Evidence for surfactant production by the haloarchaeon Haloferax sp. MSNC14 in hydrocarbon-containing media

The potential for surfactant production by the extreme halophilic archaeon Haloferax sp. MSNC14 in the presence of individual hydrocarbon substrates was studied. This strain was selected for its ability to grow on different types of hydrocarbons at high NaCl concentrations. Linear (n-heptadecane or C17) and isoprenoid (pristane) alkanes, a polyaromatic hydrocarbon (phenanthrene) and ammonium acetate (highly water-soluble control compound) were used as growth substrates. The adherence potential was demonstrated by the ability of the cells to adhere to liquid or solid hydrocarbons. The biosurfactant production was indicated by the reduction of the surface tension (ST) and by the emulsification activity (EA) of cell-free supernatants. Growth on acetate was accompanied by a low EA (lower than 0.1) and a high ST (~70 mN/m), whereas an important EA (up to 0.68 ± 0.08) and a reduction of ST (down to 32 ± 2.3 mN/m) were observed during growth on the different hydrocarbons. Both ST and EA varied with the growth phase. The adhesion to hydrocarbons was higher when cells were grown on C17 (by 60–70 %) and pristane (by 30–50 %) than on phenanthrene (~25 %). The results demonstrated that strain MNSC14 was able to increase the bioavailability of insoluble hydrocarbons, thus facilitating their uptake and their biodegradation even at high salt concentration.     

Quantifying the biodegradation of phenanthrene by Pseudomonas stutzeri P16 in the presence of a nonionic surfactant.

The low water solubility of polycyclic aromatic hydrocarbons is believed to limit their availability to microorganisms, which is a potential problem for bioremediation of polycyclic aromatic hydrocarbon-contaminated sites. Surfactants have been suggested to enhance the bioavailability of hydrophobic compounds, but both negative and positive effects of surfactants on biodegradation have been reported in the literature. Earlier, we presented mechanistic models of the effects of surfactants on phenanthrene dissolution and on the biodegradation kinetics of phenanthrene solubilized in surfactant micelles. In this study, we combined the biodegradation and dissolution models to quantify the influence of the surfactant Tergitol NP-10 on biodegradation of solid-phase phenanthrene by Pseudomonas stutzeri P16. Although micellized phenanthrene does not appear to be available directly to the bacterium, the ability of the surfactant to increase the phenanthrene dissolution rate resulted in an overall increase in bacterial growth rate in the presence of the surfactant. Experimental observations could be predicted well by the derived model with measured biokinetic and dissolution parameters. The proposed model therefore can serve as a base case for understanding the physical-chemical effects of surfactants on nonaqueous hydrocarbon bioavailability.     

Mechanisms for enhanced biodegradation of petroleum hydrocarbons by a microbe-colonized gas-liquid foam

AIMS: A microbe-colonized gas-liquid foam formulation has been previously shown to provide enhanced biodegradation capabilities in soil microcosms. The present study considers the reservoir properties of this foam and how this affects hydrocarbon degradation rates. METHODS AND RESULTS: Oxygen solubility in protein hydrolysate solutions draining from aerated and oxygenated foams was measured. The suitability of oxygenated foam to enhance the degradation of n-hexadecane in soil microcosms was assessed. Sorption of bacterial isolates at the gas-liquid interface was also investigated using a range of microscopy techniques. CONCLUSIONS: Oxygenated bioactive foam enhanced biodegradation rates by improving oxygen availability and transfer. Biodegradation of n-hexadecane was also stimulated by the protein hydrolysate used and by the inclusion of known bacterial hydrocarbon-degrading bacteria. The interaction of bacteria with the gas-liquid interface was shown to be a significant factor governing the drainage of the bacteria from the bioactive foam. SIGNIFICANCE AND IMPACT OF THE STUDY: Protein hydrolysate-based bioactive foam may be a suitable treatment technology to enhance the biodegradation of petroleum hydrocarbons in soil.     

Anaerobic biodegradation of aromatic hydrocarbons: pathways and prospects

Aromatic hydrocarbons contaminate many environments worldwide, and their removal often relies on microbial bioremediation. Whereas aerobic biodegradation has been well studied for decades, anaerobic hydrocarbon biodegradation is a nascent field undergoing rapid shifts in concept and scope. This review presents known metabolic pathways used by microbes to degrade aromatic hydrocarbons using various terminal electron acceptors; an outline of the few catabolic genes and enzymes currently characterized; and speculation about current and potential applications for anaerobic degradation of aromatic hydrocarbons.     

细菌在油水界面粘附的理论、特性及应用

细菌在油水界面粘附主要应用于烷烃污染的环境修复、石油开采与加工、食品加工等方面,其研究已经引起各界的广泛关注。本文基于XDLVO理论阐述细菌在油水界面的粘附机理;总结细菌表面特性、油相及水相性质对细菌粘附的影响;介绍细菌粘附作用在微生物驱油、生物乳化与破乳以及烷烃降解方面的应用,并对今后的研究方向提出展望。     

Biodegradation of crude oil saturated fraction supported on clays

The role of clay minerals in crude oil saturated hydrocarbon removal during biodegradation was investigated in aqueous clay/saturated hydrocarbon microcosm experiments with a hydrocarbon degrading microorganism community. The clay minerals used for this study were montmorillonite, palygorskite, saponite and kaolinite. The clay mineral samples were treated with hydrochloric acid and didecyldimethylammonium bromide to produce acid activated- and organoclays respectively which were used in this study. The production of organoclay was restricted to only montmorillonite and saponite because of their relative high CEC. The study indicated that acid activated clays, organoclays and unmodified kaolinite, were inhibitory to biodegradation of the hydrocarbon saturates. Unmodified saponite was neutral to biodegradation of the hydrocarbon saturates. However, unmodified palygorskite and montmorillonite were stimulatory to biodegradation of the hydrocarbon saturated fraction and appears to do so as a result of the clays’ ability to provide high surface area for the accumulation of microbes and nutrients such that the nutrients were within the ‘vicinity’ of the microbes. Adsorption of the saturated hydrocarbons was not significant during biodegradation.     

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.     

Mass transfer and hydrocarbon biodegradation of aged soil in slurry phase

Addition of toluene into slurry phase laboratory microcosm is proposed in order to increase desorption rate of hydrocarbons and as an alternative to improve bioavailability of hydrocarbon in aged soils. Our studies showed that toluene has a positive effect on desorption of total petroleum hydrocarbons (TPH). Addition of 14,000 mg toluene/kg of soil, in highly polluted soil, increased the consumption rate of hydrocarbons three times in comparison to control without solvent. In 30 days the initial TPH concentration in soil, 292,000 mg/kg, diminished 45%. Although toluene was able to dissolve complex organic compounds such as asphaltene fraction, it probably yielded a highly toxic toluene-hydrocarbons phase. The inhibitory effect of toluene-TPH was also studied. A substrate inhibition model was used: the k(m) and k(i) constants were 57 and 490 mg TPH/L liquid phase, respectively. Experimental data were well described when the proposed model included sequential desorption and biodegradation phenomena. Damk?hler number evaluation showed that rate of mass transfer was the limiting step in overall biodegradation in nonsolvent control. When high concentration of toluene was added, then bioreaction was the limiting step, but inhibitory effect should be considered. However, toluene addition at low concentrations facilitates the biodegradation of aromatic compounds.     

Microbial Factors Rather Than Bioavailability Limit the Rate and Extent of PAH Biodegradation in Aged Crude Oil Contaminated Model Soils

The rate and extent of polynuclear aromatic hydrocarbons (PAH) biodegradation in a set of aged model soils that had been contaminated with crude oil at the high concentrations (i.e.,>20,000?mg/kg) normally found in the environment were measured in 90-week slurry bioremediation experiments. Soil properties such as organic matter content, mineral type, particle diameter, surface area, and porosity did not significantly influence the PAH biodegradation kinetics among the 10 different model soils. A comparison of aged and freshly spiked soils indicates that aging affects the biodegradation rate and extent only for higher-molecular-weight PAHs, while the effects of aging are insignificant for 4-ring PAHs and total PAHs. In all model soils with the exception of kaolinite clay, the rate of abiotic desorption was faster than the rate of biodegradation during the initial phase of bioremediation treatment, indicating that PAH biodegradation was limited by microbial factors. Similarly, any of the higher-molecular-weight PAHs that were still present after 90 weeks of treatment were released rapidly during abiotic desorption tests, which demonstrates that bioavailability limitations were not responsible for the recalcitrance of these hydrocarbons. Indeed, an analysis of microbial counts indicates that a severe reduction in hydrocarbon degrader populations may be responsible for the observed incomplete PAH biodegradation. Therefore, it can be concluded that the recalcitrance of PAHs during bioremediation is not necessarily due to bioavailability limitations and that these residual contaminants therefore might pose a greater risk to environmental receptors than previously thought.     

Petroleum Pollution Bioremediation Using Water-Insoluble Uric Acid as the Nitrogen Source

The biodegradation of hydrocarbon pollutants in open systems is limited by the availability of a utilizable nitrogen source. This limitation can be overcome by using uric acid. Enrichment cultures grown on crude oil-uric acid media yielded mixed and pure cultures that degraded petroleum. In a simulated open system, uric acid bound to crude oil and was available for bacterial growth and petroleum biodegradation.     

Hydrocarbon degradation by a soil microbial population with beta-cyclodextrin as surfactant to enhance bioavailability

In general the biodegradation of nonchlorinated aliphatic and aromatic hydrocarbons is influenced by their bioavailability. Hydrocarbons are very poorly soluble in water. They are easily adsorbed to clay or humus fractions in the soil, and pass very slowly to the aqueous phase, where they are metabolised by microorganisms. Surfactants that increase their solubility and improve their bioavailability can thereby accelerate degradation. Cyclodextrins are natural compounds that form soluble complexes with hydrophobic molecules. They are widely used in medicine and harmless to microorganisms and enzymes. This paper describes their in vitro effect on the biodegradative activity of a microbial population isolated from a petroleum-polluted soil, as shown by the decrease of dodecane (C12), tetracosane (C24) anthracene and naphthalene added individually as the sole carbon source to mineral medium liquid cultures. beta-cyclodextrin accelerated the degradation of all four hydrocarbons, particularly naphthalene, and influenced the growth kinetics as shown by a higher biomass yield and better utilization of hydrocarbon as a carbon and energy source. Its low cost, biocompatibility and effective acceleration of degradation make beta-cyclodextrin an attractive option for bioremediation.     

Stimulation of Diesel Fuel Biodegradation by Indigenous Nitrogen Fixing Bacterial Consortia

Abstract Successful stimulation of N₂ fixation and petroleum hydrocarbon degradation in indigenous microbial consortia may decrease exogenous N requirements and reduce environmental impacts of bioremediation following petroleum pollution. This study explored the biodegradation of petroleum pollution by indigenous N₂ fixing marine microbial consortia. Particulate organic carbon (POC) in the form of ground, sterile corn-slash (post-harvest leaves and stems) was added to diesel fuel amended coastal water samples to stimulate biodegradation of petroleum hydrocarbons by native microorganisms capable of supplying a portion of their own N. It was hypothesized that addition of POC to petroleum amended water samples from N-limited coastal waters would promote the growth of N₂ fixing consortia and enhance biodegradation of petroleum. Manipulative experiments were conducted using samples from coastal waters (marinas and less polluted control site) to determine the effects of POC amendment on biodegradation of petroleum pollution by native microbial consortia. Structure and function of the microbial consortia were determined by measurement of N₂ fixation (acetylene reduction), hydrocarbon biodegradation (¹⁴C hexadecane mineralization), bacterial biomass (AODC), number of hydrocarbon degrading bacteria (MPN), and bacterial productivity (³H-thymidine incorporation). Throughout this study there was a consistent enhancement of petroleum hydrocarbon degradation in response to the addition of POC. Stimulation of diesel fuel biodegradation following the addition of POC was likely attributable to increases in bacterial N₂ fixation, diesel fuel bioavailability, bacterial biomass, and metabolic activity. Toxicity of the bulk phase water did not appear to be a factor affecting biodegradation of diesel fuel following POC addition. These results indicate that the addition of POC to diesel-fuel-polluted systems stimulated indigenous N₂ fixing microbial consortia to degrade petroleum hydrocarbons. Received: 29 December 1998; Accepted: 6 April 1999     

Adhesion to the hydrocarbon phase increases phenanthrene degradation by <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> LP6a

Microbial adhesion is an important factor that can influence biodegradation of poorly water soluble hydrocarbons such as phenanthrene. This study examined how adhesion to an oil–water interface, as mediated by 1-dodecanol, enhanced phenanthrene biodegradation by Pseudomonas fluorescens LP6a. Phenanthrene was dissolved in heptamethylnonane and added to the aerobic aqueous growth medium to form a two phase mixture. 1-Dodecanol was non-toxic and furthermore could be biodegraded slowly by this strain. The alcohol promoted adhesion of the bacterial cells to the oil–water interface without significantly changing the interfacial or surface tension. Introducing 1-dodecanol at concentrations from 217 to 4,100 mg l⁻¹ increased phenanthrene biodegradation by about 30% after 120 h incubation. After 100 h incubation, cultures initially containing 120 or 160 mg l⁻¹ 1-dodecanol had mineralized >10% of the phenanthrene whereas those incubated without 1-dodecanol had mineralized only 4.5%. The production and accumulation of putative phenanthrene metabolites in the aqueous phase of cultures likewise increased in response to the addition of 1-dodecanol. The results suggest that enhanced adhesion of bacterial cells to the oil–water interface was the main factor responsible for enhanced biodegradation of phenanthrene to presumed polar metabolites and to CO₂.     

Enhanced Biodegradation of Casablanca Crude Oil by A Microbial Consortium in Presence of a Rhamnolipid Produced by Pseudomonas Aeruginosa AT10

The biodegradation of oil products in the environment is often limited by their low water solubility and dissolution rate. Rhamnolipids produced by Pseudomonas aeruginosa AT10 were investigated for their potential to enhance bioavailability and hence the biodegradation of crude oil by a microbial consortium in liquid medium. The characterization of the rhamnolipids produced by strain AT10 showed the effectiveness of emulsification of complex mixtures. The addition of rhamnolipids accelerates the biodegradation of total petroleum hydrocarbons from 32% to 61% at 10 days of incubation. Nevertheless, the enhancement of biosurfactant addition was more noticeable in the case of the group of isoprenoids from the aliphatic fraction and the alkylated polycyclic aromatic hydrocarbons (PHAS) from the aromatic fraction. The biodegradation of some targeted isoprenoids increased from 16% to 70% and for some alkylated PAHs from 9% to 44%.     

The reduction of wax precipitation in waxy crude oils by <Emphasis Type="Italic">Pseudomonas</Emphasis> species

Crude oil with different concentrations was subjected to Pseudomonas species at 37 degrees C and various incubation periods. The results showed that Pseudomonas species grew faster at 1% (v/v) concentration of crude oil and exhibited high biodegradation ability within 1 week. On measuring the emulsification activity and emulsion stability during different stages of growth, in various immiscible hydrocarbons, it appeared that the species was able to produce a stable emulsion with a maximum at the end of stationary phase of growth. The gas chromatography analysis of the saturated hydrocarbons of crude oil showed that, an increase in concentration of iso-alkanes in the range of C15-C20, and a bioconversion of heavy iso-alkanes in the range of C21-C22+. Chemical analysis of crude oil by liquid chromatographic technique before and after growth showed that, the saturated alkanes were more degradable than aromatic and asphaltenic compounds. Treatment by Pseudomonas species may possibly be an effective method for the biodegradation of heavy paraffinic hydrocarbon leading to an enhancement in crude oil properties.     

Distribution of Hydrocarbon-Utilizing Microorganisms and Hydrocarbon Biodegradation Potentials in Alaskan Continental Shelf Areas

Hydrocarbon-utilizing microorganisms were enumerated from Alaskan continental shelf areas by using plate counts and a new most-probable-number procedure based on mineralization of ¹⁴C-labeled hydrocarbons. Hydrocarbon utilizers were ubiquitously distributed, with no significant overall concentration differences between sampling regions or between surface water and sediment samples. There were, however, significant seasonal differences in numbers of hydrocarbon utilizers. Distribution of hydrocarbon utilizers within Cook Inlet was positively correlated with occurrence of hydrocarbons in the environment. Hydrocarbon biodegradation potentials were measured by using ¹⁴C-radiolabeled hydrocarbon-spiked crude oil. There was no significant correlation between numbers of hydrocarbon utilizers and hydrocarbon biodegradation potentials. The biodegradation potentials showed large seasonal variations in the Beaufort Sea, probably due to seasonal depletion of available nutrients. Non-nutrient-limited biodegradation potentials followed the order hexadecane > naphthalene pristane > benzanthracene. In Cook Inlet, biodegradation potentials for hexadecane and naphthalene were dependent on availability of inorganic nutrients. Biodegradation potentials for pristane and benzanthracene were restricted, probably by resistance to attack by available enzymes in the indigenous population.     

Physical and metabolic interactions of Pseudomonas sp. strain JA5-B45 and Rhodococcus sp. strain F9-D79 during growth on crude oil and effect of a chemical surfactant on them

Methods to enhance crude oil biodegradation by mixed bacterial cultures, for example, (bio)surfactant addition, are complicated by the diversity of microbial populations within a given culture. The physical and metabolic interactions between Rhodococcus sp. strain F9-D79 and Pseudomonas sp. strain JA5-B45 were examined during growth on Bow River crude oil. The effects of a nonionic chemical surfactant, Igepal CO-630 (nonylphenol ethoxylate), also were evaluated. Strain F9-D79 grew attached to the oil-water interface and produced a mycolic acid-containing capsule. Crude oil emulsification and surface activity were associated with the cellular fraction. Strain JA5-B45 grew in the aqueous phase and was unable to emulsify oil, but cell-free supernatants mediated kerosene-water emulsion formation. In coculture, stable emulsions were formed and strain JA5-B45 had an affinity for the capsule produced by strain F9-D79. Igepal CO-630 inhibited F9-D79 cells from adhering to the interface, and cells grew dispersed in the aqueous phase as 0.5-microm cocci rather than 2.5-microm rods. The surfactant increased total petroleum hydrocarbon removal by strain JA5-B45 from 4 to 22% and included both saturated compounds and aromatics. In coculture, TPH removal increased from 13 to 40% following surfactant addition. The culture pH normally increased from 7.0 to between 7.5 and 8.5, although addition of Igepal CO-630 to F9-D79 cultures resulted in a drop to pH 5.5. We suggest a dual role for the nonylphenol ethoxylate surfactant in the coculture: (i) to improve hydrocarbon uptake by strain JA5-B45 through emulsification and (ii) to prevent strain F9-D79 from adhering to the oil-water interface, indirectly increasing hydrocarbon availability. These varied effects on hydrocarbon biodegradation could explain some of the known diversity of surfactant effects.     

Relation between Candida maltosa Hydrophobicity and Hydrocarbon Biodegradation

Summary The growth of Candida maltosa on hydrocarbons (dodecane and hexadecane) was influenced by adding various natural and synthetic surfactants. Microbial adhesion to the hydrocarbon was used to measure the surface cell hydrophobicity of the yeast, which in the presence of a synthetic surfactant correlated with the degree of hydrocarbon biodegradation. Non-ionic surfactants caused the highest degree of hydrocarbon biodegradation corresponding the lowest hydrophobicity. A different correlation was observed with natural surfactants, of which saponin was the most effective for hydrocarbon biodegradation, though the concentration of this surfactant had no influence on surface cell hydrophobicity.