Effects of rhamnolipids on cell surface hydrophobicity of PAH degrading bacteria and the biodegradation of phenanthrene

A bibliography study of Shewanella oneidensis biofilm

This study employs a bibliography study method to evaluate 472 papers focused on Shewanella oneidensis biofilms. Biofilms, which are formed when microorganisms adhere to surfaces or interfaces, play a crucial role in various natural, engineered, and medical settings. Within biofilms, microorganisms are enclosed in extracellular polymeric substances (EPS), creating a stable working environment. This characteristic enhances the practicality of biofilm-based systems in natural bioreactors, as they are less susceptible to temperature and pH fluctuations compared to enzyme-based bioprocesses. Shewanella oneidensis, a nonpathogenic bacterium with the ability to transfer electrons, serves as an example of a species isolated from its environment that exhibits extensive biofilm applications. These applications, such as heavy metal removal, offer potential benefits for environmental engineering and human health. This paper presents a comprehensive examination and review of the biology and engineering aspects of Shewanella biofilms, providing valuable insights into their functionality.

Influences of Four Kinds of Surfactants on Biodegradations of Tar-Rich Coal in the Ordos Basin by Bacillus bicheniformis

The biodegradation of tar-rich coal in the Ordos Basin was carried out by Bacillus licheniformis (B. licheniformis) under actions of four kinds of surfactants, namely, a biological surfactant (Rh), a nonionic surfactant (Triton X-100), an anionic surfactant (LAS), and a cationic surfactant (DTAB). The biodegradation rates under the actions of Triton X-100, LAS, Rh, DTAB, and the control group (without surfactant) were 59.8%, 54.3%, 51.6%, 17.3%, and 43.5%, respectively. The biodegradation mechanism was studied by examining the influences of surfactants on coal samples, bacteria, and degradation products in the degradation process. The results demonstrated that Rh, Triton X-100, and LAS could promote bacterial growth, while DTAB had the opposite effect. Four surfactants all increased the cell surface hydrophobicity (CSH) of B. licheniformis, and Triton X-100 demonstrated the most significant promotion of CSH. The order of improvement in microbial cell permeability by surfactants was DTAB > TritonX-100 > LAS > Rh > control group. In the presence of four surfactants, Triton X-100 exhibited the best hydrophilicity improvement for oxidized coal. Overall, among the four surfactants, Triton X-100 ranked first in enhancing the CSH of bacteria and the hydrophilicity of oxidized coal and second in improving microbial cell permeability; thus, Triton X-100 was the most suitable surfactant for promoting B. licheniformis's biodegradation of tar-rich coal. The GC-MS showed that, after the action of Triton X-100, the amount of the identified degradation compounds in the toluene extract of the liquid product decreased by 16 compared to the control group, the amount of dichloromethane extract decreased by 6, and the amount of ethyl acetate extract increased by 6. Simultaneously, the contents of alkanes in the extracts of toluene and dichloromethane decreased, lipids increased, and ethyl acetate extract exhibited little change. The FTIR analysis of the coal sample suggested that, under the action of Triton X-100, compared to oxidized coal, the Har/H and A(CH2)/A(CH3) of the remaining coal decreased by 0.07 and 1.38, respectively, indicating that Triton X-100 enhanced the degradation of aromatic and aliphatic structures of oxidized coal. Therefore, adding a suitable surfactant can promote the biodegradation of tar-rich coal and enrich its degradation product.

Phenanthrene removal from a spent sediment washing solution in a continuous-flow stirred-tank reactor

The issue of polycyclic aromatic hydrocarbons (PAHs) is widespread in marine sediments involving ecological systems and human health. Sediment washing (SW) has proven to be the most effective remediation approach for sediments polluted by PAHs, such as phenanthrene (PHE). However, SW still raises waste handling concerns due to a considerable amount of effluents generated downstream. In this context, the biological treatment of a PHE- and ethanol-containing spent SW solution can represent a highly efficient and environmentally-friendly strategy, but its knowledge is still scarce in scientific literature and no studies have so far been conducted in continuous mode. Therefore, a synthetic PHE-polluted SW solution was biologically treated in a 1 L aerated continuous-flow stirred-tank reactor for 129 days by evaluating the effect of different pH values, aeration flowrates and hydraulic retention times as operating parameters over five successive phases. A PHE removal efficiency of up to 75-94% was achieved by an acclimated PHE-degrading consortium mainly composed of Proteobacteria, Bacteroidota and Firmicutes phyla through biodegradation following the adsorption mechanism. PHE biodegradation, mainly occurring via the benzoate route due to the presence of PAH-related-degrading functional genes and a phthalate accumulation up to 46 mg/L, was also accompanied by a reduction of dissolved organic carbon and ammonia nitrogen above 99% in the treated SW solution.

Elaborating the role of rhamnolipids on the formation of humic substances during rice straw composting based on Fenton pretreatment and fungal inoculation

Composting is a green and sustainable way to dispose and reuse agricultural wastes, but the low degradation rate during composting hinders its application. This study was conducted to explore the effect of added surfactant rhamnolipids after Fenton pretreatment and inoculation of fungi (Aspergillus fumigatus) into the compost on the formation of humic substances (HS) during rice straw composting, and explored the effect of this method. The results showed that rhamnolipids speeded up the degradation of organic matter and HS formation during composting. Rhamnolipids promoted the generation of lignocellulose-degrading products after Fenton pretreatment and fungal inoculation. The differential products benzoic acid, ferulic acid, 2, 4-Di-tert-butylphenol and syringic acid were obtained. Additionally, key fungal species and modules were identified using multivariate statistical analysis. Reducing sugars, pH, and total nitrogen were the key environmental factors that affected HS formation. This study provides a theoretical basis for the high-quality transformation of agricultural wastes.

Effects of Comamonas testosteroni on dissipation of polycyclic aromatic hydrocarbons and the response of endogenous bacteria for soil bioremediation

Bioremediation is a promising method of treating polycyclic aromatic hydrocarbons (PAHs) in contaminated soil; however, the understanding of the efficiency and the way of microbial inoculants work in complex soil environments is limited. Comamonas testosteroni (Ct) strains could efficiently degrade PAHs, especially naphthalene (Nap) and phenanthrene (Phe). This study aimed to explore the functional role of Ct in soil indigenous microorganisms and analyze the effect of Ct addition on PAHs concentration in PAH-contaminated soil. The results showed that inoculation with Ct degraded naphthalene (Nap), phenanthrene (Phe), and benzo [α] pyrene (BaP) significantly; the degradation rates were 63.38%, 81.18%, and 37.98% on day 25, respectively, suggesting that the low molecular weights of Nap and Phe were more easily degraded by microorganisms than those of BaP. We speculated that BaP and Phe might be converted into Nap for further degradation, which is the main reason for the low degradation rate of Nap detected after 10-25 days. Network analysis showed that inoculation with Ct significantly increased bacteria community abundance closely related to PAHs. Structural equation models confirmed that Steroidobacter, as functional bacteria, could affect the degradation of Nap and BaP. Inoculated Ct effectively enhanced the synergy among indigenous bacteria to degrade PAHs. This finding will help understand the function of inoculated Ct strains in PAH-contaminated soil at the laboratory level.

A review on biosurfactant producing bacteria for remediation of petroleum contaminated soils

The discharge of potentially toxic petroleum hydrocarbons into the environment has been a matter of concern, as these organic pollutants accumulate in many ecosystems due to their hydrophobicity and low bioavailability. Petroleum hydrocarbons are neurotoxic and carcinogenic organic pollutants, extremely harmful to human and environmental health. Traditional treatment methods for removing hydrocarbons from polluted areas, including various mechanical and chemical strategies, are ineffective and costly. However, many indigenous microorganisms in soil and water can utilise hydrocarbon compounds as sources of carbon and energy and hence, can be employed to degrade hydrocarbon contaminants. Therefore, bioremediation using bacteria that degrade petroleum hydrocarbons is commonly viewed as an environmentally acceptable and effective method. The efficacy of bioremediation can be boosted further by using potential biosurfactant-producing microorganisms, as biosurfactants reduce surface tension, promote emulsification and micelle formation, making hydrocarbons bio-available for microbial breakdown. Further, introducing nanoparticles can improve the solubility of hydrophobic hydrocarbons as well as microbial synthesis of biosurfactants, hence establishing a favourable environment for microbial breakdown of these chemicals. The review provides insights into the role of microbes in the bioremediation of soils contaminated with petroleum hydrocarbons and emphasises the significance of biosurfactants and potential biosurfactant-producing bacteria. The review partly focusses on how nanotechnology is being employed in different critical bioremediation processes.

Dimethyl phthalate destroys the cell membrane structural integrity of Pseudomonas fluorescens

A Gram-negative bacteria (Pseudomonas fluorescens) was exposed to different concentrations (0, 20, and 40 mg/L) of dimethyl phthalate (DMP) for 8 h, and then Fourier transform infrared spectroscopy (FTIR) analysis, lipopolysaccharide content detection, analysis of fatty acids, calcein release test, proteomics, non-targeted metabolomics, and enzyme activity assays were used to evaluate the toxicological effect of DMP on P. fluorescens. The results showed that DMP exposure caused an increase in the unsaturated fatty acid/saturated fatty acid (UFA/SFA) ratio and in the release of lipopolysaccharides (LPSs) from the cell outer membrane (OM) of P. fluorescens. Moreover, DMP regulated the abundances of phosphatidyl ethanolamine (PE) and phosphatidyl glycerol (PG) of P. fluorescens and induced dye leakage from an artificial membrane. Additionally, excessive reactive oxygen species (ROS), malondialdehyde (MDA), and changes in antioxidant enzymes (i.e., catalase [CAT] and superoxide dismutase [SOD]) activities, as well as the inhibition of Ca²⁺-Mg²⁺-ATPase and Na⁺/K⁺-ATPase activities in P. fluorescens, which were induced by the DMP. In summary, DMP could disrupt the lipid asymmetry of the outer membrane, increase the fluidity of the cell membrane, and destroy the integrity of the cell membrane of P. fluorescens through lipid peroxidation, oxidative stress, and ion imbalance.

Surfactant assisted microwave irradiation pretreatment of corncob: Effect on hydrogen production capacity, energy consumption and physiochemical structure

The combination pretreatment strategy is an effective way to intensify photo-fermentative biohydrogen production (PFHP) process. In this study, the synergistic effects of microwave irradiation and surfactants on the hydrogen production performance, energy analysis and structural characteristics was evaluated. Results revealed that hydrogen production performance was improved after microwave irradiation pretreatment (MIP) and surfactants assisted microwave irradiation pretreatment (SMIP). SMIP group had a higher cumulative hydrogen yield (CHY) of 367.87 ± 6.481 mL compared with control group (223.26 ± 4.329 mL) and MIP group (303.66 ± 3.366 mL), which was an increase of 36.01% and 64.77%, respectively. Energy evaluation analysis showed that the energy ratio of SMIP (0.49) was higher than that of MIP (0.37) in the PFHP system, therefore, SMIP can save more energy. After SMIP, the corncob lignocellulose structure was greatly damaged, which was verified by SEM, FTIR, XRD and XPS analyses.

Bioremediation of PAHs and heavy metals co-contaminated soils: Challenges and enhancement strategies

Systemic studies on the bioremediation of co-contaminated PAHs and heavy metals are lacking, and this paper provides an in-depth review on the topic. The released sources and transport of co-contaminated PAHs and heavy metals, including their co-occurrence through formation of cation-π interactions and their adsorption in soil are examined. Moreover, it is investigated that co-contamination of PAHs and heavy metals can drive a synergistic positive influence on bioremediation through enhanced secretion of extracellular polymeric substances (EPSs), production of biosynthetic genes, organic acid and enzymatic proliferation. However, PAHs molecular structure, PAHs-heavy metals bioavailability and their interactive cytotoxic effects on microorganisms can exert a challenging influence on the bioremediation under co-contaminated conditions. The fluctuations in bioavailability for microorganisms are associated with soil properties, chemical coordinative interactions, and biological activities under the co-contaminated PAHs-heavy metals conditions. The interactive cytotoxicity caused by the emergence of co-contaminants includes microbial cell disruption, denaturation of DNA and protein structure, and deregulation of antioxidant biological molecules. Finally, this paper presents the emerging strategies to overcome the bioavailability problems and recommends the use of biostimulation and bioaugmentation along with the microbial immobilization for enhanced bioremediation of PAHs-heavy metals co-contaminated sites. Better knowledge of the bioremediation potential is imperative to improve the use of these approaches for the sustainable and cost-effective remediation of PAHs and heavy metals co-contamination in the near future.

How humic acid and Tween80 improve the phenanthrene biodegradation efficiency: Insight from cellular characteristics and quantitative proteomics

Polycyclic aromatic hydrocarbons (PAHs) are toxic and recalcitrant pollutants, with an urgent need for bioremediation. Systematic biodegradation studies show that surfactant-mediated bioremediation is still poorly understood. Here, we investigated a comprehensive cellular response pattern of the PAH degrading strain B. subtilis ZL09-26 to (non-)green surfactants at the cellular and proteomic levels. Eight characteristic cellular factor investigations and detailed quantitative proteomics analyses were performed to understand the highly enhanced phenanthrene (PHE) degradation efficiency (2.8- to 3-fold improvement) of ZL09-26 by humic acid (HA) or Tween80. The commonly upregulated pathway and proteins (Arginine generation, LacI-family transcriptional regulator, and Lactate dehydrogenase) and various metabolic pathways (such as phenanthrene degradation upstream pathway and central carbon metabolism) jointly govern the change of cellular behaviors and improvement of PHE transport, emulsification, and degradation in a network manner. The obtained molecular knowledge empowers engineers to expand the application of surfactants in the biodegradation of PAHs and other pollutants.

Studies on antibacterial and chemotaxis properties of Pseudomonas aeruginosa TEN01 biomass-derived sustainable biosurfactant

Biosurfactant producing bacterial strains were isolated from oil-contaminated sites at Chennai Petroleum Corporation Limited, Chennai, the potential strain was selected and identified as Pseudomonas aeruginosa TEN01 by 16 S rRNA sequencing technique. Biosurfactant was produced from cassava solid waste from the sago industry. Further, it was extracted by solvent extraction and partially purified by column chromatography. The partially purified biosurfactant was qualitatively analyzed by Thin Layer Chromatography (TLC), quantitatively analyzed by anthrone assay and characterized by Fourier Transform Infra-Red Spectroscopy (FT-IR) and Gas Chromatography-Mass Spectrometry (GC-MS). R_f value and chemical groups confirm the presence of glycolipid in the partially purified biosurfactant. GC-MS results confirmed the presence of long-chain fatty acids and carbohydrate which is found to be mainly present in glycolipids. Biosurfactants are surface-active molecules which have been found to be the best alternative to chemical-based surfactants. The present study focuses on modifying the cell surface using a biosurfactant from P. aeruginosa TEN01 to enhance membrane permeabilization. Antibacterial and chemotaxis properties of biosurfactant from P. aeruginosa TEN01 were found to be better towards Xenorhabdus poinarii, a bio-pesticide producing microbial strain, X. poinarii exhibited 81.7% adhesion to hydrocarbons upon biosurfactant treatment as analyzed by Bacterial Adhesion to Hydrocarbon (BATH) assay. The alteration in the membrane permeability was tested in X. poinarii using biosurfactant and chemical surfactants viz. Sodium dodecyl sulfate (SDS) and toluene by estimating the amount of intracellular protein released. High protein recovery (51.55%) was achieved with a biosurfactant. Cell viability in the biosurfactant-treated cells was also high (93.98%) in comparison to cells treated with chemical surfactants. Increased recovery of intracellular protein along with high cell viability makes the biosurfactant a potential candidate for application in numerous environmental fields.

Aeromonas sobria Induces Proinflammatory Cytokines Production in Mouse Macrophages via Activating NLRP3 Inflammasome Signaling Pathways

Aeromonas sobria, a common conditional pathogenic bacteria, is widely distributed in the environment and causes gastroenteritis in humans or septicemia in fish. Of all Aeromonas species, A. sobria is the most frequently isolated from human infections especially in immunocompromised subjects. Innate immunity is the first protection system of organism to resist non-specific pathogens invasion; however, the immune response process of hosts against A. sobria infection re\mains unexplored. The present study established an A. sobria infection model using primary mouse peritoneal macrophages (PMφs). The adherence and cytotoxicity of A. sobria on PMφs were determined by May-Grünwald Giemsa staining and LDH release measurement. Pro-inflammatory cytokine expression levels were measured using qPCR, western blotting, and ELISA methods. We also investigated the levels of ASC oligomerization and determined the roles of active caspase-1 in IL-1β secretion through inhibition assays and explored the activated pattern recognition receptors through immunofluorescence. We further elucidated the roles of activated inflammasome in regulating the host's inflammatory response through inhibition combined with ELISA assays. Our results showed that A. sobria induced lytic cell death and LDH release, whereas it had no adhesive properties on PMφs. A. sobria triggered various proinflammatory cytokine transcription level upregulation, and IL-1β occupied the highest levels. The pro-IL-1β protein expression levels increased in a dose-dependent manner with MOI ranging from 1 to 100. This process was regulated by ASC-dependent inflammasome, which cleavage pro-IL-1β into active IL-1β p17 with activated caspase-1 p20. Meanwhile, the expression levels of NLRP3 receptor significantly increased, location analysis revealed puncta-like surrounding nuclear, and inhibition of NLRP3 inflammasome downregulated caspase-1 activation and IL-1β secretion. Blocking of NLRP3 inflammasome activation through K⁺ efflux and cathepsin B or caspase approaches downregulated A. sobria-induced proinflammatory cytokine production. Overall, these data indicated that A. sobria induced proinflammatory cytokine production in PMφs through activating NLRP3 inflammasome signaling pathways.

A novel optical biosensor for in situ and small-scale monitoring of bacterial transport in saturated columns

In situ monitoring techniques can provide new insight into bacterial transport after inoculating exogenous bacteria into contaminated soils for bioremediation. A real-time and non-destructive optical sensor (the optrode) was employed to monitor in situ transport of two fluorescently labelled bacteria - Green Fluorescent Protein (Gfp)-labelled, hydrophilic Pseudomonas putida and Tomato Fluorescent Protein (td)-labelled, hydrophobic Rhodococcus erythropolis, in a saturated sand column with and without rhamnolipid surfactant. In situ measurements were made at three sampling ports in the column with the optrode in two sets of column experiments. In Experiment 1, liquid samples were extracted for ex situ analyses (plate counts and fluorescence), while in Experiment 2 no liquid samples were extracted. Extracting liquid samples for ex situ analyses in Experiment 1 disturbed in situ measurements; in situ measured bacterial concentrations were lower, or a significant lag in breakthrough occurred relative to ex situ measurements. In Experiment 2, the optrode worked well in monitoring bacterial transport, which gave consistent transport parameters at each sampling port. Moreover, the optrode enabled the impact of bacterial hydrophobicity and rhamnolipid surfactant on bacterial transport to be observed. Specifically, hydrophilic P. putida was transported faster through the column than hydrophobic R. erythropolis; we infer from this result that fewer P. putida cells adsorb to sand particles than do R. erythropolis cells. The rhamnolipid surfactant enhanced the transport of both hydrophilic and hydrophobic bacteria. These two observations are consistent with Lifshitz-van der Waals forces and acid-base interactions between bacteria and sand.

Investigation of biosurfactants produced by three indigenous bacterial strains, their growth kinetics and their anthracene and fluorene tolerance

The study explored the polycyclic aromatic hydrocarbon tolerance of indigenous biosurfactant producing microorganisms. Three bacterial species were isolated from crude oil contaminated sites of Haldia, West Bengal. The three species were screened for biosurfactant production and identified by 16S rRNA sequencing as Brevundimonas sp. IITISM 11, Pseudomonas sp. IITISM 19 and Pseudomonas sp. IITISM 24. The strains showed emulsification activities of 51%, 57% and 63%, respectively. The purified biosurfactants were characterised using FT-IR, GC-MS and NMR spectroscopy and found to have structural similarities to glycolipopeptides, cyclic lipopeptides and glycolipids. The biosurfactants produced were found to be stable under a wide range of temperature (0-100 °C), pH (4-12) and salinity (up to 20% NaCl). Moreover, the strains displayed tolerance to high concentrations (275 mg/L) of anthracene and fluorene and showed a good amount of cell surface hydrophobicity with different hydrocarbons. The study reports the production and characterisation of biosurfactant by Brevundimonas sp. for the first time. Additionally, the kinetic parameters of the bacterial strains grown on up to 300 mg/L concentration of anthracene and fluorene, ranged between 0.0131 and 0.0156 µ_max (h^-1), while the K_s(mg/L) ranged between 59.28 and 102.66 for Monod's Model. For Haldane-Andrew's model, µ_max (h^-1) varied between 0.0168 and 0.0198. The inhibition constant was highest for Pseudomonas sp. IITISM 19 on anthracene and Brevundimonas sp. IITISM 11 on fluorene. The findings of the study suggest that indigenous biosurfactant producing strains have tolerance to high PAH concentrations and can be exploited for bioremediation purposes.

Surfactant-facilitated alginate-biochar beads embedded with PAH-degrading bacteria and their application in wastewater treatment

Immobilized Pseudomonas aeruginosa beads with alginate and biochar as composite carriers and a nonionic surfactant (TX100) as degradation promoter were prepared by the gel embedding method. The optimal preparation parameters for the biochar addition amount and the concentrations of the bacterial suspension and TX100 were 1%, OD₆₀₀ = 1 and 200 mg/L, respectively. The addition of TX100 can simultaneously promote biochar sorption of PAHs and PAH degradation by P. aeruginosa. The removal ratio of acenaphthene was 24% higher for the TX100-facilitated immobilized bacterial beads than the beads in the absence of TX100. The surfactant-facilitated immobilized bacterial beads can thoroughly remove PAHs in wastewater under the conditions of 10~50 °C, pH 2.5~10.5, and less than 0.2 mol/L NaCl. The immobilized bacterial beads are suitable for continuous-flow reactors, and 2-mm-diameter beads will achieve better application results than larger beads. The new immobilized material can be widely used in various wastewater treatment reactors and in the in situ remediation of organic polluted water.

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

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.

Multilevel changes in bacterial properties on long-term exposure to hydrocarbons and impact of these cells on fresh-water communities

To handle the impact of habitat transformations, the microbial cells developed mechanisms aimed at adjustment of their biological processes in response to signals indicating environmental changes. One of the first changes in their properties is observed on their surface, which has direct contact with the dynamically varying surroundings. In this study, we present results of changes in the cell surface properties which may have a decisive impact on the xenobiotics' bioavailability and microbial cell survival. These changes influence their ability to remove xenobiotics by accelerating and empowering this process. Moreover, the application of microorganisms exposed for long-term to hydrocarbons in bioremediation processes might have positive impact on biodegradation of the latter in the natural environment as well as natural microbial community diversity. This study demonstrates a variety of microbial cell mechanisms of adaptation to long-term exposure to hydrocarbons and their potential as the bioremediation tools.

The LuxI/LuxR-Type Quorum Sensing System Regulates Degradation of Polycyclic Aromatic Hydrocarbons via Two Mechanisms

Members of the Sphingomonadales are renowned for their ability to degrade polycyclic aromatic hydrocarbons (PAHs). However, little is known about the regulatory mechanisms of the degradative pathway. Using cross-feeding bioassay, a functional LuxI/LuxR-type acyl-homoserine lactone (AHL)-mediated quorum sensing (QS) system was identified from Croceicoccus naphthovorans PQ-2, a member of the order Sphingomonadales. Inactivation of the QS system resulted in a significant decrease in PAHs degradation. The QS system positively controlled the expression of three PAH-degrading genes (ahdA1e, xylE and xylG) and a regulatory gene ardR, which are located on the large plasmid. Interestingly, the transcription levels of these three PAH-degrading genes were significantly down-regulated in the ardR mutant. In addition, bacterial cell surface hydrophobicity and cell morphology were altered in the QS-deficient mutant. Therefore, the QS system in strain PQ-2 positively regulates PAH degradation via two mechanisms: (i) by induction of PAH-degrading genes directly and/or indirectly; and (ii) by an increase of bacterial cell surface hydrophobicity. The findings of this study improve our understanding of how the QS system influences the degradation of PAHs, therefore facilitating the development of new strategies for the bioremediation of PAHs.

Potential use of biochar and rhamnolipid biosurfactant for remediation of crude oil-contaminated coastal wetland soil: Ecotoxicity assessment

Remediation of wetland soils contaminated with petroleum hydrocarbons is a challenging task. Biosurfactant and biochar have been used in oil remediation. However, little is known about the ecotoxicity of these materials when applied in wetland ecosystems. In this study, the ecotoxicity of biochar and rhamnolipid (RL) biosurfactant as crude oil remediation strategies in a Louisiana wetland soil was investigated. A pot experiment was set up with wetland soil treated with/without crude oil followed by subjecting to application of 1% biochar and various levels of RL ranging from 0.1% to 1.4%. The ecotoxicity was evaluated regarding to high plant (S. Alterniflora), algae, and soil microbes. Specifically, after a 30-day growth in a controlled chamber, plant biomass change as well as shoot/root ratio was measured. Algae growth was estimated by quantifying chlorophyll by spectrometry following separation, and soil microbial community was characterized by phospholipid fatty acids analysis. Results showed that plant can tolerate RL level up to 0.8%, while algae growth was strongly inhibited at RL > 0.1%. Algal biomass was significantly increased by biochar, which offset the negative impact of oil and RL. Additionally, soil microbial community shift caused by crude oil and RL was alleviated by biochar with promoting Gram-positive bacteria, actinomycetes, and arbuscular mycorrhizal fungi. Overall, this study shows that integrated treatment of biochar and RL has the lowest ecotoxicity to plant and algae when used in oil remediation of contaminated wetland soils.

Removal of acenaphthene from wastewater by Pseudomonas sp. in anaerobic conditions: the effects of extra and intracellular substances

Sorption and degradation are considered two primary modes of pollutant removal by microorganisms, and extracellular polymeric substances (EPS) have been shown to play an important role in these biological processes. However, their role in removing refractory organic pollutants the effects of intracellular substances in microorganisms remain unclear. In this study, we investigated both the removal mechanism and intracellular substances involved in removing the pollutant acenaphthene (ACE) from Pseudomonas sp. bacteria in anaerobic conditions. The results indicated that the ACE was mainly adsorbed rather than degraded by bacteria. Moreover, ACE had little impact on EPS secretion at concentrations ranging 0-3 mg/L. Cell walls and membranes accounted for more than 70% of ACE adsorption, whereas intra-cellular substances accounted for about 10-25% and the effect of other components on ACE adsorption was not obvious. A possible mechanism of ACE removal by bacteria is proposed.

Bio-removal of tetracycline antibiotics under the consortium with probiotics Bacillus clausii T and Bacillus amyloliquefaciens producing biosurfactants

The contamination of the aquatic environments by tetracycline antibiotics (TCs) is an increasingly pressing issue. Here, we used the addition of exogenous surfactants and in situ biosynthesis of biosurfactants to remove tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC), and their mixtures using the co-culture of probiotic Bacillus clausii T and Bacillus amyloliquefaciens HM618 producing surfactin. The addition of exogenous biosurfactants to remove TCs was superior to nonionic surfactants. The maximal bio-removal efficiencies for OTC and CTC among mixed antibiotics under the co-culture of B. clausii T and B. amyloliquefaciens HM618 were 76.6% and 88.9%, respectively, which were both better than the efficiency of the pure culture of B. clausii T. TCs were removed mainly through biotransformation rather than absorption and hydrolysis. The removal efficiency was in the order CTC > OTC > TC. The co-culture of B. clausii T and B. amyloliquefaciens HM618 alleviated the cytotoxicity of OTC and CTC. The toxicity of the biotransformation products was lower than that of the parent compounds. Demethylation, hydroxylation, and dehydration are likely the major mechanisms of TC biotransformation. These results illustrate the potential of using surfactants in the bioremediation of tetracycline antibiotics, and provide new avenues for further exploration of the bioremediation of antibiotics pollution.

Different bioavailability of phenanthrene to two bacterial species and effects of trehalose lipids on the bioavailability

Effects of trehalose lipids produced from Rhodococcus erythropolis ATCC 4277 on phenanthrene (PHE) mineralization by two soil microorganisms were investigated. Biodegradation experiments were conducted, with and without the biosurfactant, in three batch systems: water, soil, and soil-water slurry. PHE sorption to the soil did not limit the mineralization by the test microorganisms, Pseudomonas strain R (PR) and Sphingomonas sp. strain P5-2 (SP5-2). Both microorganisms, however, demonstrated significant difference in the PHE mineralization capability in the systems. While SP5-2 mineralized PHE faster than PR in liquid culture, PR having more hydrophobic surface greatly exceeded SP5-2 in ability to access soil-sorbed PHE. While the addition of the biosurfactant little affected the apparent cell hydrophobicity of SP5-2, it substantially improved PHE mineralization by this strain in all systems tested. Contrary to SP5-2, the apparent cell hydrophobicity was significantly stimulated with increasing concentration of the biosurfactant for PR. However, the biosurfactant had no significant effect on PHE mineralization by this microorganism. The results demonstrated that the addition of the biosurfactant may have great potential for remediation of sites contaminated with polycyclic aromatic hydrocarbons but its effects and benefits may be dependent on characteristics of microorganisms involved and environmental conditions.

Biodegradation of Petroleum Hydrocarbons by Bacillus subtilis BL-27, a Strain with Weak Hydrophobicity

The biodegradation of petroleum hydrocarbons has many potential applications and has attracted much attention recently. The hydrocarbon-degrading bacterium BL-27 was isolated from petroleum-polluted soil and was compounded with surfactants to improve biodegradation. Its 16S rDNA and rpoD gene sequences indicated that it was a strain of Bacillus subtilis. Strain BL-27 had extensive adaptability and degradability within a broad range of temperatures (25–50 °C), pH (4.0–10.0) and salinity (0–50 g/L NaCl). Under optimal conditions (45 °C, pH 7.0, 1% NaCl), the strain was able to degrade 65% of crude oil (0.3%, w/v) within 5 days using GC-MS analysis. Notably, strain BL-27 had weak cell surface hydrophobicity. The adherence rate of BL-27 to n-hexadecane was 29.6% with sucrose as carbon source and slightly increased to 33.5% with diesel oil (0.3%, w/v) as the sole carbon source, indicating that the cell surface of BL-27 is relatively hydrophilic. The strain was tolerant to SDS, Tween 80, surfactin, and rhamnolipids at a concentration of 500 mg/L. The cell surface hydrophobicity reduced more with the addition of surfactants, while the chemical dispersants, SDS (50–100 mg/L) and Tween 80 (200–500 mg/L), significantly increased the strain’s ability to biodegrade, reaching 75–80%. These results indicated that BL-27 has the potential to be used for the bioremediation of hydrocarbon pollutants and could have promising applications in the petrochemical industry.

Investigation and Assessment for an effective approach to the reclamation of Polycyclic Aromatic Hydrocarbon (PAHs) contaminated site: SIN Bagnoli, Italy

Native plant species were screened for their remediation potential for the removal of Polycyclic Aromatic Hydrocarbons (PAHs) contaminated soil of Bagnoli brownfield site (Southern Italy). Soils at this site contain all of the PAHs congeners at concentration levels well above the contamination threshold limits established by Italian environmental legislation for residential/recreational land use, which represent the remediation target. The concentration of 13 High Molecular Weight Polycyclic Aromatic Hydrocarbons in soil rhizosphere, plants roots and plants leaves was assessed in order to evaluate native plants suitability for a gentle remediation of the study area. Analysis of soil microorganisms are provides important knowledge about bioremediation approach. Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria are the main phyla of bacteria observed in polluted soil. Functional metagenomics showed changes in dioxygenases, laccase, protocatechuate, and benzoate-degrading enzyme genes. Indolacetic acid production, siderophores release, exopolysaccharides production and ammonia production are the key for the selection of the rhizosphere bacterial population. Our data demonstrated that the natural plant-bacteria partnership is the best strategy for the remediation of a PAHs-contaminated soil.

Integrated approach to enhance the anaerobic biodegradation of benz[α]anthracene: A high-molecule-weight polycyclic aromatic hydrocarbon in sludge by simultaneously improving the bioavailability and microbial activity

The biodegradation of benz[α]anthracene (BaA), which was a high-molecule-weight PAH, was enhanced via a combination of alkaline and alkyl polyglucosides (APG) treatment during waste activated sludge (WAS) anaerobic fermentation. The biodegradation efficiency of BaA was increased from 14.1% in the control to 30.2 and 47.8% in pH 10 and pH 10 & APG reactors, respectively. Mechanism investigations found that the alkaline and APG treatments stimulated the processes of BaA desorption from sludge and transfer/entry into microorganisms, and ultimately improved the BaA bioavailability. Meanwhile, the huge released substrates from WAS not only served as carbon sources but also involved in the electron transfer among microorganisms which contributed to the BaA biodegradation process. Moreover, the microbial activities involved in BaA biodegradation, including the abundances of functional bacteria, activities of enzymes and quantities of genes, were also incremented due to the alkaline and APG treatments. Overall, the simultaneous improvement of BaA bioavailability and microbial activities enhanced its biodegradation efficiency.

Mixed-surfactant-enhanced phytoremediation of PAHs in soil: Bioavailability of PAHs and responses of microbial community structure

The present study was conducted to explore the mechanisms of surfactant-enhanced phytoremediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs), focusing on the bioavailability of PAHs and microbial diversity. We investigated the remediation efficiencies of phenanthrene and pyrene after the addition of mixed surfactants (sodium dodecyl benzene sulfonate (SDBS) and Tween 80) of different ratios (1:1, 1:2, and 2:1) at the concentration of 100 mg/kg to soils cultured with ryegrass (Lolium multiflorum L.). The fractions of phenanthrene and pyrene were determined using a sequential extraction method, and the microbial diversity was evaluated using 16S rRNA gene high-throughput sequencing. The results showed that mixed surfactants could enhance the remediation efficiencies of PAHs, and mainly occurred in the initial 21 days. Mixed surfactants at the ratio of 1:1 (HM1) showed the best remediation efficiency in enhancing the dissipation of pyrene in 21 days. Mixed surfactants showed little effects on the removal of phenanthrene. In general, HM1 significantly decreased the bioavailable, bound and residual fractions of pyrene; additionally, higher abundances of PAH-degradation bacteria and degradation-related genes were observed. Pearson correlation analysis among PAH degraders, degradation-related genes and bioavailable fraction of PAHs was performed. Our results indicated that mixed surfactants could promote the transformation of pyrene from the bound and residual fractions to bioavailable fractions and enhance the abundances of PAH degradation bacteria and PAH degradation-related genes, thereby enhancing the degradation of pyrene.

Biodegradation of phenanthrene by biodemulsifier-producing strain Achromobacter sp. LH-1 and the study on its metabolisms and fermentation kinetics

Despite many reports of the use of biodegradation to remove contaminants, the biodegradation of polycyclic aromatic hydrocarbons (PAHs) is challenging because of the hydrophobicities and low aqueous solubilities of most PAHs. In this study, phenanthrene (PHE) was used as a sole carbon and energy source to screen and identify Achromobacter sp. LH-1 for the production of biodemulsifiers that enhance the bioavailability and solubilization of PAHs. LH-1 achieved a 94% degradation rate and a 40% mineralization rate with 100 mg/L PHE. Additionally, LH-1 degraded various PAHs, and the factors that influenced the growth and PAHs degradation activity of LH-1 were not only the toxicities and structures of the substances but also the acclimation of LH-1 to these substances. Three kinetic models were used to describe the fermentation processes of cell growth, product formation and substrate degradation over time. Finally, multiple PHE degradation pathways were proposed to be utilized by strain LH-1.

Biodegradation of clotrimazole and modification of cell properties after metabolic stress and upon addition of saponins

Azole fungicides constitute an extensive group of potential emerging pollutants which can be found in natural environment. This study focuses on the biodegradation of clotrimazole and the characterization of cell surface properties of microorganisms capable of degradation of this compound. The influence of long-term contact of bacteria with clotrimazole and the impact of the addition of Saponaria officinalis extract on cell surface modification was also checked. The biodegradation of clotrimazole did not exceed 70%. The presence of plant extract increased biodegradation of fungicide. The cells metabolic activity after one-month exposure to clotrimazole was the highest for each tested strain. Moreover, metabolic stress led to a strong modification of cell surface properties. The results are promising for determining the impact of clotrimazole on environmental microorganisms.

Mechanisms for rhamnolipids-mediated biodegradation of hydrophobic organic compounds

The widespread existence of hydrophobic organic compounds (HOCs) in soil and water poses a potential health hazard to human, such as skin diseases, heart diseases, carcinogenesis, etc. Surfactant-enhanced bioremediation has been regarded as one of the most viable technologies to treat HOCs contaminated soil and groundwater. As a biosurfactant that has been intensively studied, rhamnolipids have shown to enhance biodegradation of HOCs in the environment, however, the underlying mechanisms are not fully disclosed. In this paper, properties and production of rhamnolipids are summarized. Then effects of rhamnolipids on the biodegradation of HOCs, including solubilization, altering cell affinity to HOCs, and facilitating microbial uptake are reviewed in detail. Special attention is paid to how rhamnolipids change the bioavailability of HOCs, which are crucial for understanding the mechanism of rhamnolipids-mediated biodegradation. The biodegradation and toxicity of rhamnolipids are also discussed. Finally, perspectives and future research directions are proposed. This review adds insight to rhamnolipids-enhanced biodegradation process, and helps in application of rhamnolipids in bioremediation.

Rhamnolipid influences biosorption and biodegradation of phenanthrene by phenanthrene-degrading strain Pseudomonas sp. Ph6

Given the sub-lethal risks of synthetic surfactants, rhamnolipid is a promising class of biosurfactants with the potential to promote the bioavailability of polycyclic aromatic hydrocarbons (PAHs), to provide a favorable substitute for synthetic surfactants. However, few previous studies have integrated the behavior and mechanism behind rhamnolipid-influenced PAH biosorption and biodegradation. This is, to our knowledge, the first report of a bacterial envelope regulated link between phenanthrene (PHE) biosorption and biodegradation by rhamnolipid-induced PHE-degrading strain Pseudomonas sp. Ph6. Rhamnolipid (0─400 mg L^-1) can change the cell-surface zeta potential, cell surface hydrophobicity (CSH), cell ultra-microstructure and functional groups, and then alter PHE biosorption and biodegradation of Ph6. Greater amounts of PHE sorbed on cell envelopes results in more PHE diffusing into cytochylema, thus favoring PHE intracellular biodegradation of Ph6. Rhamnolipid (≤100 mg L^-1) could change the microstructures and functional groups of cell envelopes of Ph6, enhance the cell-surface zeta potential and CSH, thus consequently favor PHE biosorption and biodegradation by strain Ph6. By contrast, rhamnolipid at higher concentrations (≥200 mg L^-1) hindered PHE biosorption and biodegradation. Rhamnolipid, as a biosurfactant, can be successfully utilized as an additive to improve the microbial biodegradation of PAHs in the environments.

The Impact of Biosurfactants on Microbial Cell Properties Leading to Hydrocarbon Bioavailability Increase

The environment pollution with hydrophobic hydrocarbons is a serious problem that requires development of efficient strategies that would lead to bioremediation of contaminated areas. One of the common methods used for enhancement of biodegradation of pollutants is the addition of biosurfactants. Several mechanisms have been postulated as responsible for hydrocarbons bioavailability enhancement with biosurfactants. They include solubilization and desorption of pollutants as well as modification of bacteria cell surface properties. The presented review contains a wide discussion of these mechanisms in the context of alteration of bioremediation efficiency with biosurfactants. It brings new light to such a complex and important issue.

Butylbenzene and tert-Butylbenzene-Sorption on Sand Particles and Biodegradation in the Presence of Plant Natural Surfactants

The effects of hydrocarbons sorption on sand and saponins presence in the system on butylbenzene and tert-butylbenzene biological degradation was investigated. Additionally, the impact of saponins-containing plant extracts on environmental microorganisms was studied. Results of cell surface property measurements in samples with saponins only revealed changes in cell surface hydrophobicity, electrokinetic potential and membrane permeability when compared to corresponding values for glucose-grown microbes. Subsequently, in sorption experiments, the hydrocarbon adsorption kinetics in bacteria-free samples were better explained with the pseudo-second order kinetic model as compared to the pseudo-first order and intraparticular diffusion models. Moreover, the equilibrium data fitted better to the Freundlich isotherm for both benzene derivatives. In the samples combining hydrocarbons sorption and biological degradation in the presence of saponins, alkane-substituted hydrocarbons removal was accelerated from 40% to 90% after 14 days and the best surfactant in this aspect was S. officinalis extract.

Biodegradation of Di-(2-ethylhexyl) Phthalate by Rhodococcus ruber YC-YT1 in Contaminated Water and Soil

Di-(2-ethylehxyl) phthalate (DEHP) is one of the most broadly representative phthalic acid esters (PAEs) used as a plasticizer in polyvinyl chloride (PVC) production, and is considered to be an endocrine-disrupting chemical. DEHP and its monoester metabolites are responsible for adverse effects on human health. An efficient DEHP-degrading bacterial strain Rhodococcus ruber YC-YT1, with super salt tolerance (0⁻12% NaCl), is the first DEHP-degrader isolated from marine plastic debris found in coastal saline seawater. Strain YC-YT1 completely degraded 100 mg/L DEHP within three days (pH 7.0, 30 °C). According to high-performance liquid chromatography⁻mass spectrometry (HPLC-MS) analysis, DEHP was transformed by strain YC-YT1 into phthalate (PA) via mono (2-ethylehxyl) phthalate (MEHP), then PA was used for cell growth. Furthermore, YC-YT1 metabolized initial concentrations of DEHP ranging from 0.5 to 1000 mg/L. Especially, YC-YT1 degraded up to 60% of the 0.5 mg/L initial DEHP concentration. Moreover, compared with previous reports, strain YC-YT1 had the largest substrate spectrum, degrading up to 13 kinds of PAEs as well as diphenyl, p-nitrophenol, PA, benzoic acid, phenol, protocatechuic acid, salicylic acid, catechol, and 1,2,3,3-tetrachlorobenzene. The excellent environmental adaptability of strain YC-YT1 contributed to its ability to adjust its cell surface hydrophobicity (CSH) so that 79.7⁻95.9% of DEHP-contaminated agricultural soil, river water, coastal sediment, and coastal seawater were remedied. These results demonstrate that R. ruber YC-YT1 has vast potential to bioremediate various DEHP-contaminated environments, especially in saline environments.

Enhanced utilization of fluorene by Paenibacillus sp. PRNK-6: Effect of rhamnolipid biosurfactant and synthetic surfactants

The present investigation was to study the effect of different non-ionic surfactants (Tween-80, Tween-60, Tween-40, Tween-20, Triton X-100) and a rhamnolipid biosurfactant on the degradation of fluorene by Paenibacillus sp. PRNK-6. An enhancement in the growth, as well as fluorene utilization by this strain were observed in the presence of biosurfactant and non-ionic surfactants except Tween-20 and Triton X-100. Triton X-100 and Tween-20 were toxic to this bacterium. The strain PRNK-6 utilized 75% of fluorene (280mg/L) in 24h in an unamended condition. On the other hand, the complete utilization of higher concentration fluorene (320mg/L) by this strain was noticed when the medium was amended with Tween-80 (1.5% v/v) within 24h of incubation. Whereas, 90.6%, 96.5% and 96.7% of fluorene (280mg/L) was utilized when amended with Tween-60 (3.5% v/v), Tween-40 (3% v/v) and biosurfactant (25mg/L) respectively. Biosurfactant promoted the fluorene degradation potential of PRNK-6 as 96.2% of 320mg/L fluorene was degraded within 24h. Further, the added tween series surfactants and a biosurfactant have increased the cell surface hydrophobicity of the PRNK-6. Thus correlating with the enhanced degradation of the fluorene.

Improved polycyclic aromatic hydrocarbon degradation in a crude oil by individual and a consortium of bacteria

In this study, we report the ability of Stenotrophomonas maltophilia, Ochrobactrum anthropi, Pseudomonas mendocina, Microbacterium esteraromaticum and Pseudomonas aeruginosa to degrade multiple polycyclic aromatic hydrocarbons (PAHs) present in crude oil. The PAHs in the crude oil sample obtained from Digboi oil refinery, India were estimated to be naphthalene (10.0 mg L^-1), fluorene (1.9 mg L^-1), phenanthrene (3.5 mg L^-1) and benzo(b)fluoranthene (6.5 mg L^-1). Exposure of individual bacteria to crude oil showed high rate of biodegradation of specific PAHs by M. esteraromaticum, 81.4%-naphthalene; P. aeruginosa, 67.1%-phenanthrene and 61.0%-benzo(b)fluoranthene; S. maltophilia, 47.9%-fluorene in 45 days. However, consortium of these bacteria showed enhanced biodegradation of 89.1%-naphthalene, 63.8%-fluorene, 81% of phenanthrene and 72.8% benzo(b)fluoranthene in the crude oil. The degradation was further improved up to 10% by consortium on addition of 40 μg mL^-1 rhamnolipid JBR-425 biosurfactant. These results suggest that the developed bacterial consortium has significant potential in PAH remediation.

Advances in applications of rhamnolipids biosurfactant in environmental remediation: A review

The objective of this review is to provide a comprehensive overview of the advances in the applications of rhamnolipids biosurfactants in soil and ground water remediation for removal of petroleum hydrocarbon and heavy metal contaminants. The properties of rhamnolipids associated with the contaminant removal, that is, solubilization, emulsification, dispersion, foaming, wetting, complexation, and the ability to modify bacterial cell surface properties, were reviewed in the first place. Then current remediation technologies with integration of rhamnolipid were summarized, and the effects and mechanisms for rhamnolipid to facilitate contaminant removal for these technologies were discussed. Finally rhamnolipid-based methods for remediation of the sites co-contaminated by petroleum hydrocarbons and heavy metals were presented and discussed. The review is expected to enhance our understanding on environmental aspects of rhamnolipid and provide some important information to guide the extending use of this fascinating chemical in remediation applications.

Removal of acenaphthene from water by Triton X-100-facilitated biochar-immobilized Pseudomonas aeruginosa

By adding the nonionic surfactant Triton X-100 and using biochar as an immobilization carrier, a Triton X-100-facilitated biochar-immobilized Pseudomonas aeruginosa (TFBIP) material was prepared using the sorption method and was used to treat acenaphthene in water. The results showed that a low concentration of Triton X-100 simultaneously promoted the sorption capacity of the biochar and the degradation activity of P. aeruginosa, thereby significantly enhancing the removal of acenaphthene from water by the immobilized P. aeruginosa material. Compared with the control without Triton X-100, a low concentration of Triton X-100 significantly increased the acenaphthene removal rate by 20–50%. The optimal conditions for preparing the TFBIP were a loading time of 24 h, the use of a bacterial suspension with a concentration of OD₆₀₀ = 0.2, and a Triton X-100 concentration of 10 mg L⁻¹. The optimized TFBIP material could efficiently remove acenaphthene from water at temperatures of 10–50 °C, pH values of 4.5–10.5, and NaCl concentrations of up to 0.2 mol L⁻¹. The new TFBIP material can be used for the treatment of wastewater and may also be directly used for the remediation of soils contaminated with organic pollutants.

A new efficient PAH-degrading bacterial material was produced by using biochar as an immobilization carrier and adding nonionic surfactant.

Rhamnolipid-aided biodegradation of carbendazim by Rhodococcus sp. D-1: Characteristics, products, and phytotoxicity

We successfully isolated Rhodococcus sp. D-1, an efficient carbendazim-degrading bacterium that degraded 98.20% carbendazim (200ppm) within 5days. Carbendazim was first processed into 2-aminobenzimidazole, converted to 2-hydroxybenzimidazole, and then further mineralized by subsequent processing. After genomic analysis, we hypothesized that D-1 may express a new kind of enzyme capable of hydrolyzing carbendazim. In addition, the effect of the biodegradable biosurfactant rhamnolipid on the rate and extent of carbendazim degradation was assessed in batch analyses. Notably, rhamnolipid affected carbendazim biodegradation in a concentration-dependent manner with maximum biodegradation efficiency at 50ppm (at the critical micelle concentration, CMC) (97.33% degradation within 2days), whereas 150ppm (3 CMC) rhamnolipid inhibited initial degradation (0.01%, 99.26% degradation within 2 and 5days, respectively). Both carbendazim emulsification and favorable changes in cell surface characteristics likely facilitated its direct uptake and subsequent biodegradation. Moreover, rhamnolipid facilitated carbendazim detoxification. Collectively, these results offer preliminary guidelines for the biological removal of carbendazim from the environment.

Drivers and applications of integrated clean-up technologies for surfactant-enhanced remediation of environments contaminated with polycyclic aromatic hydrocarbons (PAHs)

Surfactant-enhanced remediation (SER) is considered as a promising and efficient remediation approach. This review summarizes and discusses main drivers on the application of SER in removing polycyclic aromatic hydrocarbons (PAHs) from contaminated soil and water. The effect of PAH-PAH interactions on SER efficiency is, for the first time, illustrated in an SER review. Interactions between mixed PAHs could enhance, decrease, or have no impact on surfactants' solubilization power towards PAHs, thus affecting the optimal usage of surfactants for SER. Although SER can transfer PAHs from soil/non-aqueous phase liquids to the aqueous phase, the harmful impact of PAHs still exists. To decrease the level of PAHs in SER solutions, a series of SER-based integrated cleanup technologies have been developed including surfactant-enhanced bioremediation (SEBR), surfactant-enhanced phytoremediation (SEPR) and SER-advanced oxidation processes (SER-AOPs). In this review, the general considerations and corresponding applications of the integrated cleanup technologies are summarized and discussed. Compared with SER-AOPs, SEBR and SEPR need less operation cost, yet require more treatment time. To successfully achieve the field application of surfactant-based technologies, massive production of the cost-effective green surfactants (i.e. biosurfactants) and comprehensive evaluation of the drivers and the global cost of SER-based cleanup technologies need to be performed in the future.

Construction of PAH-degrading mixed microbial consortia by induced selection in soil

Bioremediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soils through the biostimulation and bioaugmentation processes can be a strategy for the clean-up of oil spills and environmental accidents. In this work, an induced microbial selection method using PAH-polluted soils was successfully used to construct two microbial consortia exhibiting high degradation levels of low and high molecular weight PAHs. Six fungal and seven bacterial native strains were used to construct mixed consortia with the ability to tolerate high amounts of phenanthrene (Phe), pyrene (Pyr) and benzo(a)pyrene (BaP) and utilize these compounds as a sole carbon source. In addition, we used two engineered PAH-degrading fungal strains producing heterologous ligninolytic enzymes. After a previous selection using microbial antagonism tests, the selection was performed in microcosm systems and monitored using PCR-DGGE, CO₂ evolution and PAH quantitation. The resulting consortia (i.e., C1 and C2) were able to degrade up to 92% of Phe, 64% of Pyr and 65% of BaP out of 1000 mg kg^-1 of a mixture of Phe, Pyr and BaP (1:1:1) after a two-week incubation. The results indicate that constructed microbial consortia have high potential for soil bioremediation by bioaugmentation and biostimulation and may be effective for the treatment of sites polluted with PAHs due to their elevated tolerance to aromatic compounds, their capacity to utilize them as energy source.

Comparative proteomics reveal the mechanism of Tween80 enhanced phenanthrene biodegradation by Sphingomonas sp. GY2B

Previous study concerning the effects of surfactants on phenanthrene biodegradation focused on observing the changes of cell characteristics of Sphingomonas sp. GY2B. However, the impact of surfactants on the expression of bacterial proteins, controlling phenanthrene transport and catabolism, remains obscure. To overcome the knowledge gap, comparative proteomic approaches were used to investigate protein expressions of Sphingomonas sp. GY2B during phenanthrene biodegradation in the presence and absence of a nonionic surfactant, Tween80. A total of 23 up-regulated and 19 down-regulated proteins were detected upon Tween80 treatment. Tween80 could regulate ion transport (e.g. H⁺) in cell membrane to provide driving force (ATP) for the transmembrane transport of phenanthrene thus increasing its uptake and biodegradation by GY2B. Moreover, Tween80 probably increased GY2B vitality and growth by inducing the expression of peptidylprolyl isomerase to stabilize cell membrane, increasing the abundances of proteins involved in intracellular metabolic pathways (e.g. TCA cycle), as well as decreasing the abundances of translation/transcription-related proteins and cysteine desulfurase, thereby facilitating phenanthrene biodegradation. This study may facilitate a better understanding of the mechanisms that regulate surfactants-enhanced biodegradation of PAHs at the proteomic level.

Pyrene biodegradation enhancement potential of lipopeptide biosurfactant produced by Paenibacillus dendritiformis CN5 strain

Effect of biosurfactant on biodegradation of pyrene was studied using a microbial consortium predominantly composed of Pseudomonas viridiflava (49.5%) and Pseudomonas nitroreducens (32.5%) in a batch experiment containing lipopeptidic biosurfactant, produced by Paenibacillus dendritiformis CN5 strain, and mineral salt medium. The results showed that the lipopeptide at 600 and 300mgL^-1 enhanced pyrene degradation to 83.5% and 67% respectively in 24days compared to 16% degradation in its absence. However degradation of pyrene was reduced to 57% as the lipopeptide supplementation was raised to 900mgL^-1. This demonstrates that the biodegradation of pyrene was found to increase with an increase in the lipopeptide concentration up to a threshold level. The experimental data were fitted to the logistic kinetic model which provided best fit with a coefficient of determination (R²) values≥0.97. Maximum specific growth rate, μ_max of 0.97 and 0.69d^-1 were achieved in the 600 and 300mgL^-1 lipopeptide amendments in comparison to 0.54d^-1 in the unamended one. The carrying capacity, X_max increased 4.4-fold in 600mgL^-1 lipopeptide supplemented samples in comparison to its absence. Generally the lipopeptide showed potential application in improving bioremediation of polycyclic aromatic hydrocarbons contaminated environmental media.

Effects of rhamnolipids on the cell surface characteristics of Sphingomonas sp. GY2B and the biodegradation of phenanthrene

The mechanism of the interaction of rhamnolipids on strain GY2B.

Stimulatory effect and adsorption behavior of rhamnolipids on lignocelluloses degradation system

Di-rhamnolipid and mixed rhamnolipid were added to rice straw degrading system to investigate their mechanism of stimulatory effect. By batch adsorption experiments, it was shown that the equilibrium adsorption time of rhamnolipids on rice straw single system was the shortest (50min). The adsorption capacity of Trichoderma reesei single system was the strongest, whose Q_e,exp for di-rhamnolipid and mixed rhamnolipid was 10.57×10^-2mg·g^-1 and 8.13×10^-2mg·g^-1, respectively. The adsorption of rhamnolipids on consortia system was not the simple adduct of the two single systems. The adsorption of rhamnolipids on the three different systems might belong to chemisorptions. SEM and FTIR analyses were used to observe the morphology and to analyze the chemical functions in lignocellulosic biomass degradation with rhamnolipid. It was shown that after addition of rhamnolipids, the basic tissue in rice straw was severely destroyed and hydrogen bond was formed between biosurfactant and bacteria in lignocellulose degrading system.