Presence Of Rhamnolipid Research Articles

Biosurfactant-mediated transport of tetracycline antibiotics in saturated porous media: Combined effects of the chemical properties of contaminants and solution chemistry conditions

The mobility of tetracycline antibiotics (TCs) in saturated aquifers is possibly affected by the presence of biosurfactants, which are widespread in the aquatic/soil environments. This study investigated the mobility characteristics of various tetracyclines—specifically tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC)—within quartz sand columns in the presence of rhamnolipid, a common biosurfactant. Exogenous rhamnolipid significantly inhibited the transport of the three TCs over the pH range of 5.0–9.0 (e.g., the mass of retained TC, OTC, and CTC increased from 32.6 %, 26.9 %, and 39.2 % (in the absence rhamnolipid) to 39.4 %, 38.9 %, and 51.7 % (in the presence of rhamnolipid), respectively). This observation could be attributed to the bridging effects of this biosurfactant. Specifically, the hydrophilic head of rhamnolipid molecules is likely associated with the surfaces of sand grains through surface complexation and/or hydrogen bonding interactions. Accordingly, the hydrophobic moieties of the deposited rhamnolipid molecules (i.e., the aliphatic chains) interact with the hydrophobic groups of TCs molecules via hydrophobic interactions. Interestingly, the extent of the inhibitory effect on CTC mobility was greater than that on OTC and TC, which was related to the different hydrophobic characteristics of the three antibiotics. Furthermore, the inhibitory effect of rhamnolipid on the transport of TCs diminished as the pH of the background solution increased. This observation was attributed to the weakened bridging effects, resulting from the reduced deposition of the biosurfactant on the sand surfaces. Additionally, the cation-bridging mechanism involved in the retention of TCs in the addition of rhamnolipid when the background electrolyte was Ca2+ (i.e., Ca2+ ions served as bridging agents between the deposited rhamnolipid molecules and TCs). The insightful findings enhance our understanding of the critical roles of biosurfactants in influencing the environmental dynamics and ultimate fate of conventional antibiotic pollutants within groundwater systems.

Effect of biosurfactants on the transport of polyethylene microplastics in saturated porous media

Microplastic (MP) pollution has become a significant global environmental issue, and the potential application of biosurfactants in soil remediation has attracted considerable attention. However, the effects of biosurfactants on the transport and environmental risks of MPs are not fully understood. This study investigated the transport of polyethylene (PE) in the presence of two types of biosurfactants: typical anionic biosurfactant (rhamnolipids) and non-ionic biosurfactant (sophorolipids) using column experiments. We explored the potential mechanisms involving PE surface roughness and the influence of dissolved organic matter (DOM) on PE transport in the column under the action of biosurfactants, utilizing the Wenzel equation and fluorescence analysis. The results revealed that both the concentration of biosurfactants and the surface roughness of PE were advantageous for the adhesion of biosurfactants to the PE surface, thereby enhancing the mobility of PE in the column. The proportion of hydrophobic substances in various DOM sources is a critical factor that enhances PE transport in the column. However, the biosurfactant-mediated enhancement of PE transport was inhibited by the biosurfactant-DOM mixture. This was mainly due to DOM occupying the adhesion sites of biosurfactants on PE surfaces. Moreover, the mobility of PE in the presence of sophorolipids is higher than that in the presence of rhamnolipids because the combined hydrophobic and electrostatic forces between PE and sophorolipids create synergistic effects that improve PE stability. Additionally, the mobility of PE increased with rising pH and decreasing ionic strength. These findings provide a more comprehensive understanding of MP transport when using biosurfactants for soil remediation.

Insight into the inhibitory mechanism of rhamnolipid biosurfactant on the mobility of sulfonamide antibiotics in saturated soil porous media

The mobility and deposition of sulfonamide antibiotics (SAs) in soil porous media may be impacted by the presence of rhamnolipid (a typical biosurfactant), which is ubiquitous in the natural environment. Herein, the transport characteristics of various SAs, such as sulfamerazine (SMZ), sulfamethazine (SMT), and sulfanilamide (SNM) in soil columns with rhamnolipid, were explored. The mobility of SAs in the soil columns was in the sequence of SNM > SMT > SMZ. The observation was mainly due to the differences in the hydrophobic properties of various antibiotics. Interestingly, rhamnolipid inhibited the mobility of the three SAs over a broad solution pH range (5.0–9.0) primarily because of the interactions between the hydrophobic groups of the deposited rhamnolipid on the soil surfaces and parts of SAs molecules (i.e., rhamnolipid acted as a bridging agent between soil and antibiotic). Furthermore, at a given rhamnolipid concentration, the inhibitory effect of rhamnolipid on SMZ transport was the greatest among the three antibiotics due to SMZ’s greatest hydrophobicity. Additionally, the transport-inhibition influence of rhamnolipid declined as the solution pH values rose. This phenomenon was attributed to the decline of the bridge effects induced by the decreased adsorbed rhamnolipid on soil surfaces. Innovative findings from this study provide helpful information regarding the contribution of biosurfactants on the environmental behaviors of these ubiquitous antibiotic contaminants in soil-water systems.

Isolation and Characterization of Biosurfactant-Producing Soil Fungus Penicillium sp.

In this study, a fungal species was isolated from rhizospheric soil and identified as Penicillium sp. by ITS sequencing. The Penicillium sp. has been screened for the biosurfactant production, viz., haemolytic activity, oil spreading assay and emulsification index. The biosurfactant from cell-free supernatant was extracted using acid precipitation followed by solvent-solvent extraction. The physiochemical properties of the extracted biosurfactant were analysed using FTIR; the major peaks that show at 1720 cm-1, 1531 cm-1, 1419 cm-1, 1251 cm-1 and 1010 cm-1 correspond to aliphatic chains, sugars and ester carbonyl groups. The fatty acids present in the extracted biosurfactant were analysed using GCMS, in which a molecular mass of 256 and 284 m/z showed the presence of n-hexadecenoic acid and octadecanoic acid respectively which indicate the presence of rhamnolipid, which is a major biosurfactant. The biosurfactant extracted from Penicllium sp. demonstrated antibacterial activity against Escherichia coli and Staphylococcus aureus. In future perspectives, the biosurfactant extracted from the isolated species holds great potential as a broad-spectrum antibacterial agent and could be utilized in various healthcare applications.

Effects of Natural Rhamnolipid Mixture on Dioleoylphosphatidylcholine Model Membrane Depending on Method of Preparation and Sterol Content.

Rhamnolipids as biosurfactants have a potentially wide range of applications, for example, as "green" surfactants or components of drug delivery systems, which is associated with the features of their interaction with cell membranes. However, as noted in the literature, those kind of features have not been sufficiently studied now. This paper presents a study of the interaction of a natural mixture of rhamnolipids produced by bacteria of the rhizosphere zone of plants Pseudomonas aeruginosa with model membranes-liposomes based on dioleoylphosphatidylcholine (DOPC), depending on the method of their preparation and the content of sterols-ergosterol, cholesterol, lanosterol. Liposomes with rhamnolipids were prepared by two protocols: with film method from a mixture of DOPC and rhamnolipids; with film method from DOPC and injection of water solution of rhamnolipids. Joint analysis of the data of 31P NMR spectroscopy and ATR-FTIR spectroscopy showed that in the presence of rhamnolipids, the mobility of the head group of the DOPC phospholipid increases, the conformational disorder of the hydrophobic tail increases, and the degree of hydration of the C=O and P=O groups of the phospholipid decreases. It can be assumed that, when prepared from a mixture, rhamnolipids are incorporated into the membrane in the form of clusters and are located closer to the middle of the bilayer; while when prepared by injection, rhamnolipid molecules migrate into the membrane in the form of individual molecules and are located closer to the head part of phospholipids. The sterol composition of the model membrane also affects the interaction of rhamnolipids with the membrane. Here it is worth noting the possible presence of type of interaction between rhamnolipids and ergosterol differ from other investigated sterols, due to which rhamnolipid molecules are embedded in the area where ergosterol is located.

Simultaneous acidic air biofiltration of toluene and styrene mixture in the presence of rhamnolipids: Performance evaluation and neural model analysis

Biotrickling filters (BTFs) supplied with di-rhamnolipids have been proven to improve biodegradability and bioavailability of singly fed hydrophobic volatile organic compounds (VOCs). However, BTFs performance could be significantly impacted for multi-component mixtures. Herein, the performance of lab-scale fungal-BTF was evaluated for the co-treatment of toluene-styrene gas-phase mixture and compared to previous single runs of both VOCs. For equal ratios of the VOCs, the total removal efficiencies (REtotal) ranged from 89.1% to 74% by varying the total inlet loading rates (LRtotal) from 199.1 to 295.2 g m−3 h−1 at empty bed residence times (EBRT) of 90 and 60 s. Both VOCs were efficiently removed (up to RE 90%) at 199.1 g m−3 h−1 inlet LRtotal and 90 s EBRT. Shortening EBRT to 60 s revealed that styrene degradation was kinetic-limited, whereas toluene was less impacted, indicating styrene inhibition and preferential toluene utilization. Increasing toluene:styrene ratio to 2:1 (v./v.) improved styrene biodegradation and mineralization. Neural network model was developed for the binary mixture which highlighted the interaction effects between input and output variables. The model provided high predictive accuracy (R2-0.993) and revealed significant information towards improving future BTFs design.

Precipitation of calcium carbonate in the presence of rhamnolipids in alginate hydrogels as a model of biomineralization

This paper reports the effects of rhamnolipids presence in the alginate hydrogel and CO32- solution, on the precipitation of CaCO3 in the Ca2+ loaded alginate hydrogel. Characteristics of the formed particles are discussed. Model conditions containing alginate hydrogel and rhamnolipids were used in order to mimic the natural environment of biomineralization in biofilms. It has been shown that rhamnolipids affect the characteristics of precipitated calcium carbonate effect of using these biosurfactants depends on their concentration as well as whether they are directly present in the hydrogel matrix or the carbonate solution surrounding the hydrogel. The greatest effect compared to the control samples was found for the rhamnolipids in the form of micelles directly present in the hydrogel with the CaCl2 cross-linked solution at concentration of 0.05 M. These conditions result in the highest increase in vaterite content, specific surface area, and pore volume. The mechanism of CaCO3 precipitation in alginate hydrogel containing rhamnolipids has been proposed.

Performance evaluation of fungal biotrickling filter for styrene destruction: Experimental and artificial neural networks modeling

Removal of styrene vapors was investigated using a fungi-cultured biotrickling filter (BTF) in the presence of rhamnolipid. Evaluations at empty bed residence times (EBRTs) of 90, 60, and 30 s and inlet loading rates (LRs) ranging from 25.5 to 186.1 g m−3 h−1 were conducted. The maximum elimination capacity (EC) of 173.7 g m−3 h−1 was obtained at an inlet LR of 186.1 g m−3 h−1 at 90 s EBRT. Reducing the EBRT to 60 and 30 s resulted in decline of removal efficiency (RE). The performance of BTF was modeled using artificial neural network (ANN) to predict styrene RE using measurable inputs, inlet LR, EBRT, and pressure drop. The model performance was assessed by mean square error and overall coefficient of correlation. The influence of different input parameters on the output was analyzed using casual index. Styrene removal was positively influenced by the increase in EBRTs, negatively impacted by its inlet LRs, while pressure drop had a negligible effect. The BTF was then exposed to intermittent loading phases by varying operational conditions during the non-loading periods. The results from this study confirmed that rhamnolipids could enhance the BTF performance for handling transient load variations at unsteady-state conditions.

Effects of Piper betle Leaf Extract on Biofilm and Rhamnolipid Formation of Pseudomonas aeruginosa

High mortality rate and antimicrobial resistance are still becoming world-wide problems, due to Pseudomonas aeruginosa’s (P. aeruginosa) virulence and its ability to form biofilm. Biofilm’s formation is affected by the presence of rhamnolipid, whose production is regulated by quorum sensing systems. Piper betle (P. betle) possesses antimicrobial, antioxidant, anti-inflammatory and immunomodulatory properties. The aim of our study is to investigate the effects of P. betle leaf’s extract against biofilm formation and rhamnolipid production of P. aeruginosa. Active compounds of P. betle were identified using plate chromatography. Agar dilution method was used to determine the minimum biofilm inhibitory concentration (MBIC) of methanolic leaf extract of P. betle. A biofilm-producing P. aeruginosa isolate in the polystyrene plate adherence test was selected for confirmation of biofilm production by Scanning Electron Microscopy (SEM), after P. betle administration. Rhamnolipid detection and evaluation were performed by interpreting halo formed around the well. After administration of various concentrations of P. betle leaf extract on the microplate well, it was concluded that the MBIC of P. betle leaf extract on P. aeruginosa was 0.4%. Methanolic extract of P. betle leaf extract at concentration of 0.4% showed that P. aeruginosa could not form biofilm at all, although the bacteria could still aggregate and form a matrix. After linear regression analysis, beta-coefficient was obtained at -0.931 for P. betle leaf extract. It can be concluded that P. betle leaf extract was effective in inhibiting the growth of biofilm and formation of rhamnolipid by P. aeruginosa. The increase in concentration of P. betle leaf extract was inversely proportional to the diameter of the halo rhamnolipid formed. The higher the level of P. betel leaf extract, the smaller the diameter of the halo rhamnolipid formed.

Silver nanoparticles stabilized by ramnolipids: Effect of pH

Rhamnolipids are glycolipid biosurfactants that have remarkable physicochemical characteristics, such as the capacity for self-assembly, which makes these biomolecules a promising option for application in nanobiotechnology. Rhamnolipids produced from a low-cost carbon source (glycerol) were used to stabilize silver nanoparticles. Silver nanoparticles (AgNPs) have been the subject of studies due to their physical chemical as well as biological properties, which corroborate their catalytic and antimicrobial activity. We compared nanoparticles obtained with three different pH values during synthesis (5, 7 and 9) in the presence of rhamnolipids. Dynamic light scattering showed that larger particles were formed at pH 5 (78–190 nm) compared to pH 7 (6.5–43 nm) and 9 (5.6–28.1 nm). Moreover, nanoparticle stability (analyzed based on the zeta potential) was enhanced with the increase in pH from 5 to 9 (−29.86 ± 1.04, −37.83 ± 0.90 and −40.33 ± 0.57 mV, respectively). Field emission gun scanning electron microscopy confirmed the round morphology of the silver nanoparticles. The LSPR spectra of AgNP for the pHs studied are conserved. In conclusion, different pH values in the presence of rhamnolipids used in the synthesis of silver nanoparticles directly affect nanoparticle size and stability.

Rhamnolipid pretreatment enhances methane production from two-phase anaerobic digestion of waste activated sludge

In this work, a rhamnolipid (RL) pretreatment technology was proposed to promote methane production from two-phase anaerobic digestion of waste activated sludge. In the first phase (i.e., acidogenic phase), the WAS hydrolysis and acidogenesis were significantly enhanced after RL pretreatment for 4 day, under which the concentration of soluble protein and the short-chain fatty acids (SCFA) in the presence of RL at 0.04 g/g TSS was respectively 2.50 and 5.02 times higher than that without RL pretreatment. However, methane production was inhibited in the presence of RL. In the second phase (i.e., methanogenic phase), batch biochemical methane potential tests suggested that the addition of RL is effective in promoting anaerobic methane production. With an increase of RL dosage from 0 to 0.04 g/g TSS, the cumulative methane yield increased from 100.42 ± 3.01 to 168.90 ± 5.42 mL. Although the added RL could be utilized to produce methane, it was not the major contributor to the enhancement of methane yield. Further analysis revealed that total cumulative yield from the entire two-phase anaerobic digestion (sum of the yield of the acidogenic phase and methanogenic phase) increased from 113.42 ± 3.56 to 164.18 ± 5.20 mL when RL dosage increased from 0 to 0.03 g/g TSS, indicating that the addition of RL induced positive effect on the methane production of the entire two-phase anaerobic digestion. The enzyme activity analysis showed that although higher dosages of RL still inhibited the microorganisms related to methanogenesis to some extends in the methanogenic phase, the inhibitory effect was significantly weakened compared to the acidogenic phase. Microbial analysis revealed that RL reduced the abundance of Candidatus_Methanofastidiosum sp. while increased the abundance of Methanosaeta sp., causing the major methanogenesis pathway to change from hydrogenotrophic to aceticlastic. Moreover, the community of hydrolytic microbes and acidogens was shifted in the direction that is conducive to hydrolysis-acidogenesis. The findings reported not only expand the application field of RL, but also may provide supports for sustainable operation of wastewater treatment plants (WWTPs).

Application of a novel process using biosurfactant rhamnolipid to reduce bioclogging in quartz sand during artificial recharge

Bioclogging can significantly reduce the permeability of porous media, restricting the application of artificial recharge. In this study, the quantitative efficiency and mechanism by which rhamnolipid (RL) biosurfactant prevents bioclogging during artificial recharge were investigated in both batch-reactor and column systems. The batch experiments indicated that the adsorption of bacteria onto quartz sand surface was significantly reduced in the presence of RL. The adsorption isotherm data were well fitted to the Freundlich model. The Freundlich sorption affinities (Kf) of bacteria in the presence of 0, 20, 40, and 80 mg/L RL were 3.20, 1.55, 0.79, and 1.21, respectively. In the microplate biofilm experiments, the addition of 40 mg/L of RL (40 RL) reduced the total biomass to 17.4%. The percolation sand column experiments demonstrated the efficacy of RL alleviating bioclogging. More time was taken (18 h) for the 40 RL group to achieve a relative hydraulic conductivity (K′) of 0.20 compared with the group without the addition of RL (0 RL) (12 h). Meanwhile, the accumulation of bacterial cells and the production of extracellular polymeric substances (EPS), which are the main contributors to bioclogging, were lower in groups with RL than in those without RL. The optimal concentration of RL is 40 mg/L. The decreasing degree of K′ in different experimental groups was linearly correlated with RL-dependent cell surface hydrophobicity (CSH). The results of both batch and column experiments indicate that the RL reduced the adsorption capacity of bacteria onto the surface of porous media by modifying the hydrophobicity of the bacteria, reducing bioclogging in artificial recharging. This study therefore provides insights and guidances for reducing bioclogging, thereby enhancing the efficiency of artificial recharge.

Enhanced biodegradation of 17α-ethinylestradiol by rhamnolipids in sediment/water systems

Environmental context The steroid hormone 17α-ethinylestradiol (EE2) has been established as a highly estrogenic substance, which potentially causes serious harm to environmental health. Rhamnolipids are a widely researched glycolipid used for the degradation of organic pollutants. Therefore, this study focused on the change of biodegradation of EE2 affected by rhamnolipids in sediment/water systems, showing increased and more rapid degradation. Abstract Rhamnolipids can enhance the remediation of hydrophobic organic pollutants in the environment. However, the rhamnolipid-associated biodegradation of hormones has rarely been investigated. In this study, aerobic biodegradation shake-flask experiments were conducted to investigate biosurfactant-associated biodegradation of 17α-ethinylestradiol (EE2) in sediment/water systems and to assess how the biodegradation rate is influenced by rhamnolipids produced by Pseudomonas aeruginosa MIG-N146. Results showed that EE2 biodegradability is significantly increased with increasing rhamnolipid concentration. An improved pseudo-first-order kinetic equation was established to simulate enhanced EE2 biodegradation at varying rhamnolipid concentrations. The biodegradation rate (k) initially increased marginally, and then increased rapidly with rhamnolipid concentrations exceeding the effective critical micelle concentration. The degree of enhancement of organic biodegradation was mainly affected by organic mass transfer, owing to rhamnolipidic micellar solubilisation, and by rhamnolipids acting as a primary substrate to stimulate the microbial consortium. Analysis results through various techniques indicated the formation of three main types of metabolic intermediates, with diverse polarity and biodegradability characteristics, in the process of EE2 biodegradation. Thus, it was concluded that the presence of rhamnolipids did not negatively affect the processes of EE2 biotransformation by indigenous microorganisms in the original sediment/water systems. This study presents an effective potential application of rhamnolipidic surfactants for enhancement of EE2 biodegradation in sediment/water systems.

Rhamnolipid-assisted mycoremediation of polycyclic aromatic hydrocarbons by Trametes hirsuta coupled with enhanced ligninolytic enzyme production

ABSTRACT The present study deals with the development of a wood assisted fungal system (WAFS) from wood chips using Trametes hirsuta to remove polycyclic aromatic hydrocarbons (PAHs) in BRW. The WAFS exhibited a 1.4-fold higher ligninolytic enzyme production than free fungi in the effluent. Further, to understand PAHs bioremediation by T. hirsuta, biodegradation along with biosorption were studied in model PAHs, phenanthrene (Phe) and benzo (a) pyrene (BaP), in the presence of synthesized rhamnolipids. The WAFS mineralized up to an average of 91.26% Phe and 87.72 % BaP along with biosorption of 12.35% Phe and 18.36 % BaP within 12 days. Thus, the addition of rhamnolipids showed 1.2-fold enhanced biodegradation. However, rhamnolipid concentrations beyond 50 ppm reduced the degradation efficiency of WAFS. Moreover, the degradation capability of total aromatic hydrocarbon (TAH) in biorefinery wastewater by WAFS is 1.8-fold higher than that of free fungi, which confirms the effectiveness of the system. Implications: Simultaneous application of white-rot fungus along with surfactant into a pollutant environment affects the microenvironment of the fungus and reduces the production of their degradative enzymes. In addition, the requirement of periodical supplement of external nutrient in the real-time matrix for the growth of white rot fungi may trigger competitive growth of indigenous microorganisms. Considering this glitch, the current work utilizes the carpenter waste for the strategical develop a wood assisted fungal system to protect the microenvironment of the fungi in the presence of rhamnolipids and contribute to their survival in real time matrix, with enhanced PAHs degradation efficiency.

The degradation of bisphenol A by laccase: Effect of biosurfactant addition on the reaction kinetics under various conditions

In this study, the enzymatic remediation of bisphenol A (BPA) from synthetic wastewater samples by laccase has been investigated in the presence (and also in the absence) of rhamnolipid (RL) biosurfactant. Different BPA, laccase and RL concentrations (spanning from 0.5 ppm to 2 CMC) have been utilized. Additionally, the kinetics and the extent of BPA removal at different temperatures, pH values and salinity levels have been examined in the presence and the absence of RL. The obtained results showed that the optimum concentration of RL is 1 ppm. At this RL concentration, about 23% increase in the BPA removal extent (after 2 h of treatment) was achieved. Additionally, the rate of BPA removal has been also boosted in the presence of RL. It has been observed that the addition of the biosurfactant improved, yet to varied degrees, both the extent and the kinetics of BPA removal under all examined conditions. Furthermore, the addition of RL did not alter the optimal reaction temperature (50 °C) and pH (5.8) of the BPA-laccase system. RL addition was still beneficial even under a high salinity level (29.22 g/L NaCl). The findings reported in this study suggest the potential application of RL as an eco-friendly and effective additive to enhance the rate and the extent of enzymatic treatment of phenolic wastewaters.

Experimental study on drag coefficient of a rising bubble in the presence of rhamnolipid as a biosurfactant

Industrial processes do not often deal with a pure fluid. Impurities can affect physical properties of gas-liquid systems, resulting in change of gas bubbles velocity. Purpose of the study was to determine drag coefficient of a bubble rising through a contaminated fluid. As well as, a comparison was done between conditions of a free rising bubble and a rising bubble in wall-bounded flow. Thus, the behavior of a single air bubble rises in aqueous rhamnolipid solutions within two columns with different dimensions was studied experimentally. The experiments were conducted at high Reynolds numbers compared to other researches. The results revealed that effect of the surfactant in wall-bounded flow was much less than free flow whereas bubble terminal velocity was close to the one in a pure fluid and independent of concentration. Moreover, terminal velocity of the free rising bubble decreased as the solution concentration increased for the one less than critical micelle concentration. After that, it kept constant. Furthermore, resulted drag coefficient did not change significantly in different biosurfactant concentrations. The results showed that in high Reynolds number, drag coefficient was a function of Eötvös number and independent of Reynolds and Morton numbers. Consequently, two empirical correlations were presented to predict the terminal velocity and drag coefficient based on surface tension and Eötvös number, respectively.

Removal of Heavy Metals Using Rhamnolipid Biosurfactant on Manganese Nodules

The objective of this study is to identify the feasibility of using rhamnolipid biosurfactant to remediate heavy metals contained in manganese nodules collected from the Clarion-Clipperton Fracture Zone, Pacific Ocean. Deep-sea manganese nodules may represent one of the most important future natural resources for heavy metals due to the depletion of resources on land. Since international marine environment guidelines for deep-sea mining will be set up by international organisations in the 2020s, remediation technologies are urgently required for deep-sea mining tailings. We show that rhamnolipid biosurfactant is an environmentally friendly substance and can be successfully used for the remediation of heavy metals in deep-sea mining tailings under various reaction conditions. Rhamnolipids therefore represent a useful extracting agent for heavy metals in deep-sea mining tailings. The removal of nickel (Ni), copper (Cu), and cadmium (Cd) would be enhanced in the presence of rhamnolipids with specific reaction times and concentrations. Future actual remediation technologies should be developed using rhamnolipid biosurfactant on the basis of these results.

Shift of Soil Polycyclic Aromatic Hydrocarbons (PAHs) Dissipation Pattern and Microbial Community Composition due to Rhamnolipid Supplementation

Biosurfactants are promising substitutes for chemical surfactants during polycyclic aromatic hydrocarbon (PAH) bioremediation. However, recent studies have revealed contrasting findings and critical knowledge gaps regarding the impacts of biosurfactants on the soil PAH biodegradation efficiency and microbial community. Here, a laboratory study was conducted to evaluate the impact of rhamnolipid on the PAH dissipation efficiency and microbial community structure during the time-course incubation. The data showed that the contribution ratio of biotic loss and abiotic loss depended on the ring number of PAH. In the microcosms supplemented with 20 μg g−1 rhamnolipid, the biodegradation efficiencies of phenanthrene, fluoranthene, and pyrene increased by 10.1%, 12.3%, and 22.0%, respectively, compared to those in the rhamnolipid-free treatment after incubation for 7 days. In contrast, rhamnolipid either had no impact on or inhibited PAH degradation in the later time points (21–35 days). The abundance of bacterial 16S rRNA and phnAc genes showed significant increase in soil amended of both PAH and rhamnolipid. MiSeq sequencing results revealed that potential PAHs-degrading Massilia, Bacillus, Lysobacter, Archrobacter, and Phenylobacterium became dominant genera in PAH treatment, irrespective of the rhamnolipid added. Nevertheless, PAH addition in the presence of rhamnolipid also significantly stimulated the growth of Delftia, Brevundimonas, Tumebacillus, and Geobacillus. In contrast, the rhamnolipid altered the microbial community composition through the selection of Gaiella, Solirubrobacter, Nocardioides, and Bacillus. The results reveal the intensive selectivity effect of PAH and rhamnolipid on the soil microbes that are involved in bioremediation, and highlight the positive effect on PAHs biodegradation.

Enhanced biodegradation of n-hexane from the air stream using rhamnolipid in a biofilter packed with a mixture of compost, scoria, sugar beet pulp and poplar tree skin

Biofiltration of n-hexane vapors with and without using rhamnolipid biosurfactant was investigated on a laboratory scale biofilter packed with compost, scoria, sugar beet pulp, and poplar tree skin at empty bed residence times (EBRT) of 30, 60 and 120s for a period of 131 days. Acclimation of microorganism in the biofilter was achieved in 31 days with an average n-hexane concentration of 0.269 gm −3 and EBRTs of 120s. The results demonstrated that average removal efficiencies (RE) for the corresponding EBRT with n-hexane loading rates (IL) of 6.7–137 gm −3 h −1 were 18.7 ± 1.67%, 28.9 ± 4.06% and 46.8 ± 8.2% without biosurfactant. While, the average REs in presence of the biosurfactant were 23.98 ± 4.08%, 42.4 ± 9.7% and 85.13 ± 10.44% at EBRTs of 30, 60 and 120s, respectively. About 53% of n-hexane removal was related to the segment 1 of the biofilter, where the bacterial and fungi population of its biofilm was 2 × 10 15 and 1.3 × 10 9 CFU g −1 (dry weight), respectively, which was significantly more than the other segments. For all the tested inlet concentrations, the RE was significantly increased by increasing EBRT and decreasing IL of n-hexane. The results of this study confirm the efficiency enhancement of rhamnolipid in biofiltration of hydrophobic compounds such as n-hexane from air streams. • Biofiltration of n-hexane vapors was investigated in the presence and absence of rhamnolipid biosurfactant. • Removal efficiency of n-hexane increased from 46 to 86% in the presence of rhamnolipid. • About 53% of n-hexane removal was related to the segment 1 of the biofilter. • Increasing the biofiltration of hydrophilic compounds by rhamnolipid.

Multidimensional Toxicity of Rhamnolipid Extracts Obtained From Creosote‐Contaminated Soil

In this study, a comprehensive research on the toxicity of rhamnolipids and their influence on the toxicity of water extracts obtained from creosote‐contaminated soil is performed. The obtained extracts contain organic compounds from the studied soil, which are eluted by pure water as well as solutions of rhamnolipids at different concentrations (ranging from 150 to 1500 mg L−1 where 150 mg L−1 corresponds with 1× critical micelle concentration (CMC). GC‐MS analyses allow for classification of the organic compounds into groups representing (i) 2‐ and 3‐ring polycyclic aromatic hydrocarbons (PAHs), (ii) 4‐ and 5‐ring PAHs, (iii) monoaromatic phenols, (iv) N‐heterocyclic compounds, and (v) other organic compounds. The addition of rhamnolipids reduces the elution of polar compounds and promoted the elution of hydrophobic compounds from soil (the elution of polycyclic hydrocarbons increases with increasing concentration of rhamnolipids). Moreover, HPLC‐MS analyses indicates a drop of the concentration of rhamnolipids compared to the initial concentration, suggesting a sorption of rhamnolipids on the soil matrix. Experiments regarding the toxicity toward activated sludge microorganisms (dehydrogenase activity assay), phytotoxicity (Phytotestkits), mutagenicity (Ames test), and cytotoxicity (MTT test) of extracts with and without rhamnolipids are also conducted. It is found that rhamnolipids increased the toxicity of the extracts toward microorganisms of activated sludge, phytotoxicity, cytotoxicity as well as mutagenicity toward Salmonella typhimurium TA 1537. The increasing toxicity in the presence of rhamnolipids can both be associated with increased bioavailability of toxic organic compounds as well as the toxicity of rhamnolipids.