Biosurfactant mediated bioelectrokinetic remediation of diesel contaminated environment

Current trends in bioremediation and bio-integrated treatment of petroleum hydrocarbons

Petroleum hydrocarbons and their derivatives constitute the leading group of environmental pollutants worldwide. In the present global scenario, petroleum and natural gas production, exploration, petroleum refining, and other anthropogenic activities produce huge amounts of hazardous petroleum wastes that accumulate in the terrestrial and marine environment. Due to their carcinogenic, neurotoxic, and mutagenic characteristics, petroleum pollutants pose severe risks to human health and exert ecotoxicological effects on the ecosystems. To mitigate petroleum hydrocarbons (PHs) contamination, implementing "green technologies" for effective cleanup and restoration of an affected environment is considered as a pragmatic approach. This review provides a comprehensive outline of newly emerging bioremediation technologies, for instance; nanobioremediation, electrokinetic bioremediation, vermiremediation, multifunctional and sustainably implemented on-site applied biotechnologies such as; natural attenuation, biostimulation, bioaugmentation, bioventing, phytoremediation and multi-process hybrid technologies. Additionally, the scope of the effectiveness and limitations of individual technologies in treating the petroleum hydrocarbon polluted sites are also evaluated.

Biodegradation of monocrotophos, cypermethrin & fipronil by Proteus myxofaciens VITVJ1: A plant - microbe based remediation

Current study was focused on the degradation of pesticides such as Monocrotophos, Cypermethrin & Fipronil (M, C & F) using phyto and rhizoremediation strategies. The isolate Proteus myxofaciens (VITVJ1) obtained from agricultural soil was capable of degrading M, C & F. The bacteria exhibited resistance to all the pesticides (M, C & F) up to 1500 ppm and was also capable of forming biofilms. The degraded products identified using Gas Chromatography-Mass Spectroscopy (GC-MS) and FTIR was further used for deriving the degradation pathway. The end product of M, C & F was acetic acid and 3-phenoxy benzoic acid which was confirmed by the presence of functional groups such as C=O and OH. Seed germination assay revealed the non-toxic nature of the degraded products with increased germination index in the treatments augmented with degraded products. The candidate genes such as opdA gene, Est gene and MnP1gene was amplified with the amplicon size of 700bp, 1200bp and 500bp respectively. P. myxofaciens not only degraded M, C & F, but was also found to be a plant growth promoting rhizobacteria. Since, it was capable of producing Indole Acetic acid (IAA), siderophore and was able to solubilize insoluble phosphate. Therefore, VITVJ1 upon augmentation to the rhizoremediation setup aided the degradation of pesticides with increase in plant growth as compared to that of the phytoremediation setup. To our knowledge this is the first study where P. myxofaciens has been effectively used for the degradation of three different classes of pesticides, which could also enhance the growth of plants and simultaneously degrade M, C & F.

Characterization of Diesel Degrading Indigenous Bacterial Strains, Acinetobacter pittii and Pseudomonas aeruginosa, Isolated from Oil Contaminated Soils

In this study, 13 diesel degrading bacteria were isolated from the oil contaminated soils and the promising strains identified as Acinetobacter pittii ED1 and Pseudomonas aeruginosa BN were evaluated for their diesel degrading capabilities. These strains degraded the diesel optimally at 30 °C, pH 7.0 and 1% diesel concentration. Both the strains produced biofilm at 1% diesel concentration indicating their ability to tolerate diesel induced abiotic stress. Gravimetric analysis of the spent medium after 7 days of incubation showed that A. pittii ED1 and P. aeruginosa BN degraded 68.61% and 76% diesel, respectively, while biodegradation reached more than 90% after 21 days. Fourier Transform Infrared (FTIR) analysis of the degraded diesel showed 1636.67 cm-1 (C=C stretch, N-H bond) peak corresponding to alkenes and primary amines, while GC-TOF-MS analysis showed decline in hydrocarbon intensities after 7 days of incubation. The present study revealed that newly isolated A. pittii ED1 and P. aeruginosa BN were able to degrade diesel hydrocarbons (C11-C18, and C19-C24) efficiently and have potential for bioremediation of the oil-contaminated sites.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-024-01317-3.

Isolation and screening of antimicrobial biosurfactants obtained from mangrove plant root-associated bacteria

The unique properties of biosurfactants obtained from microbes, including their activity at extreme temperatures, make them more attractive than synthetic alternatives. Henceforth, the principle objective is to isolate and detect the antibacterial and antifungal activities of the biosurfactants produced from bacteria of the economically competitive mangrove ecosystem. Using the serial dilution method, 53 bacterial strains were recovered from the Manakudy mangrove forest in Kanyakumari, India, for the investigation. Different biosurfactant screening methods and morphological and biochemical tests were opted to select the potential biosurfactant producer. After the initial screening, two strains were discovered by 16S rRNA gene sequencing followed by extraction using chloroform: methanol (2:1) by the precipitation method. The partially purified biosurfactants were then screened for antimicrobial properties against pathogens including Mucor sp., Trichoderma sp. Morphological, biochemical, and 16S rRNA gene sequencing identified the two strains to be gram-positive, rod-shaped bacteria namely Virgibacillus halodentrificans CMST-ZI (GenBank Accession No.: OL336402.1) and Pseudomonas pseudoalcaligenes CMST-ZI (GenBank Accession No (10 K): OL308085.1). The two extracted biosurfactants viz., 1,2-benzenedicarboxylic acid, mono (2-ethylhexyl) ester, as well as cycloheptane efficiently inhibited human pathogens, including Enterococcus faecalis, and fungi, including Mucor sp., Trichoderma sp., indicated by the formation of a zone of inhibition in pharmacological screening. Thus, there is a growing interest in the prospective application of these biosurfactants isolated from marine microbes, exhibiting antimicrobial properties which can be further studied as a potential candidate in biomedical studies and eco-friendly novel drug development.

Technological and economic analysis of electrokinetic remediation of contaminated soil: A global perspective and its application in Indian scenario

Globally million hectares of land annually is getting contaminated by heavy metalloids like As, Cd, Cr, Hg, Pb, Co, Cu, Ni, Zn, and Se, with current concentrations in soil above geo-baseline or regulatory standards. The heavy metals are highly toxic, mobile, and persistent and hence require immediate and effective mitigation. There are many available remediation techniques like surface capping, encapsulation, landfilling, soil flushing, soil washing, electrokinetic extraction, stabilization, solidification, vitrification, phytoremediation, and bioremediation which have been evolved to clean up heavy metal-contaminated sites. Nevertheless, all of the technologies have some applicability and limitations making the soil remediation initiative unsustainable. Among the available technologies, electrokinetic remediation (EKR) has been comparatively recognized to mitigate contaminated sites via both in-situ and ex-situ approaches due to its efficiency, suitability for use in low permeability soil, and requirement of low potential gradient. The work critically analyzes the EKR concerning techno, economic, and sustainability aspect for evaluating its application on various substrates and environmental conditions. The current soil contamination status in India is presented and the application of EKR for the heavy metal remediation from soil has been evaluated. The present work summaries a comprehensive and exhaustive review on EKR technology proving its effectiveness for a country like India where the huge amount of waste generated could not be treated due to lack of infrastructure, technology, and economic constraints.

Natural surfactant mediated bioremediation approaches for contaminated soil

The treatment of environmental pollution by employing microorganisms is a promising technology, termed bioremediation, which has several advantages over the other established conventional remediation techniques. Consequently, there is an urgent inevitability to develop pragmatic techniques for bioremediation, accompanied by the potency of detoxifying soil environments completely. The bioremediation of contaminated soils has been shown to be an alternative that could be an economically viable way to restore polluted soil. The soil environments have long been extremely polluted by a number of contaminants, like agrochemicals, polyaromatic hydrocarbons, heavy metals, emerging pollutants, etc. In order to achieve a quick remediation overcoming several difficulties the utility of biosurfactants became an excellent advancement and that is why, nowadays, the biosurfactant mediated recovery of soil is a focus of interest to the researcher of the environmental science field specifically. This review provides an outline of the present scenario of soil bioremediation by employing a microbial biosurfactant. In addition to this, a brief account of the pollutants is highlighted along with how they contaminate the soil. Finally, we address the future outlook for bioremediation technologies that can be executed with a superior efficiency to restore a polluted area, even though its practical applicability has been cultivated tremendously over the few decades.

An overview of bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils

The global problem of petroleum contamination in soils seriously threatens environmental safety and human health. Current studies have successfully demonstrated the feasibility of bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils due to their easy implementation, environmental benignity, and enhanced removal efficiency compared to bioremediation. This paper reviewed recent progress and development associated with bioelectrokinetic and bioelectrochemical remediation of petroleum-contaminated soils. The working principles, removal efficiencies, affecting factors, and constraints of the two technologies were thoroughly summarized and discussed. The potentials, challenges, and future perspectives were also deliberated to shed light on how to overcome the barriers and realize widespread implementation on large scales of these two technologies.

Sophorolipid modification enables high reactivity and electron selectivity of nanoscale zerovalent iron toward hexavalent chromium

Nanoscale zero-valent iron is considered to be a promising nanostructure for environmental remediation, while increasing the electron selectivity of nanoscale zerovalent iron (nZVI) during target contaminant removal is still a challenge (electron selectivity, defined as the percentage of electrons transferred to the target contaminants over the number of electrons donated by nZVI). In this study, the strategy for increasing the reactivity and electron selectivity of nZVI via sophorolipid (SL-nZVI) modification was proposed. The results showed that the removal efficiency and electron selectivity of SL-nZVI toward Cr(VI) was 99.99% and 56.30%, which was higher than that of nZVI (61.16%, 25.91%). Meanwhile, the particles were well characterized and the mechanism for enhanced reactivity and electron selectivity was investigated. Specially, both the morphology and BET specific surface area characterization suggested that stability against aggregation was higher in SL-nZVI nanoparticles than in nZVI. Besides, X-ray photoelectron spectroscopy (XPS), Tafel polarization curves, and Electrochemical impedance spectroscopy also indicated that the introduction of sophorolipid successfully prevent the nanoparticles from oxidation and benefit the electron transferring. In addition, a water contact angle test revealed that SL-nZVI nanoparticles were less hydrophilic (contact angle = 34.8°) than nZVI (contact angle = 23.9°). Therefore, in terms of reactivity, sophorolipid modification inhibited the aggregation of the nanoparticles and enhanced the electrical conductivity. For electron selectivity, the introduction of sophorolipid not only benefited Cr(VI) adsorption and the electron transfer from Fe⁰ to the surface-adsorbed Cr(VI) that followed but also reduced the possibility of side reactions between Fe⁰ and H₂O. This study demonstrates that the introduction of sophorolipid is an effective strategy for developing a highly efficient nZVI-based nanocomposite system and highlights the potential role of sophorolipid in improving the electron selectivity of nZVI.

Sustainable production of biosurfactants via valorisation of industrial wastes as alternate feedstocks

Globally, the rapid increase in the human population has given rise to a variety of industries, which have produced a variety of wastes. Due to their detrimental effects on both human and environmental health, pollutants from industry have taken centre stage among the various types of waste produced. The amount of waste produced has therefore increased the demand for effective waste management. In order to create valuable chemicals for sustainable waste management, trash must be viewed as valuable addition. One of the most environmentally beneficial and sustainable choices is to use garbage to make biosurfactants. The utilization of waste in the production of biosurfactant provides lower processing costs, higher availability of feedstock and environmental friendly product along with its characteristics. The current review focuses on the use of industrial wastes in the creation of sustainable biosurfactants and discusses how biosurfactants are categorized. Waste generation in the fruit industry, agro-based industries, as well as sugar-industry and dairy-based industries is documented. Each waste and wastewater are listed along with its benefits and drawbacks. This review places a strong emphasis on waste management, which has important implications for the bioeconomy. It also offers the most recent scientific literature on industrial waste, including information on the role of renewable feedstock for the production of biosurfactants, as well as the difficulties and unmet research needs in this area.

A comprehensive study on microbial-surfactants from bioproduction scale-up toward electrokinetics remediation of environmental pollutants: Challenges and perspectives

Currently, researchers have focused on electrokinetic (EK) bioremediation due to its potential to remove a wide-range of pollutants. Further, to improve their performance, synthetic surfactants are employed as effective additives because of their excellent solubility and mobility. Synthetic surfactants have an excessive position in industries since they are well-established, cheap, and easily available. Nevertheless, these surfactants have adverse environmental effects and could be detrimental to aquatic and terrestrial life. Owing to social and environmental awareness, there is a rising demand for bio-based surfactants in the global market, from environmental sustainability to public health, because of their excellent surface and interfacial activity, higher and stable emulsifying property, biodegradability, non- or low toxicity, better selectivity and specificity at extreme environmental conditions. Unfortunately, challenges to biosurfactants, like expensive raw materials, low yields, and purification processes, hinder their applicability to large-scale. To date, extensive research has already been conducted for production scale-up using multidisciplinary approaches. However, it is still essential to research and develop high-yielding bacteria for bioproduction through traditional and biotechnological advances to reduce production costs. Herein, this review evaluates the recent progress made on microbial-surfactants for bioproduction scale-up and provides detailed information on traditional and advanced genetic engineering approaches for cost-effective bioproduction. Furthermore, this study emphasized the role of electrokinetic (EK) bioremediation and discussed the application of BioS-mediated EK for various pollutants remediation.

Construction, application and validation of a new algorithm for determining light nonaqueous-phase liquid fluxes in unsaturated zones

An analytical algorithm coupling free-phase migration, precipitation, and natural attenuation through volatilization and biodegradation (FPVB) was developed to calculate the flux of light nonaqueous-phase liquid (LNAPL) leaking from unsaturated zone to groundwater. Sandbox and soil column experiments were performed to identify the LNAPL migration characteristics and states to provide data to establish and verify FPVB algorithm. For free-phase migration, the Kinematic Oily Pollutant Transport (KOPT) model was used to determine LNAPL movement velocity and leakage time. The correlations of water saturation, residual LNAPL saturation and the cumulative dissolution ratio of residual LNAPL were described using an empirical formula for the precipitation leaching process. Equations for diesel volatilization kinetics and first order degradation were used to describe the natural attenuation processes. Coupling the algorithms for the different stages gave the final FPVB algorithm. The FPVB algorithm was used to describe the pollution situation at a real site, and the results were consistent with the actual situation. The FPVB algorithm could be used to quickly assess the scale and degree of pollution with little information on the parameters for the actual LNAPL leakage event.

Polycyclic aromatic hydrocarbon sequestration by intertidal phototrophic biofilms cultivated in hydrophobic and hydrophilic biofilm-promoting culture vessels

Phototrophic biofilms collected from intertidal sediments of the world's largest tidal mangrove forest were cultured in two sets of a biofilm-promoting culture vessel having hydrophilic glass surface and hydrophobic polymethyl methacrylate surface wherein 16 priority polycyclic aromatic hydrocarbons (PAHs) were spiked. Biofilms from three locations of the forest were most active in sequestering 98-100% of the spiked pollutants. PAH challenge did not alter the biofilm phototrophic community composition; rather biofilm biomass production and synthesis of photosynthetic pigments and extracellular polymeric substances (EPS) were enhanced. Photosynthetic pigment and EPS synthesis were sensitive to vessel-surface property. The lowest mean residual amounts of PAHs in the liquid medium as well as inside the biofilm were recorded in the very biofilm cultivated in the hydrophobic flask where highest values of biofilm biomass, total chlorophyll, released polysaccharidic (RPS) carbohydrates, RPS uronic acids, capsular polysaccharidic (CPS) carbohydrates, CPS proteins, CPS uronic acids and EPS hydrophobicity were obtained. Ratios of released RPS proteins: polysaccharides increased during PAH sequestration whereas the ratios of CPS proteins: polysaccharides remained constant. Efficacious PAH removal by the overlying phototrophic biofilm will reduce the entry of these contaminants in the sediments underneath and this strategy could be a model for "monitored natural recovery".

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.

Biostimulation and Bioaugmentation of Soils Contaminated with Decachlorobiphenyl (PCB-209) Using Native Bacterial Strains Individually and in Consortia

Historically, microorganisms have proven to be efficient alternatives for the removal of PCBs, since these contaminants continue to be a major problem for human health and the environment. In this work, the removal of decachlorobiphenyl (PCB-209) was evaluated using native bacterial strains individually and in consortia through biostimulation and bioaugmentation processes. Bacillus sp. DCB13, Staphylococcus sp. DCB28, and Acinetobacter sp. DCB104 were biostimulated in a minimal medium that initially contained biphenyl and later PCB-209 for adaptation as a carbon source. The removal potential of PCB-209 by bacterial strains was evaluated in a bioaugmentation process under aerobic conditions. Using a completely randomized design, ten different treatments were evaluated. Finally, the bacterial growth (CFU/g of soil) and the chemical characteristics of the bioaugmented soil were determined, as was the content of PCB-209 removed by gas chromatography–mass spectrometry. Strains DCB13, DCB28, and DCB104 showed cell growth (>3.4 × 105 CFU/mL) during 120 h of biostimulation, with a marked difference between treatments with biphenyl compared with those where PCB-209 was added. Strains DCB13 and DCB104 (3.4 × 105 CFU/mL and 2.0 × 106 CFU/mL, respectively) grew better with PCB-209, while DCB28 grew better with biphenyl (4.5 × 106 CFU/mL). In bioaugmented soils contaminated with PCB-209, the strains showed maximum growth when inoculated in a consortium (>2.0 × 104 CFU/g). The results showe that the range of the bacterial elimination of PCB-209 in the treatments was from 9.58 to 17.33 mg/kg. The highest elimination potential of PCB-209 was obtained when the bacterial strains were inoculated in a consortium. These findings open a wide perspective for the use of native bacteria for the cleaning and restoration of soils contaminated by toxic chemicals.

Biodegradation of di-n-octyl phthalate by Gordonia sp. Lff and its application in soil

A previous isolated Gordonia sp. (Lff) was used to degrade di-n-octyl phthalate (DOP) contamination in both aqueous solution and soil. The influence of temperature, pH, inoculum size, salt content and initial concentration of DOP on DOP degradation by Lff were analysed. The response of soil bacterial community to DOP and Lff was also analysed by Illumina MiSeq sequence method. Results showed that the optimal temperature, pH, inoculum size and salt content were 35^oC, 8.0, 5% and <5%, respectively. Under the optimal condition, more than 91.25% of DOP with different initial concentrations (100-2000 mg/L) could be degraded by Lff. Kinetics analysis indicated that biodegradation of DOP by Lff could be described by first-order kinetics (R² > 0.917) with the half-life (t_1/2) changing irregularly between 0.58 and 0.83 d. In addition, Lff enhanced the removal of DOP in soil and alleviated the toxicity of DOP on soil microorganisms. Furthermore, its influence on soil bacterial community is not obvious. These results suggested that Lff was effective in remediating DOP contamination in different environments.

Potentially toxic elements contamination and its removal by aquatic weeds in the riverine system: A comparative approach

Thamirabarani river acquires large untreated sewage effluents from the Tirunelveli and Thoothukudi districts of South Tamil Nadu. This study examined the concentration of trace elements in water, sediment, and phytoaccumulation potential of aquatic weeds viz., A. cristata, E. crassipes, S. natans, and P. stratiotes, growing along Srivaikundam dam of Thamirabarani river. The Pb, As, Hg, Cd, and Ni concentrations in water were slightly higher than the US Food and Drug Administration (USFDA) drinking water guidelines; however, their accumulation in sediment was below WHO's sediment quality guideline. This study concludes that the phytoaccumulation factor (PAF) and translocation factor (TF) was >1 in E. crassipes and A. cristata, representing them as hyperaccumulators, suitable for phytoremediation in polluted localities. E. crassipes, A. cristata, and S. natans accumulated (100-500 fold) higher trace elements concentrations than that present in the water. Also, the concentrations of trace elements found in the aquatic weeds were below the recommended levels for the critical plant range (CRP). These selected aquatic weeds are more suitable for plant hybridization to be modified as superbug plants.

Cost reduction strategies in the remediation of petroleum hydrocarbon contaminated soil

Petroleum hydrocarbon spill on land pollutes soil and reduces its ecosystem. Hydrocarbon transport in the soil is aided by several biological, physical, and chemical processes. However, pore characteristics play a major role in the distribution within the soil matrix. Restoring land use after spills necessitates remediation using cost-effective technologies. Several remediation technologies have been demonstrated at different scales, and research is ongoing to improve their performances towards the reduction of treatment costs. The process of removing the contaminants in the soil is through one or a combination of containment, separation, and degradation methods under the influence of biological, physical, chemical, and electrically-dominated processes. Generally, performance improvement is achieved through the introduction of products/materials and/or energy. Nevertheless, the technologies can be categorized based on effectiveness period as short, medium, and long term. The treatment cost of short, medium, and long-term technologies are usually in the range of $39 - 331/t (/tonne), $22 - 131/t, and $8 - 131/t, respectively. However, the total cost depends on other factors such as site location, capital cost, and permitting. This review compiles cost-saving strategies reported for different techniques used in remediating petroleum hydrocarbon polluted soil. We discuss the principles of contaminant removal, performance enhancing methods, and the cost-effectiveness analysis of selected technologies.

Remediation of diesel-contaminated soil by alkoxyethanol aqueous two-phase system

The increasing diesel pollution accidents pose a serious threat to the ecological environment and human health. Remediation of diesel-contaminated soil (DCS) has attracted widespread attention during the past few decades. This work proposed an approach for the remediation of DCS by alkoxyethanol aqueous two-phase extraction (ATPE), which was an application of this small molecule aqueous two-phase system (ATPS). In addition, the influence of temperature, stirring speed, stirring time, and solid-liquid ratio on the removal of diesel was explored respectively. The removal efficiency of diesel could reach more than 97.18% in 18 min. Meanwhile, ATPS had high reusability, and the removal efficiency remained above 85.17% in the reuse process. Alkoxyethanol ATPE could effectively remove diesel hydrocarbons with different carbon chain lengths and the remediation process hardly caused residual organic solvents on the soil surface according to the analysis of gas chromatography-mass spectrometry (GC-MS) and Fourier transforms infrared (FT-IR), which could be regarded as the distinct advantage compared to the traditional surfactant washing method and organic solvent extraction method. The study of soil physicochemical properties and wheat germination proved that the soil structure and properties changed little after ATPE remediation. And finally, the mechanism of alkoxyethanol ATPE was intensively discussed according to the remediation characteristic. This work provided an efficient method for the remediation of DCS and widened the application fields of alkoxyethanol ATPS as well.

Characterization of bacterial community in oil-contaminated soil and its biodegradation efficiency of high molecular weight (>C40) hydrocarbon

In this study, two biosurfactant producing Pseudomonas aeruginosa sp. were isolated from motor oil contaminated soil for crude oil, alkane and PAH degradation studies. Metagenomics analysis identified as proteobacteria phyla was the dominant. Isolated two bacterial species were well grown in mineral salt medium with 1% of crude oil, alkanes (dotriacontane and tetratetracontane) and PAH (pyrene, benzopyrene and anthracene) as sole carbon sources. Total biodegradation efficiency (BE) of strains PP3 and PP4 in Crude oil degradation evaluated by the analysis of gas chromatography and mass spectrometry was 50% and 86% respectively. BE of PP3, PP4 and mixed consortium in alkane biodegradation were 46%, 47% and 36%, respectively. BE of PP3, PP4 and mixed consortium in PAH biodegradation were 22%, 48% and 35%, respectively. Based on the results revealed that strain pp4 was more efficient bacteria to degrade the crude oil, alkane and PAH than pp3. This was due to the higher production of biosurfactant by PP4 than PP3 and also confirmed in the test of emulsification index (E₂₄). FTIR results showed that the produced biosurfactant could partially solubilize the crude oil hydrocarbons, alkanes and PAH and confirmed as glycolipid (rhamnolipid) in nature. Thus, the obtained results from the GCMS showed that all hydrocarbons were utilized by bacteria as carbon source for biosurfactant production and utilize the high molecular weight hydrocarbons. Based on the present study we can suggest that identified potential biosurfactant producing bacteria are used for biodegradation of high molecular weight hydrocarbon (>C40).

Mechanism of bio-electrokinetic remediation of pyrene contaminated soil: Effects of an electric field on the degradation pathway and microbial metabolic processes

In this study, the mechanism of bio-electrokinetic (BIO-EK) remediation to improve the degradation of pyrene was evaluated based on an analysis of the intermediate products and the microbial community. The results show that BIO-EK remediation has a higher pyrene degradation efficiency on pyrene and its intermediate products than the bioremediation and electrokinetic (EK) remediation processes. A series of intermediate products were detected. According to the type of the intermediate products, two degradation pathways, biological metabolism and electrochemical oxidation, are proposed in the BIO-EK remediation of pyrene. Furthermore, the primary microbial taxa involved in the pollutant degradation changed, which led to variations in the functional gene components. The abundant and functional genes related to metabolism were specifically analyzed. The results indicate that the electric field promotes the expression of metabolisms associated with 14 carbohydrates, 13 lipids, 13 amino acids, five energies, and in particular, 11 xenobiotics. These results suggest that in addition to the promotion effect on the microbial metabolism caused by the electric field, BIO-EK remediation can promote the degradation of pollutants due to the coexistence of a microbial metabolic pathway and an electrochemical oxidation pathway.

A biogenic microbial biosurfactin that degrades difenoconazole fungicide with potential antimicrobial and oil displacement properties

Surfactin is a bacterial lipopeptide and an influential biosurfactant mainly known for excellent surfactant ability. The amphiphilic nature of surfactin helps it to sustain under hydrophobic and hydrophilic conditions. In this investigation, a bacterium strain (BTKU3) that produces biosurfactant were isolated from oil-contaminated soil. Based on the blue agar plate (Bap) assay, the BTKU3 strain was found to be promising for biosurfactant production. This strain was later identified as a Lysinibacillus sp. by 16S rRNA sequencing. The characteristics of extracted bacterial surfactin were evidenced by FTIR with the presence of amine, C-H, CO, CC, esters, thiocarbonyl and asymmetric aliphatic C-H stretch molecular structural groups. Further, the extracted bacterial biosurfactant material was subjected to Liquid Chromatography-Mass Spectroscopy (LCMS), and it was identified and confirmed as surfactin with an elution time of 3.1 min and m/z value of 1034. The emulsification and oil displacement tests further proved the surfactin ability with 83% of coconut oil emulsion index and 80 % oil displacement ability with diesel, respectively. Lysinibacillus sp. BTKU3 strain also proved its efficacy in the degradation of difenoconazole by utilizing a capacity of 9.1 μg ml^-1. Thus, it is inferred that the Lysinibacillus sp. BTKU3 strain plays a significant role in the production of surfactin, which positively acts as an antimicrobial agent and reduces contaminants in polluted sites.

A review study on new aspects of biodemulsifiers: Production, features and their application in wastewater treatment

The effluent produced in refineries is in the form of an oil/water emulsion that must be treated. These emulsions are often stable and a suitable method must be used to separate the oil from the emulsion. Recently, biosurfactants or biodemulsifiers have received much attention to reduce the interfacial tension between two liquids. Biodemulsifiers are produced by microorganisms and have several benefits over chemical demulsifiers such as low-toxic, biodegradability, eco-friendly and easy synthesis. They can eliminate two phases by changing the interfacial forces between the water and oil molecules. Biosurfactants are categorized based on the molecular weight of their compounds (low or high molecular weight). Sophorolipids, lipopeptides rhamnolipids, trehalolipids, glycolipid, lipoproteins, lichenysin, surfactin, and polymeric biosurfactants are several types of biosurfactants, which are produced by bacteria or fungi. This review study provides a deep evaluation of biosurfactants in the demulsification process. To this end, different types of biosurfactants, the synthesis method of various biosurfactants using various microorganisms, features of biosurfactants, and the role of biodemulsifiers in the demulsification process are thoroughly discussed. Also, the impact of various efficient factors like pH, microorganism type, temperature, the oil content in the emulsion, and gravity on biodemulsificaion was studied. Finally, the mechanism of the demulsification process was discussed. According to previous studies, rhamnolipid biodemulsifier showed the highest biodemulsification efficiency (100%) in the removal of oil from an emulsion.

Crude oil biodegradation potential of biosurfactant-producing Pseudomonas aeruginosa and Meyerozyma sp

This study investigates the potential of crude oil degrading capabilities of biosurfactant-producing strains of Pseudomonas aeruginosa MF069166 and Meyerozyma sp. MF138126. P. aeruginosa produced mono-/di-rhamnolipids congeners whereas, Meyerozyma sp. produced acidic and lactonic forms of sophorolipids with crude oil. The values of critical micelle concentrations of rhamnolipids and sophorolipids were 40 mg/L and 50 mg/L with reductions in surface tension of water to 29 mN/m and 33 mN/m. Dynamic light scattering revealed that the average diameter of micellar aggregates of rhamnolipids ranged between 300 and 350 nm and the average size of sophorolipids micelles was 309 nm and 380 nm. Biosurfactants from P. aeruginosa and Meyerozyma sp. exhibited emulsification activities of 87% and 84% in crude oil. Cell surface hydrophobicity of both strains was higher in the presence of hydrophobic contaminants. The biosurfactants showed stability under varying pH, NaCl concentrations and temperatures. Gravimetric and GC-MS analyses demonstrated that P. aeruginosa degraded 91% of the petroleum hydrocarbons while Meyerozyma sp. showed 87% biodegradation efficiency. P. aeruginosa and Meyerozyma sp. have also been found to degrade halogen-containing compounds and showed excellent crude oil degradation efficiency. It is concluded that both strains have high potential of applications in the bioremediation of hydrocarbons-contaminated sites.

Bioremediation of ossein effluents using the filamentous marine cyanobacterium Cylindrospermum stagnale

Wastewater containg proteinaceous ossein effluents are problematic to be treated. We studied the possibility to treat ossein effluents with the marine cyanobacterium strain Cylindrospermum stagnale. After optimizing the culture conditions of the bacterium, three different types of ossein effluents were tested: dicalcium phosphate (DCP), high total dissolved solids (HTDS) and low total dissolved (LTDS). The effluents were diluted with sea water at the following ratios 1:1, 2:1 and 3:2. The optimum operating conditions were at 3000 lux light intensity and 37 °C temperature. The highest degradation of ossein effluens by C. stagnale was attained for a dilution ratio of 1:1. However, less diluted ossein effluents reduced the growth of C. stagnale drastically. The degradation was shown by measuring the chlorophyll a content and the dry weight of bacterial cells during a seven-day incubation period degradation. Fourier Transform Infrared Spectroscopy (FT-IR) analysis verified the degradation showing the presence of the degradation products of ossein (i.e. calcium carbonate and calcite) in the culture medium. Lipid composition in fatty acids appeared to be suitable for biofuel production. The results showed that the marine cyanobacterium C. stagnale can be used to treat ossein effluents, and at the same time, to produce biofuel in a sustainable way.

Investigating the potential of bioremediation in aged oil-polluted hypersaline soils in the south oilfields of Iran

To date, studies for bioremediation of oil-polluted hypersaline soils have been neglected or limited to specific spots. Hence, in this study, ten samples of oil field soils in the Khuzestan province of Iran were collected to evaluate bioremediation's feasibility. These samples were analyzed for their physicochemical properties as well as the most probable number of total and hydrocarbon-degrading bacteria. Thirty-nine hydrocarbon-degrading bacteria were isolated from these soils over a 1-month incubation in an MSM medium enriched with diesel oil as the sole source of carbon. As revealed by 16S-rRNA analysis, the identified strains belonged to the genera Ochrobactrum, Microbacterium, and Bacillus with a high frequency of Ochrobactrum species. Additionally, by using degenerate primers, the third group of alkB gene was detected in Ochrobactrum and Microbacterium isolates through the touchdown nested PCR method for the first time. Ochrobactrum species possessing the alkB gene showed the highest population, and therefore, the highest adaptation to harsh environmental conditions. Most isolates showed outstanding results in the ability to grow with crude and diesel oil and tolerate high salt percentages, biosurfactant production, and emulsification activity, which are considered the most effective factors in bioremediation of such environments. Considering the soil analysis, limiting factors in bioremediation like available phosphorous, and the abundance of bacteria with remediation traits in these soils, these extremely polluted environments can be refined.

Catabolic enzyme activities during biodegradation of three-ring PAHs by novel DTU-1Y and DTU-7P strains isolated from petroleum-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants having health hazards. PAH-utilizing bacterial strains were isolated from petroleum-contaminated soil from siding area, Bijwasan supply location of BPCL, Delhi, India. Bacterial strains with different morphology were isolated and acclimatized to a mixture of low molecular weight PAH compounds in the concentration range of 50-10,000 mg/L. Two bacterial strains surviving at 10,000 mg/L PAH concentration were identified as Kocuria flava and Rhodococcus pyridinivorans, based on 16S rRNA gene sequencing and phylogenetic analysis over MEGA X, are reported for the first time for PAH degradation. The strain K. flava could degrade phenanthrene, anthracene, and fluorene with efficiency of 55.13%, 59.01%, and 63.46%, whereas R. pyridinivorans exhibited 62.03%, 64.99%, and 66.79% degradation for respective PAHs at initial PAH concentration of 10 mg/L. Slightly lower degradation of phenanthrene could be attributed to its more stable chemical structure. The consortium of both the strains degraded 61.32%, 64.72%, and 66.64%, of 10 mg/L of phenanthrene, anthracene, and fluorene, respectively, in 15 days of incubation period indicating no synergistic or antagonistic effect towards degradation. Catechol 2,3-dioxygenase (C23O), dehydrogenase and peroxidase enzyme activities during PAH degradation coincided with degradation of PAHs, thus highlighting the role of these enzymes in catabolising three-ring PAHs. This is the first investigation confirming the participation of C23O, dehydrogenase and peroxidases enzyme profiles throughout the period of degradation. The study concludes that these strains can play significant role in microbial remediation of PAH-contaminated environment.

Optimization of growth conditions for enhancing the production of microbial laccase and its application in treating antibiotic contamination in wastewater

In this work, seven indigenous macrofungal isolates were selected to screen for their laccase production capability. Among them, isolates viz., Pleurotus eryngii, Pleurotus florida, Pleurotus sajor caju and Gandoderma lucidum were found to exhibit high laccase activity in the preliminary studies and were thus selected for the optimization studies with an aim to enhance laccase production. The pH optimization studies were carried out between pH range of 4-6. The laccase activity and biomass were found to be optimum at pH 4, 4.5, 4.5 and 5 for P. eryngii, P. florida, P. sajor caju and G. lucidum, respectively. Optimization studies with chemical inducers namely, tannic acid, 2,6 dimethoxyphenol and copper sulphate at three different concentration levels were conducted and tannic acid at 2 mM concentration was found to increase the laccase activity to about 45% followed by 2,6 dimethoxyphenol (2 mM) with an increase of about 43% and copper sulphate (0.1 mM) showing 21% increase in the yield. Biodegradation studies utilizing laccase isolated from P. eryngii, P. florida and P. sajor caju was carried out for a commonly detected fluoroquinolone antibiotic, levofloxacin, in water and pharmaceutical wastewater. The results indicated that the degradation efficiency of levofloxacin using laccase isolated from P. eryngii (88.9%) was comparable to commercial laccase (89%). When the cost economics of using crude laccase was evaluated against commercial laccase it was evident that the total cost of the treatment could be reduced by 71.7% if commercial grade laccase was replaced by crude enzyme extracted from indigenous macrofungi such Pleurotus eryngii, Pleurotus florida, and Pleurotus sajor caju indicating a promising and cost-effective alternative for wastewater treatment.

Development and Genetic Engineering of Hyper-Producing Microbial Strains for Improved Synthesis of Biosurfactants

Current research energies are fixated on the synthesis of environmentally friendly and non-hazardous products, which include finding and recognizing biosurfactants that can substitute synthetic surfactants. Microbial biosurfactants are surface-active compounds synthesized intracellularly or extracellularly. To use biosurfactants in various industries, it is essential to understand scientific engagements that demonstrate its potentials as real advancement in the 21st century. Other than applying a substantial effect on the world economic market, engineered hyper-producing microbial strains in combination with optimized cultivation parameters have made it probable for many industrial companies to receive the profits of 'green' biosurfactant innovation. There needs to be an emphasis on the worldwide state of biosurfactant synthesis, expression of biosurfactant genes in expressive host systems, the recent developments, and prospects in this line of research. Thus, molecular dynamics with respect to genetic engineering of biosynthetic genes are proposed as new biotechnological tools for development, improved synthesis, and applications of biosurfactants. For example, mutant and hyper-producing recombinants have been designed efficaciously to advance the nature, quantity, and quality of biosurfactants. The fastidious and deliberate investigation will prompt a comprehension of the molecular dynamics and phenomena in new microorganisms. Throughout the decade, valuable data on the molecular genetics of biosurfactant have been produced, and this solid foundation would encourage application-oriented yields of the biosurfactant production industry and expand its utilization in diverse fields. Therefore, the conversations among different interdisciplinary experts from various scientific interests such as microbiology, biochemistry, molecular biology, and genetics are indispensable and significant to accomplish these objectives.