Fabrication of bovine serum albumin nanofibrils: Physicochemical characteristics, emulsifying and foaming activities.

Bovine serum albumin nanofibrils (BSNs) were fabricated under thermal treatment (85 °C) at acidic condition (pH 2.0) and the incubation time on the structural, and physicochemical characteristics were probed. The formation and development of BSNs have been detected and confirmed by Thioflavin T (ThT) fluorescence and circular dichroism (CD) measurements. The structural alterations of bovine serum albumin (BSA) have also been investigated using intrinsic fluorescence and Congo red (CGR) UV-vis spectroscopy. Atomic force microscopy (AFM) outcomes displayed the morphologies of BSNs at varied time, with a diameter of about 3 nm and a contour length of about 200 nm at 24 h. The apparent viscosities of BSNs at three different pH were in the following order: pH 3.0 > pH 5.0 > pH 7.0. Emulsifying and foaming properties of BSA were pronouncedly enhanced through fibrillation, which was highly correlated with the interfacial properties and structural characteristics. Highest EAI 54.2 m2/g was attained at 48 h and no pronounced alterations were observed for EAI at 24 h and 48 h. Maximum value of FC was obtained at 48 h for BSA. This study will provide some useful information in understanding the formation of BSNs and broaden their application in food systems as functional food ingredients.

High mono-rhamnolipids production by a novel isolate Pseudomonas aeruginosa LP20 from oily sludge: characterization, optimization, and potential application.

This study aims to isolate microbial strains for producing mono-rhamnolipids with high proportion. Oily sludge is rich in petroleum and contains diverse biosurfactant-producing strains. A biosurfactant-producing strain LP20 was isolated from oily sludge, identified as Pseudomonas aeruginosa based on phylogenetic analysis of 16S rRNA. High-performance liquid chromatography-mass spectrometry results indicated that biosurfactants produced from LP20 were rhamnolipids, mainly containing Rha-C8-C10, Rha-C10-C10, Rha-Rha-C8-C10, Rha-Rha-C10-C10, Rha-C10-C12:1, and Rha-C10-C12. Interestingly, more mono-rhamnolipids were produced by strain LP20 with a relative abundance of 64.5%. Pseudomonas aeruginosa LP20 optimally produced rhamnolipids at a pH of 7.0 and a salinity of 0.1% using glycerol and nitrate. The culture medium for rhamnolipids by strain LP20 was optimized by response surface methodology. LP20 produced rhamnolipids up to 6.9 g L-1, increased by 116%. Rhamnolipids produced from LP20 decreased the water surface tension to 28.1 mN m-1 with a critical micelle concentration of 60 mg L-1. The produced rhamnolipids emulsified many hydrocarbons with EI24 values higher than 56% and showed antimicrobial activity against Staphylococcus aureus and Cladosporium sp. with inhibition rates 48.5% and 17.9%, respectively. Pseudomonas aeruginosa LP20 produced more proportion of mono-rhamnolipids, and the LP20 rhamnolipids exhibited favorable activities and promising potential in microbial-enhanced oil recovery, bioremediation, and agricultural biocontrol.

Unveiling the structure-emulsifying function relationship of truncated recombinant forms of the SA01-OmpA protein opens up a new vista in bioemulsifiers.

The emulsifying ability of SA01-OmpA (outer membrane protein A from Acinetobacter sp. SA01) was found to be constrained by challenges like low production efficiency and high costs associated with protein recovery from E. coli inclusion bodies, as described in our previous study. The present study sought to benefit from the advantages of the targeted truncating of SA01-OmpA protein, taking into account the reduced propensity of protein expression as inclusion bodies and cytotoxicity. Here, the structure and activity relationship of two truncated recombinant forms of SA01-OmpA protein was unraveled through a hybrid approach based on experimental data and computational methodologies, representing an innovative bioemulsifier with advantageous emulsifying activity. The recombinant truncated SA01-OmpA variants were cloned and heterologously expressed in E. coli host cells and subsequently purified. The results showed increased emulsifying activity of N-terminally truncated SA01-OmpA (NT-OmpA) compared to full-length SA01-OmpA. Molecular dynamics (MD) simulations analysis demonstrated a direct correlation between the C-terminally truncated SA01-OmpA (CT-OmpA) and its expression as inclusion bodies. Analysis of the structure-activity relationship of truncated variants of SA01-OmpA revealed that, compared to the full-length protein, deletion of the ß-barrel portion from the N-terminal of SA01-OmpA increased the emulsifying activity of NT-OmpA while lowering its expression as inclusion bodies. Contrary to the full-length protein, the N-terminally truncated SA01-OmpA was not as cytotoxic, according to the MTT assay, FCM analysis, and AO/EB staining. The findings of this extensive study advance our knowledge of SA01-OmpA at the molecular level as well as the design and development of efficient bioemulsifiers.IMPORTANCEPrevious research (Shahryari et al. 2021, mSystems 6: e01175-20) introduced and characterized the SA01-OmpA protein as a multifaceted protein with a variety of functions, including maintaining cellular homeostasis under oxidative stress conditions, biofilm formation, outer membrane vesicles (OMV) biogenesis, and beneficial emulsifying capacity. By truncating the SA01-OmpA protein, the current study presents a unique method for developing protein-type bioemulsifiers. The findings indicate that the N-terminally truncated SA01-OmpA (NT-OmpA) has the potential to fully replace full-length SA01-OmpA as a novel bioemulsifier with significant emulsifying activity. This study opens up a new frontier in bioemulsifiers, shedding light on a possible relationship between the structure and activity of SA01-OmpA truncated forms.

Astonishing emulsifying properties of a novel exopolysaccharide produced from Bacillus velezensis BABA50.

Microbial exopolysaccharides (EPSs) are currently under intensive research in various applications. However, studies on EPS from Bacillus velezensis are rare and the emulsifying properties of this EPS have not been studied previously. An EPS produced by a novel B. velezensis BABA50 strain isolated from an Algerian hot spring was characterised. The results of structural, morphological and thermal analyses showed a heteropolymeric structure containing galactose, glucose, glucuronic acid and N-acetyl glucosamine. Analyses revealed the presence of carbonyl and hydroxyl groups, branched and highly porous structure and relevant thermal stability compared to other EPSs with a high degradation temperature of 260 °C and 38% of residual mass at 800 °C. EPS from B. velezensis BABA50 presents distinct polymer in terms of structure and composition compared to previously described EPS with excellent emulsifying and antioxidant activities; this EPS holds great potential in the food and cosmetic industries as a thermostable emulsifier and antioxidant agent.

Recovery of soy whey protein from soy whey wastewater at various cavitation jet pretreatment time and their structural and emulsifying properties.

Protein-polysaccharide composite is of great significance for the development of soluble protein recovery process. This study investigated the effects of cavitation jet (CJ) pretreatment at different time (0, 60, 120, 180, 240, 300 s) intervals on the recovery of soy whey protein (SWP) from soy whey wastewater using chitosan (CH). In addition, the structure and properties of the SWP/CH complexes were examined. The results showed that the recovery yield of SWP reached 84.44 % when the CJ pretreatment time was 180 s, and the EAI and ESI values of the SWP/CH complex increased from 32.39 m2/g and 21 min to 48.47 m2/g and 32 min, respectively. In the CJ pretreatment process, SWP promotes the recombination with chitosan through electrostatic interaction and hydrogen bond, while hydrophobic interaction is also involved. This study has guiding significance for CJ technology in the recovery and utilization of protein in industrial wastewater.

Silver Ions Drive Ordered Self-Assembly Mechanisms and Inherent Properties of Lignin Nanoflowers.

Designing anisotropic lignin-based particles and promoting the high-value utilization of lignin have nowadays drawn much attention from scientists. However, systematic studies addressing the self-assembly mechanisms of anisotropic lignin-based particles are scarce. In this work, an interaction including the electrostatic forces and chelating forces between lignin and Ag+ was regulated via carboxymethylation modification. Subsequently, the aggregation morphology of carboxymethylated lignin in a Ag+ solution was observed via SEM. The result showed that a large number of Ag+ intercalated into the lignin molecules when the grafting degree of the carboxyl groups increased from 0.17 mmol/g to 0.53 mmol/g, which caused the lignin molecules to gradually transform from disordered blocks to ordered layers. Dynamics research indicated that the adsorption process of Ag+ in carboxymethylated lignin conforms to the Pseudo-first-order kinetic model. The saturated adsorption amount of Ag+ in the carboxymethylated lignin reached 1981.7 mg/g when the grafting rate of carboxyl groups increased to 0.53 mmol/g, which then fully intercalated into lignin molecules and formed a layered structure. The thermodynamic parameters showed that the thermal adsorption process conforms to the Langmuir model, which indicates that Ag+ is monolayer-adsorbed and intercalated into lignin molecules. Meanwhile, the ΔH values are more than 0, which suggests that this adsorption process is a endothermic reaction and that a higher temperature is conducive to an adsorption reaction. Therefore, self-assembly of lignin in a Ag+ solution under 70 °C is more conducive to the formation of a nanoflower structure, which is consistent with our experimental result. Finally, pH-responsive Pickering emulsions were successfully prepared using a lignin-based nanoflowers, which demonstrated their potential as a catalytic platform in the interface catalysis field. This work offers a deeper understanding into the formation mechanism of anisotropic lignin-based nanoflowers and hopes to be helpful for designing and preparing anisotropic lignin-based particles.

Effects of pile fermentation on the physicochemical, functional, and biological properties of tea polysaccharides.

This study investigated the influence of pile fermentation on the physicochemical, functional, and biological properties of tea polysaccharides (TPS). Results indicated that the extraction yield, uronic acid content, and polyphenol content of TPS greatly increased from 1.8, 13.1 and 6.3 % to 4.1, 27.9, and 7.8 %, respectively, but the molecular weight markedly decreased from 153.7 to 76.0 kDa after pile fermentation. Additionally, the interfacial, emulsion formation, and emulsion stabilization properties of TPS were significantly improved after pile fermentation. For instance, 1.0 wt% TPS isolated from dark tea (D-TPS) can fabricate 8.0 wt% MCT oil-in-water nanoemulsion (d32 ≈ 159 nm) with potent storage stability. Moreover, the antioxidant and α-glucosidase inhibitory activities of D-TPS was higher than that of TPS isolated from sun-dried raw tea (R-TPS). Overall, this study indicated that pile fermentation markedly affected the physicochemical and structural characteristics of TPS, thereby improving their functional and biological properties.

Structural characterization and physicochemical properties of the exopolysaccharide produced by the moderately halophilic bacterium Chromohalobacter salexigens, strain 3EQS1.

A strain, 3EQS1, was isolated from a salt sample taken from Lake Qarun (Fayoum Province, Egypt). On the basis of physiological, biochemical, and phylogenetic analyses, the strain was classified as Chromohalobacter salexigens. By 72 h of growth at 25 °C, strain 3EQS1 produced large amounts (15.1 g L-1) of exopolysaccharide (EPS) in a liquid mineral medium (initial pH 8.0) containing 10% sucrose and 10% NaCl. The EPS was precipitated from the cell-free culture medium with chilled ethanol and was purified by gel-permeation and anion-exchange chromatography. The molecular mass of the EPS was 0.9 × 106 Da. Chemical analyses, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy showed that the EPS was a linear ß-D-(2 → 6)-linked fructan (levan). In aqueous solution, the EPS tended to form supramolecular aggregates with a critical aggregation concentration of 240 µg mL-1. The EPS had high emulsifying activity (E24, %) against kerosene (31.2 ± 0.4%), sunflower oil (76.9 ± 1.3%), and crude oil (98.9 ± 0.8%), and it also had surfactant properties. A 0.1% (w/v) aqueous EPS solution reduced the surface tension of water by 11.9%. The levan of C. salexigens 3EQS1 may be useful in various biotechnological processes.

Lipase-catalyzed synthesis of antibacterial and antioxidative erythorbyl ricinoleate with high emulsifying activity.

Erythorbyl ricinoleate (ERO) was synthesized as a novel multi-functional emulsifier with antibacterial and antioxidative activities via lipase-catalyzed esterification between erythorbic acid and ricinoleic acid. Esterification regioselectively produced ERO (6-O-ricinoleoyl-erythorbate) of 238.67 mM at 48 h. ERO effectively reduced interfacial tension to 2.66 mN/m at its critical micelle concentration (0.73 mM), compared with other erythorbyl fatty acid esters (EFEs). Oil-in-water (O/W) emulsion stabilized by ERO remained stable for 15 days with a droplet size of 256.3 nm and polydispersity index of 0.22, whereas the emulsion stabilized by the other EFEs became unstable within six days. ERO had antibacterial activity against Gram-positive bacteria with minimum inhibitory concentrations from 0.2 to 0.6 mM. In O/W emulsion, ERO exhibited higher antioxidative activity than erythorbic acid against lipid oxidation. These findings suggest that ERO has high potential as multi-functional food additive to control lipid oxidation and bacterial contamination for O/W emulsion foods.

The temporal evolution mechanism of structure and function of oxidized soy protein aggregates.

The emulsifying activity of soy protein would decrease after long-term storage, which caused huge economic losses to food processing plants. This study explored the temporal evolution mechanism of oxidation on the structure and function of soy protein aggregates, which would improve the application of soy protein in food industry. Decreased α-helix and increased random coil were observed at the initial oxidation stage (0-4 h), which induced increases in hydrophobicity and disulfide bond content. In addition, emulsibility increased significantly. However, when the oxidation time extended to 6-12 h, the soluble aggregates transformed into insoluble aggregates with large particle size, low solubility, and molecular flexibility. Surface hydrophobicity and emulsifying activity were reduced, resulting in bridging flocculation of emulsion droplets. Mutual transformation between components is affected by factors that include spatial conformation and intermolecular forces, which eventually lead to functional changes in the protein molecules.

Isolation and identification of the alga-symbiotic bacterium Gordonia and characterisation of its exopolysaccharide.

An exopolysaccharide (EPS)-producing bacterium TD18, isolated from the culture broth of green alga Scenedesmus obliquus, was identified as Gordonia terrae based on the 100% identity of 16S rRNA sequences and designated Gordonia terrae TD18. The results of compositional and structural analyses and physiochemical tests show that (1) the exopolysaccharide produced by G. terrae TD18 (TD18-EPS) is an acidic hetero-polysaccharide with a molecular weight of 23 kDa, consisting of glucose, mannose, galactose and glucuronic acid, and (2) TD18-EPS is of high thermal stability with a degradation temperature of 308 °C, the solution of which is non-Newtonian pseudoplastic fluid exhibiting good emulsifying properties over a wide range of temperatures, pH and NaCl concentrations. Hence, Gordonia terrae TD18 is the first alga-symbiotic Gordonia strain identified thus far, while TD18-EPS is unique in terms of composition and structure, different from the known Gordonia EPS, with excellent physiochemical properties and thus has potential applications in industry.

Altering functional properties of rice protein hydrolysates by covalent conjugation with chlorogenic acid.

Proteins and phenolic compounds are common components in foods that readily interact with each other to yield complexes, leading to changes in the functional properties. In this study, we investigated the effect of covalent conjugation of rice protein hydrolysates (RPH) with chlorogenic acid (CA) on the structural and functional properties of RPH. Three RPH-CA conjugates were prepared by the alkaline, enzyme, and free radical methods, respectively. Covalent conjugation decreased the content of free amino, thiol, and tyrosine groups, and increased in the amount of CA bounds from 15.23 to 21.11 nmol/mg. Moreover, the circular dichroism analysis revealed that covalent conjugation resulted in an increase of random coils. The emulsifying activity and antioxidant capacity of RPH were also improved by the covalent conjugation with CA. This work provides a better understanding of the formation of hydrolysates-chlorogenic acid conjugates, contributing to improving the functional properties of foods.

Exopolysaccharide Produced by Pediococcus pentosaceus E8: Structure, Bio-Activities, and Its Potential Application.

The novel exopolysaccharide EPS-E8, secreted by Pediococcus pentosaceus E8, was obtained by anion-exchange and gel filtration chromatography. Structural analyses identified EPS-E8 as a heteropolysaccharide containing mannose, glucose, and galactose. Its major backbone consists of →2)-α-D-Manp-(1→2,6)-α-D-Glcp-(1→6)-α-D-Manp-(1→, and its molecular weight is 5.02 × 104 g/mol. Using atomic force microscopy and scanning electron microscopy, many spherical and irregular reticular-like shapes were observed in the microstructure of EPS-E8. EPS-E8 has outstanding thermal stability (305.7°C). Both the zeta potential absolute value and average particle diameter increased gradually with increasing concentration. Moreover, at a concentration of 10 mg/ml, the antioxidant capacities of, 1-Diphenyl-2-picrylhydrazyl (DPPH), ABTS and hydroxyl radical were 50.62 ± 0.5%, 52.17 ± 1.4%, and 58.91 ± 0.7%, respectively. EPS-E8 possesses excellent emulsifying properties against several food-grade oils, and its activity is retained under various conditions (temperature, pH, and ionic strength). Finally, we found that EPS-E8 as a polysaccharide-based coating could reduce the weight loss and malondialdehyde (MDA) content of strawberry, as well as preserving the vitamin C and soluble solid content during storage at 20°C. Together, the results support the potential application of EPS-E8 as an emulsifier, and a polysaccharide-based coating in fruit preservation.

A functional analysis of the effects of the molecular weight of dextran on ε-polylysine-dextran conjugate created through the maillard reaction.

The present study mainly examines the effects of molecular weight of dextran on the reaction rate and functional characteristics between ε-polylysine (PL) and dextran. The reaction kinetics, grafting degree and gel permeation chromatography are employed to evaluate the reaction rate and extent of these lard reaction. We find low activation energy (Ea) values that indicate that dextran with high molecular weight (HMD) exhibits a higher reaction rate with PL than that that of dextran with middle molecular weight (MMD) and low molecular weight (LMD). As for the functional characteristics of the formed conjugate, the conjugate of PL-HMD possesses a higher emulsifying activity, and PL-LMD exhibits higher antimicrobial activity than other molecular weight of dextran. We observe that long heating time at high temperatures can induce the partial degradation of the formed conjugates, which is reflected in the decreasing of the emulsifying and antimicrobial activity of PL-dextran conjugates.

Sustainable production and characterization of medium-molecular weight welan gum produced by a Sphingomonas sp. RW.

Welan gum is widely used in food, concrete, and oil recovery for its excellent stability and unique rheological properties. This study describes an engineered Sphingomonas sp. RW strain deficient in the lyase gene (welR) and outlines its application in an industrial by-product fermentation strategy to produce welan gum. The yield of the engineered strain was enhanced to 25.11 ± 0.05 g/L, whereas the broth viscosity (2110 mPas) increased by 281.81%. The welan gum produced by Sphingomonas sp. RW was named medium-molecular weight welan gum (MMWG, ~350 kDa). FT-IR and monosaccharide composition analysis revealed that the MMWG was composed of l-mannose, l-rhamnose, glucuronic acid, and glucose (with mole ratios of 1:4.46:1.26:2.82). Significantly, MMWG had favorable hydroxyl radical scavenging activity and emulsifying capacity. These results provide a strategy for cost-effective welan gum production and enrich the properties of welan gum with different molecular weight.

Differences in the properties of extracellular polymeric substances responsible for PAH degradation isolated from Mycobacterium gilvum SN12 grown on pyrene and benzo[a]pyrene.

This study aimed to evaluate the differences in the characteristics of extracellular polymeric substances (EPSs) secreted by Mycobacterium gilvum SN12 (M.g. SN12) cultured on pyrene (Pyr) and benzo[a]pyrene (BaP). A heating method was used to extract EPSs from M.g. SN12, and the composition, emulsifying activity, and morphology of EPS extracts were investigated. Results showed that EPS extracts varied significantly with Pyr or BaP addition to the bacterial cultures. The concentration of proteins and carbohydrates, the main components of the EPS extracts, first increased and then decreased, with an increase in the concentration of Pyr (0-120 mg L-1) and BaP (0-120 mg L-1). A similar trend was observed for the emulsifying activity of the EPS extracts. EPSs extracted from all cultures exhibited a compact structure with a smooth surface, except for EPSs extracted from BaP-grown M.g. SN12, which revealed a more fragile and softer surface. These findings suggest that Pyr and BaP had different influences on the properties of isolated EPSs, providing insights into the mechanism underlying polycyclic aromatic hydrocarbons (PAHs) biodegradation by some EPS-secreting bacteria. To the best of our knowledge, this is the first report on the texture profile of EPS samples extracted from M.g. SN12 grown on PAHs.

Dark septate endophytes (DSE): potential bioremedial promoters of oil derivatives.

Oil spills are a global environmental problem. One of the management tools used to solve this problem is phytoremediation, a process that uses the capacity of plants and microorganisms to metabolize the components of the oil. The aims of the present study were to isolate, identify and characterize the fungi obtained from plants growing in an oil-contaminated area and evaluate their growth response and emulsifying and degrading capacity in two petroleum derivatives (kerosene and lube oil). Four dark septate endophytes (DSE) strains were isolated and identified: Exserohilum pedicellatum, Ophiosphaerella sp., and two Alternaria alternata strains. E. pedicellatum was found in an oil-contaminated environment for the first time. All strains were grown in kerosene, although some showed inhibition, whereas in lube oil, all showed growth induction. Ophiosphaerella sp. showed "drops" in kerosene, but the four strains showed surfactant capacity in lube oil. Ophiosphaerella sp. showed the highest emulsifying activity index but both A. alternata strains presented the highest lube oil degradation, which was directly related to the weight of the fungal biomass. There was not relationship between emulsifying capacity and oil degradation. However, these fungi show technological potential for application in phytoremediation processes.

Ultrasound-assisted alkaline proteinase extraction enhances the yield of pecan protein and modifies its functional properties.

To enhance the extraction yield of pecan protein and modify its functional properties, this study investigated whether both ultrasound and enzyme have a synergistic impact on the extraction of pecan (Carya illinoinensis (Wangenh.) K. Koch) protein. The highest protein extraction rate (25.51%) was obtained under the conditions of 1415.43 W.cm-2, 15 min, pH 10.0, 50 °C, and 1% (w/w) alkaline proteinase. Owing to its high shear, mechanical energy and cavitation, the ultrasound process increased the solubility of the substrate making it readily accessible to the enzyme, thereby accelerating the chemical reaction and improving the yield of the protein. The optimized ultrasound-assisted enzymatic method (400 W, 20 kHz, 5 s/3s) effectively changed the secondary and tertiary structure of the pecan protein. The results of surface hydrophobicity, intrinsic fluorescence spectra, sulfhydryl content and scanning electron microscopy all indicated the unfolding of protein and exposure of hydrophobic groups and sulfhydryl groups. Moreover, the protein obtained by this method showed higher solubility (70.77%), higher emulsifying activity (120.56 m2/g), smaller particle size (326.7 nm), and better dispersion (0.305) than single ultrasound and non-ultrasound methods (p < 0.05). To conclude, ultrasound-assisted enzymatic method could be an appropriate technique to improve the yield and quality of the pecan protein. The study also provides a theoretical basis for the application of pecan protein in food processing.

Design and validation of an expeditious analytical method to quantify the emulsifying activity during biosurfactants/bioemulsifiers production.

Biosurfactants (BS) and bioemulsifiers (BE) are amphiphilic molecules that are produced by a wide range of microorganisms. Although the chemical composition of BS and BE is different, both BS/BE have recognized emulsifying properties, which are the focus of this study. Herein, a rapid and simple analytical method to quantify the emulsifying activity (EA) of a product produced by the actinomycete Gordonia alkanivorans strain 1B (BS/BE), which exhibits emulsifying properties, was developed. The analytical approach was based on the ability of a BS/BE solution to form a stable emulsion when mixed with n-heptane. So, using 4 mL screw cap glass tubes (10 × 75 mm, ND10 caps with PTFE septum), the EA was assessed by adding 1 mL of n-heptane to 1 mL of an aqueous solution containing the test product, mix by vortexing at high speed (2 min) and place the tube in an upright stable position for 10 min before analyzing. A set of emulsification tests with increasing volumes of test product solutions was carried out until 100% emulsion was obtained in the organic phase. One emulsification unit was defined as the minimum volume of product (Volmin of emulsifier/surfactant, up to 1 mL) needed to form and maintain 100% emulsion in the organic phase. The corresponding emulsifying activity value is presented in U/mL, and it is calculated as: EA (product) = 1 U/Volmin (mL). Further validation by testing several synthetic surfactants and industrial/domestic dishwashing detergents, in parallel with the bacterial crude BS/BE, towards emulsifying activity determination (U/mL) was performed demonstrating the wide range of the method applicability. Moreover, the specific emulsifying activity for each product tested was estimated though correlation analysis (linear regression) between volumetric emulsifying activity (U/mL) and product concentration (g/L). Indeed, this new analytical approach to quantify the emulsifying activity is accurate and reproducible, and consequently it can be a promising tool to apply in screening/monitorization studies on BS/BE production enabling reliable comparisons.

Enhanced production of mono-rhamnolipid in Pseudomonas aeruginosa and application potential in agriculture and petroleum industry.

Differences in the rhamnolipid structures must result in its different activities, thus affecting its application effect. The rhlC gene in Pseudomonas aeruginosa SG was knocked out to construct strain P. aeruginosa SGΔrhlC. Rhamnolipid production was enhanced by 23.3% through knocking out rhlC gene. P. aeruginosa SGΔrhlC produced 14.22 g/L of rhamnolipid using glycerol and nitrate. Five kinds of mono-rhamnolipid but no di-rhamnolipid were produced by strain SGΔrhlC. The main rhamnolipid homologues were Rha-C10-C10, Rha-C10-C12:1 and Rha-C10-C12. Mono-rhamnolipid exhibited better antimicrobial activity to Escherichia coli, Staphylococcus aureus, Aspergillus niger and Penicillium chrysogenum. Rhamnolipid produced from strain SGΔrhlC showed greater emulsifying activity to crude oil with EI24 of 84.73%. Rhamnolipid produced from strain SGΔrhlC efficiently washed oily sludge at 35 °C. High-producing strain P. aeruginosa SGΔrhlC and its produced mono-rhamnolipid are more promising in agriculture and petroleum industry. This study is a step forward to the tailor-made biosynthesis and application of rhamnolipid.