Hydrocarbon Biodegradation Potential Research Articles

Distribution and biodegradation potential of polycyclic aromatic hydrocarbons (PAHs) accumulated in media of a stormwater bioretention

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds that can be captured and accumulate in the bioretention cell media, which may lead to secondary pollution and ecological risks. This research aimed to understand the spatial distribution of 16 priority PAHs in bioretention media, identify their sources, evaluate their ecological impact, and assess the potential for their aerobic biodegradation. The highest total PAH concentration (25.5 ± 1.7 μg/g) was observed 1.83 m from the inlet and 10–15 cm deep. The individual PAHs with the highest concentrations were benzo [g,h,i]perylene in February (1.8 ± 0.8 μg/g) and pyrene in June (1.8 ± 0.8 μg/g). Data indicated that primary sources of PAHs were fossil fuel combustion and petroleum. The ecological impact and toxicity of the media were assessed by probable effect concentrations (PECs) and benzo [a]pyrene total toxicity equivalent (BaP-TEQ). The results showed that the concentrations of pyrene and chrysene exceeded the PECs, and the average BaP-TEQ was 1.64 μg/g, primarily caused by benzo [a]pyrene. The functional gene (C12O) of PAH-ring cleaving dioxygenases (PAH-RCD) was present in the surface media, which indicated that aerobic biodegradation of PAHs was possible. Overall, this study revealed the PAHs accumulated most at medium distance and depth, where biodegradation may be limited. Thus, the accumulation of PAHs below the surface of the bioretention cell may need to be considered during long-term operation and maintenance.

Alkan Hidrokarbonları Parçalayan Enterobacter ludwigii strain D8 Suşunun Petrolle Kirlenmiş Topraklardan İzolasyonu ve Karakterizasyonu

A bacterial strain has been isolated from petroleum contaminated soil with in southeastern Turkey. This isolated strain was characterized to determine its hydrocarbon biodegradation potential. Phenotypic features and of 16 S gene sequence analysis of rRNA revealed that strain D8 belongs to the Enterobacter genus and most closely resembles Enterobacter ludwigii (100%). The optimum temperature and pH values for the growth of E. ludwigii D8 were found to be 30°C and 5.0, respectively. This bacterial strain grew in long and medium chain hydrocarbons such as 1% decane, pentadecane and squalene separately at the end of 3 day incubation in the basal medium (BM) under optimum conditions. It was shown that E. ludwigii strain D8 degrades about 27% of crude oil incubated for 5 days, while it degrades 29% of pentadecane after 3 days of incubation determined by Gas chromatography-MS analysis. The biodegradation potential of petroleum hydrocarbons of E. ludwigii strain D8 isolated and characterized in this study indicates that this strain may play a role in the bioremediation process.

Ecotoxicity and bioremediation potential assessment of soil from oil refinery station area

PurposeThe aim of the present study was to evaluate the toxicity and biodegradation potential of oil hydrocarbons contaminated soil samples obtained from different depths at an oil refinery station area. An approach involving chemical, microbiological, respirometry and ecotoxicity assessment of soil polluted by oil hydrocarbons was adopted, in order to determine the biodegradability of pollutants and ecotoxicological effects of natural attenuation strategy.MethodsThe ecotoxicity of soil samples was evaluated using an ostracod test kit and a seed germination test. The results of the phytotoxicity assay were expressed as a percentage of seedling emergence and as the relative yield of fresh and dry biomass compared to control plants. The intrinsic biodegradation potential of the contaminated soil was examined using a Micro-Oxymax respirometer. Intrinsic biodegradation rates were estimated from the slopes of linear regressions curves plotted for cumulative O2 uptake. The obtained values were then entered in the mass balance equation for the stoichiometric reaction of hydrocarbon decomposition and converted per kg of soil per day.ResultsAlthough the tested contaminants were biodegradable in the respirometric assay, they were slightly to moderately toxic to plants and extremely toxic to ostracods. The noxious effects raised with the increased concentration of contaminants. The monocotyledonous oat was more tolerant to higher concentrations of oil hydrocarbons than the other test plants, indicating its greater suitability for soil reclamation purposes.ConclusionBy assessing phytotoxicity and effect on ostracod mortality and progress of soil self-decontamination process, proper approach of reclamation of demoted area can be provided.

Hydrocarbon biodegradation potential of microbial communities from high Arctic beaches in Canada's Northwest Passage

Sea ice loss is opening shipping routes in Canada's Northwest Passage, increasing the risk of an oil spill. Harnessing the capabilities of endemic microorganisms to degrade oil may be an effective remediation strategy for contaminated shorelines; however, limited data exists along Canada's Northwest Passage. In this study, hydrocarbon biodegradation potential of microbial communities from eight high Arctic beaches was assessed. Across high Arctic beaches, community composition was distinct, potential hydrocarbon-degrading genera were detected and microbial communities were able to degrade hydrocarbons (hexadecane, naphthalene, and alkanes) at low temperature (4 °C). Hexadecane and naphthalene biodegradation were stimulated by nutrients, but nutrients had little effect on Ultra Low Sulfur Fuel Oil biodegradation. Oiled microcosms showed a significant enrichment of Pseudomonas and Rhodococcus. Nutrient-amended microcosms showed increased abundances of key hydrocarbon biodegradation genes (alkB and CYP153). Ultimately, this work provides insight into hydrocarbon biodegradation on Arctic shorelines and oil-spill remediation in Canada's Northwest Passage.

Biodegradation potential of polycyclic aromatic hydrocarbons in Taihu Lake sediments

ABSTRACT To assess the biodegradation potential of polycyclic aromatic hydrocarbons (PAHs) in sediments, sediment microcosms were constructed with sediments collected from six lake zones with different trophic statuses in Taihu Lake. The presence and concentration of PAH-degrading bacteria (PDB) were estimated by the most probable number (MPN) method. After 85 d of aerobic and anaerobic incubation, spiked PAHs (phenanthrene, pyrene, and benzo[a]pyrene) were partially degraded by indigenous sediment microorganisms. Large differences in PAH degradation were observed depending on the molecular size of the PAHs. The PAH removal efficiency in sediments under aerobic conditions was higher than that under anaerobic conditions. MPN analyses showed a higher abundance of degrading microflora in the high PAH-contaminated sites than in the low PAH-contaminated sites. Moreover, the anaerobic PDB populations in the sediments from the six different sites were much higher than those of aerobic PDB. The PAH biodegradation capability in sediments was associated with the geochemical conditions and bacterial populations. PDB showed a broad spatial distribution, thereby implying that they played an important role in the natural attenuation and cycling of PAHs in Taihu Lake. This work indicates that PAHs remain a concern in Taihu Lake sediments and can provide useful information for further bioremediation of PAH-contaminated sediments.

A Comparison between Chemical and Natural Dispersion of a North Sea Oil-spill

ABSTRACT The application of dispersants to an oil-slick is a key remediation tool and thus understanding its effectiveness is vital. Two in situ oil slicks were created in the North Sea (off the coast of The Netherlands), one left to natural processes whilst dispersant (Slickgone NS) was applied to the other. GC-MS analysis of seawater from the surface slick, and at 1.5 and 5 m below the slick, revealed only two samples with measurable hydrocarbons (221 ± 92 μg ml−1 seawater), from the surface of the “Slickgone Dispersed” oil-slick ~25.5 hours after oil-slick formation, which was likely due to environmental conditions hindering sampling. Additionally, 16S rRNA gene quantitative PCR and amplicon analysis revealed extremely limited growth of obligate hydrocarbonoclastic bacteria (OHCB), detected at a relative abundance of <1×10-6 %. Furthermore, the Ecological Index of Hydrocarbon Exposure (EIHE) score, which quantifies the proportion of the bacterial community with hydrocarbon-biodegradation potential, was extremely low at 0.012 (scale of 0 – 1). This very low abundance of hydrocarbon-degrading bacteria at the time of sampling, even in samples with measurable hydrocarbons, could potentially be attributed to nutrient limitation (~25.5 hours after oil-slick creation total inorganic nitrogen was 3.33 μM and phosphorus was undetectable). The results of this study highlight a limited capacity for the environment, during this relatively short period, to naturally attenuate oil.

Transmembrane transport mechanism of n-hexadecane by Candida tropicalis: Kinetic study and proteomic analysis

Yeasts are the most predominant petroleum hydrocarbon-degrading fungi isolated from petroleum-contaminated soil. However, information of the transmembrane transport of petroleum hydrocarbon into yeast cells is limited. The present study was designed to explore the transmembrane transport mechanisms of the typical petroleum hydrocarbon n-hexadecane in Candida tropicalis cells with petroleum hydrocarbon biodegradation potential. Yeast cells were treated with n-hexadecane in different scenarios, and the percentage of intracellular n-hexadecane and transport dynamics were investigated accordingly. The intracellular concentration of n-hexadecane increased within 15 min, and transportation was inhibited by NaN3, an ATPase inhibitor. The uptake kinetics of n-hexadecane were well fitted by the Michaelis-Menten model, and Kt values ranged from 152.49 to 194.93 mg/L. All these findings indicated that n-hexadecane might cross the yeast cells in an energy-dependent manner and exhibit an affinity with the cell transport system. Moreover, the differentially expressed membrane proteins induced by n-hexadecane were identified and quantified by tandem mass tag labeling coupled with liquid chromatography tandem mass spectrometry analysis. The proteome analysis results demonstrated that energy production and conversion accounted for a large proportion of the functional classifications of the differentially expressed proteins, providing further evidence that sufficient energy supply is essential for transmembrane transport. Protein functional analysis also suggested that differentially expressed proteins associated with transmembrane transport processes are clearly enriched in endocytosis and phagosome pathways (p < 0.05), and the analysis supported the notion that the underlying transmembrane transport mechanism might be associated with endocytosis and phagosome pathways, revealing a new mechanism of n-hexadecane internalization by Candida tropicalis.

Enrichment and key features of a robust and consistent indigenous marine-cognate microbial consortium growing on oily bilge wastewaters.

Oily bilge wastewater (OBW) is a hazardous hydrocarbon-waste generated by ships worldwide. In this research, we enriched, characterized and study the hydrocarbon biodegradation potential of a microbial consortium from the bilges of maritime ships. The consortium cZ presented a biodegradation efficiency of 66.65% for total petroleum hydrocarbons, 72.33% for aromatics and 97.76% removal of n-alkanes. This consortium showed the ability to grow in OBWs of diverse origin and concentration. A 67-fold increase in biomass was achieved using a Sequential Batch Reactor with OBW as the only carbon and energy source. The bacterial community composition of the enriched OBW bacterial consortium at the final stable stage was characterized by 16S amplicon Illumina sequencing showing that 25 out of 915 of the emerged predominant bacterial types detected summed up for 84% of total composition. Out of the 140 taxa detected, 13 alone accumulated 94.9% of the reads and were classified as Marinobacter, Alcanivorax, Parvibaculum, Flavobacteriaceae, Gammaproteobacteria PYR10d3, Novispirillum and Xanthomonadaceae among the most predominant, followed by Thalassospira, Shewanella, Rhodospirillaceae, Gammaprotobacteria, Rhodobacteriaceae and Achromobacter. The microbial community from OBW bioreactor enrichments is intrinsically diverse with clear selection of predominant types and remarkably exhibiting consistent and efficient biodegradation achieved without any nutrient or surfactant addition. Due to there is very little information available in the OBW biodegradation field, this work contributes to the body of knowledge surrounding the treatment improvement of this toxic waste and its potential application in wastewater management.

Hydrocarbon-Degrading Microbial Communities Are Site Specific, and Their Activity Is Limited by Synergies in Temperature and Nutrient Availability in Surface Ocean Waters.

The objective of this study was to quantify the potential for hydrocarbon biodegradation in surface waters of three sites, representing geographic regions of major oil exploration (Beaufort Sea in the Arctic, northern Gulf of Mexico [GOM], and southern GOM), in a systematic experimental design that incorporated gradients in temperature and the availability of major nutrients. Surface seawater was amended in microcosms with Macondo surrogate oil to simulate an oil slick, and microcosms were incubated, with or without nutrient amendment, at temperatures ranging from 4 to 38ºC. Using respiration rate as a proxy, distinct temperature responses were observed in surface seawater microcosms based on geographic origin; biodegradation was nearly always more rapid in the Arctic site samples than in the GOM samples. Nutrient amendment enhanced respiration rates by a factor of approximately 6, stimulated microbial growth, and generally elevated the taxonomic diversity of microbial communities within the optimal temperature range for activity at each site, while diversity remained the same or was lower at temperatures deviating from optimal conditions. Taken together, our results advance the understanding of how bacterioplankton communities from different geographic regions respond to oil perturbation. A pulsed disturbance of oil is proposed to favor copiotrophic r-strategists that are adapted to pointed seasonal inputs of phytoplankton carbon, displaying carbon and nutrient limitations, rather than oil exposure history. Further understanding of the ecological mechanisms underpinning the complex environmental controls of hydrocarbon degradation is required for improvement of predictive models of the fate and transport of spilled oil in marine environments.IMPORTANCE The risk of an oil spill accident in pristine regions of the world's oceans is increasing due to the development and transport of crude oil resources, especially in the Arctic region, as a result of the opening of ice-free transportation routes, and there is currently no consensus regarding the complex interplay among the environmental controls of petroleum hydrocarbon biodegradation for predictive modeling. We examined the hydrocarbon biodegradation potential of bacterioplankton from three representative geographic regions of oil exploration. Our results showed that rates of aerobic respiration coupled to hydrocarbon degradation in surface ocean waters are controlled to a large extent by effects of temperature and nutrient limitation; hydrocarbon exposure history did not appear to have a major impact. Further, the relationship between temperature and biodegradation rates is linked to microbial community structure, which is specific to the geographic origin.

Biodegradation potential of polycyclic aromatic hydrocarbons by immobilized Klebsiella sp. in soil washing effluent

A strain KL (Klebsiella sp.), with a high polycyclic aromatic hydrocarbons (PAHs) degradation efficiency, was isolated and purified. Immobilization of strain KL using a boric acid-CaCl2 cross-linking method based on polyvinyl alcohol (PVA)-sodium alginate (SA)-nano alumina (ALNPs) composite was investigated for removal of phenanthrene (PHE), fluoranthene (FLA), and pyrene (PYR) in soil washing effluent. The concentration of PVA, SA, and ALNPs in immobilized beads had significant effects on the physicochemical properties and biodegradation performance. When beads had a PVA, SA, and ALNPs content of 10% (w/v), 0.8% (w/v), and 0.7% (w/v), and the initial biomass dosage was 10% (v/v), the biodegradation efficiency and mass transfer performance of the immobilized beads were optimal with the specific surface area of 13.3971 m2/g. Scanning electron microscopy (SEM) showed that the surface of immobilized beads was dense. The growth and adhesion of cells inside the beads were adequate, and pores of the beads were abundant and irregularly staggered. The immobilization method was successfully applied to the treatment of the three PAHs in soil washing effluent. Adsorption of beads contributed to PAHs removal in the initial stage of degradation. Higher residual concentrations of Tween 80 in the soil washing effluent have toxic effects on strain KL growth and reduce the PAHs degradation capacity. Tween 80 of 2500 mg/L was proper conditions for PAHs biodegradation efficiency. Compared to freely suspended KL cells, the removal rates of PHE, FLA, and PYR using the immobilization method on the 30th day were increased by 15.91%, 17.07%, and 19.08%, respectively.

Impact of nanoparticles on transcriptional regulation of catabolic genes of petroleum hydrocarbon-degrading bacteria in contaminated soil microcosms.

This study was conducted to determine what effects nanoparticles (NPs) like TiO2 , ZnO, and Ag may pose on natural attenuation processes of petroleum hydrocarbons in contaminated soils. The solid NPs used were identified using x-ray diffraction technique and their average size was certified as 18.2, 16.9, and 18.3 nm for Ag-NPs, ZnO-NPs, and TiO2 -NPs, respectively. NPs in soil microcosms behave differently where it was dissolved as in case of Ag-NPs, partially dissolved as in ZnO-NPs or changed into other crystalline phase as in TiO2 -NPs. In this investigation, catabolic gene encoding catechol 2,3 dioxygenase (C23DO) was selected specifically as biomarker for monitoring hydrocarbon biodegradation potential by measuring its transcripts by RT-qPCR. TiO2 -NPs amended microcosms showed almost no change in C23DO expression profile or bacterial community which were dominated by Bacillus sp., Mycobacterium sp., Microbacterium sp., Clostridium sp., beside uncultured bacteria, including uncultured proteobacteria, Thauera sp. and Clostridia. XRD pattern suggested that TiO2 -NPs in microcosms were changed into other non-inhibitory crystalline phase, consequently, showing the maximum degradation profile for most low molecular weight oil fractions and partially for the high molecular weight ones. Increasing ZnO-NPs concentration in microcosms resulted in a reduction in the expression of C23DO with a concomitant slight deteriorative effect on bacterial populations ending up with elimination of Clostridium sp., Thauera sp., and uncultured proteobacteria. The oil-degradation efficiency was reduced compared to TiO2 -NPs amended microcosms. In microcosms, Ag-NPs were not detected in the crystalline form but were available in the ionic form that inhibited most bacterial populations and resulted in a limited degradation profile of oil, specifically the low molecular weight fractions. Ag-NPs amended microcosms showed a significant reduction (80%) in C23DO gene expression and a detrimental effect on bacterial populations including key players like Mycobacterium sp., Microbacterium sp., and Thauera sp. involved in the biodegradation of petroleum hydrocarbons.

Isolation and Characterization of Hydrocarbon Utilizing Yeast (HUY) Isolates from Palm Wine

Several studies have reported on the capabilities of different yeasts to utilize hydrocarbons hence the need to ascertain the petroleum hydrocarbon biodegradation potential of yeast isolated from palm wine. The study aimed at isolation, characterization and testing of yeasts from palm wine for biodegradation of petroleum hydrocarbons. Hydrocarbon utilizing yeasts (HUY) were isolated from palm wine, a rich sugar substrate from a non-oil impacted environment using Bacto Bushnell Haas broth. The medium composed of 0.2 g MgSO4, 0.02 g CaCl2, 1 g KH2PO4, 1 g K2HPO4, 0.05 g FeCl2, 1 g/L NH4NO3, pH (7.2 ± 0.2) and mineral salt broth comprising of 4.4 g KH2PO4, 8 g (NH4)2SO4, 2 g Na2HPO4&#183H2O, MgSO4&#1837H2O, 0.1 g FeSO4, 0.01 g/L CaCl2, pH (4.5 ± 0.2) supplemented with palm wine (0.5%) and crude oil (1%). Yeasts isolated from an enriched medium and palm wine showed similarities. Yeast isolates were further screened for hydrocarbon degrading potentials using the Bacto Bushnell Haas broth containing 2, 6-dichlorophenol indophenols as the indicator agent. The isolates were identified using microscopic, macroscopic, fermentation and molecular characteristics as Candida adriatica (ZIM 2468) and Candida taoyuanica (MYA-4700).

Biodegradation potential of polycyclic aromatic hydrocarbons by bacteria strains enriched from Yangtze River sediments

ABSTRACTMicrobial degradation is an effective method for the removal of polycyclic aromatic hydrocarbons (PAHs) compounds from polluted sediments. Surface sediments collected from Yangtze River in the downtown area of Chongqing were found to contain PAH concentrations to various different degrees. Two bacteria strains (termed PJ1 and PJ2) isolated from the sediment samples could use phenanthrene (Phe) and fluoranthene (Flu) as carbon sources for growth thereby degrading these two PAH compounds. Using 16S rDNA gene sequencing, the isolates were identified as Sphingomonas sp. and Klebsiella sp., respectively. Biodegradation assays showed that the PJ1 presented an efficient degradation capability compared to PJ2 in cultures with the initial Phe and Flu concentrations ranging from 20 to 200 mg/L. The highest rates of Phe and Flu biodegradation by PJ1 reached 74.32% and 58.18% after incubation for 15 and 30 days, respectively. This is the first report on the biodegradation potential of the bacterial from surface sediments of an industrial area upstream of the Gorge Reservoir.

Biodegradation potential of hydrocarbons in petroleum refinery effluents using a continuous anaerobic-aerobic hybrid system

We investigated a novel wastewater treatment method for the remediation of crude oil refinery effluents with large number of recalcitrant organic compounds. The treatment system consists of an up-flow anaerobic sludge blanket (UASB) reactor and an aerobic packed-bed biofilm reactor (PBBR) in combinatory pattern to increase the efficiency of treatment and to remove polycyclic aromatic hydrocarbons (PAHs) of the wastewater. The mean chemical oxygen demand (COD) removal efficiency in the UASB reactor and PBBR over 118 days of sampling was 68.48% and 38.28%, respectively. The total COD removal efficiency of the system was 81.07%. The GC-MS abundance and area values for each of the substances in the effluent decreased greatly from the corresponding value in the influent. Specifically, the PAHs were totally removed during the treatment process. This study presents a feasible technology for the treatment of refinery effluents.

Isolation and Investigation of Biodegradation Potential of Multiple Polycyclic Aromatic Hydrocarbons (PAHs) Degrading Marine Bacteria near Bhavnagar Coast, India

Present work deals with modified isolation methods for indigenous microorganisms with a capability to use both low molecular weight (LMW) and high molecular weight (HMW)PAHs, which are pervasive recalcitrant pollutants. Methods such as biphasic enrichment, and specific isolation methods has resulted in the isolation of organisms such as Sphingomonas, Pseudomonas, Mycobacterium, Achromobacter, and Streptomyces species with efficacy to degrade majority of LMW PAHs up to 85% after four days of experiments, which is substantially rapid rate of degradation attributed by microorganisms. Moreover, the organisms had shown up to 30% degradation of HMW PAHs within the same time frame, making the isolation strategies more credible. The study thus, holds prime importance of conquering the difficulties in the isolation of multiple hydrocarbons degrading microorganisms, which can be further applied for the successful application for bioremediation of hydrocarbon impacted environments.

Hydrocarbon Biodegradation by Endophytic Bacteria from Neem Leaves

An attempt has been made to isolate endophytic bacteria with hydrocarbon degradation potential from neem leaves (Azadirachta indica). Fifty two endophytic bacteria were isolated from neem leaves following pre-sterilisation and were screened for hydrocarbon biodegradation potential. Totally eight bacterial isolates showed positive reaction out of which two isolates showed prominent potential for hydrocarbon degradation within 3 days. Based on Bergey's manual of Systematic Bacteriology, both the strains were identified as: Bacillus sp and Pseudomonas sp. Molecular characterisation and phylogenetic analysis support the classification of both the isolates as new strains as they showed around 96% and 98% similarity with Bacillus licheniformis and Pseudomonas stutzeri respectively, by performing BLAST search in NCBI database. The 16S rRNA sequences of both the isolates were deposited in Genbank under the accession number KF909124 and KF909125, respectively.

Biodegradation potential of petroleum hydrocarbons by bacteria and mixed bacterial consortium isolated from contaminated sites

The aim of this study was to isolate, characterize, and evaluate the potential of petroleum hydrocarbon (PHC)-degrading bacterial strains from oil-contaminated soil in the Meerut region. Among 59 oil-degrading bacterial cultures isolated from the oil-contaminated soil samples, 1 Bacillus species, 2 species of Pseudomonas, and 1 species of Micrococcus, identified on the basis of biochemical and 16s rDNA sequencing, were found to have the ability to utilize PHCs such as benzene, diesel, toluene, anthracene, and naphthalene. These strains were selected for further study to measure the quantitative determination of PHC metabolization. Along with these selected strains, a mixed bacterial consortium was formulated and used for PHC degradation. Among the individual strains, Pseudomonas sp. APHP9 performed better than the other bacterial isolates. Maximum biodegradation of benzene and toluene was done by the bacterial consortium. The mean growth rate constant (K) of soil isolates also increased with a successive increase in PHC concentration. Moreover, Bacillus sp. APHP6, Pseudomonas sp. APHP9, Pseudomonas sp. APBP1, Micrococcus sp. APIO4, and the consortium resulted in a 54.8%, 60.2%, 40.9%, 32.5%, and 66.2% decrease in benzene concentration and a 61.2%, 68.4%, 53.7%, 39.3%, and 75.4% decrease in diesel concentration, respectively, after 6 days of incubation as estimated by HPLC analysis.

Synergism of Wild Grass and Hydrocarbonoclastic Bacteria in Petroleum Biodegradation

Synergism of Wild Grass and Hydrocarbonoclastic Bacteria in Petroleum Biodegradation

Assessment of polycyclic aromatic hydrocarbon biodegradation potential in mangrove sediment from Don Hoi Lot, Samut Songkram Province, Thailand

To assess the biodegradation potential of mixed polycyclic aromatic hydrocarbons (PAHs) in mangrove sediments. Sediment microcosms were constructed with sediment collected from Don Hoi Lot, Samut Songkram Province, Thailand, by supplementation with a mixture of acenaphthene, phenanthrene and pyrene. At the end of 8 weeks, low molecular weight PAHs, acenaphthene and phenanthrene were completely degraded. PCR-denaturing gradient gel electrophoresis profile suggests that Marinobacter, Enterobacter and Dethiosulfatibacter play important roles in PAH degradation in mangrove sediment. Furthermore, six PAH-degrading bacteria were isolated consisting of novel phenanthrene-degrading Dyella sp. and Luteibacter sp., phenanthrene-degrading Burkholderia sp., acenaphthene-degrading Alcaligenes sp. and pyrene-degrading Ochrobactrum sp. Moreover, dioxygenase genes could be detected both in sediment microcosms as well as in all of the isolated strains. These results demonstrated that indigenous bacteria in the mangrove sediment had the ability to degrade phenanthrene in the presence of mixture PAHs with high efficacy. Culture and nonculture methods were combined to assess PAH biodegradation in mangrove sediment. Two novel phenanthrene-degrading bacteria were isolated. Three genera of bacteria that play important roles in PAH degradation were indicated by nonculture approach. Moreover, dioxygenase genes could be detected. This information is useful for further bioremediation of PAH-contaminated mangrove sediments.

Simultaneous hydrocarbon biodegradation and biosurfactant production by oilfield-selected bacteria

To study the bacterial diversity associated with hydrocarbon biodegradation potentiality and biosurfactant production of Tunisian oilfields bacteria. Eight Tunisian hydrocarbonoclastic oilfields bacteria have been isolated and selected for further characterization studies. Phylogenetic analysis revealed that three thermophilic strains belonged to the genera Geobacillus, Bacillus and Brevibacillus, and that five mesophilic strains belonged to the genera Pseudomonas, Lysinibacillus, Achromobacter and Halomonas. The bacterial strains were cultivated on crude oil as sole carbon and energy sources, in the presence of different NaCl concentrations (1, 5 and 10%, w/v), and at 37 or 55°C. The hydrocarbon biodegradation potential of each strain was quantified by GC-MS. Strain C450R, phylogenetically related to the species Pseudomonas aeruginosa, showed the maximum crude oil degradation potentiality. During the growth of strain C450R on crude oil (2%, v/v), the emulsifying activity (E24) and glycoside content increased and reached values of 77 and 1.33 g l(-1), respectively. In addition, the surface tension (ST) decreased from 68 to 35.1 mN m(-1), suggesting the production of a rhamnolipid biosurfactant. Crude biosurfactant had been partially purified and characterized. It showed interest stability against temperature and salinity increasing and important emulsifying activity against oils and hydrocarbons. The results of this study showed the presence of diverse aerobic bacteria in Tunisian oilfields including mesophilic, thermophilic and halotolerant strains with interesting aliphatic hydrocarbon degradation potentiality, mainly for the most biosurfactant produced strains. It may be suggested that the bacterial isolates are suitable candidates for practical field application for effective in situ bioremediation of hydrocarbon-contaminated sites.