Microbial biosurfactant research: time to improve the rigour in the reporting of synthesis, functional characterization and process development

Bioemulsifier from sponge-associated bacteria reduces staphylococcal biofilm

Biofilm formation is a major health concern and studies have been pursued to find compounds able to prevent biofilm establishment and remove pre-existing biofilms. While biosurfactants (BS) have been well-known for possessing antibiofilm activities, bioemulsifiers (BE) are still scarcely explored for this purpose. The present study aimed to evaluate the bioemulsifying properties of cell-free supernatants produced by Bacillaceae and Vibrio strains isolated from marine sponges and investigate their antiadhesive and antibiofilm activities against different pathogenic Gram-positive and Gram-negative bacteria. The BE production by the marine strains was confirmed by the emulsion test, drop-collapsing, oil-displacement, cell hydrophobicity and hemolysis assays. Notably, Bacillus cereus 64BHI1101 displayed remarkable emulsifying activity and the ultrastructure analysis of its BE extract (BE64-1) revealed the presence of structures typically observed in macromolecules composed of polysaccharides and proteins. BE64-1 showed notable antiadhesive and antibiofilm activities against Staphylococcus aureus, with a reduction of adherence of up to 100 % and a dispersion of biofilm of 80 %, without affecting its growth. BE64-1 also showed inhibition of Staphylococcus epidermidis and Escherichia coli biofilm formation and adhesion. Thus, this study provides a starting point for exploring the antiadhesive and antibiofilm activities of BE from sponge-associated bacteria, which could serve as a valuable tool for future research to combat S. aureus biofilms.

A new biosurfactant-producing strain, Fictibacillus nanhaiensis ME46, isolated from an oil field in China

The genus Fictibacillus contains twelve species significant in the synthesis of cellulose-degrading enzymes and phenylalanine dehydrogenase, isolated mainly from marine sedimentary environments. Here, we report a new biosurfactant-producing strain, Fictibacillus nanhaiensis ME46, isolated from Daqing oil field in China. The biosurfactant extracted from Strain ME46 was determined as surfactin, one of the representative families of lipopeptide biosurfactants. The yield of the surfactin produced by strain ME46 was 0.62 g·L-1 as determined by high-performance liquid chromatography, and the critical micelle concentration (CMC) of the surfactin was estimated to be about 68 mg·L-1 and the surface tension at CMC was 35.1 mN·m-1. This study extended our knowledge about the role of the species Fictibacillus nanhaiensis in the ecosystem of natural environments such as the oil field.

Common operational issues and possible solutions for sustainable biosurfactant production from lignocellulosic feedstock

Surfactants are compounds with high surface activity and emulsifying property. These compounds find application in food, medical, pharmaceutical, and petroleum industries, as well as in agriculture, bioremediation, cleaning, cosmetics, and personal care product formulations. Due to their widespread use and environmental persistence, ensuring biodegradability and sustainability is necessary so as not to harm the environment. Biosurfactants, i.e., surfactants of plant or microbial origin produced from lignocellulosic feedstock, perform better than their petrochemically derived counterparts on the scale of net-carbon-negativity. Although many biosurfactants are commercially available, their high cost of production justifies their application only in expensive pharmaceuticals and cosmetics. Besides, the annual number of new biosurfactant compounds reported is less, compared to that of chemical surfactants. Multiple operational issues persist in the biosurfactant value chain. In this review, we have categorized some of these issues based on their relative position in the value chain - hurdles occurring during planning, upstream processes, production stage, and downstream processes - alongside plausible solutions. Moreover, we have presented the available paths forward for this industry in terms of process development and integrated pretreatment, combining conventional tried-and-tested strategies, such as reactor designing and statistical optimization with cutting-edge technologies including metabolic modeling and artificial intelligence. The development of techno-economically feasible biosurfactant production processes would be instrumental in the complete substitution of petrochemical surfactants, rather than mere supplementation.

Three strategy rules of filamentous fungi in hydrocarbon remediation: an overview

Remediation of hydrocarbon contaminations requires much attention nowadays since it causes detrimental effects on land and even worse impacts on aquatic environments. Tools of bioremediation especially filamentous fungi permissible for cleaning up as much as conceivable, at least they turn into non-toxic residues with less consumed periods. Inorganic chemicals, CO2, H2O, and cell biomass are produced as a result of the breakdown and mineralization of petroleum hydrocarbon pollutants. This paper presents a detailed overview of three strategic rules of filamentous fungi in remediating the various aliphatic, and aromatic hydrocarbon compounds: utilizing carbons from hydrocarbons as sole energy, Co-metabolism manners (Enzymatic and Non-enzymatic theories), and Biosorption approaches. Upliftment in the degradation rate of complex hydrocarbon by the Filamentous Fungi in consortia scenario we can say, "Fungal Talk", which includes a variety of cellular mechanisms, including biosurfactant production, biomineralization, and precipitation, etc., This review not only displays its efficiency but showcases the field applications - cost-effective, reliable, eco-friendly, easy to culture as biomass, applicable in both land and any water bodies in operational environment cleanups. Nevertheless, the potentiality of fungi-human interaction has not been fully understood, henceforth further studies are highly endorsed with spore pathogenicity of the fungal species capable of high remediation rate, and the gene knockout study, if the specific peptides cause toxicity to any living matters via Genomics and Proteomics approaches, before application of any in situ or ex situ environments.

Sustainable biorefinery approach by utilizing xylose fraction of lignocellulosic biomass

Lignocellulosic biomass (LCB) has been a lucrative feedstock for developing biochemical products due to its rich organic content, low carbon footprint and abundant accessibility. The recalcitrant nature of this feedstock is a foremost bottleneck. It needs suitable pretreatment techniques to achieve a high yield of sugar fractions such as glucose and xylose with low inhibitory components. Cellulosic sugars are commonly used for the bio-manufacturing process, and the xylose sugar, which is predominant in the hemicellulosic fraction, is rejected as most cell factories lack the five‑carbon metabolic pathways. In the present review, more emphasis was placed on the efficient pretreatment techniques developed for disintegrating LCB and enhancing xylose sugars. Further, the transformation of the xylose to value-added products through chemo-catalytic routes was highlighted. In addition, the review also recapitulates the sustainable production of biochemicals by native xylose assimilating microbes and engineering the metabolic pathway to ameliorate biomanufacturing using xylose as the sole carbon source. Overall, this review will give an edge on the bioprocessing of microbial metabolism for the efficient utilization of xylose in the LCB.

Unlocking the potential of biosurfactants: Production, applications, market challenges, and opportunities for agro-industrial waste valorization

Biosurfactants are eco-friendly compounds with unique properties and promising potential as sustainable alternatives to chemical surfactants. The current review explores the multifaceted nature of biosurfactant production and applications, highlighting key fermentative parameters and microorganisms able to convert carbon-containing sources into biosurfactants. A spotlight is given on biosurfactants' obstacles in the global market, focusing on production costs and the challenges of large-scale synthesis. Innovative approaches to valorizing agro-industrial waste were discussed, documenting the utilization of lignocellulosic waste, food waste, oily waste, and agro-industrial wastewater in the segment. This strategy strongly contributes to large-scale, cost-effective, and environmentally friendly biosurfactant production, while the recent advances in waste valorization pave the way for a sustainable society.

Structural characterization of a nonionic rhamnolipid from Burkholderia lata

We present the isolation and structural characterization of a novel nonionic dirhamnolipid methyl ester produced by the bacterium Burkholderia lata. The structure and the absolute configuration of the isolated dirhamnolipid bearing a symmetrical C14-C14 methyl ester chain were thoroughly investigated through chemical degradation and spectroscopic methods including 1D and 2D NMR analysis, HR-ESI-TOF-MS, chiral GC-MS, and polarimetry. Our work represents the first mention in the literature of a rhamnolipid methyl ester from Burkholderia species.

Microbial Biosurfactant: Candida bombicola as a Potential Remediator of Environments Contaminated by Heavy Metals

Industrial interest in surfactants of microbial origin has intensified recently due to the characteristics of these compounds, such as biodegradability and reduced toxicity, and their efficiency in removing heavy metals and hydrophobic organic compounds from soils and waters. The aim of this study was to produce a biosurfactant using Candida bombicola URM 3712 in a low-cost medium containing 5.0% molasses, 3.0% corn steep liquor and 2.5% residual frying oil for 144 h at 200 rmp. Measurements of engine oil tension and emulsification were made under extreme conditions of temperature (0 °C, 5 °C, 70 °C, 100 °C and 120 °C), pH (2-12) and NaCl concentrations (2-12), demonstrating the stability of the biosurfactant. The isolated biosurfactant was characterized as an anionic molecule with the ability to reduce the surface tension of water from 72 to 29 mN/m, with a critical micellar concentration of 0.5%. The biosurfactant had no toxic effect on vegetable seeds or on Eisenia fetida as a bioindicator. Applications in the removal of heavy metals from contaminated soils under dynamic conditions demonstrated the potential of the crude and isolated biosurfactant in the removal of Fe, Zn and Pb with percentages between 70 and 88%, with the highest removal of Pb being 48%. The highest percentage of removal was obtained using the cell-free metabolic liquid, which was able to remove 48, 71 and 88% of lead, zinc and iron from the soil, respectively. Tests in packed columns also confirmed the biosurfactant's ability to remove Fe, Zn and Pb between 40 and 65%. The removal kinetics demonstrated an increasing percentage, reaching removal of 50, 70 and 85% for Pb, Zn and Fe, respectively, reaching a greater removal efficiency at the end of 24 h. The biosurfactant was also able to significantly reduce the electrical conductivity of solutions containing heavy metals. The biosurfactant produced by Candida bombicola has potential as an adjuvant in industrial processes for remediating soils and effluents polluted by inorganic contaminants.

The potential of Burkholderia thailandensis E264 for co-valorization of C5 and C6 sugars into multiple value-added bio-products

Despite known metabolic versatility of Burkholderia spp., sugar metabolism and end-product synthesis patterns in Burkholderia thailandensis have been poorly characterized. This work has demonstrated that B. thailandensis is capable of simultaneously uptaking glucose and xylose and accumulating up to 64% of its dry mass as poly(3-hydroxyalkanoate) (PHA) biopolymers, resulting in a PHA titer of up to 3.8 g L-1 in shake flasks. Rhamnolipids - mainly (68-75%) in the form of Rha-Rha-C14-C14 - were produced concomitantly with a titer typically in the range of 0.2-0.4 g L-1. Gluconic and xylonic acids were also detected in titers of up to 5.3 g L-1, and while gluconic acid appeared to be back consumed, xylonic acid formed as a major end product. This first example of co-production of three products from mixed sugars using B. thailandensis paves the way for improving biorefinery economics.

Simple method for quantification of anionic biosurfactants in aqueous solutions

Biosurfactants are microbial products that have applications as cleaning agents, emulsifiers, and dispersants. Detection and quantification of biosurfactants can be done by various methods, including colorimetric tests, high performance liquid chromatography (HPLC) coupled to several types of detectors, and tests that take advantage of biosurfactants reducing surface tension of aqueous liquids, allowing for spreading and droplet formation of oils. We present a new and simple method for quantifying biosurfactants by their ability, on paper, to reduce surface tension of aqueous solutions, causing droplet dispersion on an oiled surface in correlation with biosurfactant content. We validated this method with rhamnolipids, surfactin, sophorolipids, and ananatoside B; all are anionic microbial surfactants. Linear ranges for quantification in aqueous solutions for all tested biosurfactants were between 10 and 500 µM. Our method showed time-dependent biosurfactant accumulation in cultures of Pseudomonas aeruginosa strains PA14 and PAO1, and Burkholderia thailandensis E264. Mutants in genes responsible for surfactant production showed negligible activity on oiled paper. In summary, our simple assay provides the opportunity to quantify biosurfactant contents of aqueous solutions, for a diversity of surfactants, by means readily available in any laboratory.

Biosurfactant from Pseudomonas fragi enhances the competitive advantage of Pseudomonas but reduces the overall spoilage ability of the microbial community in chilled meat

Biosurfactants from Pseudomonas spp. have been reported to exhibit antibacterial and anti-adhesive properties, but their role during meat spoilage remains unclear. In this study, the biosurfactant was isolated from an isolate of Pseudomonas fragi with strong spoilage potential, and its surface tension and emulsification ability were determined. The chemical and microbial characteristics of the biosurfactant-treated meat samples were periodically analyzed. The results demonstrated that the biosurfactant produced by P. fragi could reduce surface tension and showed good emulsification properties. For the in situ spoilage trials, biosurfactant from P. fragi changed the microbial diversity on meat, helping Pseudomonas establish a dominant position in the population. However, biosurfactant treatment caused chicken meat to exhibit a weaker spoilage state, as indicated by the growth of psychrophilic microorganisms, total volatile basic nitrogen (TVBN) and meat color. These results provide practical information for understanding the role of P. fragi biosurfactant during chilled meat storage.

A comprehensive review on production of bio-surfactants by bio-degradation of waste carbohydrate feedstocks: an approach towards sustainable development

The advancement of science and technology demands chemistry which is safer, smarter and green by nature. The sustainability of science thus requires well-behaved alternates that best suit the demand. Bio-surfactants are surface active compounds, established to affect surface chemistry. In general, microbial bio-surfactants are a group of structurally diverse molecules produced by different microbes. A large number of bio-surfactants are produced during hydrocarbon degradation by hydrocarbonoclistic microorganisms during their own growth on carbohydrates and the production rate is influenced by the rate of degradation of carbohydrates. The production of such biological surfactants is thus of greater importance. This write up is a dedicated review to update the existing knowledge of inexpensive carbohydrate sources as substrates, microorganisms and technologies of biosurfactant production. This is an economy friendly as well as sustainable approach which will facilitate achieving some sustainable development goals. The production is dependent on the fermentation strategies, different factors of the microbial culture broth and downstream processing; these all have been elaborately presented in this article.

Metagenomic insight on consortium degradation of soil weathered petroleum and its supplement based on gene abundance change

Petroleum biodegradation is of importance for the mitigation of secondary pollutants from soil chemical remediation. Describing the gene abundance change of the petroleum degradation emerged as an important practice for success. In this study, an indigenous consortium with targeting-enzyme was utilized to develop a degradative system that was later subjected to metagenomic analysis on the soil microbial community. Centering on ko00625 pathway, abundance change of dehydrogenase gene was firstly found increasing from groups D, DS to DC in turn, just in an opposite direction with that of oxygenase. In addition, gene abundance of responsive mechanism went rising with degradative process as well. This finding sufficiently promoted that equal attention should be paid to both degradative and responsive processes. Hydrogen donor system was innovatively built on the consortium-used soil to satisfy the demand of dehydrogenase gene tendency and to sustain further petroleum degradation. Anaerobic pine-needle soil was supplemented to this system, bi-functionally serving as dehydrogenase substrate with nutrients and hydrogen donor. In doing so, two successive degradations optimally achieved the total removal rate 75.6-78.7% for petroleum hydrocarbon. The conception on the gene abundance changes and its corresponding supplement helps industries of concern to develop geno-tag guided framework.

Glycolipid Biosurfactants in Skincare Applications: Challenges and Recommendations for Future Exploitation

The 21st century has seen a substantial increase in the industrial applications of glycolipid biosurfactant technology. The market value of the glycolipid class of molecules, sophorolipids, was estimated to be USD 409.84 million in 2021, with that of rhamnolipid molecules projected to reach USD 2.7 billion by 2026. In the skincare industry, sophorolipid and rhamnolipid biosurfactants have demonstrated the potential to offer a natural, sustainable, and skin-compatible alternative to synthetically derived surfactant compounds. However, there are still many barriers to the wide-scale market adoption of glycolipid technology. These barriers include low product yield (particularly for rhamnolipids) and potential pathogenicity of some native glycolipid-producing microorganisms. Additionally, the use of impure preparations and/or poorly characterised congeners as well as low-throughput methodologies in the safety and bioactivity assessment of sophorolipids and rhamnolipids challenges their increased utilisation in both academic research and skincare applications. This review considers the current trend towards the utilisation of sophorolipid and rhamnolipid biosurfactants as substitutes to synthetically derived surfactant molecules in skincare applications, the challenges associated with their application, and relevant solutions proposed by the biotechnology industry. In addition, we recommend experimental techniques/methodologies, which, if employed, could contribute significantly to increasing the acceptance of glycolipid biosurfactants for use in skincare applications while maintaining consistency in biosurfactant research outputs.

Production, characterization, and kinetic modeling of biosurfactant synthesis by Pseudomonas aeruginosa gi |KP 163922|: a mechanism perspective

Kinetic studies and modeling of production parameters are essential for developing economical biosurfactant production processes. This study will provide a perspective on mechanistic reaction pathways to metabolize Waste Engine Oil (WEO). The results will provide relevant information on (i) WEO concentration above which growth inhibition occurs, (ii) chemical changes in WEO during biodegradation, and (iii) understanding of growth kinetics for the strain utilizing complex substrates. Laboratory scale experiments were conducted to study the kinetics and biodegradation potential of the strain Pseudomonas aeruginosa gi |KP 163922| over a range (0.5-8% (v/v)) of initial WEO concentration for 168 h. The kinetic models, such as Monod, Powell, Edward, Luong, and Haldane, were evaluated by fitting the experimental results in respective model equations. An unprecedented characterization of the substrate before and after degradation is presented, along with biosurfactant characterization. The secretion of biosurfactant during the growth, validated by surface tension reduction (72.07 ± 1.14 to 29.32 ± 1.08 mN/m), facilitated the biodegradation of WEO to less harmful components. The strain showed an increase in maximum specific growth rate (µ_max) from 0.0185 to 0.1415 h^-1 upto 49.92 mg/L WEO concentration. Maximum WEO degradation was found to be ~ 94% gravimetrically. The Luong model (adj. R² = 0.97) adapted the experimental data using a non-linear regression method. Biochemical, ¹H NMR, and FTIR analysis of the produced biosurfactant revealed a mixture of mono- and di- rhamnolipid. The degradation compounds in WEO were identified using FTIR, ¹H NMR, and GC-MS analysis to deduce the mechanism.

Sustainable rhamnolipids production in the next decade - Advancing with Burkholderia thailandensis as a potent biocatalytic strain

Rhamnolipids are one of the most promising eco-friendly green glycolipids for bio-replacements of commercially available fossil fuel-based surfactants. However, the current industrial biotechnology practices cannot meet the required standards due to the low production yields, expensive biomass feedstocks, complicated processing, and opportunistic pathogenic nature of the conventional rhamnolipid producer strains. To overcome these problems, it has become important to realize non-pathogenic producer substitutes and high-yielding strategies supporting biomass-based production. We hereby review the inherent characteristics of Burkholderia thailandensis E264 which favor its competence towards such sustainable rhamnolipid biosynthesis. The underlying biosynthetic networks of this species have unveiled unique substrate specificity, carbon flux control and rhamnolipid congener profile. Acknowledging such desirable traits, the present review provides critical insights towards metabolism, regulation, upscaling, and applications of B. thailandensis rhamnolipids. Identification of their unique and naturally inducible physiology has proved to be beneficial for achieving previously unmet redox balance and metabolic flux requirements in rhamnolipids production. These developments in part are targeted by the strategic optimization of B. thailandensis valorizing low-cost substrates ranging from agro-industrial byproducts to next generation (waste) fractions. Accordingly, safer bioconversions can propel the industrial rhamnolipids in advanced biorefinery domains to promote circular economy, reduce carbon footprint and increased applicability as both social and environment friendly bioproducts.

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.

Production and characterization of bioemulsifier by Parapedobacter indicus

The current study evaluated Parapedobacter indicus MCC 2546 for its potential to produce a bioemulsifier (BE). Screening methods performed for BE production by P. indicus MCC 2546 showed good lipase activity, positive drop collapse test, and oil-spreading activity. Furthermore, it showed maximum emulsification activity (225 EU/ml) and emulsification index (E24 50%) at 37°C in Luria Bertani broth at 72 h with olive oil as a substrate. The optimal pH and NaCl concentration for maximum emulsification activity were 7 and 1%, respectively. P. indicus MCC 2546 lowered the surface tension of the culture medium from 59.65 to 50.42 ± 0.78 mN/m. BE produced was composed of 70% protein and 30% carbohydrate, which showed the protein-polysaccharide nature of the BE. Furthermore, Fourier transform infrared spectroscopy analysis confirmed the same. P. indicus MCC 2546 showed a catecholate type of siderophore production. This is the first report on BE and siderophore production by the genus Parapedobacter.

Mono-Rhamnolipid Biosurfactants Synthesized by Pseudomonas aeruginosa Detrimentally Affect Colorectal Cancer Cells

Over the past 15 years, glycolipid-type biosurfactant compounds have been postulated as novel, naturally synthesized anticancer agents. This study utilized a recombinant strain of Pseudomonas aeruginosa to biosynthesize a preparation of mono-rhamnolipids that were purified via both liquid and solid-phase extraction, characterized by HPLC-MS, and utilized to treat two colorectal cancer cell lines (HCT-116 and Caco2) and a healthy colonic epithelial cell line CCD-841-CoN. Additionally, the anticancer activity of these mono-rhamnolipids was compared to an alternative naturally derived anticancer agent, Piceatannol. XTT cell viability assays showed that treatment with mono-rhamnolipid significantly reduced the viability of both colorectal cancer cell lines whilst having little effect on the healthy colonic epithelial cell line. At the concentrations tested mono-rhamnolipids were also shown to be more cytotoxic to the colorectal cancer cells than Piceatannol. Staining of mono-rhamnolipid-treated cells with propidium iodine and acridine orange appeared to show that these compounds induced necrosis in both colorectal cancer cell lines. These data provide an early in vitro proof-of-principle for utilizing these compounds either as active pharmaceutical ingredient for the treatment of colorectal cancer or incorporations into nutraceutical formulations to potentially prevent gastrointestinal tract cancer.

Integrated biorefineries for repurposing of food wastes into value-added products

Food waste (FW) generated through various scenarios from farm to fork causes serious environmental problems when either incinerated or disposed inappropriately. The presence of significant amounts of carbohydrates, proteins, and lipids enable FW to serve as sustainable and renewable feedstock for the biorefineries. Implementation of multiple substrates and product biorefinery as a platform could pursue an immense potential of reducing costs for bio-based process and improving its commercial viability. The review focuses on conversion of surplus FW into range of value-added products including biosurfactants, biopolymers, diols, and bioenergy. The review includes in-depth description of various types of FW, their chemical and nutrient compositions, current valorization techniques and regulations. Further, it describes limitations of FW as feedstock for biorefineries. In the end, review discuss future scope to provide a clear path for sustainable and net-zero carbon biorefineries.

An Nuclear Magnetic Resonance Fingerprint Matching Approach for the Identification and Structural Re-Evaluation of Pseudomonas Lipopeptides

Cyclic lipopeptides (CLiPs) are secondary metabolites secreted by a range of bacterial phyla. CLiPs from Pseudomonas in particular, display diverse structural variations in terms of the number of amino acid residues, macrocycle size, amino acid identity, and stereochemistry (e.g., d- versus l-amino acids). Reports detailing the discovery of novel or already characterized CLiPs from new sources appear regularly in literature. Increasingly, however, the lack of detailed characterization threatens to cause considerable confusion, especially if configurational heterogeneity is present for one or more amino acids. Using Pseudomonas CLiPs from the Bananamide, Orfamide, and Xantholysin groups as test cases, we demonstrate and validate that the combined 1H and 13C Nuclear Magnetic Resonance (NMR) chemical shifts of CLiPs constitute a spectral fingerprint that is sufficiently sensitive to differentiate between possible diastereomers of a particular sequence even when they only differ in a single d/l configuration. Rapid screening, involving simple matching of the NMR fingerprint of a newly isolated CLiP with that of a reference CLiP of known stereochemistry, can then be applied to resolve dead-ends in configurational characterization and avoid the much more cumbersome chemical characterization protocols. Even when the stereochemistry of a particular reference CLiP remains to be established, its spectral fingerprint allows to quickly verify whether a newly isolated CLiP is novel or already present in the reference collection. We show NMR fingerprinting leads to a simple approach for early on dereplication which should become more effective as more fingerprints are collected. To benefit research involving CLiPs, we have made a publicly available data repository accompanied by a 'knowledge base' at https://www.rhizoclip.be, where we present an overview of published NMR fingerprint data of characterized CLiPs, together with literature data on the originally determined structures. IMPORTANCE Pseudomonas CLiPs are ubiquitous specialized metabolites, impacting the producer's lifestyle and interactions with the (a)biotic environment. Consequently, they generate interest for agricultural and clinical applications. Establishing structure-activity relationships as a premise to their development is hindered because full structural characterization including stereochemical information requires labor-intensive analyses, without guarantee for success. Moreover, increasing use of superficial comparison with previously characterized CLiPs introduces or propagates erroneous attributions, clouding further scientific progress. We provide a generally applicable characterization methodology based on matching NMR spectral fingerprints of newly isolated CLiPs to natural and synthetic reference compounds with (un)known stereochemistry. In addition, NMR fingerprinting is shown to provide a suitable basis for structural dereplication. A publicly available reference compound repository promises to facilitate participation of the lipopeptide research community in structural assessment and dereplication of newly isolated CLiPs, which should also support further developments in genome mining for novel CLiPs.

Microbial sophorolipids inhibit colorectal tumour cell growth in vitro and restore haematocrit in Apcmin+/- mice

Abstract

Sophorolipids are glycolipid biosurfactants consisting of a carbohydrate sophorose head with a fatty acid tail and exist in either an acidic or lactonic form. Sophorolipids are gaining interest as potential cancer chemotherapeutics due to their inhibitory effects on a range of tumour cell lines. Currently, most anti-cancer studies reporting the effects of sophorolipids have focused on lactonic preparations with the effects of acidic sophorolipids yet to be elucidated. We produced a 94% pure acidic sophorolipid preparation which proved to be non-toxic to normal human colonic and lung cells. In contrast, we observed a dose-dependent reduction in viability of colorectal cancer lines treated with the same preparation. Acidic sophorolipids induced apoptosis and necrosis, reduced migration, and inhibited colony formation in all cancer cell lines tested. Furthermore, oral administration of 50 mg kg⁻¹ acidic sophorolipids over 70 days to Apc^min+/− mice was well tolerated and resulted in an increased haematocrit, as well as reducing splenic size and red pulp area. Oral feeding did not affect tumour numbers or sizes in this model. This is the first study to show that acidic sophorolipids dose-dependently and specifically reduces colon cancer cell viability in addition to reducing tumour-associated bleeding in the Apc^min+/− mouse model.

Key points

• Acidic sophorolipids are produced by yeast species such as Starmerella bombicola.

• Acidic sophorolipids selectively killed colorectal cells with no effect on healthy gut epithelia.

• Acidic sophorolipids reduced tumour-associated gut bleed in a colorectal mouse model.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12115-6.

Biosurfactant-Producing Mucor Strains: Selection, Screening, and Chemical Characterization

Biosurfactants are amphiphilic molecules with surface tension reducing activities. Among biosurfactant producers, fungi have been identified as promising organisms. While many studies have investigated biosurfactant production in fungal species from the Ascomycota and Basidiomycota phyla, less is known concerning species from the Mucoromycota phylum. In this context, the aim of this study was to screen and optimize biosurfactant production in 24 fungal strains, including seven Mucor, three Lichtheimia, and one Absidia species. After cultivation in a medium stimulating surfactant production, the surface activity of cell-free supernatants was measured using both oil spreading and parafilm M tests. Among them, five Mucor strain cell-free supernatants belonging to M. circinelloides, M. lanceolatus, M. mucedo, M. racemosus, and M. plumbeus, showed oil repulsion. Then, the impact of the medium composition on surfactant production was evaluated for eight strains. Three of them, i.e., Mucor circinelloides UBOCC-A-109190, Mucor plumbeus UBOCC-A-111133, and Mucor mucedo UBOCC-A-101353 showed an interesting surfactant production potential, reducing the medium surface tension to 36, 31, and 32 mN/m, respectively. A preliminary characterization of the surfactant molecules produced by these strains was performed and showed that these compounds belonged to the glycolipid family.

Biosurfactants as Anticancer Agents: Glycolipids Affect Skin Cells in a Differential Manner Dependent on Chemical Structure

Melanomas account for 80% of skin cancer deaths. Due to the strong relationship between melanomas and U.V. radiation, sunscreens have been recommended for use as a primary preventative measure. However, there is a need for targeted, less invasive treatment strategies. Glycolipids such as sophorolipids and rhamnolipids are microbially derived biosurfactants possessing bioactive properties such as antimicrobial, immunomodulatory and anticancer effects. This study aimed to ascertain the differing effects of glycolipids on skin cells. Highly purified and fully characterized preparations of sophorolipids and rhamnolipids were used to treat spontaneously transformed human keratinocyte (HaCaT) and the human malignant melanocyte (SK-MEL-28) cell lines. Cell viability and morphological analyses revealed that glycolipids have differential effects on the skin cells dependent on their chemical structure. Lactonic sophorolipids and mono-rhamnolipids were shown to have a significantly detrimental effect on melanoma cell viability compared to healthy human keratinocytes. These glycolipids were shown to induce cell death via necrosis. Additionally, sophorolipids were shown to significantly inhibit SK-MEL-28 cell migration. These findings suggest that glycolipids could be used as bioactive agents with selective inhibitory effects. As such, glycolipids could be a substitute for synthetically derived surfactants in sunscreens to provide additional benefit and have the potential as novel anti-skin-cancer therapies.

Characterization and Cytotoxicity of Pseudomonas Mediated Rhamnolipids Against Breast Cancer MDA-MB-231 Cell Line

A biosurfactant producing bacterium was identified as Pseudomonas aeruginosa DNM50 based on molecular characterization (NCBI accession no. MK351591). Structural characterization using MALDI-TOF revealed the presence of 12 different congeners of rhamnolipid such as Rha-C8-C8:1, Rha-C10-C8:1, Rha-C10-C10, Rha-C10-C12:1, Rha-C16:1, Rha-C16, Rha-C17:1, Rha-Rha-C10:1-C10:1, Rha-Rha-C10-C12, Rha-Rha-C10-C8, Rha-Rha-C10-C8:1, and Rha-Rha-C8-C8. The radical scavenging activity of rhamnolipid (DNM50RL) was determined by 2, 3-diphenyl-1-picrylhydrazyl (DPPH) assay which showed an IC₅₀ value of 101.8 μg/ ml. The cytotoxic activity was investigated against MDA-MB-231 breast cancer cell line by MTT (4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide) assay which showed a very low IC50 of 0.05 μg/ ml at 72 h of treatment. Further, its activity was confirmed by resazurin and trypan blue assay with IC₅₀ values of 0.01 μg/ml and 0.64 μg/ ml at 72 h of treatment, respectively. Thus, the DNM50RL would play a vital role in the treatment of breast cancer targeting inhibition of p38MAPK.

Isolation and Identification of Bacteria with Surface and Antibacterial Activity from the Gut of Mediterranean Grey Mullets

Fish gut represents a peculiar ecological niche where bacteria can transit and reside to play vital roles by producing bio-compounds with nutritional, immunomodulatory and other functions. This complex microbial ecosystem reflects several factors (environment, feeding regimen, fish species, etc.). The objective of the present study was the identification of intestinal microbial strains able to produce molecules called biosurfactants (BSs), which were tested for surface and antibacterial activity in order to select a group of probiotic bacteria for aquaculture use. Forty-two bacterial isolates from the digestive tracts of twenty Mediterranean grey mullets were screened for testing emulsifying (E-24), surface and antibiotic activities. Fifty percent of bacteria, ascribed to Pseudomonas aeruginosa, Pseudomonas sp., P. putida and P. anguilliseptica, P. stutzeri, P. protegens and Enterobacter ludwigii were found to be surfactant producers. Of the tested strains, 26.6% exhibited an antibacterial activity against Staphylococcus aureus (10.0 ± 0.0–14.5 ± 0.7 mm inhibition zone), and among them, 23.3% of isolates also showed inhibitory activity vs. Proteus mirabilis (10.0 ± 0.0–18.5 ± 0.7 mm inhibition zone) and 6.6% vs. Klebsiella pneumoniae (11.5 ± 0.7–17.5 ± 0.7 mm inhibition zone). According to preliminary chemical analysis, the bioactive compounds are suggested to be ascribed to the class of glycolipids. This works indicated that fish gut is a source of bioactive compounds which deserves to be explored.

Water-Sulfuric Acid Foam as a Possible Habitat for Hypothetical Microbial Community in the Cloud Layer of Venus

The data available at the moment suggest that ancient Venus was covered by extensive bodies of water which could harbor life. Later, however, the drastic overheating of the planet made the surface of Venus uninhabitable for Earth-type life forms. Nevertheless, hypothetical Venusian organisms could have gradually adapted to conditions within the cloud layer of Venus-the only niche containing liquid water where the Earth-type extremophiles could survive. Here we hypothesize that the unified internal volume of a microbial community habitat is represented by the heterophase liquid-gas foam structure of Venusian clouds. Such unity of internal space within foam water volume facilitates microbial cells movements and trophic interactions between microorganisms that creates favorable conditions for the effective development of a true microbial community. The stabilization of a foam heterophase structure can be provided by various surfactants including those synthesized by living cells and products released during cell lysis. Such a foam system could harbor a microbial community of different species of (poly)extremophilic microorganisms that are capable of photo- and chemosynthesis and may be closely integrated into aero-geochemical processes including the processes of high-temperature polymer synthesis on the planet's surface. Different complex nanostructures transferred to the cloud layers by convection flows could further contribute to the stabilization of heterophase liquid-gas foam structure and participate in chemical and photochemical reactions, thus supporting ecosystem stability.

Response and oil degradation activities of a northeast Atlantic bacterial community to biogenic and synthetic surfactants

BACKGROUND

Biosurfactants are naturally derived products that play a similar role to synthetic dispersants in oil spill response but are easily biodegradable and less toxic. Using a combination of analytical chemistry, 16S rRNA amplicon sequencing and simulation-based approaches, this study investigated the microbial community dynamics, ecological drivers, functional diversity and robustness, and oil biodegradation potential of a northeast Atlantic marine microbial community to crude oil when exposed to rhamnolipid or synthetic dispersant Finasol OSR52.

RESULTS

Psychrophilic Colwellia and Oleispira dominated the community in both the rhamnolipid and Finasol OSR52 treatments initially but later community structure across treatments diverged significantly: Rhodobacteraceae and Vibrio dominated the Finasol-amended treatment, whereas Colwellia, Oleispira, and later Cycloclasticus and Alcanivorax, dominated the rhamnolipid-amended treatment. Key aromatic hydrocarbon-degrading bacteria, like Cycloclasticus, was not observed in the Finasol treatment but it was abundant in the oil-only and rhamnolipid-amended treatments. Overall, Finasol had a significant negative impact on the community diversity, weakened the taxa-functional robustness of the community, and caused a stronger environmental filtering, more so than oil-only and rhamnolipid-amended oil treatments. Rhamnolipid-amended and oil-only treatments had the highest functional diversity, however, the overall oil biodegradation was greater in the Finasol treatment, but aromatic biodegradation was highest in the rhamnolipid treatment.

CONCLUSION

Overall, the natural marine microbial community in the northeast Atlantic responded differently to crude oil dispersed with either synthetic or biogenic surfactants over time, but oil degradation was more enhanced by the synthetic dispersant. Collectively, our results advance the understanding of how rhamnolipid biosurfactants and synthetic dispersant Finasol affect the natural marine microbial community in the FSC, supporting their potential application in oil spills. Video abstract.

Crude oil biodegradation potential of biosurfactant-producing Pseudomonas aeruginosa and Meyerozyma sp

This study investigates the potential of crude oil degrading capabilities of biosurfactant-producing strains of Pseudomonas aeruginosa MF069166 and Meyerozyma sp. MF138126. P. aeruginosa produced mono-/di-rhamnolipids congeners whereas, Meyerozyma sp. produced acidic and lactonic forms of sophorolipids with crude oil. The values of critical micelle concentrations of rhamnolipids and sophorolipids were 40 mg/L and 50 mg/L with reductions in surface tension of water to 29 mN/m and 33 mN/m. Dynamic light scattering revealed that the average diameter of micellar aggregates of rhamnolipids ranged between 300 and 350 nm and the average size of sophorolipids micelles was 309 nm and 380 nm. Biosurfactants from P. aeruginosa and Meyerozyma sp. exhibited emulsification activities of 87% and 84% in crude oil. Cell surface hydrophobicity of both strains was higher in the presence of hydrophobic contaminants. The biosurfactants showed stability under varying pH, NaCl concentrations and temperatures. Gravimetric and GC-MS analyses demonstrated that P. aeruginosa degraded 91% of the petroleum hydrocarbons while Meyerozyma sp. showed 87% biodegradation efficiency. P. aeruginosa and Meyerozyma sp. have also been found to degrade halogen-containing compounds and showed excellent crude oil degradation efficiency. It is concluded that both strains have high potential of applications in the bioremediation of hydrocarbons-contaminated sites.

Screening Strategies for Biosurfactant Discovery

The isolation and screening of bacteria and fungi for the production of surface-active compounds has been the basis for the majority of the biosurfactants discovered to date. Hence, a wide variety of well-established and relatively simple methods are available for screening, mostly focused on the detection of surface or interfacial activity of the culture supernatant. However, the success of any biodiscovery effort, specifically aiming to access novelty, relies directly on the characteristics being screened for and the uniqueness of the microorganisms being screened. Therefore, given that rather few novel biosurfactant structures have been discovered during the last decade, advanced strategies are now needed to widen access to novel chemistries and properties. In addition, more modern Omics technologies should be considered to the traditional culture-based approaches for biosurfactant discovery. This chapter summarizes the screening methods and strategies typically used for the discovery of biosurfactants and highlights some of the Omics-based approaches that have resulted in the discovery of unique biosurfactants. These studies illustrate the potentially enormous diversity that has yet to be unlocked and how we can begin to tap into these biological resources.

Exploiting Microbes in the Petroleum Field: Analyzing the Credibility of Microbial Enhanced Oil Recovery (MEOR)

Crude oil is a major energy source that is exploited globally to achieve economic growth. To meet the growing demands for oil, in an environment of stringent environmental regulations and economic and technical pressure, industries have been required to develop novel oil salvaging techniques. The remaining ~70% of the world’s conventional oil (one-third of the available total petroleum) is trapped in depleted and marginal reservoirs, and could thus be potentially recovered and used. The only means of extracting this oil is via microbial enhanced oil recovery (MEOR). This tertiary oil recovery method employs indigenous microorganisms and their metabolic products to enhance oil mobilization. Although a significant amount of research has been undertaken on MEOR, the absence of convincing evidence has contributed to the petroleum industry’s low interest, as evidenced by the issuance of 400+ patents on MEOR that have not been accepted by this sector. The majority of the world’s MEOR field trials are briefly described in this review. However, the presented research fails to provide valid verification that the microbial system has the potential to address the identified constraints. Rather than promising certainty, MEOR will persist as an unverified concept unless further research and investigations are carried out.

Glycolipid Biosurfactant Production from Waste Cooking Oils by Yeast: Review of Substrates, Producers and Products

Biosurfactants are a microbially synthesized alternative to synthetic surfactants, one of the most important bulk chemicals. Some yeast species are proven to be exceptional biosurfactant producers, while others are emerging producers. A set of factors affects the type, amount, and properties of the biosurfactant produced, as well as the environmental impact and costs of biosurfactant’s production. Exploring waste cooking oil as a substrate for biosurfactants’ production serves as an effective cost-cutting strategy, yet it has some limitations. This review explores the existing knowledge on utilizing waste cooking oil as a feedstock to produce glycolipid biosurfactants by yeast. The review focuses specifically on the differences created by using raw cooking oil or waste cooking oil as the substrate on the ability of various yeast species to synthesize sophorolipids, rhamnolipids, mannosylerythritol lipids, and other glycolipids and the substrate’s impact on the composition, properties, and limitations in the application of biosurfactants.

Role of Postbiotics in Diabetes Mellitus: Current Knowledge and Future Perspectives

In the last decade, the gastrointestinal microbiota has been recognised as being essential for health. Indeed, several publications have documented the suitability of probiotics, prebiotics, and symbiotics in the management of different diseases such as diabetes mellitus (DM). Advances in laboratory techniques have allowed the identification and characterisation of new biologically active molecules, referred to as “postbiotics”. Postbiotics are defined as functional bioactive compounds obtained from food-grade microorganisms that confer health benefits when administered in adequate amounts. They include cell structures, secreted molecules or metabolic by-products, and inanimate microorganisms. This heterogeneous group of molecules presents a broad range of mechanisms and may exhibit some advantages over traditional “biotics” such as probiotics and prebiotics. Owing to the growing incidence of DM worldwide and the implications of the microbiota in the disease progression, postbiotics appear to be good candidates as novel therapeutic targets. In the present review, we summarise the current knowledge about postbiotic compounds and their potential application in diabetes management. Additionally, we envision future perspectives on this topic. In summary, the results indicate that postbiotics hold promise as a potential novel therapeutic strategy for DM.

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.

Production of Sophorolipid Biosurfactant by Insect Derived Novel Yeast Metschnikowia churdharensis f.a., sp. nov., and Its Antifungal Activity Against Plant and Human Pathogens

Biosurfactants are potential biomolecules that have extensive utilization in cosmetics, medicines, bioremediation and processed foods. Yeast produced biosurfactants offer thermal resistance, antioxidant activity, and no risk of pathogenicity, illustrating their promising use in food formulations. The present study is aimed to assess potential of biosurfactant screened from a novel yeast and their inhibition against food spoilage fungi. A novel asexual ascomycetes yeast strain CIG-6A^T producing biosurfactant, was isolated from the gut of stingless bee from Churdhar, HP, India. The phylogenetic analysis revealed that the strain CIG-6A^T was closely related to Metschnikowia koreensis, showing 94.38% sequence similarity in the D1D2 region for which the name Metschnikowia churdharensis f.a., sp. nov., is proposed. The strain CIG-6A^T was able to produce sophorolipid biosurfactant under optimum conditions. Sophorolipid biosurfactant from strain CIG-6A^T effectively reduced the surface tension from 72.8 to 35 mN/m. Sophorolipid biosurfactant was characterized using TLC, FTIR, GC-MS and LC-MS techniques and was a mixture of both acidic and lactonic forms. Sophorolipid assessed promising activity against pathogenic fungi viz. Fusarium oxysporum (MTCC 9913), Fusarium solani (MTCC 350), and Colletotrichum gloeosporioides (MTCC 2190). The inhibitory effect of biosurfactant CIG-6A^T against F. solani was studied and MIC was 49 μgm/ml, further confirmed through confocal laser scanning microscopy. We illustrated the antifungal activity of sophorolipid biosurfactant from Metschnikowia genus for the first time and suggested a novel antifungal compound against food spoilage and human fungal pathogen.