Nonionic surfactants induced changes in cell characteristics and phenanthrene degradation ability of Sphingomonas sp. GY2B

Synergistic enhancement of polycyclic aromatic hydrocarbon degradation by Arthrobacter sp. SZ-3 and Pseudomonas putida B6-2 under high Tween80 concentration: mechanisms and efficiency

This study investigates the advantages of combined microbial degradation of polycyclic aromatic hydrocarbons (PAHs) in reducing the inhibitory effects of high-concentration eluents commonly used in soil washing. A microbial synergistic strategy was proposed using Arthrobacter sp. SZ-3 and Pseudomonas putida B6-2 as the key bacteria in the presence of Tween 80. The results show that in systems with Tween 80, the SZ-3 strain exhibits a strong capacity to degrade three types of PAH compounds, while the B6-2 strain follows multiple degradation pathways. Mixed bacteria achieved degradation rates 60.70% higher than single bacteria at varying concentrations of Tween 80. Additionally, the average growth rates of mixed bacteria increased by 1.17-1.37 times, aligning with the changes in the functional group. Protein activity detection within each degradation system corresponded with growth quantity and the cyclic variation characteristics of ETS enzyme activity. Notably, the ETS activity of mixed bacteria was 150% higher than that of single bacteria. At a Tween 80 concentration of 500 mg/L, the degradation rates of PAHs (Phe, Flu, Pyr) by mixed bacteria were significantly higher than those by single bacteria. The catechol 1,2-dioxygenase activity of mixed bacteria was 2.30 times higher than that of single bacteria. While Tween 80 did not alter the PAH degradation pathways, it significantly influenced the accumulation amount and duration of the characteristic intermediate product. This provides a reference for the remediation of recalcitrant pollutants under conditions involving high-concentration surfactants.

Biotechnological potentials of surfactants in coal utilization: a review

The quest for scientifically advanced and sustainable solutions is driven by growing environmental and economic issues associated with coal mining, processing, and utilization. Consequently, within the coal industry, there is a growing recognition of the potential of microbial applications in fostering innovative technologies. Microbial-based coal solubilization, coal beneficiation, and coal dust suppression are green alternatives to traditional thermochemical and leaching technologies and better meet the need for ecologically sound and economically viable choices. Surfactant-mediated approaches have emerged as powerful tools for modeling, simulation, and optimization of coal-microbial systems and continue to gain prominence in clean coal fuel production, particularly in microbiological co-processing, conversion, and beneficiation. Surfactants (surface-active agents) are amphiphilic compounds that can reduce surface tension and enhance the solubility of hydrophobic molecules. A wide range of surfactant properties can be achieved by either directly influencing microbial growth factors, stimulants, and substrates or indirectly serving as frothers, collectors, and modifiers in the processing and utilization of coal. This review highlights the significant biotechnological potential of surfactants by providing a thorough overview of their involvement in coal biodegradation, bioprocessing, and biobeneficiation, acknowledging their importance as crucial steps in coal consumption.

Biodegradation of phthalic acid esters (PAEs) by Janthinobacterium sp. strain E1 under stress conditions

Phthalates esters (PAEs) are a kind of polymeric material additives widely been added into plastics to improve products' flexibility. It can easily cause environmental pollution which are hazards to public health. In this study, we isolated an efficient PAEs degrading strain, Janthinobacterium sp. E1, and determined its degradation effect of di-2-ethylhexyl phthalate (DEHP) under stress conditions. Strain E1 showed an obvious advantage in pollutants degradation under various environmental stress conditions. Degradation halo clearly occurred around the colony of strain E1 on agar plate supplemented with triglyceride. Strain E1's esterase is a constitutively expressed intracellular enzyme. The esterase purified from strain E1 showed a higher catalytic effect on short-chain PAEs than long-chain PAEs. The input of DEHP, DBP (dibutyl phthalate) and DMP (dimethyl phthalate) into the tested soil did not change the species composition of soil prokaryotic community, but altered the dominant species in specific environmental conditions. And the community diversity and richness decreased to a certain extent. However, the diversity and richness of the microbial community were improved after the contaminated soil was treated with the strain E1. Our results also suggested that strain E1 exhibited a tremendous potential in environmental bioremediation in the real environment, which provides a new insight into the elimination of the pollutants contamination in the urban environment.

Controllable chemical redox reactions to couple microbial degradation for organic contaminated sites remediation: A review

Global environmental concern over organic contaminated sites has been progressively conspicuous during the process of urbanization and industrial restructuring. While traditional physical or chemical remediation technologies may significantly destroy the soil structure and function, coupling moderate chemical degradation with microbial remediation becomes a potential way for the green, economic, and efficient remediation of contaminated sites. Hence, this work systematically elucidates why and how to couple chemical technology with microbial remediation, mainly focused on the controllable redox reactions of organic contaminants. The rational design of materials structure, selective generation of reactive oxygen species, and estimation of degradation pathway are described for chemical oxidation. Meanwhile, current progress on efficient and selective reductions of organic contaminants (i.e., dechlorination, defluorination, -NO2 reduction) is introduced. Combined with the microbial remediation of contaminated sites, several consideration factors of how to couple chemical and microbial remediation are proposed based on both fundamental and practical points of view. This review will advance the understanding and development of chemical-microbial coupled remediation for organic contaminated sites.

Transcriptomic and biochemical analysis of metabolic remodeling in Bacillus subtilis MSC4 under Benzo[a]pyrene stress

Polyaromatic benzo[a]pyrene (B[a]P) is a toxic carcinogenic environmental pollutant, and the use of microorganisms to remediate B[a]P contamination is considered to be one of the most effective strategies. However, there is still a gap in studying the metabolic remodeling of microorganisms under B[a]P stress. In this study, our systematically investigated the effects of B[a]P on the metabolism of Bacillus subtilis MSC4 based on transcriptomic, molecular and biochemical analyses. The results showed that in response to B[a]P stress, MSC4 formed more biofilm matrix and endospores, the structure of the endospores also was changed, which led to a reduction in their resistance and made them more difficult to germinate. In addition to an increase in glycolysis activity, the activities of tricarboxylic acid cycle, pentose phosphate pathway and the electron transport chain were decreased. B[a]P stress forced MSC4 to strengthen arginine synthesis, urea cycle, and urea decomposition, meanwhile, synthesize more ribonucleotides. The activity of DNA replication, transcription activities and the expression of multiple ribosomal protein genes were reduced. Moreover, all of the reported enzymes involved in B[a]P degradation showed decreased transcript abundance, and the degradation of B[a]P caused significant up-regulation of the gene expression of the acid inducible enzyme OxdC and the synthesis of acetoin. In addition, the cytotoxicity of B[a]P to bacteria was directly displayed in four aspects: increased intracellular level of reactive oxygen species (ROS), elevated cell membrane permeability, up-regulation of the cell envelope stress-sensing two-component system LiaRS, and downregulation of siderophores biosynthesis. Finally, B[a]P also caused morphological changes in the cells, with some cells exhibiting significant deformation and concavity. These findings provide effective research directions for targeted improvement the cellular activity of B[a]P-degrading strains, and is beneficial for further application of microorganisms to remediate B[a]P -contaminated soils.

Pan-metagenome reveals the abiotic stress resistome of cigar tobacco phyllosphere microbiome

The important role of microbial associations in mediating plant protection and responses to abiotic stresses has been widely recognized. However, there have been limited studies on the functional profile of the phyllosphere microbiota from tobacco (Nicotiana tabacum), hindering our understanding of the mechanisms underlying stress resilience in this representative and easy-to-cultivate model species from the solanaceous family. To address this knowledge gap, our study employed shotgun metagenomic sequencing for the first time to analyze the genetic catalog and identify putative plant growth promoting bacteria (PGPB) candidates that confer abiotic stress resilience throughout the growth period of cigar tobacco in the phyllosphere. We identified abundant genes from specific bacterial lineages, particularly Pseudomonas, within the cigar tobacco phyllospheric microbiome. These genes were found to confer resilience against a wide range of stressors, including osmotic and drought stress, heavy metal toxicity, temperature perturbation, organic pollutants, oxidative stress, and UV light damage. In addition, we conducted a virome mining analysis on the metagenome to explore the potential roles of viruses in driving microbial adaptation to environmental stresses. Our results identified a total of 3,320 scaffolds predicted to be viral from the cigar tobacco phyllosphere metagenome, with various phages infecting Pseudomonas, Burkholderia, Enterobacteria, Ralstonia, and related viruses. Within the virome, we also annotated genes associated with abiotic stress resilience, such as alkaline phosphatase D (phoD) for nutrient solubilization and glutamate-5-semialdehyde dehydrogenase (proA) for osmolyte synthesis. These findings shed light on the unexplored roles of viruses in facilitating and transferring abiotic stress resilience in the phyllospheric microbiome through beneficial interactions with their hosts. The findings from this study have important implications for agricultural practices, as they offer potential strategies for harnessing the capabilities of the phyllosphere microbiome to enhance stress tolerance in crop plants.

Potential of some microbial isolates on diesel hydrocarbons removal, bio surfactant production and biofilm formation

Potential of Arthrobacter citreus B27Pet, Bacillus thuringiensis B48Pet and Candida catnulata to produce biosurfactant using four different carbon sources (naphthalene, hexadecane, diesel and petroleum crude oil) was investigated. Removal of petroleum crude oil from aqueous culture and degradation of diesel were also determined using single and mixed culture of strains. The biofilm existence in single and mixed culture of strains was considered using naphthalene, hexadecane and diesel in culture medium. Cell surface hydrophobicity of A. citreus was higher than other isolates which also showed maximum surface tension reduction and emulsification index. As a whole, remarkable biosurfactant production occurred using petroleum crude oil as a carbon source in medium. A. citreus was found to be more robust than other tested strains in removal efficiency of crude oil due to its biosurfactant production capability. Statistically significant positive correlation was observed between biofilm existence and surface tension using diesel and hexadecane as carbon source. Overall diesel biodegradation efficiency by the mix culture of three applied strains was about 75% within a short period of time (10 days) which was accompanied with high biofilm production.

Surfactant-enhanced anoxic degradation of polycyclic aromatic hydrocarbons (PAHs) in aged subsurface soil at high temperature (60 °C)

Thermally enhanced anoxic biodegradation is emerging as a promising method for removing PAHs from subsurface soil. However, some PAHs still remain in soil following remediation with thermally enhanced anoxic degradation due to low bioavailability of these residual PAHs. The effects of five surfactants (Tween 80, TX 100, Brij 30, SDS, and SDBS) on the desorption of PAHs, anoxic degradation of PAHs, and native bacteria in soil at high temperature (60 °C) were evaluated in this study. The desorption of PAHs in soil increased as surfactant concentration increased. Low doses of surfactants (0.08%, w/w) enhanced the growth of potential PAHs degrading bacteria and promoted the anoxic degradation of PAHs, whereas high doses of surfactants (0.3%-0.8%, w/w) displayed the opposite effect, and the degree of inhibition increased with increasing surfactant concentration. The results also indicated that the inhibitory effect of anionic surfactants (SDS and SDBS) on microbial growth and PAHs degradation is stronger than that of nonionic surfactants (Tween 80, TX 100 and Brij 30) at the same concentration. These results suggest a feasible way of enhancing the anoxic degradation of PAHs in soil where heat cannot be effectively utilized when in situ thermal desorption (ISTD) technology is used.

Brij-58 supplementation enhances menaquinone-7 biosynthesis and secretion in Bacillus natto

Menaquinone-7 is a form of vitamin K₂ that has been shown to have numerous healthy benefits. In this study, several surfactants were investigated to enhance the production of menaquinone-7 in Bacillus natto. Results showed that Brij-58 supplementation influenced the cell membrane via adsorption, and changed the interfacial tension of fermentation broth, while the changes in the state and the composition of the cell membrane enhanced the secretion and biosynthesis of menaquinone-7. The total production and secretion rate of menaquinone-7 increased by 48.0% and 56.2% respectively. During fermentation, the integrity of the cell membrane decreased by 82.9% while the permeability increased by 158% when the maximum secretory rate was reached. Furthermore, Brij-58 supplementation induced the stress response in bacteria, resulting in hyperpolarization of the membrane, and increased membrane ATPase activity. Finally, changes in fatty acid composition increased membrane fluidity by 30.1%. This study provided an effective strategy to enhance menaquinone-7 yield in Bacillus natto and revealed the mechanism of Brij-58 supplementation in menaquinone-7 production. KEY POINTS: • MK-7 yield in Bacillus natto was significantly increased by Brij-58 supplementation. • Brij-58 could be adsorbed on cell surface and change fermentation environment. • Brij-58 supplementation could affect the state and composition of the cell membrane.

The role of multi-low molecular weight organic acids on phenanthrene biodegradation: Insight from cellular characteristics and proteomics

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic and ubiquitous pollutants that need to be solved. The low-molecular-weight organic acid (LMWOA) holds the promise to accelerate the capacity of microbes to degrade PAHs. However, the degradation mechanism(s) with multi-LMWOAs has not been understood yet, which is closer to the complex environmental biodegradation in nature. Here, we demonstrated a comprehensive cellular and proteomic response pattern by investigating the relationship between a model PAH degrading strain, B. subtilis ZL09-26, and the mixture LMWOAs (citric acid, glutaric acid, and oxalic acid). As a result, multi-LMWOAs introduced a highly enhanced phenanthrene (PHE) degradation efficiency with up to 3.1-fold improvement at 72 h, which is accompanied by the enhancement of strain growth and activity, but the releasement of membrane damages and oxidative stresses. Moreover, a detailed proteomic analysis revealed that the synergistic perturbation of various metabolic pathways jointly governed the change of cellular behaviors and improved PHE degradation in a network manner. The obtained knowledge provides a foundation for designing the artificial LMWOAs mixtures and guides the rational remediation of contaminated soils using bio-stimulation techniques.

Surfactant-enhanced bioremediation of petroleum-contaminated soil and microbial community response: A field study

Surfactant-enhanced bioremediation (SEBR) is frequently employed to clean up soil polluted with petroleum hydrocarbons, but few studies have focused on how surfactants affect microbial communities and different fractions of petroleum hydrocarbons, particularly in the field. Here, the surfactants sodium dodecyl benzene sulfonate (SDBS), alpha olefin sulfonate (AOS), Triton X-100 (TX-100), Tween80, and rhamnolipid were combined with the oil-degrading bacterium Pseudomonas sp. SB to remediate oil-contaminated soil in the laboratory. AOS gave the highest removal efficiency (65.1%) of total petroleum hydrocarbons (TPHs). Therefore, AOS was used in a field experiment with Pseudomonas sp. SB and the removal efficiency of TPHs and long-chain hydrocarbons C21-C40 reached 57.4 and 53.0%, respectively, significantly higher than the other treatments. During bioremediation the addition of Pseudomonas sp. SB significantly stimulated the growth of bacterial genera such as Alcanivorax, Luteimonas, Parvibaculum, Stenotrophomonas, and Pseudomonas and AOS further stimulated the growth of Sphingobacterium, Pseudomonas and Alcanivorax. This study validates the feasibility of surfactant-enhanced bioremediation in the field and partly reveals the mechanism of surfactant-enhanced bioremediation from the perspective of changes in different fractions of petroleum and microbial community dynamics.

Surfactant-enhanced mobilization of persistent organic pollutants: Potential for soil and sediment remediation and unintended consequences

This review aims to provide an overview of the sources and reactions of persistent organic pollutants (POPs) and surfactants in soil and sediments, the surfactant-enhanced solubilisation of POPs, and the unintended consequences of surfactant-induced remediation of soil and sediments contaminated with POPs. POPs include chemical compounds that are recalcitrant to natural degradation through photolytic, chemical, and biological processes in the environment. POPs are potentially toxic compounds mainly used in pesticides, solvents, pharmaceuticals, or industrial applications and pose a significant and persistent risk to the ecosystem and human health. Surfactants can serve as detergents, wetting and foaming compounds, emulsifiers, or dispersants, and have been used extensively to promote the solubilization of POPs and their subsequent removal from environmental matrices, including solid wastes, soil, and sediments. However, improper use of surfactants for remediation of POPs may lead to unintended consequences that include toxicity of surfactants to soil microorganisms and plants, and leaching of POPs, thereby resulting in groundwater contamination.

Elsholtzia splendens promotes phenanthrene and polychlorinated biphenyl degradation under Cu stress through enrichment of microbial degraders

Co-contamination of heavy metals and organic pollutants is widespread in the environment. Metal-tolerant/hyperaccumulating plants have the advantage of enhancing co-operation between plants and rhizospheric microbes under heavy metal stress, but the underlying mechanism remains unclear. In the present study, the effects of Elsholtzia splendens and Lolium perenne on the rhizospheric microbial community and degraders of phenanthrene (PHE) and polychlorinated biphenyls (PCBs) were investigated. The results showed E. splendens could tolerate high Cu concentrations, while L. perenne was sensitive to Cu toxicity. Although Cu played the most important role in microbial community construction, both E. splendens and L. perenne caused shifts in the rhizospheric microbial community. For PHE and PCB degradation, L. perenne was more efficient under low Cu concentrations, whereas E. splendens performed better under high Cu concentrations. This difference can be attributed to shifts in the degrader community and key degradation genes identified by stable isotope probing. Moreover, higher abundances of various genes for organic pollutant degradation were observed in the rhizosphere of E. splendens than L. perenne based on gene prediction under high Cu stress. Our study reveals underlying mechanism of the advantages of heavy metal-tolerant plants for organic pollutant removal in soils co-contaminated with heavy metals.

Coupling of desorption of phenanthrene from marine sediments and biodegradation of the sediment washing solution in a novel biochar immobilized-cell reactor

The recurrent dredging of marine sediments needs the use of ex-situ technologies such as sediment washing (SW) to effectively remove polycyclic aromatic hydrocarbons. Notwithstanding, the large volumes of generated spent SW effluents require adequate treatment by employing highly-efficient, inexpensive and environmentally-friendly solutions. This study proposes the phenanthrene (PHE) desorption from sediments using Tween® 80 (TW80) as extracting agent and the treatment of the resulting spent SW solution in a biochar (BC) immobilized-cell bioreactor. The SW process reached the highest PHE removal of about 91% using a surfactant solution containing 10,800 mg L^-1 of TW80. The generated amount of spent PHE-polluted SW solution can be controlled by keeping a solid to liquid ratio of 1:4. A PHE degradation of up to 96% was subsequently achieved after 43 days of continuous reactor operation, aerobically treating the TW80 solution in the BC immobilized-cell bioreactor with a hydraulic retention time of 3.5 days. Brevundimonas, Chryseobacterium, Dysgonomonas, Nubsella, and both uncultured Weeksellaceae and Xanthobacteraceae genera were mainly involved in PHE biodegradation. A rough economic study showed a total cost of 342.60 € ton^-1 of sediment, including the SW operations, TW80 and BC supply and the biological treatment of the SW solution.

Integrated Whole-Cell Biocatalysis for Trehalose Production from Maltose Using Permeabilized Pseudomonas monteilii Cells and Bioremoval of Byproduct

Trehalose is a non-conventional sugar with potent applications in the food, healthcare and biopharma industries. In this study, trehalose was synthesized from maltose using whole-cell Pseudomonas monteilii TBRC 1196 producing trehalose synthase (TreS) as the biocatalyst. The reaction condition was optimized using 1% Triton X-100 permeabilized cells. According to our central composite design (CCD) experiment, the optimal process was achieved at 35°C and pH 8.0 for 24 h, resulting in the maximum trehalose yield of 51.60 g/g after 12 h using an initial cell loading of 94 g/l. Scale-up production in a lab-scale bioreactor led to the final trehalose concentration of 51.91 g/l with a yield of 51.60 g/g and productivity of 4.37 g/l/h together with 8.24 g/l glucose as a byproduct. A one-pot process integrating trehalose production and byproduct bioremoval showed 53.35% trehalose yield from 107.4 g/l after 15 h by permeabilized P. moteilii cells. The residual maltose and glucose were subsequently removed by Saccharomyces cerevisiae TBRC 12153, resulting in trehalose recovery of 99.23% with 24.85 g/l ethanol obtained as a co-product. The present work provides an integrated alternative process for trehalose production from maltose syrup in bio-industry.

Remediation of petroleum hydrocarbons-contaminated soil: Analysis based on Chinese patents

Increasing soil petroleum hydrocarbons (PHs) pollution have caused world-wide concerns. The removal of PHs from soils mainly involves physical, chemical, biological processes and their combinations. To date, most reviews in this field based on research articles, but limited papers focused on the integration of remediation technologies from the perspective of patents. In this study, 20-years Chinese patents related to the remediation of soil PHs were comprehensively analyzed. It showed an increasing number of patent applications and the patents' quantity were positively correlated with Chinese GDP over the years, suggesting the more the economy developed the more environmental problems and corresponding solutions emerged. In addition, chemical technologies were mostly used in a combination to achieve faster and better effects, while the physical technologies were often used alone due to high costs. In all PHs remediation techniques, bacteria-based bioremediation was the most used from 2000 to 2019. Bacillus spp. and Pseudomonas spp. were the most used bacteria for PHs treatment because these taxa were widely harboring functions such as biosurfactant production and hydrocarbon degradation. The future research on joint technologies combining microbial and physicochemical ones for better remediation effect and application are highly encouraged.

Efficient biodegradation of phenanthrene using Pseudomonas stutzeri LSH-PAH1 with the addition of sophorolipids: Alleviation of biotoxicity and cometabolism studies

Phenanthrene (PHE) is widely distributed, and it can cause genotoxicity in humans by interacting with enzymes in the body. A current challenge for PHE bioremediation is the inhibitory effect of biotoxic intermediates on bacterial growth. Notably, the aerobic biotransformation processes for PHE in the presence of sophorolipids have been poorly studied. Here, a PHE-degrading strain was isolated from sediments and identified as Pseudomonas stutzeri and named LSH-PAH1. It was observed that 1-naphthol (a biotoxic substance that can inhibit strain growth) was produced during the PHE metabolism process of LSH-PAH1. The biodegradation ratio increased from 21.4% to 91.7% within 48 h after the addition of sophorolipids. Unexpectedly, this addition accelerated the metabolic process for 1-naphthol rather than causing its accumulation. The cometabolism of 1-naphthol and sophorolipids alleviated the biotoxic effects for the strain, which was verified by gene expression analysis. We identified a new PHE-degrading strain and provided a mechanism for PHE biodegradation using LSH-PAH1 with the addition of sophorolipids, which provides a reference for practical applications of the bioremediation of PHE and study of the cometabolism of biotoxic intermediates.

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.

Root exuded low-molecular-weight organic acids affected the phenanthrene degrader differently: A multi-omics study

As a class of highly toxic and persistent organic pollutants, polycyclic aromatic hydrocarbons (PAHs) are an increasingly urgent environmental problem. Low-molecular-weight organic acids (LMWOAs) are important factors that regulate the degradation of PAHs by plant rhizosphere microorganisms, which affect the absorption of PAHs by plant roots. However, the comprehensive mechanisms by which LMWOAs influence the biodegradation of PAHs at cellular and omics levels are still unknown. Here, we systematically analyzed the roles of citric, glutaric and oxalic acid in the PAH-degradation process, and investigated the mechanisms through which these three LMWOAs enhance phenanthrene (PHE) biodegradation by B. subtilis ZL09-26. The results showed that LMWOAs can improve the solubility and biodegradation of PHE, enhance cell growth and activity, and relieve membrane and oxidative stress. Citric acid enhanced PHE biodegradation mainly by improving the strain's cell proliferation and activity, while glutaric and oxalic acid accelerated PHE biodegradation mainly by improving the expression of enzymes and providing energy for the cells of B. subtilis ZL09-26. This study provides new insights into rhizospheric bioremediation mechanisms, which may enable the development of new biostimulation techniques to improve the bioremediation of PAHs.

Primary biodegradation and mineralization of aryl organophosphate flame retardants by Rhodococcus-Sphingopyxis consortium

In this study, the biodegradation towards aryl organophosphate flame retardants (aryl-OPFRs) was investigated by the Rhodococcus-Sphingopyxis consortium, mixture of strain Rhodococcus sp. YC-JH2 and Sphingopyxis sp. YC-JH3. The optimal ratio between the two composition strains was determined as 1:1. Under the optimum condition (pH 8, 35 °C and 0% salinity), the consortium could utilize aryl-OPFRs as sole carbon source and degrade them rapidly with half-life of 4.53, 21.11 and 23.0 h for triphenyl phosphate (TPhP), tricresyl phosphate (TCrP) and 2-ethylhexyl diphenyl phosphate (EHDPP) respectively. The consortium maintained high degrading efficiency under a wide of range of pH (6-10), temperature (20-40 °C) and salinity (0-6%). Besides, the consortium could rapidly degrade high concentration of TPhP and no inhibitory effect towards degradation speed was observed up to 500 mg/L. The effect of metal ions and surfactants was estimated. Most metal ions exhibited significant inhibition, except Zn²⁺ and Pb²⁺, which showed no effect or slight promotion. Ionic surfactants could severely reduce the degrading capacity, while nonionic surfactants showed no effect. With abundant inoculation of the consortium, mineralization higher than 75% could be achieved within a week. This study provides efficient microorganisms for bioremediation of aryl-OPFRs contamination.

Removal of PAHs at high concentrations in a soil washing solution containing TX-100 via simultaneous sorption and biodegradation processes by immobilized degrading bacteria in PVA-SA hydrogel beads

Soil washing process enhanced by surfactants is a promising technique in removing organic pollutants from soil. In this work, a simultaneous sorption and biodegradation technique was used to remove 16 PAHs from a soil washing solution (SWS) obtained by rinsing a heavily contaminated soil from a coking plant with Triton X-100 (TX-100). This was done by immobilizing a pyrene-degrading bacterial strain in polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads. Removal performance of free bacteria, blank PVA-SA beads and beads with immobilized degrading bacteria at a low, medium and high initial concentration was evaluated. The recycling and removal performance of the used beads were also examined. Our findings showed that hydrogel beads with immobilized bacteria at a medium concentration can remove around 77% ∑16PAHs from SWS in 96 h. The beads can be recycled and reused to treat a new SWS; 32-55% ∑16PAHs was removed in 24 h. The bead provided protection for bacteria against the co-existing substances such as TX-100. The bacteria-immobilized beads are more efficient and sustainable than free bacteria and blank beads due to simultaneous sorption and biodegradation processes, thus providing a solid reference for possible industrial application of bacteria immobilization technique to deal with SWSs with complex composition.

Nicosulfuron inhibits atrazine biodegradation by Arthrobacter sp. DNS10:Influencing mechanisms insight from bacteria viability, gene transcription and reactive oxygen species production

Nicosulfuron is a sulfonylurea family herbicide which is commonly applied together with the triazine herbicide atrazine in agricultural practice. However, whether nicosulfuron can influence the biodegradation of atrazine is unclear. Therefore, the influence of nicosulfuron on atrazine removal as well as on cell viability and transcription of atrazine chlorohydrolase gene (trzN) in Arthrobacter sp. DNS10 was investigated in this study. Our results demonstrated that 76.0% of atrazine was degraded in the absence of nicosulfuron after 48h of culture, whereas 63.9, 49.1 and 42.6% was degraded in the presence of 1, 5, and 10 mg/L of nicosulfuron, respectively. Nicosulfuron also induced an increase in the level of intracellular reactive oxygen species (ROS), thereby damaging the cell membrane integrity and inhibiting the growth of the strain DNS10. Flow cytometry analysis revealed that the cell viability of strain DNS10 decreased with an increase in nicosulfuron concentration. The transcription of trzN in strain DNS10 exposed to the three described levels of nicosulfuron was 0.99, 0.72 and 0.52 times, respectively, that without nicosulfuron. In brief, nicosulfuron could inhibit atrazine removal efficiency by strain DNS10 by inducing the over-production of ROS which ultimately enhances the population of membrane-damaged cells, as well as reducing cell viability and trzN transcription. The outcomes of the present study provide new insights into the mechanism of nicosulfuron inhibition on atrazine biodegradation by strain DNS10.

Effects of spent mushroom substrate on the dissipation of polycyclic aromatic hydrocarbons in agricultural soil

Spent mushroom substrate (SMS) is an agricultural waste with a high potential for polycyclic aromatic hydrocarbons (PAH) removal in aged contaminated soils. In this study, fresh and air-dried Pleurotus ostreatus, Pleurotus eryngii, and Auricularia auricular SMSs were used to remove PAHs in agricultural soil under 60-day incubation. The potential of SMS in PAH dissipation was studied by detecting the dissipation rate and the soil physicochemical index, enzyme activity, PAH-degradation bacterial biomass, and microbial diversity. Results showed that SMS significantly enhanced the dissipation of PAHs and fresh SMS had a better effect than air-dried SMS. The highest dissipation rate of 16 PAHs was 34.5%, which was observed in soil amended with fresh P. eryngii SMS, and the PAH dissipation rates with low and high molecular weights were 41.3% and 19.4%, respectively. By comparison, fresh P. eryngii SMS presented high nutrient contents, which promoted the development of PAH-degrading bacteria and changed the soil bacterial community involved in degradation, thereby promoting the PAH dissipation. The lignin-degrading enzymes in fresh SMS were abundant, and the laccase and manganese peroxidase activities in the treatment of fresh P. eryngii SMS was higher than those in other treatments. Fresh P. eryngii SMS improved the relative abundance of Microbacterium, Rhizobium, and Pseudomonas in soil, which were all related to PAH degradation. Consequently, adding fresh P. eryngii SMS was an effective method for remediating aged PAH-contaminated agricultural soils.

A study on the degradation efficiency of fluoranthene and the transmembrane protein mechanism of Rhodococcus sp. BAP-1 based on iTRAQ

Based on previous studies that examined the whole proteome of Rhodococcus sp. BAP-1 during the degradation of polycyclic aromatic hydrocarbons (PAHs), transmembrane proteins have a large role in the degradation of fluoranthene. To further study the specific functions and mechanisms of transmembrane proteins from Rhodococcus sp. BAP-1 involved in the degradation process of fluoranthene, the degradation of PAHs and the membrane permeability were determined. In addition, the isobaric tags for relative and absolute quantization (iTRAQ) method were used to conduct a proteomics analysis of Rhodococcus sp. BAP-1 after exposure to fluoranthene for 1 d, 3 d, and 6 d. The results showed that the degradation rate was the highest on the first and sixth days, and the membrane permeability was also the highest on the sixth day. The iTRAQ analysis results showed 18, 29, and 48 upregulated proteins and 111, 97, and 21 downregulated proteins in the 1 d group vs control group, 3 d group vs control group, and 6 d group vs control group samples respectively. According to a Clusters of Orthologous Groups of proteins (COG) analysis, amino acid transport and metabolism are the most important functions. According to functional analysis from the gene ontology (GO) database, the oxidation-reduction process is the most important biological process; transporter activity is the main molecular function; and transmembrane proteins are the most important in the cell composition. This study combined the degradation rate, membrane permeability and transmembrane protein functions to analyze the functions and mechanisms of transmembrane proteins from Rhodococcus sp. BAP-1, which are involved in the degradation of fluoranthene at the protein level, and this study provides a solid foundation for further research on the metabolic processes of bacteria.

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.

Characterization of an 17β-estradiol-degrading bacterium Stenotrophomonas maltophilia SJTL3 tolerant to adverse environmental factors

Bioremediation of environmental estrogens requires microorganisms with stable degradation efficiency and great stress tolerance in complex environments. In this work, Stenotrophomonas maltophilia SJTL3 isolated from wastewater was found to be able to degrade over 90% of 10 μg/mL 17β-estradiol (E2) in a week and the degradation dynamic was fitted by the first-order kinetic equations. Estrone was the first and major intermediate of E2 biodegradation. Strain SJTL3 exhibited strong tolerance to several adverse conditions like extreme pH (3.0-11.0), high osmolality (2%), co-existing heavy metals (6.25 μg/mL of Cu²⁺) and surfactants (5 CMC of Tween 80), and retained normal cell vitality and stable E2-degradaing efficiency. In solid soil, strain SJTL3 could remove nearly 100% of 1 μg/mL of E2 after the bacteria inoculation and 8-day culture. As to the contamination of 10 μg/mL E2 in soil, the biodegradation efficiency was about 90%. The further obtainment of the whole genome of strain SJTL3 and genome analysis revealed that this strain contained not only the potential genes responsible for estrogen degradation, but also the genes encoding proteins involved in stress tolerance. This work could promote the estrogen-biodegrading mechanism study and provide insights into the bioremediation application.

How to accurately assess surfactant biodegradation-impact of sorption on the validity of results

Surfactants not only are widely used in biotechnological processes but also constitute significant contaminants of the modern world. Among many reports, there is a shortage of works which summarize the issue of surfactant sorption to biomass in a way that would elucidate the biological factors for analysts and analytical factors for microbiologists. The main factor, which is not as obvious as one would expect, is associated with the susceptibility of analytical approaches to errors resulting from incorrect handling of biomass. In case of several publications reviewed in the framework of this study, it was not possible to establish whether the decrease of the analytical signal observed by the authors actually resulted from biodegradation of the surfactant. This review emphasizes the necessity to consider the possibility of surfactant sorption to microbial cells, which may result in significant detection errors as well as conceptual inconsistency. In addition, a reference study regarding representative surfactants (cationic, anionic and non-ionic) as well as yeast, Gram-negative, Gram-positive bacteria, and activated sludge was provided to highlight the possible errors which may arise from disregarding sorption processes when determining degradation of surfactants. This particularly applies to systems which include ionic surfactants and activated sludge as sorption may account for 90% of the observed depletion of the surfactant. Therefore, a systematic approach was proposed in order to improve the credibility of the obtained results. Finally, the need to employ additional procedures was highlighted which may be required in order to verify that the decrease of surfactant concentration results from biodegradation processes.

Bioaccumulation and distribution of cadmium by Burkholderia cepacia GYP1 under oligotrophic condition and mechanism analysis at proteome level

Bacteria have been applied for the bioremediation of cadmium-contaminated environment. Less is known about the bioaccumulation of high concentration of Cd over time under the oligotrophic environment. Burkholderia cepacia GYP1, which was isolated from multiple heavy metal contaminated farmland, was studied for its bioaccumulation mechanism of Cd under oligotrophic condition. GYP1 possessed highly accumulation capacity for cadmium reaching 116 mg Cd/g biomass (dry weight). ATR-FTIR, electron microscopy, flow cytometry along with subcellular fraction demonstrated that the uptake and distribution of cadmium varied with the increased amount of cadmium of GYP1 cell during the 7-day treatment time: the accumulation of cadmium was mainly on the outer membrane at the beginning (within 1 day), and the intracellular cadmium kept increased and held stable after 2 days, after that, the increased amount of cadmium mainly located extracellularly, related to the secreted EPS. Further mechanism analysis of bioaccumulation of Cd by GYP1 based on iTRAQ-based proteomics showed that Cd(II) could trigger the up-regulation of the Cd²⁺/Zn²⁺-exporting ATPase, type VI protein secretion systems, and glutathione-S-transferase that are related to cadmium response, which may contribute to maintain the intracellular cadmium homeostasis. In summary, the immobilization of Cd(II) by B. cepacia GYP1 contains three steps:(1) fast immobilization of Cd(II) on the cell surface coordinated with functional groups, (2) transport of Cd(II) to cells and accumulation in cytoplasm, and (3) efflux of intracellular Cd(II) depended on energy and the entrapped or adsorbed of extracellular Cd(II) by EPS. Our study provided the understanding of the cadmium accumulation process of B. cepacia GYP1 under oligotrophic condition, which would be helpful in bioremediation of natural cadmium contaminated environment.

A Highly Efficient Tumor-Targeting Nanoprobe with a Novel Cell Membrane Permeability Mechanism

Efficient tumor targeting has been a great challenge in the clinic for a very long time. The traditional targeting methods based on enhanced permeability and retention (EPR) effects show only an ≈5% targeting rate. To solve this problem, a new graphene-based tumor cell nuclear targeting fluorescent nanoprobe (GTTN), with a new tumor-targeting mechanism, is developed. GTTN is a graphene-like single-crystalline structure amphiphilic fluorescent probe with a periphery that is functionalized by sulfonic and hydroxyl groups. This probe has the characteristic of specific tumor cell targeting, as it can directly cross the cell membrane and specifically target to the tumor cell nucleus by the changed permeability of the tumor cell membranes in the tumor tissue. This new targeting mechanism is named the cell membrane permeability targeting (CMPT) mechanism, which is very different from the EPR effect. These probes can recognize tumor tissue at a very early stage and track the invasion and metastasis of tumor cells at the single cell level. The tumor-targeting rate is improved from less than 5% to more than 50%. This achievement in efficient and accurate tumor cell targeting will speed up the arrival of a new era of tumor diagnosis and treatment.

Cell changes and differential proteomic analysis during biodegradation of decabromodiphenyl ether (BDE-209) byPseudomonas aeruginosa

BDE-209 is a persistent organic pollutant. To promote microbial biodegradation of BDE-209 and gain further insight into its mechanism, cell changes and differential proteomic analysis ofP. aeruginosaduring biodegradation were studied.

Petroleum Hydrocarbon-Degrading Bacteria for the Remediation of Oil Pollution Under Aerobic Conditions: A Perspective Analysis

With the sharp increase in population and modernization of society, environmental pollution resulting from petroleum hydrocarbons has increased, resulting in an urgent need for remediation. Petroleum hydrocarbon-degrading bacteria are ubiquitous in nature and can utilize these compounds as sources of carbon and energy. Bacteria displaying such capabilities are often exploited for the bioremediation of petroleum oil-contaminated environments. Recently, microbial remediation technology has developed rapidly and achieved major gains. However, this technology is not omnipotent. It is affected by many environmental factors that hinder its practical application, limiting the large-scale application of the technology. This paper provides an overview of the recent literature referring to the usage of bacteria as biodegraders, discusses barriers regarding the implementation of this microbial technology, and provides suggestions for further developments.

Efficiency of surfactant-enhanced bioremediation of aged polycyclic aromatic hydrocarbon-contaminated soil: Link with bioavailability and the dynamics of the bacterial community

Shifts in the bacterial-community dynamics, bioavailability, and biodegradation of polycyclic aromatic hydrocarbons (PAHs) of chronically contaminated soil were analyzed in Triton X-100-treated microcosms at the critical micelle concentration (T-CMC) and at two sub-CMC doses. Only the sub-CMC-dose microcosms reached sorbed-PAH concentrations significantly lower than the control: 166±32 and 135±4mgkg^-1 dry soil versus 266±51mgkg^-1; consequently an increase in high- and low-molecular-weight PAHs biodegradation was observed. After 63days of incubation pyrosequencing data evidenced differences in diversity and composition between the surfactant-modified microcosms and the control, with those with sub-CMC doses containing a predominance of the orders Sphingomonadales, Acidobacteriales, and Gemmatimonadales (groups of known PAHs-degrading capability). The T-CMC microcosm exhibited a lower richness and diversity index with a marked predominance of the order Xanthomonadales, mainly represented by the Stenotrophomonas genus, a PAHs- and Triton X-100-degrading bacterium. In the T-CMC microcosm, whereas the initial surface tension was 35mNm^-1, after 63days of incubation an increase up to 40mNm^-1 was registered. The previous observation and the gas-chromatography data indicated that the surfactant may have been degraded at the CMC by a highly selective bacterial community with a consequent negative impact on PAHs biodegradation. This work obtained strong evidence for the involvement of physicochemical and biologic influences determining the different behaviors of the studied microcosms. The results reported here contribute significantly to an optimization of, surfactant-enhanced bioremediation strategies for chronically contaminated soil since the application of doses below the CMC would reduce the overall costs.

Complete genome sequencing and analysis of endophytic Sphingomonas sp. LK11 and its potential in plant growth

Our study aimed to elucidate the plant growth-promoting characteristics and the structure and composition of Sphingomonas sp. LK11 genome using the single molecule real-time (SMRT) sequencing technology of Pacific Biosciences. The results revealed that LK11 produces different types of gibberellins (GAs) in pure culture and significantly improves soybean plant growth by influencing endogenous GAs compared with non-inoculated control plants. Detailed genomic analyses revealed that the Sphingomonas sp. LK11 genome consists of a circular chromosome (3.78 Mbp; 66.2% G+C content) and two circular plasmids (122,975 bps and 34,160 bps; 63 and 65% G+C content, respectively). Annotation showed that the LK11 genome consists of 3656 protein-coding genes, 59 tRNAs, and 4 complete rRNA operons. Functional analyses predicted that LK11 encodes genes for phosphate solubilization and nitrate/nitrite ammonification, which are beneficial for promoting plant growth. Genes for production of catalases, superoxide dismutase, and peroxidases that confer resistance to oxidative stress in plants were also identified in LK11. Moreover, genes for trehalose and glycine betaine biosynthesis were also found in LK11 genome. Similarly, Sphingomonas spp. analysis revealed an open pan-genome and a total of 8507 genes were identified in the Sphingomonas spp. pan-genome and about 1356 orthologous genes were found to comprise the core genome. However, the number of genomes analyzed was not enough to describe complete gene sets. Our findings indicated that the genetic makeup of Sphingomonas sp. LK11 can be utilized as an eco-friendly bioresource for cleaning contaminated sites and promoting growth of plants confronted with environmental perturbations.

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.

Nonionic surfactants and their effects on asymmetric reduction of 2-octanone with Saccharomyces cerevisiae

In an aqueous buffer system, serious reverse and side reactions were found in the asymmetric reduction of 2-octanone with Saccharomyces cerevisiae. However, some nonionic surfactants added to the aqueous buffer system improved the bioreduction process by decreasing the reverse and side reaction rates in addition to effectively increasing the average positive reaction rate. Further, a shorter carbon chain length of hydrophilic or hydrophobic moieties in surfactants resulted in a higher yield of (S)-2-octanol. The alkylphenol ethoxylate surfactants had a less influence than polyoxyethylenesorbitan trialiphatic surfactants on the product e.e. It suggested that the product e.e. resulting from the change of carbon chain length of the hydrophobic moieties varied markedly compared with the change of carbon chain length of the hydrophilic moiety. Emulsifier OP-10 and Tween 20 markedly enhanced the yield and product e.e. at the concentration of 0.4 mmol L⁻¹ with a yield of 73.3 and 93.2%, and the product e.e. of 99.2 and 99.3%, respectively, at the reaction time of 96 h.

Comparative transcriptomic evidence for Tween80-enhanced biodegradation of phenanthrene by Sphingomonas sp. GY2B

Previous study of the effects of surfactants on the biodegradation of phenanthrene focused on investigating alterations of the cell characteristics of Sphingomonas sp. GY2B. However, genes regulation associated with biodegradation and biological processes in response to the presence of surfactants, remains unclear. In this study, comparative transcriptome analysis was conducted to observe the gene expression of GY2B during phenanthrene biodegradation in the presence and absence of Tween80. A diverse set of genes was regulated by Tween80, leading to increased biodegradation of phenanthrene by GY2B: (i) Tween80 increased expression of genes related to H⁺ transport in the plasma membrane to provide a driving force (i.e., ATP) for accelerating transmembrane transport of phenanthrene with increasing Tween80 concentrations, thereby enhancing the uptake and degradation of phenanthrene by GY2B; (ii) Tween80 (1 and 8 CMC) promoted intracellular biodegradation of phenanthrene by stimulating expression of genes encoding dioxygenases and monooxygenase, increasing expression of genes involved in intracellular metabolic processes (e.g., TCA cycle); and (iii) Tween80 likely increased GY2B vitality and growth by inducing expression of genes associated with ABC transporters and protein transport, regulating genes involved in other biological processes (e.g., transcription, translation).

Environmental biodegradation of halophenols by activated sludge from two different sewage treatment plants

Halophenols make a group of aromatic compounds that are resistible to biodegradation by environmental microorganisms. In this study, the biodegradation of 4-bromo-, 4-chloro- and 4-fluorophenols was studied with two types of activated sludges (from a small rural plant and from a bigger municipal plant) as an inoculum. Because of their wide use, surfactants are present in the wastewater and inhibitors enhance the biodegradation of different pollutants; the influence of natural surfactants on halophenols' biodegradation was also tested. Both types of activated sludge contained bacterial strains which were active in the halophenols' biodegradation process. The coexistence of surfactants and halophenols in the wastewater does not prevent microorganisms from effective halophenols' biodegradation. Moreover, surfactants can enhance the effectiveness of halophenols' removal from the environment. Different cell surface modifications of two isolated bacterial strains were observed in the same system of halophenols with or without surfactants. Halophenols and surfactants may also induce changes in bacteria cell surface properties.

Impact of potent bioremediation enhancing plant extracts on Raoultella ornithinolytica properties

Long-term contact of microorganisms with different compounds in the environment can cause significant changes in cell metabolism. Surfactants adsorption on cell surface or incorporation in the cell membrane, lead to their modification, which helps microorganisms adopt to the conditions of metabolic stress. The main objective of this study was to investigate the effects of three saponin-reach plant extracts from Hedera helix, Saponaria officinalis and Sapindus mucorossi on growth and adaptation of Raoultella ornithinolytica to high concentrations of these substances. For this purpose we investigated cell surface properties, membrane fatty acids and genetic changes of the microorganisms. The results revealed that prolonged exposure of the microorganisms to high concentrations of these surfactants can induce genetic changes of their genes. Moreover, the adaptation to contact with high concentrations of saponins was also associated with changes in composition of fatty acids responsible for the stabilisation of membrane structure and the increase in membrane permeability. The changes affected also the outer layer of cells. A significant increase (p < 0.05) in the cell surface hydrophobicity of tested strain was also observed. The cells after long-term contact with S. officinalis and S. mucorossi acquire properties that may be favourable in hydrophobic substances bioremediation.

Alkyl Xylosides: Physico-Chemical Properties and Influence on Environmental Bacteria Cells

A group of four selected non-ionic surfactants based on carbohydrates, namely octyl d-xyloside (C8X), nonyl d-xyloside (C9X), decyl d-xyloside (C10X) and dodecyl d-xyloside (C12X), have been investigated to accomplish a better understanding of their physico-chemical properties as well as biological activities. The surface-active properties, such as critical micelle concentration (CMC), emulsion and foam stability, the impact of the compounds on cell surface hydrophobicity and cell membrane permeability together with their toxicity on the selected bacterial strains have been determined as well. The studied group of surfactants showed high surface-active properties allowing a decrease in the surface tension to values below 25 mN m-1 for dodecyl d-xyloside at the CMC. The investigated compounds did not have any toxic influence on two Pseudomonas bacterial strains at concentrations below 25 mg L-1. The studied long-chain alkyl xylosides influenced both the cell inner membrane permeability and the cell surface hydrophobicity. Furthermore, the alkyl chain length, as well as the surfactant concentration, had a significant impact on the modifications of the cell surface properties. The tested non-ionic surfactants exhibited strong surface-active properties accompanied by the significant influence on growth and properties of Pseudomonas bacteria cells.

Surfactant-enhanced remediation of polycyclic aromatic hydrocarbons: A review

Polycyclic aromatic hydrocarbons (PAHs) are toxic, mutagenic and carcinogenic organic compounds that are widely present in the environment. The bioremediation of PAHs is an economical and environmentally friendly remediation technique, but it is limited because PAHs have low water solubility and fewer bioavailable properties. The solubility and bioavailability of PAHs can be increased by using surfactants to reduce surface tension and interfacial tension; this method is called surfactant-enhanced remediation (SER). The SER of PAHs is influenced by many factors such as the type and concentration of surfactants, PAH hydrophobicity, temperature, pH, salinity, dissolved organic matter and microbial community. Furthermore, as mixed micelles have a synergistic effect on PAH solubilisation, selecting the optimum ratio of mixed surfactants leads to effective PAH remediation. Although the use of surfactants inhibits microbial activities in some cases, this could be avoided by choosing an optimum combination of surfactants and a proper microbial community for the targeted PAH(s), resulting in up to 99.99% PAH removal. This article reviews the literature on SER of PAHs, including surfactant types, the synergistic effect of mixed micelles on PAH removal, the impact of surfactants on the PAH biodegradation process, factors affecting the SER process, and the mechanisms of surfactant-enhanced solubilisation of PAHs.

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.

Biotoxicity and bioavailability of hydrophobic organic compounds solubilized in nonionic surfactant micelle phase and cloud point system

A recent work has shown that hydrophobic organic compounds solubilized in the micelle phase of some nonionic surfactants present substrate toxicity to microorganisms with increasing bioavailability. However, in cloud point systems, biotoxicity is prevented, because the compounds are solubilized into a coacervate phase, thereby leaving a fraction of compounds with cells in a dilute phase. This study extends the understanding of the relationship between substrate toxicity and bioavailability of hydrophobic organic compounds solubilized in nonionic surfactant micelle phase and cloud point system. Biotoxicity experiments were conducted with naphthalene and phenanthrene in the presence of mixed nonionic surfactants Brij30 and TMN-3, which formed a micelle phase or cloud point system at different concentrations. Saccharomyces cerevisiae, unable to degrade these compounds, was used for the biotoxicity experiments. Glucose in the cloud point system was consumed faster than in the nonionic surfactant micelle phase, indicating that the solubilized compounds had increased toxicity to cells in the nonionic surfactant micelle phase. The results were verified by subsequent biodegradation experiments. The compounds were degraded faster by PAH-degrading bacterium in the cloud point system than in the micelle phase. All these results showed that biotoxicity of the hydrophobic organic compounds increases with bioavailability in the surfactant micelle phase but remains at a low level in the cloud point system. These results provide a guideline for the application of cloud point systems as novel media for microbial transformation or biodegradation.