Presence Of Rhamnolipid Research Articles

Experimental study on hydrate anti-agglomeration in the presence of rhamnolipid.

Gas hydrates might cause a potential safety hazard in subsea flow assurance. Anti-agglomeration is a promising approach to keep subsea oil and gas pipelines free from hydrate risks. Effective anti-agglomerants could prevent hydrate agglomeration of small crystallites by lowering the capillary force between hydrate particles. Biosurfactants are widely known for their eco-friendly nature. In this work, n-octane, water and methane were used as hydrate-forming ingredients to examine the effectiveness of rhamnolipid. Our investigation was carried out at constant high pressure (10 MPa) with different water cuts, subcooling degrees and rhamnolipid mass fractions. Three agglomeration states of hydrate were observed in a high-pressure visual autoclave apparatus. Torque measurements showed that rhamnolipid could effectively prevent hydrate agglomeration with a concentration of 0.5 wt%. In addition, the structural characteristics and morphology of hydrate were observed by use of powder X-ray diffraction, Raman spectroscopy and cryo-scanning electron microscopy. We noticed that the introduction of rhamnolipid had no effect on hydrate structure, but it could increase the large and small cavity ratio value and hydration number. Through the microscopic images, we inferred that rhamnolipid could make the surface of hydrate smooth, which resulted in a more ordered surface.

Rhamnolipid-enhanced Pseudomonas putida biofilm formation on hydrophilic surfaces with toluene as the bacterium's sole carbon source

The effect of surfactants on biofilm formation depends on the surfactant type, the bacterial strain and the carrier. In order to enhance the bioremediation process in the presence of a biosurfactant, it is crucial to choose the appropriate bacterial strain and carrier for biofilm formation. In the current research, a linear correlation was observed between toluene degradation by a planktonic Pseudomonas putida culture and increasing rhamnolipid concentrations. Biofilm viability on the hydrophilic surface after 24 h was 0.3 ± 0.007 (OD 540 nm), 1.4 fold higher than on the hydrophobic surface. The hydrophobicity of the bacterial cell wall for cultures that were grown on toluene in the presence and in the absence of rhamnolipid was determined by the contact angle of water measurement on the bacterial layer as well as by the bacterial adherence to a solution of hydrocarbon (BATH test). The results showed that the bacterial cell wall surface in the presence and absence of rhamnolipid is highly hydrophilic. The viability of the biofilm which was grown on hydrophilic surfaces: treated ELISA plate and coal bottom ash was 7-fold and 13-fold higher, respectively, when the cultures were grown on toluene in the presence of rhamnolipid as compared with its absence. In conclusion, the combination of hydrophilic surfaces, rhamnolipid and P. putida may serve as a good choice for enhancing the bioremediation process of toluene.

Analysis of functional genomes from metagenomes: Revealing the accelerated electron transfer in microbial fuel cell with rhamnolipid addition

Extracellular electron transfer is the predominant electricity generation process in microbial fuel cells (MFCs). Our pervious study have proved that the anodic adsorption of rhamnolipid resulted in the Frumkin effect, which enhanced anodic microorganism attachment and accelerated anodic electron transfer. In this study, an in-depth research on the influence of rhamnolipid on functional genes of anodic biofilms metagenomes was carried out to explain its mechanism at the gene level. The result showed that the composition and distribution of functional genes in each dominant genus were different. The category of signal transduction mechanisms was the dominant function category in exoelectrogens, and its relative abundance in the metagenome significantly increased from 4.56 to 5.86% from rhamnolipid addition. Additionally, the metabolic pathway and electron flow analysis revealed that electron flows tend to choose direct electron transfer in the presence of rhamnolipids, and resulting in the increase of Coulombic efficiency from 19.10±0.79% to 27.39±1.07%.

Effects of freeze-thawing cycles on desorption behaviors of PAH-contaminated soil in the presence of a biosurfactant: a case study in western Canada.

Many regions in Canada are facing increasing environmental threats posed by oil and gas exploitation and transportation. These contaminated lands are inevitably subjected to seasonal and diurnal freeze-thawing cycles (FTCs). However, knowledge about the effect of FTCs on the behaviours of hydrophobic contaminants during the aging process of soil is limited. This study investigated the desorption characteristics of phenanthrene in aging soils in the presence of the biosurfactant rhamnolipid under diurnal and seasonal FTC treatments. It was found that the presence of rhamnolipid in soil during the aging process was able to increase the desorption efficiency of phenanthrene. In the presence of rhamnolipid above 100 mg L-1, FTCs could inhibit the sequestration of phenanthrene. Soil moisture and rhamnolipid concentration are two major factors affecting this effect. High moisture content and FTC frequency could lead to lower desorption in the early stage of FTCs due to the increased specific surface area. The sequestration of phenanthrene was less effectively hindered under seasonal FTCs than diurnal FTCs. The results from this study have important implications for understanding the role of surfactants in cold-region soil aging, and for the improvement of site remediation strategies of PAH contaminated soil in cold regions.

Interaction of curcumin with 1,2-dioctadecanoyl-sn-glycero-3-phosphocholine liposomes: Intercalation of rhamnolipids enhances membrane fluidity, permeability and stability of drug molecule

Stability of curcumin in neutral and alkaline buffer conditions has been a serious concern for its medicinal applications. We demonstrate that the stability of curucmin can be improved in 1,2-Dioctadecanoyl-sn-glycero-3-phosphocholine (DSPC) liposomes. Curcumin strongly partition into liquid crystalline phase compared to solid gel phase of DSPC liposomes. Variation of fluorescence intensity of curcumin associated with liposomes with temperature successfully determines phase transition temperature of DSPC liposomes. However, at higher molar ratio curcumin can influence phase transition temperature by intercalating into deep hydrophobic layer of liposomes and facilitating fusion of two membrane phases. Rhamnolipids (RLs) are recently being applied for various biomedical applications. Here, we have explored new insight on intercalation of rhamnolipids with DSPC liposomes. Intercalation of rhamnolipids exceptionally increases partition of curcumin into solid gel phase of DSPC liposomes, whereas this increase is moderate in liquid crystalline phase. Fluorescence quenching study establishes that permeability and fluidity of the DSPC liposomes are enhanced in the presence of RLs. Membrane permeability and fluidity can be improved further by increasing the percentage of RLs in DSPC liposomes. The phase transition temperature of DSPC liposomes decreases with increase in percentage of RLs in DSPC liposomes by encouraging fusion between solid gel and liquid crystalline phases. Intercalation of RLs is found to further boost stability of drug, curcumin, in DSPC liposomes. Thus, mixing RLs with DSPC liposomes could potentially serve as a good candidate for drug delivery application.

Effect of rhamnolipid on biodegradation of hydrocarbons in non-aqueous-phase liquid (NAPL)

ABSTRACTAliphatic and aromatic hydrocarbons are environmental pollutants of serious concern. Their bioavailability is the major limiting factor that makes the bioremediation process slow. Therefore, the present study focuses on biodegradation of non-aqueous-phase liquids (NAPL) by a halophilic consortium (Pseudomonas aeruginosa and Escherichia fergusonii) in presence of rhamnolipid as well as a rhamnolipid-producing Pseudomonas aeruginosa AMB AS7. The study was performed in microcosms, and the residual hydrocarbons after degradation were estimated by gas chromatography. It was found that the degradation of hydrocarbons in NAPL was more in presence of rhamnolipid in comparison with their biotic controls. However, among NAPL, the degradation of phenanthrene (37.5%) and octadecane (47.8%) was found to be more by co-culture of halophilic consortium and rhamnolipid-producing P. aeruginosa AMB AS7. Denaturing gradient gel electrophoresis was performed to determine the viability of different bacterial strains (halophilic and rhamnolipid-producing bacterial strain). Besides, the results also revealed that during NAPL degradation, the cell surface hydrophobicity (CSH) of halophilic consortium increased from 9.12% to 69.55% when added with 100 mg/L of rhamnolipid, whereas CSH of rhamnolipid-producing P. aeruginosa AMB AS7 was constant at 31.9%, even though it produced about 271.8 mg/L of rhamnolipid.

Surface and volumetric properties of n-octyl-β-d-glucopyranoside and rhamnolipid mixture

The measurements of surface tension, density and viscosity of aqueous solutions of n-octyl-β-d-glucopyranoside (OGP) and rhamnolipid (RL) were performed at constant concentration of OGP or RL. The measured values of the surface tension were compared to those calculated from the Joos equation as well as to the hypothetical one. The obtained results were analyzed with regard to adsorption at the water-air interface and micellization of OGP in the presence of RL and vice versa. On the basis of this analysis, the Gibbs surface excess concentration of the particular surfactants at the water-air interface, the Gibbs surface free energy of adsorption and micellization, the composition of the surface layer, the apparent and partial molar volumes of OGP and RL were determined. The Gibbs surface free energy of adsorption was calculated on the basis of the critical micelle concentration (CMC) and the surface tension values at this concentration as well as by using the Langmuir equation. The composition of the surface layer was compared to that of hypothetical one. In turn, apparent and partial molar volumes were discussed in the light of the volume of surfactant molecules on the basis of the length and angle of the bonds. From the obtained results it was deduced that there is a strong synergism in the reduction of water surface tension by the OGP and RL mixture as well as in the CMC. The adsorption of RL increases in the presence of OGP but OGP decreases in the presence of RL.

Biosurfactant as a Promoter of Methane Hydrate Formation: Thermodynamic and Kinetic Studies.

Natural gas hydrates (NGHs) are solid non-stoichiometric compounds often regarded as a next generation energy source. Successful commercialization of NGH is curtailed by lack of efficient and safe technology for generation, dissociation, storage and transportation. The present work studied the influence of environment compatible biosurfactant on gas hydrate formation. Biosurfactant was produced by Pseudomonas aeruginosa strain A11 and was characterized as rhamnolipids. Purified rhamnolipids reduced the surface tension of water from 72 mN/m to 36 mN/m with Critical Micelle Concentration (CMC) of 70 mg/l. Use of 1000 ppm rhamnolipids solution in C type silica gel bed system increased methane hydrate formation rate by 42.97% and reduced the induction time of hydrate formation by 22.63% as compared to water saturated C type silica gel. Presence of rhamnolipids also shifted methane hydrate formation temperature to higher values relative to the system without biosurfactant. Results from thermodynamic and kinetic studies suggest that rhamnolipids can be applied as environment friendly methane hydrate promoter.

Optimal production and characterization of alkaline protease from newly isolated halotolerant Jeotgalicoccus sp

Abstract A halotolerant strain UG was newly isolated from saline soil, produces an extracellular alkaline protease. The strain was identified as Jeotgalicoccus sp. on the basis of phylogenetic and phenotypic characteristics. The maximum protease yield (256.4±4.3 U/ml) was attained using optimized medium consists; peptone, K 2 HPO 4 , MgSO 4 ·7H 2 O, CaCl 2 and NaCl; pH 10 at 37 °C within 40 h. The protease secretion was calcium ion dependent and enhanced by CaCl 2 supplementation in the production medium. A protease produced by Jeotgalicoccus sp. was most active at 48 °C and pH 10. The protease was purified by three step purification pattern which resulted in ~39 fold protease purification with a yield of 38%. The molecular weight of purified protease was estimated to be 51 kDa by SDS-PAGE. The protease was inhibited by EDTA, indicating that enzyme belongs to metalloprotease class. Protease showed better activity over a wide range of NaCl (0–1.5 M) and reasonable activity in presence of Ca 2+ , Mg 2+ , K + , Mn 2+ , Cd 2+ and Sn 2+ . Furthermore, the protease was active in the presence of H 2 O 2 and sodium perborate. Also, protease showed the substantial activity in the presence of rhamnolipid and cyclodextrin. The protease from Jeotgalicoccus sp. was suggested as a better bio-additive agent for detergent industry.

Escherichia coli growth and transport in the presence of nanosilver under variable growth conditions

Nanosilver (silver nanoparticles) has the ability to anchor to the bacterial cell membrane and subsequently penetrate it, thereby causing structural changes (i.e. permeability) in the cell membrane and death of the cell. The bacterial responses to the presence of nanosilver usually vary depending on the concentration of nanosilver particles, exposure time and the bacterial physiological stage. Since bacterial anabolism dependents upon a stoichiometric ratio of carbon and inorganic elements (nutrients), the macronutrient ratio, i.e. carbon to nitrogen ratio (C/N) thus plays an important role of bacterial responses to the exposure of nanosilver. This study investigated the responses of Escherichia coli to the exposure of nanosilver under variable growth conditions. It was discovered that E. coli grown under different growth conditions had different responses to the presence of nanosilver. E. coli had least resistance to the toxicity of nanosilver when cultured under carbon-limited conditions. However, the presence of rhamnolipid, a commonly utilized biosurfactant for soil remediation increased the resistance of E. coli to nanosilver. The transport of E. coli cultured under carbon-limited conditions was further studied in silica sand columns. E. coli adsorption in silica sand increased when cultured in the presence of nanosilver. On the contrary, E. coli adsorption in silica sand was significantly reduced when cultured in the presence of rhamnolipid.

Conversion of post consumer polyethylene to the biodegradable polymer polyhydroxyalkanoate

A process for the conversion of post consumer (agricultural) polyethylene (PE) waste to the biodegradable polymer medium chain length polyhydroxyalkanoate (mcl-PHA) is reported here. The thermal treatment of PE in the absence of air (pyrolysis) generated a complex mixture of low molecular weight paraffins with carbon chain lengths from C8 to C32 (PE pyrolysis wax). Several bacterial strains were able to grow and produce PHA from this PE pyrolysis wax. The addition of biosurfactant (rhamnolipids) allowed for greater bacterial growth and PHA accumulation of the tested strains. Some strains were only capable of growth and PHA accumulation in the presence of the biosurfactant. Pseudomonas aeruginosa PAO-1 accumulated the highest level of PHA with almost 25% of the cell dry weight as PHA when supplied with the PE pyrolysis wax in the presence of rhamnolipids. The change of nitrogen source from ammonium chloride to ammonium nitrate resulted in faster bacterial growth and the earlier onset of PHA accumulation. To our knowledge, this is the first report where PE is used as a starting material for production of a biodegradable polymer.

BACTERIAL BIODEGRADATION OF ORGANOCHLORIDE COMPOUNDS

BACTERIAL BIODEGRADATION OF ORGANOCHLORIDE COMPOUNDS. Due to their recalcitrant nature, organochlorides are already found in environment and the search for alternatives to eliminate these compounds such as biodegradation using native microorganisms is of great interest. A screening trial to select environmental bacteria able to degrade DDD, PCP and dieldrin was conducted. Among 14 isolates, the soil bacteria Pseudomonas aeruginosa L2-1 showed the highest tolerance to increasing concentrations of the organochlorides and was selected for further studies. Biodegradation was assessed in liquid medium, varying the concentrations of glucose and the presence of rhamnolipids (RL). The best medium for the occurrence of biodegradation of the compounds contained 0.5% glucose, giving approximately 50% yield after three days of incubation. Results showed that the biodegradation rates of the organochlorides by P. aeruginosa L2-1 were greater at low concentrations of glucose and in the presence of rhamnolipids.

Rhamnolipid surface thermodynamic properties and transport in agricultural soil

Rhamnolipid is a biosurfactant produced by several Pseudomonas species, which can wet hydrophobic soils by lowering the cohesive and/or adhesive surface tension. Because of its biodegradability, rhamnolipid applications bring minimal adverse impact on the soil and groundwater as compared with that of chemical wetting agents. Subsequently, rhamnolipid applications have more advantages when used to improve irrigation in the agricultural soil, especially under draught conditions. In the presence of rhamnolipid, water surface tension dropped linearly with the increase of rhamnolipid concentration until the rhamnolipid critical micelle concentration (CMC) of 30mg/L was reached. Below the CMC, rhamnolipid had linear adsorption isotherms on the soil with a partition coefficient of 0.126L/kg. Rhamnolipid transport breakthrough curves had a broad and diffuse infiltration front, indicating retention of rhamnolipid on the soil increased with time. Rhamnolipid transport was found to be well represented by the advection–dispersion equation based on a local equilibrium assumption. When applied at concentrations above the CMC, the formed rhamnolipid micelles prevented rhamnolipid adsorption (both equilibrium adsorption and kinetic adsorption) in the soil. It was discovered in this research that rhamnolipid surface thermodynamic properties played the key role in controlling rhamnolipid transport. The attractive forces between rhamnolipid molecules contributed to micelle formation and facilitated rhamnolipid transport.

Enhanced Hydrolysis and Acidification of Waste Activated Sludge by Biosurfactant Rhamnolipid

The effect of biosurfactant rhamnolipid (RL) on hydrolysis and acidification of waste activated sludge (WAS) was investigated. The results indicated that RL could greatly reduce the surface tension of sludge, resulting in stimulating the hydrolysis rate of WAS and enhancing the production of short-chain fatty acids (SCFAs). With the increase of RL dosage from 0.2 to 0.5 g/g DS, the maximum soluble chemical oxygen demand (SCOD), protein and carbohydrate concentration increased correspondingly. After 6 h of hydrolysis, SCOD, protein and carbohydrate concentration increased from 371.9, 93.3 and 9.0 mg/l to 3,994.5, 800.0 and 401.4 mg/l at RL 0.3 g/g DS, respectively. Furthermore, the release of NH4 (+)-N, PO4 (3-)-P and the accumulation of SCFAs also improved in the presence of RL. The maximum SCFAs was 1,829.9 mg COD/l at RL 0.3 g/g DS, while it was only 377.7 mg COD/l for the blank test. The propionic acid and acetic acid were the mainly SCFAs produced, accounting for 50-60% of total SCFAs.

Prospects for using native and recombinant rhamnolipid producers for microbially enhanced oil recovery

EOR effects of cell-containing supernatants from cultures of native rhamnolipid producer Pseudomonas aeruginosa PA14, recombinant Escherichia coli carrying genes responsible for rhamnolipid production and P. aeruginosa PDO111 with repressed transcription of rhamnolipid production genes were studied and compared to EOR effects of chemical surfactants in experiments with sandpack columns. The P. aeruginosa PA14 rhlAB genes responsible for production of mono-rhamnolipids were PCR amplified and inserted into pNOT19 plasmid to produce a vector pF1bR4 that was used for transformation of E. coli TG2 to get recombinant strain E. coli pF1bR4. P. aeruginosa PA14, E. coli pF1bR4, and P. aeruginosa PDO111 were grown for 24h at 37°C and centrifuged at 3000rpm for 12min. MALDI-TOF analysis allowed finding previously described rhamnolipids in P. aeruginosa PA14 culture supernatant extract, but not in E. coli pF1bR4 or P. aeruginosa PDO111 extracts. Flooding and incubation tests with sandpack model columns containing two types of oil showed that culture supernatants did have EOR potential. Presence of rhamnolipids and some other biosurfactants including cell surface parts and/or bacterial cells led to enhancement of oil recovery when two different oil production mechanisms, water-flood drive and solution-gas drive, were applied.

The Influence of Rhamnolipids on Aliphatic Fractions of Diesel Oil Biodegradation by Microorganism Combinations

Twelve different bacteria-yeast combinations were tested for determination of their ability to biodegrade diesel oil. The cell surface properties of the bacterial and yeast strains were correlated with the type of carbon source used in the experiments. The highest biodegradation of diesel oil after 7days was obtained for the following combinations: Aeromonas hydrophila MR4-Yarrowia lipolytica EH 56 (87%) and Xantomonas maltophila MRP7-Candida maltosa EH15 (90%). Degradation performances of 10 of 12 combinations were enhanced by the presence of rhamnolipids. The highest increases were observed for A. hydrophila MR4-C. maltosa EH15 (from 34 to 67%), A. hydrophila MR4-C. maltosa EH60 (from 47 to 76%) and for Pseudomonas stutzeri MR7-C. maltosa EH60 (from 29 to 79%). The addition of rhamnolipids to the system reduces the removal time of diesel oil from the contaminated water and changes the microbial adhesion to hydrocarbons. Modification of the cell surface of the tested strain during biodegradation is a very important factor determining the removal of hydrophobic compounds.

Hydrolysis and acidification of waste-activated sludge in the presence of biosurfactant rhamnolipid: effect of pH

In this investigation, the effect of pH (4.0-11.0) on waste-activated sludge (WAS) hydrolysis and acidification in the presence of a biosurfactant rhamnolipid (RL) were studied. The results showed that the hydrolysis and acidification of WAS in the presence of RL at alkaline pH values were more efficient than that at acidic and near-neutral pH values. After 6h of hydrolysis, the soluble protein and carbohydrate were 1,654.7 and 675.9mg/L (pH11.0), and 825.6 and 376.0mg/L (pH7.0), whereas the values were only 315.0 and 84.0mg/L at pH4.0 and 164.1 and 32.0mg/L for the blank, respectively. After 2 or 3days of fermentation, the accumulated short-chain fatty acids (SCFAs) reached the highest and then decreased with a further increase in time at all investigated pH values. The analysis of SCFA compositions showed that acetic, propionic, and iso-valeric acids were the three main products at any pH value. A higher pH contributed to a greater proportion of acetic acid and a lesser proportion of iso-valeric acid; a lower pH resulted in a greater proportion of iso-valeric and lesser proportion of acetic acid in the initial fermentation. The proportions of acetic acid for the system with biosurfactant RL addition were 16.65, 36.33, and 62.94%, respectively, at pH4.0, 7.0, and 11.0 after 1day. Correspondingly, the proportions were 40.34, 12.60, and 11.01% for iso-valeric acid.

The Importance of Rhamnolipid-Biosurfactant-Induced Changes in Bacterial Membrane Lipids of Bacillus subtilis for the Antimicrobial Activity of Thiosulfonates

The antimicrobial properties of methyl (MTS) and ethyl (ETS) esters of thiosulfonic acid alone and in combination with rhamnolipid-biosurfactant (RL) have been characterized for their ability to disrupt the normal physiological functions of living pathogens. Bactericidal and fungicidal activities of MTS and ETS and their combination with rhamnolipid were demonstrated on strains of Pseudomonas aeruginosa, Bacillus subtilis, Alcaligenes faecalis, and Rhizopus ngtricans. It was found that the combination of rhamnolipid and thiosulfonic esters has a synergistic effect leading to decreasing of bactericidal and fungicidal concentrations of MTS and ETS. More extensively was studied the effect of rhamnolipid on the lipid composition of B. subtilis bacterial membrane. To our knowledge, in this article is reported for the first time a remarkable increase of negatively charged phospholipid cardiolipin in the presence of rhamnolipid. The capacity of RL as a surface-active substance was confirmed by scanning electron microscopy (SEM). The occurrence of surface infolds and blebs on B. subtilis shown by SEM, was not accompanied by changes in membrane permeability tested by a live/dead viability staining for fluorescence microscopy. When RL was applied in combination with MTS, a dramatic permeability shift for propidium iodide was observed in vegetative cells.

The In Vitro Rhamnolipid Biosurfactant Reduced Energy Consuming in Biodesulfurization Activity of Genetically Engineered Strain Pseudomonas aeruginosa ATCC9027

Rhamnolipid biosurfactant plays an important role in accelerated bioremediation of hydrocarbon-contaminated sites. In this article, the in vitro effects of rhamnolipid biosurfactant on reduction of energy consumption of biodesulfurization activity were evaluated in recombinant Pseudomonas aeruginosa ATCC9027. The data obtained of these analyses showed that the amount of 2-hydroxybiphenyl production in the presence of rhamnolipid was approximately 150% higher than that produced without rhamnolipid. These analyses demonstrated that the rhamnolipid is a major cause of reduction of energy consumption in biodesulfurization of resting cells. However, the rhamnolipid had no effect in reduction of energy consumption in biodesulfurization of growing cells.

Pseudomonas aeruginosa-derived rhamnolipids subvert the host innate immune response through manipulation of the human beta-defensin-2 expression

Pseudomonas aeruginosa is a well-known cause of infections especially in compromised patients. To neutralize this pathogen, the expression of antimicrobial factors in epithelial cells is crucial. In particular the human beta-defensin hBD-2 is especially active against P. aeruginosa. In this study, we identified rhamnolipids in P. aeruginosa culture supernatants that are able to prevent the pathogen-induced hBD-2 response in keratinocytes. The presence of rhamnolipids within the host cells and inhibition assays suggest that calcium-regulated pathways and protein kinase C activation are impaired by rhamnolipids. In consequence, the induction of hBD-2 in keratinocytes by P. aeruginosa-derived flagellin as well as the host's own hBD-2 mediator interleukin IL-1β is inhibited. Strikingly, rhamnolipids did not affect the release of the proinflammatory mediator interleukin IL-8 by flagellin. Thus, in addition to their function in establishment and persistence of P. aeruginosa infections, rhamnolipids can be engaged by P. aeruginosa for a targeted attenuation of the innate immunity to manage its survival and colonization on compromised epithelia.