formation

BackgroundMicrobial derived-surfactants display low eco-toxicity, diverse functionality, high biodegradability, high specificity, and stability under extreme conditions. Sophorolipids are emerging as key biosurfactants of yeast origins, used in various industrial sectors to lower surface tension. Recently, sophorolipid complexes have been applied in biomedicals and agriculture to eradicate infectious problems related to human and plant fungal pathogens. This study aimed to characterize the functional properties and antifungal activities of sophorolipids produced by a newly characterized Starmerella riodocensis GT-SL1R sp. nov. strain.ResultsStarmerella riodocensis GT-SL1R sp. nov. strain was belonged to Starmerella clade with 93.12% sequence similarity using the ITS technique for strain identification. Sophorolipids production was examined, using co-carbon substrates glucose and palm oil, with a yield on the substrate between 30 and 46%. Using shake-flasks, the S. riodocensis GT-SL1R strain produced biosurfactants with an emulsification activity of 54.59% against kerosene compared to the S. bombicola BCC5426 strain with an activity of 60.22%. Maximum productivities of GT-SL1R and the major sophorolipid-producer S. bombicola were similar at 0.8 gl−1 h−1. S. riodocensis GT-SL1R produced mixed forms of lactonic and acidic sophorolipids, shown by TCL, FTIR, and HPLC. Importantly, the complex sophorolipid mixture displayed antifungal activity against an opportunistic yeast pathogen Candida albicans by effectively reducing hyphal and biofilm formation.ConclusionsSophorolipids derived from S. riodocensis demonstrate potential industrial and biomedical applications as green surfactant and antifungal agent. Since numerous renewable bioresources and industrial wastes could be used by microbial cell factories in the biosynthesis of biosurfactants to reduce the production cost, sophorolipids hold a promising alternative to current antimicrobials in treatments against infectious diseases in humans, animals, and plants.

Rapid Construction of Green Nanopesticide Delivery Systems Using Sophorolipids as Surfactants by Flash Nanoprecipitation.

Green delivery carriers of nanopesticides, like sophorolipid biosurfactants, are of great significance to reduce environmental pollution and promote sustainable agricultural development. However, the molecular diversity of an unisolated sophorolipid mixture with almost unpredictable self-assembly properties has limited the in-depth study of its structure-activity relationship and hindered the development of green pesticide delivery systems. In this work, the acidic and lactonic sophorolipids were successfully separated from the sophorolipid mixture through silica gel column chromatography. A series of cost-effective green nanopesticides loaded with lambda-cyhalothrin (LC) were rapidly fabricated based on a combination of the acidic and lactonic sophorolipids as surfactants by flash nanoprecipitation. The effects of the acidic-to-lactonic ratio on particle size, drug loading capacity, and biological activity against Hyphantria cunea of LC-loaded nanoparticles were systematically investigated. The resultant nanopesticides exhibited a better insecticidal efficacy than a commercial emulsifiable concentrate formulation. This work opens up a novel strategy to construct scalable, cost-effective, and environmentally friendly nanopesticide systems.

Efficient production of acidic sophorolipid from rapeseed oil by Candida bombicola

AbstractOwing to the high surface activity and good biological activity, sophorolipid (SL) has been considered as one of the most promising biosurfactants in recent years. Among all of the structures of SL, acid‐type SL has gained increasing attention and application in the areas of bioremediation and daily chemical industry owing to its excellent foamability and water solubility. However, few studies focused on acid‐type SL biological production have been reported. In this study, acid‐type SL production by the yeast Candida bombicola ATCC 22214 was comprehensively evaluated and optimized. Under the optimal medium composition and fermentation conditions, the yield of SL in the shake flask reached 68.8 g L−1, in which acid‐type SL accounted for 70%. With subsequent scale‐up to a 5 L bioreactor, the yield of SL using fed‐batch fermentation strategy reached 131.2 g L−1, and the acid‐type SL accounted for 84.7%. To the best of our knowledge, the yield of acid‐type SL in this study is the highest reported currently. In addition, the SL mixture (containing 84% acid‐type SL) produced by C. bombicola ATCC 22214 had better surface activity, emulsification properties and environmental stability than current commercial SL products. This study provided a promising microbial chassis and fermentation strategy for commercial production of acid‐type SL. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd

Ultrasound assisted in situ separation of sophorolipids in multi-phase fermentation system to achieve efficient production by Candida bombicola.

Sophorolipids (SLs) are regarded as one of the most promising biosurfactants. However, high production costs are the main obstacle to extended SLs application. Semi-continuous fermentation, which is based on in situ separation, is a promising technology for achieving high SLs productivity. In this study, the sedimentation mechanism of SLs was analyzed. The formation of a hydrophobic mixture of SLs and rapeseed oil was a key factor in sedimentation. And the hydrophobicity and density of the mixture determined SLs sedimentation rate. On this basis, ultrasonic enhanced sedimentation technology (UEST) was introduced, by which the sedimentation rates were increased by 46.9%-485.4% with different ratio of rapeseed oil to SLs. UEST-assisted real-time in situ separation and semi-continuous fermentation were performed. SLs productivity and yield were 2.15gL-1 h-1 and 0.58gg-1 , respectively, simultaneously the loss ratio of cells, glucose, and rapeseed oil were significantly reduced. This study provides a new horizon for optimization of the SLs fermentation process.

Identification of Four Secreted Aspartic Protease-Like Proteins Associated With Sophorolipids Synthesis in Starmerella bombicola CGMCC 1576.

The non-pathogenic yeast Starmerella bombicola CGMCC 1576 is an efficient producer of sophorolipids (SLs). The lactonic SLs are mainly produced with yeast extract, and the acidic SLs are mainly produced with ammonium sulfate. Naturally produced SLs are a mixture of various lactonic and acidic SLs. Usually, the SL mixture is not well separated technically, and the separation cost is relatively high. In order to reduce the cost of separation, four secreted aspartic protease-like proteins were identified through proteomic analysis of fermentation broth of S. bombicola under different nitrogen source conditions. The coding genes of the four proteins, namely, sapl1, sapl2, sapl3, and sapl4, are of high sequence similarity (above 55%) and included in a gene cluster. The expression of the four genes was significantly upregulated on (NH4)2SO4 compared with that on yeast extract. The four genes were deleted together to generate a strain Δsapl. The titer of SLs in Δsapl reached 60.71 g/L after 5 days of fermentation using (NH4)2SO4 as the nitrogen source and increased by 90% compared with the wild-type strain. The concentration of acidic SLs was 55.84 g/L, accounting for 92% of the total SLs. The yield of SLs from glucose (g/g) by Δsapl was 0.78, much higher than that by wild-type strain (0.47). However, no increase of SLs production was observed in Δsapl under yeast extract condition. Compared with that of the wild-type strain, the expression levels of the key genes for SLs synthesis were all upregulated to varying degrees in Δsapl under (NH4)2SO4 conditions, and particularly, the expression level of ugta1 encoding UDP glucosyltransferase was upregulated by 14.3-fold. The results suggest that the sapl gene cluster is negatively involved in the production of SLs in the case of (NH4)2SO4 by restraining the expression of the key genes involved in SLs synthesis. The Δsapl strain is an excellent producer of high-titer and high-yield acidic SLs.

Agro-wastes and Inert Materials as Supports for the Production of Biosurfactants by Solid-state Fermentation

This study explores 9 different biomaterials (agro-wastes) and inert materials, to be used as support in SSF to produce sophorolipids (SLs) with Starmerella bombicola ATCC 22214. Winterization oil filtration cake and sugar beet molasses were the substrates. Biomaterials (lignocellulosic wastes or organic by-products) performed better than inert materials (perlite and polyurethane foams). High yields were obtained for rice husk (0.15 g SLs g−1DM) and wheat straw (0.20 g SLs g−1DM). Lactonic C18:1 predominates over acidic form in the mixture of SLs. The characterization of the process through a time course experiment shows that wheat straw is the best material to produce SLs. A proportional correlation between SLs yield and cumulative oxygen consumption was found, suggesting that cumulative oxygen content (COC) can be used as an indirect measure to monitor the SLs production.

Sophorolipids production from rice straw via SO3 micro-thermal explosion by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576.

A novel lignocellulose material, holocellulose from rice straw via the pretreatment of SO3 micro-thermal explosion, was developed to produce sophorolipids (SLs) with Wickerhamiella domercqiae var. sophorolipid CGMCC 1576. The influence factors of inoculum dose, yeast extract concentration and pH regulators (chemical regents used for adjusting/influencing pH) was investigated and discussed. Results showed that W. domercqiae can grow in the rice straw holocellulose hydrolysate, and acquire relative high SL yield of 53.70 ± 2.61 g/L in shake flask culture. Inoculum dose, yeast extract concentration and pH regulator made obvious influence on fermentation parameters, especially on final broth pH and SLs production. Furthermore, there is a strong negative linear correlation existing between final broth pH and lactonic SL or ratio of lac SL/tot SL. Additionally, comparison between SL production and non-glucose carbon sources, culture methods, microbes in previous reports was carried out. These results will be benefit for acquiring SL mixture with suitable lac SL/tot SL ratio for specific purpose and scope economically.

Molecular editing of sophorolipids by esterification of lipid moieties: Effects on interfacial properties at paraffin and synthetic crude oil-water interfaces

Sophorolipids (SLs) are naturally produced glycolipid biosurfactants that offer safe alternatives to chemical surfactants that have been identified as ecologically-hazardous. Molecular editing of SLs by esterification of the lipid tail was used to prepare a family of SL-esters whose hydrophobic moiety is extended from 18 carbons (17-HOC18:1Δ9) to 20, 24, or 28 carbons, respectively. The interfacial properties of natural and SL-esters were evaluated with paraffin and a synthetic crude oil. SL-esters reduced paraffin oil/water interfacial tension (IFT) by 89–97% and had critical aggregation concentrations (CACs) between 0.02–0.008mg/mL. SL-esters were also found to emulsify paraffin and synthetic crude oil with oil/surfactant ratios up to 200:1wt/wt for 1 week with emulsion droplet sizes below 5μm. SL-hexyl ester had the lowest CAC, 0.008mg/mL, and generally, the lowest droplet sizes, particularly at 10wt% paraffin oil. While, SL-decyl ester had the highest (97.2%) maximum%-IFT reduction and gave paraffin oil emulsions that were most stable over time. SL-ester emulsions of synthetic crude oil resulted in emulsion sizes that are similar to those with paraffin oil. However, the absence of SL-ester precipitation over the range of SL-ester/synthetic crude oil emulsions tested suggest that the affinity of SL-esters to the oil phase is enhanced by the presence of o-xylene and 1,2-dimethylcyclohexane in the crude oil formulation. A natural SL mixture consisting of 1:1 lactonic (LSL) and acidic (ASL) forms has a CAC that is about an order of magnitude larger than SL-esters. Furthermore, the natural SL mixture was unable to emulsify paraffin and synthetic oil when the ratio of oil-to-surfactant is greater than 1:1. The predictive connection between CAC and emulsion sizes is discussed. IFT and emulsion data show that SL-esters are promising surfactants for crude oil related oil compositions.

A versatile family of sophorolipid esters: Engineering surfactant structure for stabilization of lemon oil-water interfaces

Sophorolipids (SLs) are biosurfactants produced by Candida bombicola from renewable feedstocks in yields>400g/L. Molecular editing of natural SLs gave a series of n-alkyl SL-esters that, along with natural SLs, were interrogated to determine how structural changes alter SL interfacial tension (IFT), diffusion, adsorption, and emulsification at the lemon oil/water interface. SL-ethyl ester (SL-EE) reduced the IFT by 95.1% and has a critical aggregation concentration (CAC) of 0.026mg/mL while SL-hexyl ester (SL-HE) had a lower CAC, 0.02mg/mL, but a lower IFT reduction (87.5%). Adsorption behavior further highlighted differences between the SL-esters as SL-decyl ester (SL-DE) had the lowest surface excess concentration while SL-HE had the highest adsorption coefficient. The competing effects of these interfacial parameters were manifested in the relative performance of SL-esters in forming lemon oil-in-water emulsions. SL-EE had the largest average emulsion droplet size but showed no oil separation up to 200:1wt/wt oil/surfactant. Microscopy provided information on macroscopic emulsion morphologies. For example, flocculation was observed for all 1wt% SL 20wt% lemon oil emulsions. These results were corroborated by shear thinning rheological behavior. Studies were conducted with a natural SL mixture consisting of 1:1wt/wt lactonic and acidic SLs (LSL+ASL). LSL+ASL has similar emulsion properties to SL-EE at low SL concentrations while emulsions collapsed at higher SL concentrations.

Sophorolipids Production by Candida bombicola ATCC 22214 and its Potential Application in Microbial Enhanced Oil Recovery.

Biosurfactant production using Candida bombicola ATCC 22214, its characterization and potential applications in enhancing oil recovery were studied at laboratory scale. The seed media and the production media were standardized for optimal growth and biosurfactant production. The production media were tested with different carbon sources: glucose (2%w/v) and corn oil (10%v/v) added separately or concurrently. The samples were collected at 24 h interval up to 120 h and checked for growth (OD660), and biosurfactant production [surface tension (ST) and interfacial tension (IFT)]. The medium with both glucose and corn oil gave better biosurfactant production and reduced both ST and IFT to 28.56 + 0.42mN/m and 2.13 + 0.09mN/m, respectively within 72 h. The produced biosurfactant was quite stable at 13–15% salinity, pH range of 2–12, and at temperature up to 100°C. It also produced stable emulsions (%E24) with different hydrocarbons (pentane, hexane, heptane, tridecane, tetradecane, hexadecane, 1-methylnaphthalene, 2,2,4,4,6,8-heptamethylnonane, light and heavy crude oil). The produced biosurfactant was extracted using ethyl acetate and characterized as a mixture of sophorolipids (SPLs). The potential of SPLs in enhancing oil recovery was tested using core-flooding experiments under reservoir conditions, where additional 27.27% of residual oil (Sor) was recovered. This confirmed the potential of SPLs for applications in microbial enhanced oil recovery.

Gradient elution method in centrifugal partition chromatography for the separation of a complex sophorolipid mixture obtained from Candida bombicola yeasts

Sophorolipids represent an important class of natural surfactants with a variety of environmental, cosmetic, and pharmaceutical applications. Despite their promising physicochemical and biological properties, the use of sophorolipids is hampered by the lack of information regarding their individual structure-activity relationships. The major difficulty in isolating pure sophorolipids arises from the high complexity of crude fermentation media composition and from their strong structural similarities. In this work, a centrifugal partition chromatography method was developed in an original gradient elution mode for the separation of sophorolipids produced by the yeast Candida bombicola. Experiments were realized by using three sets of solvent systems composed of n-heptane, ethyl acetate, n-butanol, methanol, and water in different proportions. The separation was performed at 5 mL/min in the ascending mode by increasing progressively the polarity of the organic mobile phase. In these conditions, more than 80% of the sophorolipids present in the initial crude fermentation extract were eluted successively from the most hydrophobic lactone forms to the most hydrophilic acid forms. The structures of the isolated sophorolipids were further elucidated by HPLC and NMR analyses.

Production of sophorolipids with eicosapentaenoic acid and docosahexaenoic acid from Wickerhamiella domercqiae var. sophorolipid using fish oil as a hydrophobic carbon source

Sophorolipids (SLs) were synthesized by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576 grown on fish oil and glucose. They were purified using preparative HPLC and their structures were identified by MS/MS. The yields of total and lactonic SLs were 47 and 19gl(-1) in shake-flasks when fish oil 4% (v/v) was used with glucose in the medium. The composition of SL mixture contained more than 20 SL molecules. Several unconventional SL molecules with eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) including zero-, mono- and di-acetylated acidic SLs with EPA and a di-acetylated acidic SL with DHA were obtained. Two unconventional lactonic SL molecules, non-acetylated lactonic SL with 22:3 and non-acetylated lactonic SL with 20:0, were also obtained.

Enhancement of Sophorolipid Production of Wickerhamiella domercqiae var. sophorolipid CGMCC 1576 by Low-Energy Ion Beam Implantation

To meet the increasing demands of sophorolipids as biosurfactants and bioactive compounds, it is necessary to obtain higher and more specific sophorolipid-producing strains. One sophorolipid-producing strain, Wickerhamiella domercqiae var. sophorolipid CGMCC 1576 (Y(2A)), was mutated by low-energy nitrogen ion beam implantation. Eighteen mutants produced 20 % more sophorolipids than the wild strain, and one mutant, N3-18, produced the highest yield of sophorolipids, 104 g/l, in a shaking flask, which increased by 84.71 % than the wild strain, and further elevated to 135 g/l in a 5-l bioreactor. High performance liquid chromatography analysis showed that the composition of every sophorolipid mixture from different strains was similar, while the contents of most components from mutants were higher than that from the wild strain. Two mutants, N1-32 and N3-18, produced more acidic sophorolipid components; three lactonic sophorolipid molecules with good anticancer activities were greatly enhanced in several mutants, especially monoacetylated lactonic sophorolipid with a C18 monounsaturated fatty acid, which were enhanced by 153 and 211 % in strains N1-32 and N3-18. Low-energy nitrogen ion beam implantation was efficient for obtaining a variety of high and specific sophorolipid-producing mutants to be applied in food, cosmetic, environmental, and pharmaceutical sectors.

Structural determination and chemical esterification of the sophorolipids produced by Candida bombicola grown on glucose and α-linolenic acid

The extracellular surface-active glycolipids produced by the yeast, Candida bombicola when grown on glucose and α-linolenic acid, were analyzed by HPLC with electro-spray ionization (ESI-MS) and collision-induced dissociation mass spectrometry. The analysis confirmed that the sophorolipid (SL) mixture contained three different forms of C18:3 SL molecules: free acid, lactone and a diacetylated lactone, which has not been reported previously. Also a minor amount of diacetylated lactone form of C18:1 SL was detected. Further, the SL mixture was subjected to chemical esterification reaction with sodium methoxide. The reaction product was analyzed with ESI-MS and confirmed to be the single homogenous esterified product containing C18:3 moieties in its fatty acid chain.

Effects of nitrogen sources on production and composition of sophorolipids by Wickerhamiella domercqiae var. sophorolipid CGMCC 1576

The effects of nitrogen sources on growth of sophorolipid-producing yeast, Wickerhamiella domercqiae var. sophorolipid CGMCC 1576 and on production and composition of sophorolipids were studied. Organic nitrogen sources are more favorable for accumulation of biomass than inorganic ones. Presence of ammonium ion from different inorganic nitrogen sources (except NH(4)HCO(3)) greatly inhibited the production of lactonic sophorolipids. However, when organic nitrogen sources were used, lactonic sophorolipid production was strongly increased. Production of crystalline lactonic sophorolipids from organic/inorganic nitrogen sources was enhanced with the increase of pH value adjusted by sodium hydroxide or sodium citrate solution. Fourier-transform infrared (FT-IR), gas chromatography mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC), and mass spectra (MS) were employed to compare the composition of sophorolipid mixture obtained from different nitrogen sources. More than 15 acidic sophorolipid molecules and only 4 lactonic sophorolipid molecules were produced by using 1.27 g/l ammonium sulfate as nitrogen source; they were separated by preparative HPLC and their structures were elucidated by MS. These results suggest extraordinary regulatory effects of nitrogen source on growth and sophorolipid synthesis of W. domercqiae var. sophorolipid.

Bioactivities of Sophorolipid with Different Structures Against Human Esophageal Cancer Cells

Sophorolipids (SLs) obtained from yeast broth are mixtures of many sophorolipid molecules with different structures, and have attracted more attention since they were found to have good antimicrobial, anticancer, anti-inflammatory, and anti-HIV activities. We investigated the effects of sophorolipid molecules with different structures on human esophageal cancer cells in the present work. Ten sophorolipid (SL) molecules were separated and purified from the sophorolipids mixture using preparative HPLC, and their structures were identified by MS analyses. The effects of sophorolipid molecules with different structures on two human esophageal cancer cell lines, KYSE 109 and KYSE 450, were investigated by MTT assay. The structures of the 10 sophorolipid molecules differ in acetylation degree of sophorose, unsaturation degree of hydroxyl fatty acid, and lactonization or ring opening. The results demonstrated that the inhibition of diacetylated lactonic sophorolipid on two esophageal cancer cells (total inhibition at 30 μg/mL concentration) was stronger than that of monoacetylated lactonic sophorolipid (totally inhibition at 60 μg/mL concentration). Difference of unsaturation degree of hydroxyl fatty acid in SL molecules also had obvious influence on their cytotoxicity to esophageal cancer cells. The sophorolipid with one double bond in fatty acid part had the strongest cytotoxic effect on two esophageal cancer cells (total inhibition at 30 μg/mL concentration). Acidic sophorolipid showed hardly any anticancer activity against esophageal cancer cells. In this study, the relationship of anticancer activities of natural sophorolipid molecules and the differences in their structures was revealed, which probably further reveals the mechanism of SL bioactivities and will be helpful in the modification of SL structures to obtain more novel SLs with excellent bioactivities.

Identification and quantification of sophorolipid analogs using ultra-fast liquid chromatography–mass spectrometry

An ultra-fast liquid chromatographic method combined with atmospheric pressure chemical ionization mass detection (UHPLC/APCI-MS) has been developed for the separation and quantification of sophorolipid analogs produced by the yeast Candida bombicola. The sophorolipid mixture was produced by growing the yeast in the presence of glucose and oleic acid under higher aeration. It was found that more than 95% of the analogs are lactonic sophorolipids and all the produced sophorolipids produced were either mono- or di-acetylated. Also observed was a sophorolipid analog with a tri-unsaturated fatty acid, which has not been reported previously.

Cerulenin inhibits de novo sophorolipid synthesis of Candida bombicola

Synthesis of medium-chain sophorolipids by Candida bombicola is a challenging objective. One of the difficulties is that the obtained sophorolipids always represent a mixture of medium-chain and native de novo formed or long-chain sophorolipids. The fatty acid moiety of de novo sophorolipids is derived from the de novo synthesis of fatty acids. Fatty acid synthesis can be blocked by the antifungal agent cerulenin, an inhibitor if the fatty acid synthase (FAS) complex acting on the beta-ketoacyl thioester synthetase reaction. The toxic effect of cerulenin on C. bombicola was evaluated and 20 mg/ml was added in the stationary growth phase. No de novo formed sophorolipids were observed when the cells were cultured on merely glucose. Also when the hydrophilic substrate, 1,12-dodedanediol, was added, no de novo formed sophorolipids were detected, leading to a reduced complexity of the sophorolipid mixture.

Purification by silica gel chromatography using dialysis tubing and characterization of sophorolipids produced from Candida bombicola grown on glucose and arachidonic acid

The yeast Candida bombicola (ATCC 22214) grown on primary carbon source glucose (100 g l(-1)) and secondary carbon, arachidonic acid (2 g l(-1)) produced mixture of sophorolipids up to 1.44 g l(-1). The crude product was a heterogeneous mixture of sophorolipids, which are glycolipids of sophorose linked to the fatty acid through glycosidic bond between omega and omega-1 carbon of arachidonic acid. The derived sophorolipids were isolated by silica gel chromatography using dialysis tubing. The purified sophorolipids were characterized by ESI-MS and FT-IR. Acid hydrolysis of the resolved sophorolipids were characterized by ESI-MS for the presence of 20-hydroxy-5Z,8Z,11Z,14Z-eicosatetraenoic acid (20-HETE) and 19-hydroxy-5Z,8Z,11Z,14Z-eicosatetraenoic acid (19-HETE), compounds of pronounced pharmaceutical importance.

Amino Acid Conjugated Sophorolipids: A New Family of Biologically Active Functionalized Glycolipids

Sophorolipids (SLs) are extra cellular glycolipids produced by Candida bombicola ATCC 22214 when grown in the presence of glucose and fatty acids. These compounds have a disaccharide head group connected to a long-chain hydroxyl-fatty acid by a glycosidic bond. To explore structure-activity of modified SLs, a new family of amino acid-SL derivatives was prepared. Synthesized analogs consist of amino acids linked by amide bonds formed between their alpha-amino moiety and the carboxyl group of ring-opened SL fatty acids. Their preparation involved the following: (i) hydrolysis of a natural SL mixture with aqueous alkali to give SL free acids, (ii) coupling of free acids to protected amino acids using dicarbodiimide, and (iii) removing amino acid carboxyl protecting groups. These conjugates were evaluated for their antibacterial, anti-HIV, and spermicidal activity. All tested analogs showed antibacterial activity against both gram +ve and gram -ve organisms. Leucine-conjugated SL was most efficient. For example, the minimum inhibitory concentrations (MIC) for Moraxella sp. and E. coli were 0.83 and 1.67 mg/mL, respectively. Among the alkyl esters of amino acid conjugated SLs, the ethyl ester of leucine-SLs was most active. Against Moraxella sp., S. sanguinis, and M. imperiale, MIC values are 7.62 x 10(-4), 2.28 x 10-(3) and 1.67 mg/mL, respectively. All compounds displayed virus-inactivating activity with 50% effective concentrations (EC50) below 200 microg/mL. The EC50 of leucine-SL ethyl ester was 24.1 microg/mL, showing that it is more potent than commercial spermicide nonoxynol-9 (EC50 approximately 65 microg/mL).