Relationship of cell-wall bound fatty acids and the demulsification efficiency of demulsifying bacteria Alcaligenes sp. S-XJ-1 cultured with vegetable oils

Production and structural characterization of eco-friendly bioemulsifier SC04 from Saccharomyces cerevisiae strain MYN04 with potential applications

BACKGROUND

Bioemulsifiers are natural or microbial-based products with the ability to emulsify hydrophobic compounds in water. These compounds are biodegradable, eco-friendly, and find applications in various industries.

RESULTS

Thirteen yeasts were isolated from different sources in Alexandria, Egypt, and evaluated for their potential to produce intracellular bioemulsifiers. One yeast, isolated from a local market in Egypt, showed the highest emulsification index (EI24) value. Through 26S rRNA sequencing, this yeast was identified as Saccharomyces cerevisiae strain MYN04. The growth kinetics of the isolate were studied, and after 36 h of incubation, the highest yield of cell dry weight (CDW) was obtained at 3.17 g/L, with an EI24 of 55.6%. Experimental designs were used to investigate the effects of culture parameters on maximizing bioemulsifier SC04 production and CDW. The study achieved a maximum EI24 of 79.0 ± 2.0%. Furthermore, the crude bioemulsifier was precipitated with 50% ethanol and purified using Sephadex G-75 gel filtration chromatography. Bioemulsifier SC04 was found to consist of 27.1% carbohydrates and 72.9% proteins. Structural determination of purified bioemulsifier SC04 was carried out using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), high-performance liquid chromatography (HPLC), and nuclear magnetic resonance spectroscopy (NMR). FTIR spectroscopy revealed characteristic bands associated with carboxyl and hydroxyl groups of carbohydrates, as well as amine groups of proteins. HPLC analysis of monosaccharide composition detected the presence of mannose, galactose, and glucose. Physicochemical characterization of the fraction after gel filtration indicated that bioemulsifier SC04 is a high molecular weight protein-oligosaccharide complex. This bioemulsifier demonstrated stability at different pH values, temperatures, and salinities. At a concentration of 0.5 mg/mL, it exhibited 51.8% scavenging of DPPH radicals. Furthermore, in vitro cytotoxicity evaluation using the MTT assay revealed a noncytotoxic effect of SC04 against normal epithelial kidney cell lines.

CONCLUSIONS

This study presents a new eco-friendly bioemulsifier, named SC04, which exhibits significant emulsifying ability, antioxidant and anticancer properties, and stabilizing properties. These findings suggest that SC04 is a promising candidate for applications in the food, pharmaceutical, and industrial sectors.

Sustainable production of bioemulsifiers, a critical overview from microorganisms to promising applications

Microbial bioemulsifiers are molecules of amphiphilic nature and high molecular weight that are efficient in emulsifying two immiscible phases such as water and oil. These molecules are less effective in reducing surface tension and are synthesized by bacteria, yeast and filamentous fungi. Unlike synthetic emulsifiers, microbial bioemulsifiers have unique advantages such as biocompatibility, non-toxicity, biodegradability, efficiency at low concentrations and high selectivity under different conditions of pH, temperature and salinity. The adoption of microbial bioemulsifiers as alternatives to their synthetic counterparts has been growing in ongoing research. This article analyzes the production of microbial-based emulsifiers, the raw materials and fermentation processes used, as well as the scale-up and commercial applications of some of these biomolecules. The current trend of incorporating natural compounds into industrial formulations indicates that the search for new bioemulsifiers will continue to increase, with emphasis on performance improvement and economically viable processes.

Stress proteins, nonribosomal peptide synthetases, and polyketide synthases regulate carbon sources-mediated bio-demulsifying mechanisms of nitrate-reducing bacterium Gordonia sp. TD-4

Carbon sources have been reported to determine the bio-demulsifying performance and mechanisms. However, the genetic regulation of carbon sources-mediated bio-demulsification remains unclear. Here, the effects of β-oxidation, stress response, and nitrate metabolism on the demulsification of alkaline-surfactant-polymer flooding produced water by Gordonia sp. TD-4 were investigated. The results showed that competitive adsorption-derived demulsification was mediated by oil-soluble carbon sources (paraffin). Surface-active lipopeptides responsible for competitive adsorption-derived demulsification could be biosynthesized by the nonribosomal peptide synthetases and polyketide synthases using oil-soluble carbon sources. Bio-flocculation-derived demulsification was mediated by water-soluble carbon sources. Water-soluble carbon sources (sodium acetate and glucose) mediated the process of the dissimilatory reduction of nitrate to ammonia, which resulted in the variable accumulation of nitrite. The accumulated nitrite (>180 mg-N/L) stimulated stress response and induced the upregulation of chaperone-associated genes. The upregulation of chaperonins increased the cell surface hydrophobicity and the cation-dependent bio-flocculating performance, which were responsible for bio-flocculation-derived demulsification. The β-oxidation of fatty acids significantly affected both competitive adsorption-derived demulsification and bio-flocculation-derived demulsification. This study illustrates the synergistic effects of nitrogen sources and carbon sources on the regulation of bio-demulsifying mechanisms of TD-4 and identifies two key functional gene modules responsible for the regulation of bio-demulsifying mechanisms.

Application of α-amylase as a novel biodemulsifier for destabilizing amphiphilic polymer-flooding produced liquid treatment

The performance and de-emulsification mechanism of α-amylase, a novel environmental friendly biodemulsifier in petroleum industry, was investigated at room temperature. The effects of α-amylase on the viscosity of amphiphilic polymer solution and de-emulsification rate were studied by changing the concentration of α-amylase, temperature and salinity. Polymer molecular weight, Zeta potential, interfacial film strength and interfacial tension were measured to investigate the de-emulsification mechanism of α-amylase. The results show that α-amylase is an efficient biodemulsifier to increase the de-emulsification rate of amphiphilic polymer emulsions. Hydrolysis of α-amylase to amphiphilic polymers destroys the structure of the amphiphilic polymer, thereby reduces the viscosity and the interfacial film strength of the system. Once de-emulsification is completed, the lower layer, i.e. the emulsified layer, will be clear. Thus, α-amylase can be applied as an effective de-emulsifier for amphiphilic polymer-stabilized O/W emulsion.

Yeasts and bacterial biosurfactants as demulsifiers for petroleum derivative in seawater emulsions

Oil sludge or waste generated in transport, storage or refining forms highly stable mixtures due to the presence and additives with surfactant properties and water forming complex emulsions. Thus, demulsification is necessary to separate this residual oil from the aqueous phase for oil processing and water treatment/disposal. Most used chemical demulsifiers, although effective, are environmental contaminants and do not meet the desired levels of biodegradation. We investigated the application of microbial biosurfactants as potential natural demulsifiers of petroleum derivatives in water emulsions. Biosurfactants crude extracts, produced by yeasts (Candida guilliermondii, Candida lipolytica and Candida sphaerica) and bacteria (Pseudomonas aeruginosa, Pseudomonas cepacia and Bacillus sp.) grown in industrial residues, were tested for demulsification capacity in their crude and pure forms. The best results obtained were for bacterial biosurfactants, which were able to recover about 65% of the seawater emulsified with motor oil compared to 35–40% only for yeasts products. Biosurfactants were also tested with oil-in-water (O/W) and water-in-oil (W/O) kerosene model emulsions. No relationship between interfacial tension, cell hydrophobicity and demulsification ratios was observed with all the biosurfactants tested. Microscopic illustrations of the emulsions in the presence of the biosurfactants showed the aspects of the emulsion and demulsification process. The results obtained demonstrate the potential of these agents as demulsifiers in marine environments.

Interactions among triphenyltin degradation, phospholipid synthesis and membrane characteristics of Bacillus thuringiensis in the presence of d-malic acid

Degradation pathway and surface biosorption of triphenyltin (TPT) by effective microbes have been investigated in the past. However, unclear interactions among membrane components and TPT binding and transport are still obstacles to understanding TPT biotransformation. To reveal the mechanism involved, the phospholipid expression, membrane potential, cellular mechanism and molecular dynamics between TPT and fatty acids (FAs) during the TPT degradation process in the presence of d-malic acid (DMA) were studied. The results show that the degradation efficiency of 1 mg L^-1 TPT by Bacillus thuringiensis (1 g L^-1) with 0.5 or 1 mg L^-1 DMA reached values up to approximately 90% due to the promotion of element metabolism and cellular activity, and the depression of FA synthesis induced by DMA. The addition of DMA caused conversion of more linoleic acid into 10-oxo-12(Z)-octadecenoic acid, increased the membrane permeability, and alleviated the decrease in membrane potential, resulting in TPT transport and degradation. Fluorescence analysis reveals that the endospore of B. thuringiensis could act as an indicator for membrane potential and cellular activities. The current findings are advantageous for acceleration of biosorption, transport and removal of pollutants from natural environments.

Saponin-enhanced biomass accumulation and demulsification capability of the demulsifying bacteria Alcaligenes sp. S-XJ-1

Saponin significantly enhanced biomass accumulation and demulsification capability of the demulsifying bacteria.

Carbon source dependence of cell surface composition and demulsifying capability of Alcaligenes sp. S-XJ-1

Biodemulsifiers are environmentally friendly agents used in recycling oil or purifying water from emulsion, yet the demulsifying feature of cell-surface composition remains unclear. In this study, potentiometric titration, attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry were combined to characterize cell-surface chemical composition of demulsifying strain Alcaligenes sp. S-XJ-1 cultivated with different carbon sources. Cells cultivated with alkane contained abundant elemental nitrogen and basic functional groups, indicating that their surface was rich in proteins or peptides, which contributed to their highest demulsifying efficiency. For cells cultivated with fatty acid ester, the relatively abundant surface lipid contributed to a 50% demulsification ratio owing to the presence of more acidic functional group. The cells cultivated with glucose exhibited a high oxygen concentration (O/C ∼0.28), which indicated the presence of more polysaccharides on the cell surface. This induced the lowest demulsification ratio of 30%. It can be concluded that cell surface-associated proteins or lipids other than the polysaccharide of the demulsifying strain played a positive role in the demulsification activity. In addition, the cell-surface oligoglutamate compounds identified in situ were crucial to the demulsifying capability.

Separation and characterization of effective demulsifying substances from surface of Alcaligenes sp. S-XJ-1 and its application in water-in-kerosene emulsion

The main goal of this work was to analyze the effect of surface substances on demulsifying capability of the demulsifying strain Alcaligenes sp. S-XJ-1. The demulsifying substances were successfully separated from the cell surface with dichloromethane-alkali treatment, and exhibited 67.5% of the demulsification ratio for water-in-kerosene emulsions at a dosage of 356mg/L. FT-IR, TLC and ESI-MS analysis confirmed the presence of a carbohydrate-protein-lipid complex in the demulsifying substances with the major molecular ions from mass-to-charge ratio (m/z) 165 to 814. After the substances separated, the cell morphology changed from aggregated to dispersed, and the concentration of cell surface functional groups decreased. Cell surface hydrophobicity and the ability of cell adhesion to hydrophobic surface of the treated cells was also reduced compared with original cell. It was proved that the demulsifying substances had a significant effect on cell surface properties and accordingly with demulsifying capability of Alcaligenes sp. S-XJ-1.

Application of rhamnolipid as a novel biodemulsifier for destabilizing waste crude oil

Waste crude oil emulsion was inevitably produced in the petroleum industrial process, causing harmful impact on the ecological and social environment. In this study, rhamnolipid was for the first time investigated for demulsification of waste crude oil. As found in this paper, rhamnolipid treatment could obtain over 90% of dewatering efficiency on refractory waste crude oil and such efficient demulsification was confirmed on model emulsions. As further demonstrated on the pilot scale (100 L), rhamnolipid treatment could recover over 98% of crude oil from the wastes. The recovered oil contained less than 0.3% of water and thus can directly re-enter into refinery process while the aqueous phase can be disposed into dischargeable water due to largely reduced soluble COD after subjected to 5 days of active sludge treatment. It seems that rhamnolipids as biodemulsifiers were of great prospects in the industrial demulsification of waste crude oil.