PAH bioremediation with Rhodococcus rhodochrous ATCC 21198: Impact of cell immobilization and surfactant use on PAH treatment and post-remediation toxicity

Polycyclic aromatic hydrocarbons (PAHs) are prevalent environmental contaminants that are harmful to ecological and human health. Bioremediation is a promising technique for remediating PAHs in the environment, however bioremediation often results in the accumulation of toxic PAH metabolites. The objectives of this research were to demonstrate the cometabolic treatment of a mixture of PAHs by a pure bacterial culture, Rhodococcus rhodochrous ATCC 21198, and investigate PAH metabolites and toxicity. Additionally, the surfactant Tween ® 80 and cell immobilization techniques were used to enhance bioremediation. Total PAH removal ranged from 70-95% for fluorene, 44-89% for phenanthrene, 86-97% for anthracene, and 6.5-78% for pyrene. Maximum removal was achieved with immobilized cells in the presence of Tween ® 80. Investigation of PAH metabolites produced by 21198 revealed a complex mixture of hydroxylated compounds, quinones, and ring-fission products. Toxicity appeared to increase after bioremediation, manifesting as mortality and developmental effects in embryonic zebrafish. 21198's ability to rapidly transform PAHs of a variety of molecular structures and sizes suggests that 21198 can be a valuable microorganism for catalyzing PAH remediation. However, implementing further treatment processes to address toxic PAH metabolites should be pursued to help lower post-remediation toxicity in future studies.

Microbe cultivation guidelines to optimize rhamnolipid applications

In the growing landscape of interest in natural surfactants, selecting the appropriate one for specific applications remains challenging. The extensive, yet often unsystematized, knowledge of microbial surfactants, predominantly represented by rhamnolipids (RLs), typically does not translate beyond the conditions presented in scientific publications. This limitation stems from the numerous variables and their interdependencies that characterize microbial surfactant production. We hypothesized that a computational recipe for biosynthesizing RLs with targeted applicational properties could be developed from existing literature and experimental data. We amassed literature data on RL biosynthesis and micellar solubilization and augmented it with our experimental results on the solubilization of triglycerides (TGs), a topic underrepresented in current literature. Utilizing this data, we constructed mathematical models that can predict RL characteristics and solubilization efficiency, represented as logPRL = f(carbon and nitrogen source, parameters of biosynthesis) and logMSR = f(solubilizate, rhamnolipid (e.g. logPRL), parameters of solubilization), respectively. The models, characterized by robust R2 values of respectively 0.581-0.997 and 0.804, enabled the ranking of descriptors based on their significance and impact-positive or negative-on the predicted values. These models have been translated into ready-to-use calculators, tools designed to streamline the selection process for identifying a biosurfactant optimally suited for intended applications.

Surfactant-Mediated Effects on Hydrological and Physical Soil Properties: Data Synthesis

Soils are under the threat of a multitude of anthropogenic factors affecting the complex interplay of various physical and hydrological soil processes and properties. One such factor is the group of surface-active compounds. Surfactants have a broad range of applications and can reduce solid-liquid interfacial forces and increase wettability and dispersion of particles. Surfactant effects are context-dependent, giving rise to a wide range of reported effects on different soil processes and properties. Here, we evaluate the evidence base of surfactant research on 11 hydrological and physical soil variables. Our goal was to identify knowledge gaps and test the robustness of the proposed surfactant effects. We found that the current knowledge base is insufficient to reach strong data-backed conclusions about the effects of surfactants in soils. We identified a unique case of bias in the data as a result of conflated patterns from laboratory and field studies. We could not support the hypothesis that the surfactant charge determines soil effects for any of the tested soil variables. We believe that further experiments on surfactant-mediated effects on soil properties and processes are urgently required, paying attention, in particular, to improving experimental design and data reporting standards.

Tween-80 enhanced biodegradation of naphthalene by Klebsiella quasipneumoniae

Accidental spillage of petroleum products and industrial activities result in various hydrocarbons in the environment. While the n-hydrocarbons are readily degraded, the polycyclic aromatic hydrocarbons (PAHs) are recalcitrant to natural degradation, toxic to aquatic life and are responsible for diverse health challenges in terrestrial animals; suggesting the need for faster and more eco-friendly ways of removing PAHs from the environment. In this study, the surfactant tween-80 was used to enhance a bacterium's intrinsic naphthalene biodegradation activity. Eight bacteria isolated from oil-contaminated soils were characterised using morphological and biochemical methods. The most effective strain was identified as Klebsiella quasipneumoniae using 16S rRNA gene analysis. High-Performance Liquid Chromatography (HPLC) analyses showed that the detectable concentration of naphthalene was decreased from 500 to 157.18 μg/mL (67.4%) after 7 d in the absence of tween-80, while 99.4% removal was achieved in 3 d in the presence of tween-80 at 60 μg/mL concentration. The peaks observed in the Fourier Transform Infra-Red Spectroscopy (FTIR) spectrum of control (naphthalene), which were absent in that of the metabolites, further established naphthalene degradation. Furthermore, Gas Chromatography-Mass Spectrometer (GCMS) revealed metabolites of single aromatic ring, such as 3,4-dihydroxybenzoic acid 4-hydroxylmethylphenol, which confirmed that the removal of naphthalene is by biodegradation. Tyrosinase induction and laccase activities suggested the involvement of these enzymes in naphthalene biodegradation by the bacterium. Conclusively, a strain of K. quasipneumoniae that can effectively remove naphthalene from contaminated environments has been isolated, and its biodegradation rate was doubled in the presence of non-ionic surfactant, tween-80.

An Overview on the Treatment of Oil Pollutants in Soil Using Synthetic and Biological Surfactant Foam and Nanoparticles

Oil-contaminated soil is one of the most concerning problems due to its potential damage to human, animals, and the environment. Nanoparticles have effectively been used to degrade oil pollution in soil in the lab and in the field for a long time. In recent years, surfactant foam and nanoparticles have shown high removal of oil pollutants from contaminated soil. This review provides an overview on the remediation of oil pollutants in soil using nanoparticles, surfactant foams, and nanoparticle-stabilized surfactant foams. In particular, the fate and transport of oil compounds in the soil, the interaction of nanoparticles and surfactant foam, the removal mechanisms of nanoparticles and various surfactant foams, the effect of some factors (e.g., soil characteristics and amount, nanoparticle properties, surfactant concentration) on remediation efficiency, and some advantages and disadvantages of these methods are evaluated. Different nanoparticles and surfactant foam can be effectively utilized for treating oil compounds in contaminated soil. The treatment efficiency is dependent on many factors. Thus, optimizing these factors in each scenario is required to achieve a high remediation rate while not causing negative effects on humans, animals, and the environment. In the future, more research on the soil types, operating cost, posttreatment process, and recycling and reuse of surfactants and nanoparticles need to be conducted.

A review of the role of biosurfactants in the biodegradation of hydrophobic organopollutants: production, mode of action, biosynthesis and applications

The increasing influence of human activity and industrialization has adversely impacted the environment via pollution with organic contaminants, which are minimally soluble in water. These hydrophobic organopollutants may be present in sediment, water or biota and have created concern due to their toxic effects in mammals. The ability of microorganisms to degrade pollutants makes their use the most effective, inexpensive and ecofriendly method for environmental remediation. Microorganisms have the ability to produce natural surfactants (biosurfactants) that increase the bioavailability of hydrophobic organopollutants, which enables their use as carbon and energy sources. Due to microbial diversity in production, and the biodegradability, nontoxicity, stability and specific activity of the surfactants, the use of microbial surfactants has the potential to overcome problems associated with contamination by hydrophobic organopollutants.This review provides an overview of the current state of knowledge regarding microbial surfactant production, mode of action in the biodegradation of hydrophobic organopollutants and biosynthetic pathways as well as their applications using emergent strategy tools to remove organopollutants from the environment. It is also specified for the first time that biosurfactants are produced either as growth-associated products or secondary metabolites, and are produced in different amounts by a wide range of microorganisms.

Automated Search For The Low-lying Energy Isomers of Rhamnolipids and Related Organometallic Complexes

Rhamnolipids (RMLs) are a widely studied biosurfactant due to their high biodegradability and environmentally friendly pro duction. However, the knowledge of the structure-property relationship of RMLs is imperative for the design of highly efficient applications. Aiming to a better understanding of it at a molecular level, we performed an automated search for low energy structures of the most abundant RMLs, namely, Rha-C 10 , Rha-C 10 -C 10 , Rha-Rha-C 10 and Rha-Rha-C 10 -C 10 and their respective C 2 -congeners. Besides that, selected neutral metal complexes were also considered. We found that several low-energy congeners have internal hydrogen bonds. Moreover, geometries in "closed" conformation were always more stable than "open" ones. Fi nally, the energy differences between open and closed conformations of K + , Ni 2 + , Cu 2 + and Zn 2 + complexes were found to be 23.5 kcal mol -1 , 62.8 kcal mol -1 , 24.3 kcal mol -1 and 41.6 kcal mol -1 , respectively, indicating a huge structural reorganization after the complex formation.

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.

Microcystins can be extracted from Microcystis aeruginosa using amino acid-derived biosurfactants

Microcystin, a cyanotoxin produced by Microcystis aeruginosa growing in eutrophic waters, can promote liver tumors in people ingesting contaminated water. To date, water treatment systems have not been effective in removing or degrading these cyanotoxins. In this work, we investigated the inhibitory activity of surfactants on the growth of M. aeruginosa and their application to extract the intracellular produced cyanotoxins. The experiments involving growth inhibition and extraction of cyanotoxins were carried out using the non-biodegradable surfactant cetyl trimethyl ammonium bromide (CTAB) in addition to other biodegradable surfactants. These were Tween 80 and surfactants derived from amino acids and peptides, respectively, from arginine, SDA, and hydrolyzed peptone, SDP. We demonstrated that the tested surfactants could be used to inhibit the growth of M. aeruginosa. At this point, CTAB and SDA proved to be the most competent surfactants in reducing cyanobacterial growth. Moreover, microcystins have been successfully removed from the water employing a cloud point extraction protocol based on the use of these surfactants and ammonium sulfate.

A rhamnolipid biosurfactant increased bacterial population size but hindered hydrocarbon biodegradation in weathered contaminated soils

Surfactants are used to enhance the bioavailability of recalcitrant residual petroleum contamination during bioremediation. However, surfactants in some cases inhibit biodegradation, which is often attributed to their toxicity. Herein, we show that a rhamnolipid biosurfactant likely served as a carbon source and exhibited physiological inhibition on petroleum biodegradation. The addition of biosurfactants in mixed, batch, slurry bioreactors with soils from a petroleum-contaminated site led to a dose-dependent shift in the microbial community with a decrease in diversity and increase in population size and delayed biodegradation. Microbial community analysis indicated the enrichment of Alphaproteobacteria affiliated taxa such as Sphingomonadaceae in systems amended with biosurfactant. The diversity was significantly lower in systems with higher doses of biosurfactants compared to systems without biosurfactant. Droplet Digital PCR indicated a 30-90 fold increase in 16S rRNA copy numbers in systems with higher doses of biosurfactant than control systems without surfactant and nutrients, whereas the nutrient amendment alone led to a two-fold increase in population size. Total petroleum hydrocarbon analysis showed that the biodegradation extent was negatively impacted by rhamnolipid at the highest dose compared to lower doses (23% vs. 40%) or without the biosurfactant. Indigenous isolates cultivated from the oil-amended soil exhibited growth on rhamnolipid as a sole carbon source. A novel insight gained is how dose-dependent responses of microbial communities to biosurfactants alter the biodegradation time profile of hydrocarbons. The study highlights the significance of microbial assessment prior to surfactant-mediated bioremediation practices.

Towards Rational Biosurfactant Design-Predicting Solubilization in Rhamnolipid Solutions

The efficiency of micellar solubilization is dictated inter alia by the properties of the solubilizate, the type of surfactant, and environmental conditions of the process. We, therefore, hypothesized that using the descriptors of the aforementioned features we can predict the solubilization efficiency, expressed as molar solubilization ratio (MSR). In other words, we aimed at creating a model to find the optimal surfactant and environmental conditions in order to solubilize the substance of interest (oil, drug, etc.). We focused specifically on the solubilization in biosurfactant solutions. We collected data from literature covering the last 38 years and supplemented them with our experimental data for different biosurfactant preparations. Evolutionary algorithm (EA) and kernel support vector machines (KSVM) were used to create predictive relationships. The descriptors of biosurfactant (logP_BS, measure of purity), solubilizate (logP_sol, molecular volume), and descriptors of conditions of the measurement (T and pH) were used for modelling. We have shown that the MSR can be successfully predicted using EAs, with a mean R² _val of 0.773 ± 0.052. The parameters influencing the solubilization efficiency were ranked upon their significance. This represents the first attempt in literature to predict the MSR with the MSR calculator delivered as a result of our research.

A review on the application of chemical surfactant and surfactant foam for remediation of petroleum oil contaminated soil

Soil, exposed to petroleum oil contaminants (in the form of petrol, diesel, gasoline, crude oil, used motor oil), may cause potential damage to the environment, animal and human health. In this review article, mechanisms of the petroleum oil contaminant removal from soil by chemical surfactant systems such as surfactant solution, surfactant foam and nanoparticle stabilized surfactant foams are explained. Laboratory based research works, reported within the last decade on the application of similar systems towards the removal of petroleum oil contaminant from the soil, have been discussed. It is an important fact that the commercial implementation of the chemical surfactant based technology depends on the environmental properties (biodegradability and toxicity) of the surfactants. In recent times, surfactant foam and nanoparticle stabilized surfactant foam are becoming more popular and considered advantageous over the use of surfactant solution alone. However, more research works have to be conducted on nanoparticle stabilized foam. The impact of physicochemical properties of the nanoparticles on soil remediation has to be explored in depth.