The enhancement by surfactants of hexadecane degradation by Pseudomonas aeruginosa varies with substrate availability

Spatial distribution characteristics and degradation mechanism of microorganisms in n-hexadecane contaminated vadose zone

The damage caused by petroleum hydrocarbon pollution to soil and groundwater environment is becoming increasingly significant. The vadose zone is the only way for petroleum hydrocarbon pollutants to leak from surface into groundwater. The spatial distribution characteristics of indigenous microorganisms in vadose zone, considering presence of capillary zones, have rarely been reported. To explore the spatial distribution characteristics of indigenous microorganisms in vadose zone contaminated by petroleum hydrocarbons, a one-dimensional column migration experiment was conducted using n-hexadecane as characteristic pollutant. Soil samples were collected periodically from different heights during experiment. Corresponding environmental factors were monitored online. The microbial community structure and spatial distribution characteristics of the cumulative relative abundance were systematically analyzed using 16S rRNA sequencing. In addition, the microbial degradation mechanism of n-hexadecane was analyzed using metabolomics. The results showed that presence of capillary zone had a strong retarding effect on n-hexadecane infiltration. Leaked pollutants were mainly concentrated in areas with strong capillary action. Infiltration and displacement of NAPL-phase pollutants were major driving force for change in moisture content (θ) and electric conductivity (EC) in vadose zone. The degradation by microorganisms results in a downward trend in potential of hydrogen (pH) and oxidation-reduction potential (ORP). Five petroleum hydrocarbon-degrading bacterial phyla and 11 degradable straight-chain alkane bacterial genera were detected. Microbial degradation was strong in the area near edge of capillary zone and locations of pollutant accumulation. Mainly Sphingomonas and Nocardioides bacteria were involved in microbial degradation of n-hexadecane. Single-end oxidation involved microbial degradation of n-hexadecane (C16H34). The oxygen consumed, hexadecanoic acid (C16H32O2) produced during this process, and release of hydrogen ions (H+) were the driving factors for reduction of ORP and pH. The vadose zone in this study considered presence of capillary zone, which was more in line with actual contaminated site conditions compared with previous studies. This study systematically elucidated vertical distribution characteristics of petroleum hydrocarbon pollutants and spatiotemporal variation characteristics of indigenous microorganisms in vadose zone considered presence of capillary zone. In addition, the n-hexadecane degradation mechanism was elucidated using metabolomics. This study provides theoretical support for development of natural attenuation remediation measures for petroleum-hydrocarbon-contaminated soil and groundwater.

New Trends in Biosurfactants: From Renewable Origin to Green Enhanced Oil Recovery Applications

Enhanced oil recovery (EOR) processes are technologies used in the oil and gas industry to maximize the extraction of residual oil from reservoirs after primary and secondary recovery methods have been carried out. The injection into the reservoir of surface-active substances capable of reducing the surface tension between oil and the rock surface should favor its extraction with significant economic repercussions. However, the most commonly used surfactants in EOR are derived from petroleum, and their use can have negative environmental impacts, such as toxicity and persistence in the environment. Biosurfactants on the other hand, are derived from renewable resources and are biodegradable, making them potentially more sustainable and environmentally friendly. The present review intends to offer an updated overview of the most significant results available in scientific literature on the potential application of biosurfactants in the context of EOR processes. Aspects such as production strategies, techniques for characterizing the mechanisms of action and the pros and cons of the application of biosurfactants as a principal method for EOR will be illustrated and discussed in detail. Optimized concepts such as the HLD in biosurfactant choice and design for EOR are also discussed. The scientific findings that are illustrated and reviewed in this paper show why general emphasis needs to be placed on the development and adoption of biosurfactants in EOR as a substantial contribution to a more sustainable and environmentally friendly oil and gas industry.

Hexadecane biodegradation of high efficiency by bacterial isolates from Santos Basin sediments

The aim of the study was the investigation of bacterial diversity from sediments collected at Santos Estuarine System, regarding to their abilities for hexadecane biotransformation. Hexadecane is a medium-chain linear alkane, considered as a model molecule for hydrocarbon biodegradation studies. It is a component from aliphatic fraction of crude petroleum, commonly related to environmental contamination by diesel oil. Santos Basin is an area with historical petroleum contamination. In the present work, sediment samples from this area were inoculated in artificial seawater (ASW), containing hexadecane as carbon source. Six bacterial isolates were selected as resistant to hexadecane. Chromatographic results showed biodegradation indexes above 97%. After 48 h of culture, five of them could degrade >80% of the initial hexadecane added. These isolates were characterized by 16S rDNA gene sequencing analysis. The following species were found: Bacillus amyloliquefaciens, Staphylococcus epidermidis, Micrococcus luteus, Nitratireductor aquimarinus, and Bacillus pumilus.

Oil-Spill Triggered Shift in Indigenous Microbial Structure and Functional Dynamics in Different Marine Environmental Matrices

Microbial degradation has long been recognized as the key rescue mechanism in shaping the oil polluted marine environments and the role of indigenous populations or their functional genomics have never been explored from Indian marine environments, post an oil spill event. In the current study, high throughput metagenomic analysis, PLFA profiling and mass spectrophotometric analysis was performed in combination with metabolomics to capture signature variations among the microbial communities in sediment, water and laboratory enrichments. Contrary to the previous reports, the bloom of Pseudomonadales (specifically genus Acinetobacter) in oiled sediment and Methylococcales in oiled water outnumbered the relative abundance of Alcanivorax in response to hydrocarbon contamination. Overall enhancement of xenobiotic degradation was suggested by metabolomic analysis in sediment and water post the spill event and varying quantitative assemblage of enzymes were found to be involved in hydrocarbon utilization. Laboratory enrichments revealed the competitive advantage of sediment communities over the water communities although unique taxa belonging to the later were also found to be enriched under in vitro conditions. Simultaneous analysis of sediment and water in the study provided explicit evidences on existence of differential microbial community dynamics, offering insight into possibilities of formulating nature identical solutions for hydrocarbon pollution.

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

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

Kinetic parameters and nitrate, nitrite changes in bioremediation of Toxic Pentaerythritol Tetranitrate (PETN) contaminated soil

Background

Cleanup of areas contaminated by explosives is a public health concern. Some explosives can be carcinogenic in humans. Pentaerythritol Tetranitrate (PETN), a powerful explosive with very low water solubility, can be easily transported to ground waters.

Objective

This study was conducted to determine the removal efficiencies of PETN from soil by bioremediation, and obtain kinetic parameters of biological process.

Methods

This experimental study was conducted at the Environmental Health Engineering Lab (Isfahan University of Medical Sciences, Isfahan, Iran) in 2015–2016. In the present work, bioremediation of the explosive-polluted soils by PETN in anaerobic-aerobic landfarming method was performed. The influence of seeding and biosurfactant addition on bioremediation was also evaluated. The data were analyzed using Microsoft Excel software.

Results

The results show that, as the initial concentration of PETN increased, the lag phase was increased and the specific growth rate was increased up to 0.1/day in concentration of 50 mg/kg, and then it was decreased to 0.04/day. Subsequent decreases in specific growth rate can cause substrate inhibition. Seeding causes decrease in lag phase significantly. Biosurfactant addition had little to no impact on the length of lag phase, but biosurfactant plus seeding can increase the growth rate to 0.2/day, however, inhibitory effect of the initial concentration was started in very high concentration of PETN (150 mg/kg).

Conclusion

Biosurfactant addition and seeding together have an impressive effect on biodegradation of PETN, furthermore seeding can enhance active microbial consortium and biosurfactant can improve the poor aqueous solubility of PETN, therefore making the substrate more accessible.

Characterization of Biosurfactant Produced during Degradation of Hydrocarbons Using Crude Oil As Sole Source of Carbon

Production and spillage of petroleum hydrocarbons which is the most versatile energy resource causes disastrous environmental pollution. Elevated oil degrading performance from microorganisms is demanded for successful microbial remediation of those toxic pollutants. The employment of biosurfactant-producing and hydrocarbon-utilizing microbes enhances the effectiveness of bioremediation as biosurfactant plays a key role by making hydrocarbons bio-available for degradation. The present study aimed the isolation of a potent biosurfactant producing indigenous bacteria which can be employed for crude oil remediation, along with the characterization of the biosurfactant produced during crude oil biodegradation. A potent bacterial strain Pseudomonas aeruginosa PG1 (identified by 16s rDNA sequencing) was isolated from hydrocarbon contaminated soil that could efficiently produce biosurfactant by utilizing crude oil components as the carbon source, thereby leading to the enhanced degradation of the petroleum hydrocarbons. Strain PG1 could degrade 81.8% of total petroleum hydrocarbons (TPH) after 5 weeks of culture when grown in mineral salt media (MSM) supplemented with 2% (v/v) crude oil as the sole carbon source. GCMS analysis of the treated crude oil samples revealed that P. aeruginosa PG1 could potentially degrade various hydrocarbon contents including various PAHs present in the crude oil. Biosurfactant produced by strain PG1 in the course of crude oil degradation, promotes the reduction of surface tension (ST) of the culture medium from 51.8 to 29.6 mN m⁻¹, with the critical micelle concentration (CMC) of 56 mg L⁻¹. FTIR, LC-MS, and SEM-EDS studies revealed that the biosurfactant is a rhamnolipid comprising of both mono and di rhamnolipid congeners. The biosurfactant did not exhibit any cytotoxic effect to mouse L292 fibroblastic cell line, however, strong antibiotic activity against some pathogenic bacteria and fungus was observed.

Hydrocarbons biodegradation by activated sludge bacteria in the presence of natural and synthetic surfactants

Fuels, such as diesel oil, can have a substantial impact on the microbial equilibrium of activated sludge and have a negative influence on work of wastewater treatment plant. The primary objective of the research was to examine the possibility of using the surfactants to improve pollutants biodegradation by bacteria from activated sludge. The results showed that the addition of rhamnolipids allows to increase the hydrocarbon biodegradation from 47% up to 75% in the cultures inoculated with the consortium. The saponins increased the degradation of diesel oil by the two isolated strains: from 27% to 43% for Alcaligenes sp. and from 44% to 64% for Pseudomonas sp. The addition of surfactants to the cultures growth with diesel oil caused a significant decrease of the surface charge for Alcaligenes strain in the presence of saponins, but not in other cases. The obtained results revealed the potential of natural surfactants to support hydrocarbon biodegradation in wastewater treatment plants.

Biodegradation of diesel oil by a novel microbial consortium: comparison between co-inoculation with biosurfactant-producing strain and exogenously added biosurfactants

Bioremediation, involving the use of microorganisms to detoxify or remove pollutants, is the most interesting strategy for hydrocarbon remediation. In this aim, four hydrocarbon-degrading bacteria were isolated from oil-contaminated soil in Tunisia. They were identified by the 16S rDNA sequence analysis, as Lysinibacillus bronitolerans RI18 (KF964487), Bacillus thuringiensis RI16 (KM111604), Bacillus weihenstephanensis RI12 (KM094930), and Acinetobacter radioresistens RI7 (KJ829530). Moreover, a lipopeptide biosurfactant produced by Bacillus subtilis SPB1, confirmed to increase diesel solubility, was tested to increase diesel biodegradation along with co-inoculation with two biosurfactant-producing strains. Culture studies revealed the enhancement of diesel biodegradation by the selected consortium with the addition of SPB1 lipopeptide and in the cases of co-inoculation by biosurfactant-producing strain. In fact, an improvement of about 38.42 and 49.65 % of diesel degradation was registered in the presence of 0.1 % lipopeptide biosurfactant and when culturing B. subtilis SPB1 strain with the isolated consortium, respectively. Furthermore, the best improvement, evaluated to about 55.4 %, was recorded when using the consortium cultured with B. subtilis SPB1 and A. radioresistens RI7 strains. Gas chromatography analyses were correlated with the gravimetric evaluation of the residual hydrocarbons. Results suggested the potential applicability of the selected consortium along with the ex situ- and in situ-added biosurfactant for the effective bioremediation of diesel-contaminated water and soil.

Pseudosolubilized n-alkanes analysis and optimization of biosurfactants production by Pseudomonas sp. DG17

The pseudosolubilized medium-chain-length n-alkanes during biodegradation process, and optimization of medium composition and culture conditions for rhamnolipid production by Pseudomonas sp. DG17 using Plackett-Burman design and Box-Behnken design, were examined in this study. The results showed that pseudosolubilized concentration of C14 to C20 n-alkanes was higher than that of C24 to C26. After incubation for 120 h, pseudosolubilized C16H34 increased to 2.63 ± 0.21 mg. Meanwhile, biodegradation rates of n-alkanes decreased along with the increase of carbon chain length. Carbon-14 assay suggested that nonlabeled C14H30, C16H34, and C20H42 inhibited the biodegradation of (14)C n-octadecane, and Pseudomonas sp. DG17 utilized different alkanes simultaneously. Three significant variables (substrate concentration, salinity, and C/N) that could influence rhamnolipid production were screened by Plackett-Burman design. Results of Box-Behnken design suggested that rhamnolipid concentration could be achieved at 91.24 mg L(-1) (observed value) or 87.92 mg L(-1) (predicted value) with the optimal levels of concentration, salinity, and C/N of 400 mg L(-1), 1.5 %, and 45, respectively.

Pentachlorophenol degradation by Janibacter sp., a new actinobacterium isolated from saline sediment of arid land

Many pentachlorophenol- (PCP-) contaminated environments are characterized by low or elevated temperatures, acidic or alkaline pH, and high salt concentrations. PCP-degrading microorganisms, adapted to grow and prosper in these environments, play an important role in the biological treatment of polluted extreme habitats. A PCP-degrading bacterium was isolated and characterized from arid and saline soil in southern Tunisia and was enriched in mineral salts medium supplemented with PCP as source of carbon and energy. Based on 16S rRNA coding gene sequence analysis, the strain FAS23 was identified as Janibacter sp. As revealed by high performance liquid chromatography (HPLC) analysis, FAS23 strain was found to be efficient for PCP removal in the presence of 1% of glucose. The conditions of growth and PCP removal by FAS23 strain were found to be optimal in neutral pH and at a temperature of 30 °C. Moreover, this strain was found to be halotolerant at a range of 1-10% of NaCl and able to degrade PCP at a concentration up to 300 mg/L, while the addition of nonionic surfactant (Tween 80) enhanced the PCP removal capacity.

Uptake and trans-membrane transport of petroleum hydrocarbons by microorganisms

Petroleum-based products are a primary energy source in the industry and daily life. During the exploration, processing, transport and storage of petroleum and petroleum products, water or soil pollution occurs regularly. Biodegradation of the hydrocarbon pollutants by indigenous microorganisms is one of the primary mechanisms of removal of petroleum compounds from the environment. However, the physical contact between microorganisms and hydrophobic hydrocarbons limits the biodegradation rate. This paper presents an updated review of the petroleum hydrocarbon uptake and transport across the outer membrane of microorganisms with the help of outer membrane proteins.

Enhanced ex situ bioremediation of crude oil contaminated beach sand by supplementation with nutrients and rhamnolipids

Mediterranean coastal regions are particularly exposed to oil pollution due to extensive industrialization, urbanization and transport of crude and refined oil to and from refineries. Bioremediation of contaminated beach sand through landfarming is both simple and cost-effective to implement compared to other treatment technologies. The purpose of the present study was to investigate the effect of alternative nutrients on biodegradation of crude oil contaminated beach sand in an effort to reduce the time required for bioremediation employing only indigenous hydrocarbon degraders. A natural sandy soil was collected from Agios Onoufrios beach (Chania, Greece) and was contaminated with weathered crude oil. The indigenous microbial population in the contaminated sand was tested alone (control treatment) or in combination with inorganic nutrients (KNO3 and K2HPO4) to investigate their effects on oil biodegradation rates. In addition, the ability of biosurfactants (rhamnolipids), in the presence of organic nutrients (uric acid and lecithin), to further stimulate biodegradation was investigated in laboratory microcosms over a 45-day period. Biodegradation was tracked by GC/MS analysis of aliphatic and polycyclic aromatic hydrocarbons components and the measured concentrations were corrected for abiotic removal by hopane normalizations. It was found that the saturated fraction of the residual oil is degraded more extensively than the aromatic fraction and the bacterial growth after an incubation period of approximately 3 weeks was much greater from the bacterial growth in the control. The results show that the treatments with inorganic or organic nutrients are equally effective over almost 30 days where C12-C35n-alkanes were degraded more than 97% and polyaromatic hydrocarbons with two or three rings were degraded more than 95% within 45 days. The results clearly show that the addition of nutrients to contaminated beach sand significantly enhanced the activity of indigenous microorganisms, as well as the removal of total recoverable petroleum hydrocarbons (TRPH) over a 45-day study period.

Culturable populations of Acinetobacter can promptly respond to contamination by alkanes in mangrove sediments

This study evaluated the potential of bacterial isolates from mangrove sediments to degrade hexadecane, an paraffin hydrocarbon that is a large constituent of diesel and automobile lubricants. From a total of 18 oil-degrading isolates obtained by an enrichment technique, four isolates showed a great potential to degrade hexadecane. The strain MSIC01, which was identified by 16S rRNA gene sequencing as Acinetobacter sp., showed the best performance in degrading this hydrocarbon, being capable of completely degrading 1% (v/v) hexadecane within 48 h without releasing biosurfactants. Its hydrophobic surface probably justifies its potential to degrade high concentrations of hexadecane. Thus, the sediments from the studied mangrove harbour bacterial communities that are able to use oil as a carbon source, which is a particularly interesting feature due to the risk of oil spills in coastal areas. Moreover, Acinetobacter sp. MSIC01 emerged as a promising candidate for applications in bioremediation of contaminated mangrove sediments.

A "wrap-and-wrest" mechanism of fluorescence quenching of CdSe/ZnS quantum dots by surfactant molecules

We identified a mechanism of fluorescence quenching of CdSe/ZnS quantum dots (QDs) coated with two organic layers, octadecylamine and an amphiphilic polymer containing COOH groups, by nonionic polyoxyethylene-based (C12En) surfactants. The surfactant molecules by themselves do not affect the fluorescence of the QDs. For the quenching to occur, "wrapping" of the QDs by a bilayer of the surfactant molecules is necessary. The formation of the bilayer causes an irreversible detachment ("wresting") of the ligand molecules, accompanied by the creation of quenching sites on the QD surface. Due to its two-stage nature, we refer to the quenching mechanism as the "wrap-and-wrest" mechanism. The adsorption of the surfactant on the QD surface is a relatively slow process, occurring within minutes or hours. Such long quenching times allowed monitoring surfactant adsorption progress in real time. The fluorescence signal decays exponentially, and the decay time is inversely proportional to the surfactant concentration in solution.

Recent development in the treatment of oily sludge from petroleum industry: a review

Oily sludge is one of the most significant solid wastes generated in the petroleum industry. It is a complex emulsion of various petroleum hydrocarbons (PHCs), water, heavy metals, and solid particles. Due to its hazardous nature and increased generation quantities around the world, the effective treatment of oily sludge has attracted widespread attention. In this review, the origin, characteristics, and environmental impacts of oily sludge were introduced. Many methods have been investigated for dealing with PHCs in oily sludge either through oil recovery or sludge disposal, but little attention has been paid to handle its various heavy metals. These methods were discussed by dividing them into oil recovery and sludge disposal approaches. It was recognized that no single specific process can be considered as a panacea since each method is associated with different advantages and limitations. Future efforts should focus on the improvement of current technologies and the combination of oil recovery with sludge disposal in order to comply with both resource reuse recommendations and environmental regulations. The comprehensive examination of oily sludge treatment methods will help researchers and practitioners to have a good understanding of both recent developments and future research directions.

Biodegradation of petroleum hydrocarbons in contaminated clayey soils from a sub-arctic site: the role of aggregate size and microstructure

This study investigates the extent of biodegradation of non-volatile petroleum hydrocarbons (C16-C34) and the associated microbial activity in predominant aggregate sizes during a pilot-scale biopile experiment conducted at 15 °C, with a clayey soil, from a crude oil-impacted site in northern Canada. The in situ aggregate microstructure was characterized by N2 adsorption and X-ray CT scanning. The soils in the nutrient (N)-amended and unamended biopile tanks were comprised of macroaggregates (>2 mm) and mesoaggregates (0.25-2 mm). Nutrient addition significantly enhanced petroleum hydrocarbon biodegradation in macroaggregates, but not in mesoaggregates. At the end of 65-d biopile experiment, 42% of the C16-C34 hydrocarbons were degraded in the nutrient-amended macroaggregates, compared to 13% in the mesoaggregates. Higher microbial activity in the macroaggregates of the nutrient amended biopile was inferred from a larger increase in extractable protein concentrations, compared to the other aggregates. Terminal Restriction Fragment Length Polymorphism (T-RFLP) of 16S rRNA genes showed that there was no selection of bacterial populations in any of the aggregates during biopile treatment, suggesting that the enhanced biodegradation in nutrient-amended macroaggregates was likely due to metabolic stimulation. X-ray micro CT scanning revealed that the number of pores wider than 4 μm, which would be easily accessible by bacteria, were an order of magnitude higher in macroaggregates. Also, N2 adsorption analyses showed that pore surface areas and pore volumes per unit weight were four to five-times larger, compared to the mesoaggregates. Thus the higher porosity microstructure in macroaggregates allowed greater hydrocarbon degradation upon biostimulation by nutrient addition and aeration.

The potential of gibberellic acid 3 (GA3) and Tween-80 induced phytoremediation of co-contamination of Cd and Benzo[a]pyrene (B[a]P) using Tagetes patula

The present study was conducted to investigate the effectiveness of GA(3) and Tween-80 on enhancing the phytoremediation of Cd-B[a]P co-contaminated soils. Results showed that the addition of GA(3) and GA(3)-Tween-80 enhanced Tagetes patula growth by 14%-32% and 23%-55%, respectively, relative to the control group. However, under independent GA(3)-treated soils, Cd and B[a]P concentrations in the shoots of the plants decreased by 15%-33% and 15%-53%, respectively, compared with CK. By contrast, the shoot concentration and accumulation of Cd under GA(3)-Tween-80 treatment increased by 0.01-0.46 and 1.33-1.55 times, respectively, whereas those of B[a]P increased from 0.57 to 0.82, and 1.33 to 1.55 times, respectively, compared with those of the control. Optimal result for Cd phytoextraction was obtained under combined 5 mmol Tween-80 kg(-1) and 1 mmol GA(3) kg(-1) treatment, and the maximum removal rate of B[a]P was obtained after the application of 5 mmol Tween-80 kg(-1) and 5 mmol GA(3) kg(-1).

Evaluation of surfactants as solubilizing agents in microsomal metabolism reactions with lipophilic substrates

Solubilizing agents are routinely added when investigating the biotransformation of lipophilic substrates using hepatic microsomes. For highly lipophilic compounds, the concentration of solvent or surfactant necessary for dissolution can be detrimental to enzyme activity. This study evaluates the effect of 12 surfactants on microsomal metabolism and the ability of the same surfactants to improve the aqueous solubility of the pentabrominated diphenyl ether BDE-100, a lipophilic environmental contaminant previously found to be recalcitrant to in vitro metabolism. Of the surfactants investigated, Cremophor EL and Tween 80 displayed the best combination of increased BDE-100 solubility and minimal inhibition of microsomal metabolism. However, a comparison of the in vitro metabolism products of BDE-100 in the presence of the two surfactants revealed varying amounts of metabolites depending on the surfactant used.

Effects of surfactant micelles on solubilization and DPPH radical scavenging activity of Rutin

The interaction of the antioxidant Rutin with the radical DPPH (2,2-diphenyl-1-picrylhydrazyl) in presence of cationic (CTAB, TTAB, DTAB), non-ionic (Brij78, Brij58, Brij35), anionic (SDS) and mixed surfactant systems (CTAB-Brij58, DTAB-Brij35, SDS-Brij35) has been followed by spectrophotometric and tensiometric methods to evaluate the DPPH radical scavenging activity (RSA) of Rutin in these model self-assembled structures. The results show that the solubilization capacity of various single surfactant systems for both DPPH as well as Rutin followed the order cationics > non-ionics > anionic. The radical scavenging activity of Rutin in the solubilized form was higher within ionic micelles than in non-ionic micelles. However, the antioxidant exhibited enhanced activity for the radical in mixed cationic-non-ionic micelles compared with any of the single component micelles. In contrast, anionic-non-ionic mixed micelles modulated the activity of Rutin in-between that seen for pure anionic and non-ionic micelles only.

Carbon content reduction in a model reluctant clayey soil: slurry phase n-hexadecane bioremediation

Clayey soils contaminated with organic pollutants are nowadays one of the important environmental issues as they are highly reluctant to conventional bioremediation techniques. In this study, biodegradability of n-hexadecane as a model contaminant in oil polluted clayey soil by an indigenous bacterium was investigated. Maximal bacterial growth was achieved at 8% (v/v) n-hexadecane as sole carbon and energy sources in aqueous phase. The predominant n-hexadecane uptake mechanism was identified to be biosurfactant-mediated using bacterial adhesion to hydrocarbon (BATH) test and surface tension measurements. The effect of n-hexadecane concentration, soil to water ratio, inoculum concentration and pH on total organic carbon (TOC) reduction from kaolin soil in slurry phase was investigated at two levels in shake flasks using full factorial experimental design method where 10,000 (mg n-hexadecane)(kg soil)(-1), soil-water ratio of 1:3, 10% (v/w) inoculum and pH of 7 resulted in the highest TOC reduction of 70% within 20 days. Additionally, slurry bioreactor experiments were performed to study the effect of various aeration rates on n-hexadecane biodegradation during 9 days where 2.5 vvm was found as an appropriate aeration rate leading to 54% TOC reduction. Slurry phase bioremediation is shown to be a successful method for remediation of clayey reluctant soils.

Biodegradation of semi- and non-volatile petroleum hydrocarbons in aged, contaminated soils from a sub-Arctic site: laboratory pilot-scale experiments at site temperatures

This study evaluates the feasibility of landfarming biotreatment of petroleum-contaminated soils obtained from a sub-Arctic site at Resolution Island, Nunavut, Canada, and evaluates the changes in composition of the semi- and non-volatile petroleum hydrocarbon fractions during the biotreatment. Pilot-scale landfarming experiments were conducted in a laboratory in soil tanks under temperature profiles representative of the 3-year site air temperatures in July and August where temperature varied uniformly between 1 degrees C and 10 degrees C over 10 d. The site soils were acidic and N-deficient, but contained indigenous populations of hydrocarbon-degrading microorganisms. Biostimulation with nitrogen and phosphorus nutrient amendments to achieve C(TPH):N:P molar ratio of 100:9:1, and CaCO(3) amendment at 2000 mg Kg(-1) for maintaining neutral pH, and periodic 10-day tilling, reduced total petroleum hydrocarbon (TPH) concentrations by up to 64% over a 60-day period. The rate and extent of semi-volatile (F2: >C10-C16) and non-volatile (F3: >C16-C34) petroleum hydrocarbon fractions in the landfarms containing higher initial TPH levels ( approximately 2000 mg Kg(-1)) and lower TPH levels ( approximately 1000 mg Kg(-1)) were compared. Significant biodegradation of the F2 and F3 fractions occurred in both of those systems. First-order biodegradation rate constants of up to 0.019+/-0.001 d(-1) were determined for the F3 hydrocarbon fraction and were similar to the F2 fraction biodegradation rate constants of up to 0.024+/-0.005 d(-1). Biodegradation profiles of the C14, C16 and C18 alkanes revealed that at TPH concentrations above 1000 mg Kg(-1) these compounds are degraded concurrently, whereas below 1000 mg Kg(-1) the higher-molecular weight alkanes are preferentially degraded. After the 60-day treatment period, the TPH concentration was approximately 500 mg Kg(-1), and the residual TPH mass was largely associated with particles and aggregated particles with diameters of 0.6-2 mm, rather than the larger or finer particles and aggregates.

Biotreatment of oily wastewater by rhamnolipids in aerated active sludge system

Oily wastewater generated by various industries creates a major ecological problem throughout the world. The traditional methods for the oily wastewater treatment are inefficient and costly. Surfactants can promote the biodegradation of petroleum hydrocarbons by dispersing oil into aqueous environment. In the present study, we applied rhamnolipid-containing cell-free culture broth to enhance the biodegradation of crude oil and lubricating oil in a conventional aerobically-activated sludge system. At 20 degrees C, rhamnolipids (11.2 mg/L) increased the removal efficiency of crude oil from 17.7% (in the absence of rhamnolipids) to 63%. At 25 degrees C, the removal efficiency of crude oil was over 80% with the presence of rhamnolipids compared with 22.3% in the absence of rhamnolipids. Similarly, rhamnolipid treatment (22.5 mg/L) for 24 h at 20 degrees C significantly increased the removal rate of lubricating oil to 92% compared with 24% in the absence of rhamnolipids. The enhanced removal of hydrocarbons was mainly attributed to the improved solubility and the reduced interfacial tension by rhamnolipids. We conclude that a direct application of the crude rhamnolipid solution from cell culture is effective and economic in removing oily contaminants from wastewater.

Biosurfactant's role in bioremediation of NAPL and fermentative production

Surfactants and biosurfactants are amphipathic molecules with both hydrophilic and hydrophobic moieties that partition preferentially at the interface between fluid phases that have different degrees of polarity and hydrogen bonding which confers excellent detergency, emulsifying, foaming and dispersing traits, making them most versatile process chemicals. One of the major applications of (bio)surfactants is in environmental bioremediation field. Most synthetic organic compounds present in contaminated soils are only weakly soluble or completely insoluble in water, so they exist in the subsurface as separate liquid phase, often referred as a non-aqueous phase liquids (NAPL), which poses as threat to environment. Several studies have revealed the use of surfactants for remediation; however, several factors limit the use of surfactants in environmental remediation, mainly persistence of surfactants or their metabolites and thus potentially pose an environmental concern. Biosurfactants may provide a more cost-effective approach for subsurface remediation when used alone or in combination with synthetic surfactants. There are several advantages of biosurfactants when compared to chemical surfactants, mainly biodegradability, low toxicity, biocompatibility and ability to be synthesized from renewable feedstock. Despite having many commercially attractive properties and clear advantages compared with their synthetic counterparts, biosurfactants have not yet been employed extensively in industry because of their low yields and relatively high production and recovery costs. However, the use of mutants and recombinant hyperproducing microorganisms along with the use of cheaper raw materials and optimal growth and production conditions and more efficient recovery processes, the production of biosurfactant can be made economically feasible. Therefore, future research aiming for high-level production of biosurfactants must be focused towards the development of appropriate combinations of hyperproducing microbial strains, optimized cheaper production media and optimized process conditions, which will lead to economical commercial level biosurfactant production.

Synthesis of rhamnolipid biosurfactant and mode of hexadecane uptake by Pseudomonas species

Background

Microorganisms have devised ways by which they increase the bioavailability of many water immiscible substrates whose degradation rates are limited by their low water solubility. Hexadecane is one such water immiscible hydrocarbon substrate which forms an important constituent of oil. One major mechanism employed by hydrocarbon degrading organisms to utilize such substrates is the production of biosurfactants. However, much of the overall mechanism by which such organisms utilize hydrocarbon substrate still remains a mystery.

Results

With an aim to gain more insight into hydrocarbon uptake mechanism, an efficient biosurfactant producing and n-hexadecane utilizing Pseudomonas sp was isolated from oil contaminated soil which was found to produce rhamnolipid type of biosurfactant containing a total of 13 congeners. Biosurfactant action brought about the dispersion of hexadecane to droplets smaller than 0.22 μm increasing the availability of the hydrocarbon to the degrading organism. Involvement of biosurfactant was further confirmed by electron microscopic studies. Biosurfactant formed an emulsion with hexadecane thereby facilitating increased contact between hydrocarbon and the degrading bacteria. Interestingly, it was observed that "internalization" of "biosurfactant layered hydrocarbon droplet" was taking place suggesting a mechanism similar in appearance to active pinocytosis, a fact not earlier visually reported in bacterial systems for hydrocarbon uptake.

Conclusion

This study throws more light on the uptake mechanism of hydrocarbon by Pseudomonas aeruginosa. We report here a new and exciting line of research for hydrocarbon uptake involving internalization of biosurfactant covered hydrocarbon inside cell for subsequent breakdown.

Surfactant-mediated Biodegradation of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are toxic environmental pollutants that are known or suspected carcinogens or mutagens. Bioremediation has been used as a general way to eliminate them from the contaminated sites or aquifers, but their biodegradation is rather limited due to their low bioavailability because of their sparingly soluble nature. Surfactant-mediated biodegradation is a promising alternative. The presence of surfactants can increase the solubility of PAHs and hence potentially increase their bioavailability. However, inconclusive results have been reported on the effects of surfactant on the biodegradation of PAHs. In this work, surfactant-mediated biodegradation of PAHs is reviewed.

Linking chemical extraction to microbial degradation of 14C-hexadecane in soil

Chemical extractions have been shown to measure the biodegradable fraction of aromatic contaminants in soil; however, there is little research on the chemical prediction of aliphatic hydrocarbon degradation. The aim of this study was to investigate the potential for cyclodextrin extractions to predict hexadecane biodegradation in soil. Soils were amended with 10 or 100 mg kg(-1) of a model alkane n-hexadecane and 100 Bq g(-1) (14)C-n-hexadecane. Correlations between the extents of mineralisation and extractions of the (14)C-contaminant were determined. Solvent shake extractions and aqueous CaCl(2) extractions were poor predictors of hexadecane bioaccessibility. However, the novel HP-alpha-CD shake extraction showed close correlation (r(2)=0.90, n=36, p<0.05) to the mineralisation data. This novel extraction technique has the potential to be used to assess the biodegradable aliphatic hydrocarbon fraction in contaminated soils.

Rhamnolipid production with indigenous Pseudomonas aeruginosa EM1 isolated from oil-contaminated site

Rhamnolipid is one of the most effective and commonly used biosurfactant with wide industrial applications. Systematic strategies were applied to improve rhamnolipid (RL) production with a newly isolated indigenous strain Pseudomonas aeruginosa EM1 originating from an oil-contaminated site located in southern Taiwan. Seven carbon substrates and four nitrogen sources were examined for their effects on RL production. In addition, the effect of carbon to nitrogen (C/N) ratio on RL production was also studied. Single-factor experiments show that the most favorable carbon sources for RL production were glucose and glycerol (both at 40 g/L), giving a RL yield of 7.5 and 4.9 g/L, respectively. Meanwhile, sodium nitrate appeared to be the preferable nitrogen source, resulting in a RL production of 8.6g/L. Using NaNO(3) as the nitrogen source, an optimal C/N ratio of 26 and 52 was obtained for glucose- and glycerol-based culture, respectively. To further optimize the composition of fermentation medium, twenty experiments were designed by response surface methodology (RSM) to explore the favorable concentration of three critical components in the medium (i.e., glucose, glycerol, and NaNO(3)). The RSM analysis gave an optimal concentration of 30.5, 18.1, and 4.9 g/L for glucose, glycerol, and NaNO(3), respectively, predicting a maximum RL yield of 12.6 g/L, which is 47% higher than the best yield (8.6 g/L) obtained from preliminary selection tests and single factor experiments (glucose and NaNO(3) as the carbon and nitrogen source). The NMR and mass spectrometry analysis show that the purified RL product contained L-rhamnosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate (RL1) and L-rhamnosyl L-rhamnosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate (RL2). Meanwhile, HPLC analysis indicates that the molar ratio of RL1 and RL2 in the purified rhamnolipid product was ca. 1:1.

Adsorption of dirhamnolipid on four microorganisms and the effect on cell surface hydrophobicity

In this study, adsorption of dirhamnolipid biosurfactant on a Gram-negative Pseudomonas aeruginosa, two Gram-positive Bacillus subtilis, and a yeast, Candida lipolytica, was investigated, and the causality between the adsorption and change of cell surface hydrophobicity was discussed. The adsorption was not only specific to the microorganisms but also depended on the physiological status of the cells. Components of the biosurfactant with different rhamnosyl number or aliphatic chain length also exhibited slight difference in adsorption manner. The adsorption indeed caused the cell surface hydrophobicity to change regularly; however, the changes depended on both the concentrations of rhamnolipid solutions applied and the adsorbent physiological conditions. Orientation of rhamnolipid monomers on cell surface and micelle deposition are supposed to be the basic means of adsorption to change cell hydrophobicity at low and high rhamnolipid concentrations, respectively. This study proposed the possibility to modify cell surface hydrophobicity with biosurfactant of low concentrations, which may be of importance in in situ soil remediation.

Metabolic Diversity in Bacterial Degradation of Aromatic Compounds

Aromatic compounds pose a major threat to the environment, being mutagenic, carcinogenic, and recalcitrant. Microbes, however, have evolved the ability to utilize these highly reduced and recalcitrant compounds as a potential source of carbon and energy. Aerobic degradation of aromatics is initiated by oxidizing the aromatic ring, making them more susceptible to cleavage by ring-cleaving dioxygenases. A preponderance of aromatic degradation genes on plasmids, transposons, and integrative genetic elements (and their shuffling through horizontal gene transfer) have lead to the evolution of novel aromatic degradative pathways. This enables the microorganisms to utilize a multitude of aromatics via common routes of degradation leading to metabolic diversity. In this review, we emphasize the exquisiteness and relevance of bacterial degradation of aromatics, interlinked degradative pathways, genetic and metabolic regulation, carbon source preference, and biosurfactant production. We have also explored the avenue of metagenomics, which opens doors to a plethora of uncultured and uncharted microbial genetics and metabolism that can be used effectively for bioremediation.

Microbe-aliphatic hydrocarbon interactions in soil: implications for biodegradation and bioremediation

Aliphatic hydrocarbons make up a substantial portion of organic contamination in the terrestrial environment. However, most studies have focussed on the fate and behaviour of aromatic contaminants in soil. Despite structural differences between aromatic and aliphatic hydrocarbons, both classes of contaminants are subject to physicochemical processes, which can affect the degree of loss, sequestration and interaction with soil microflora. Given the nature of hydrocarbon contamination of soils and the importance of bioremediation strategies, understanding the fate and behaviour of aliphatic hydrocarbons is imperative, particularly microbe-contaminant interactions. Biodegradation by microbes is the key removal process of hydrocarbons in soils, which is controlled by hydrocarbon physicochemistry, environmental conditions, bioavailability and the presence of catabolically active microbes. Therefore, the aims of this review are (i) to consider the physicochemical properties of aliphatic hydrocarbons and highlight mechanisms controlling their fate and behaviour in soil; (ii) to discuss the bioavailability and bioaccessibility of aliphatic hydrocarbons in soil, with particular attention being paid to biodegradation, and (iii) to briefly consider bioremediation techniques that may be applied to remove aliphatic hydrocarbons from soil.