The antibiotic and membrane-damaging activities of cellobiose lipids and sophorose lipids

Amide Modification of Glycolipid Biosurfactants as Promising Biocompatible Antibacterial Agents

Discovering new antibacterial agents is crucial to addressing the increasing risk of bacterial infections induced by antimicrobial resistance in food and agricultural industries. Here, biocompatible acidic-type sophorolipids (ASLs) and glucolipids (GLs) prepared via chemical modification of natural sophorolipids from fermentation were functionalized via amide modification for use as potential antibacterial agents. It was found that the arginine methyl ester derivative of GLs (GLs-d-Arg-OMe) showed excellent antibacterial activity, killing more than 99.99% of Escherichia coli at 200 mg/L. The sterilization dosage of the GLs against Bacillus subtilis, Bacillus cereus, and Staphylococcus aureus was 16-64 mg/L, in contrast to 32-64 mg/L for the fungus Candida albicans. In particular, GLs-d-Arg-OMe showed the best biocompatibility with a therapeutic index of up to 18. It was shown that amide modification of glycolipids can effectively improve antibacterial activity while maintaining biocompatibility, which can be exploited for the development of novel antibiotics in food and agricultural fields.

Sophorolipids: A comprehensive review on properties and applications

Sophorolipids are surface-active glycolipids produced by several non-pathogenic yeast species and are widely used as biosurfactants in several industrial applications. Sophorolipids provide a plethora of benefits over chemically synthesized surfactants for certain applications like bioremediation, oil recovery, and pharmaceuticals. They are, for instance less toxic, more benign and environment friendly in nature, biodegradable, freely adsorb to different surfaces, self-assembly in hydrated solutions, robustness for industrial applications etc. These miraculous properties result in valuable physicochemical attributes such as low critical micelle concentrations (CMCs), reduced interfacial surface tension, and capacity to dissolve non-polar components. Moreover, they exhibit a diverse range of physicochemical, functional, and biological attributes due to their unique molecular composition and structure. In this article, we highlight the physico-chemical properties of sophorolipids, how these properties are exploited by the human community for extensive benefits and the conditions which lead to their unique tailor-made structures and how they entail their interfacial behavior. Besides, we discuss the advantages and disadvantages associated with the use of these sophorolipids. We also review their physiological and functional attributes, along with their potential commercial applications, in real-world scenario. Biosurfactants are compared to their man-made equivalents to show the variations in structure-property correlations and possible benefits. Those attempting to manufacture purported natural or green surfactant with innovative and valuable qualities can benefit from an understanding of biosurfactant features structured along the same principles. The uniqueness of this review article is the detailed physico-chemical study of the sophorolipid biosurfactant and how these properties helps in their usage and detailed explicit study of their applications in the current scenario and also covering their pros and cons.

Preparing Biosurfactant Glucolipids from Crude Sophorolipids via Chemical Modifications and Their Potential Application in the Food Industry

This investigation developed a novel strategy for efficiently preparing glucolipids (GLs) by chemically modifying crude sophorolipids. Running this strategy, crude sophorolipids were effectively transformed into GLs through deglycosylation and de-esterification, with a yield of 54.1%. The acquired GLs were then purified via stepwise extractions, and 66.2% of GLs with 95% purity was recovered. GLs are more hydrophobic and present a stronger surface activity than acidic sophorolipids (ASLs). More importantly, these GLs displayed a superior antimicrobial activity to that of ASLs against the tested Gram-positive food pathogens, with a minimum inhibitory concentration of 32-64 mg/L, except against E. coli . This activity of GLs is pH-dependent and especially more powerful under acidic conditions. The mechanism involved is possibly associated with the more efficient adsorption of GLs, as demonstrated by the hydrophobicity of the cell membrane. These GLs could be used as antimicrobial agents for food preservation and health in the food industry.

Effect of dietary sophorolipids on growth performance and gastrointestinal functionality of broiler chickens infected with Eimeria maxima

Two experiments were conducted to evaluate the effects of dietary sophorolipids (SLs) supplementation as antibiotic alternatives on growth performance and gut health of chickens infected with Eimeria maxima. In experiment 1, 336 (zero-day-old) male broilers were used. The chickens were weighed and randomly allocated to the following 6 treatments groups with 7 chickens/cage and 8 cages/treatment: control group that received a basal diet (NC), positive control group that received a basal diet and was challenged with E. maxima (PC), PC+C18:1 lactonic diacetyled SL (SL1), PC+C18:1 deacetyled SL (SL2), PC+C18:1 monoacetyled SL (SL3), and PC+C18:1 diacetyled SL (SL4). Each SL (200 mg/kg feed) was added to the corresponding treatment group. In experiment 2, 588 (zero-day-old) male broilers were used. The chickens were randomly allocated to the following experimental groups with 10 or 11 chickens/cage and 8 cages/treatment: NC, PC, PC+ monensin at 90 mg/kg feed (MO), PC+SL1 at 200 mg/kg feed (SL1 200), PC+SL1 at 500 mg/kg feed (SL1 500), PC+SL4 at 200 mg/kg feed (SL4 200), and PC+SL4 at 500 mg/kg of feed (SL4 500). The chickens and feed were weighed at 0, 7, 14, 20, and 22 d to determine growth performance. In both experiments, all chickens except the NC group were orally infected with E. maxima (10,000 oocysts/chicken) at d 14. One chicken per cage was euthanized at d 20 to sample jejunal tissue to measure lesion scores, cytokines, and tight junction (TJ) proteins. Excreta samples were collected daily between d 20 and 22 to measure oocyst numbers. Data were analyzed using Mixed Model (PROC MIXED) in SAS. In experiment 1, SLs did not affect the growth of broiler chickens, but SL4 decreased (P < 0.05) the lesion score and oocyst number compared to PC chickens. In terms of cytokines and TJ protein gene expression, SLs increased (P < 0.05) IL-1β, IL-6, IL-17F, IL-4, IL-13, occludin, and ZO1 levels compared to PC chickens. In experiment 2, monensin increased (P < 0.05) body weight, and decreased (P < 0.05) the lesion score and oocyst number compared to the PC group. SL4 500 increased (P < 0.05) average daily gain and feed conversion ratio but decreased (P < 0.05) lesion score and fecal oocyst number. SL4 decreased (P < 0.05) IL-6, IL-17F, TNFSF-15, IL-2, and IL-10 levels but increased (P < 0.05) occludin and ZO-1 levels. Overall, dietary SL supplementation, especially SL4, improved growth and gastrointestinal functionality of young broiler chickens, demonstrating significant potential as an antibiotic alternative.

Antimicrobial activity of sophorolipids against Eimeria maxima and Clostridium perfringens, and their effect on growth performance and gut health in necrotic enteritis

The in vitro antimicrobial activity of sophorolipids (SLs) against Eimeria maxima and Clostridium perfringens, and the in vivo effects of SLs on growth performance and gut health in necrotic enteritis (NE)-afflicted broiler chickens were studied. To test the direct killing effects of SLs on enteric pathogens, 2.5 × 10⁵ freshly prepared sporozoites of each Eimeria acervulina, E. maxima, and E. tenella were placed in each well of a 96-well plate, and the vegetative stage of Clostridium perfringens was prepared at 1 × 10⁹ cfu/well. Four different SLs (C18:1 lactonic diacetyled SL [SL1], C18:1 deacetyled SL [SL2], C18:1 monoacetyled SL [SL3], and C18:1 diacetyled SL [SL4]), and 2 anticoccidial chemical controls, decoquinate and monensin, were evaluated at 3 dose levels (125 µg/mL, 250 µg/mL, and 500 µg/mL). Samples were incubated at 41°C for 3 h, and microbial survival ratios were measured by using a cell counter to quantify the number of live microbes stained by fluorescent dye. A total of 336 (0-day-old) male commercial broiler chickens were used to assess the effects of SLs in vivo. Chickens were randomly allocated to 6 treatment groups (7 chickens per cage, 8 cages per treatment) as follows: a control group which received a basal diet (CON), a negative control group (NC) which received a basal diet and NE challenge, and 4 SL treatment groups with NE (NC+SL1, NC+SL2, NC+SL3, and NC+SL4). The inclusion rates of SLs in each group were 200 mg/kg of feed. NE-induced chickens were orally infected with E. maxima (10,000 oocysts/chicken) on d 14, followed by C. perfringens (1 × 10⁹ cfu/chicken) on d 19. Disease parameters measured included gut lesion scores, intestinal cytokine production, and level of tight junction protein expression. Data were analyzed using a Mixed Model (PROC MIXED) in SAS. In vitro (Experiment 1), all SLs dose-dependently decreased (P < 0.001) the viability of the three species of Eimeria sporozoites and C. perfringens. In vivo (Experiment 2), dietary SLs increased (P < 0.001) body weight and average daily gain of broiler chickens infected with NE. Dietary SL1 and SL4s increased (P < 0.05) feed conversion ratio compared to NC. Furthermore, SL1 and SL4 decreased (P < 0.05) gut lesion scores in combination with increased expression of IL1β, IL8, TNFSF15, and IL10 genes (P < 0.05) in NE-afflicted chickens. Overall, dietary SLs promoted growth performance, intestinal immune responses, and intestinal barrier integrity of NE-afflicted, young broiler chickens.

Efficient Preparation of Sophorolipids and Functionalization with Amino Acids to Furnish Potent Preservatives

The development of new preservatives is an ongoing investigation in the food industry, especially those which are safe and environmentally friendly. In this study, biosurfactant sophorolipids (SLs) functionalized with amino acids were developed as efficient preservative agents. SLs were first isolated from fermentation broth by Candida bombicola ATCC 22214, hydrolyzed, and purified by extraction. The typical recovery is around 70%, while the extracted material consists of over 90% deacetylated acidic SLs (SL-COOH). Four types of SL derivatives were then synthesized via dicyclohexylcarbodiimide amidation reactions from prepared SL-COOH. Among the derivatives produced, the arginine SL conjugates (SL-d-Arg) displayed the highest activity against Gram-positive bacteria and fungi and even inhibited the cell growth of Gram-negative bacteria and mildew. Furthermore, the arginine conjugates performed the broadest antimicrobial activity among the derivatives evaluated. The sterilization dosage of the arginine conjugates against the food-spoilage pathogen Bacillus spp. was 63-125 mg/L, in contrast to 250 mg/L for the enterotoxin producer Staphylococcus aureus and 500 mg/L for fungi. More importantly, SL-d-Arg displayed excellent biocompatibility, with a therapeutic index of over 7.94. SL-d-Arg has excellent potential as an alternative to traditional chemical preservatives.

Fungal biosurfactants, from nature to biotechnological product: bioprospection, production and potential applications

Biosurfactants are in demand by the global market as natural commodities that can be added to commercial products or use in environmental applications. These biomolecules reduce the surface/interfacial tension between fluid phases and exhibit superior stability to chemical surfactants under different physico-chemical conditions. Biotechnological production of biosurfactants is still emerging. Fungi are promising producers of these molecules with unique chemical structures, such as sophorolipids, mannosylerythritol lipids, cellobiose lipids, xylolipids, polyol lipids and hydrophobins. In this review, we aimed to contextualize concepts related to fungal biosurfactant production and its application in industry and the environment. Concepts related to the thermodynamic and physico-chemical properties of biosurfactants are presented, which allows detailed analysis of their structural and application. Promising niches for isolating biosurfactant-producing fungi are presented, as well as screening methodologies are discussed. Finally, strategies related to process parameters and variables, simultaneous production, process optimization through statistical and genetic tools, downstream processing and some aspects of commercial products formulations are presented.

Phosphate efflux as a test of plasma membrane leakage in Saccharomyces cerevisiae cells

Plasma membrane integrity is a key to cell viability. Currently, the main approach to assessing plasma membrane integrity is the detection of penetration of special dyes, such as trypan blue and propidium iodide, into the cells. However, this method needs expensive equipment: a fluorescent microscope or a flow cytometer. Besides, staining with propidium iodide occasionally gives false-positive results. Here, we suggest the phosphate (Pi) leakage assay as an approach to assess the increase in permeability of the plasma membrane of yeast cells. We studied the dependence of phosphate efflux and uptake into Saccharomyces cerevisiae cells on the composition of the incubation medium, time, and ambient pH. The difference in optimal conditions for these processes suggests that Pi efflux is not conducted by the Pi uptake system. The Pi efflux in water correlated with the proportion of cells stained with propidium iodide. This indicated that Pi efflux is associated with cytoplasmic membrane disruption in a portion of the yeast cell population. The assay of Pi efflux was used to evaluate membrane disruption in S. cerevisiae cells treated with some heavy metal ions and detergents.

Antibacterial properties of sophorolipid-modified gold surfaces against Gram positive and Gram negative pathogens

Sophorolipids are bioderived glycolipids displaying interesting antimicrobial properties. We show that they can be used to develop biocidal monolayers against Listeria ivanovii, a Gram-positive bacterium. The present work points out the dependence between the surface density and the antibacterial activity of grafted sophorolipids. It also emphasizes the broad spectrum of activity of these coatings, demonstrating their potential against both Gram-positive strains (Enteroccocus faecalis, Staphylococcus epidermidis, Streptococcus pyogenes) and Gram-negative strains (Escherichia coli, Pseudomonas aeruginosa and Salmonella typhymurium). After exposure to sophorolipids grafted onto gold, all these bacterial strains show a significant reduction in viability resulting from membrane damage as evidenced by fluorescent labelling and SEM-FEG analysis.