Oil-contaminated Soil Samples Research Articles

Fast bioremediation of petroleum-contaminated soils by a consortium of biosurfactant/bioemulsifier producing bacteria

Biodegradation of petroleum hydrocarbons as a decontamination mechanism is a relatively slow process. This study aimed to investigate the impact of a tailored consortium of bacteria with higher capacities in biosurfactant production and biodegradation on the acceleration of the biodecontamination process. To this end, 18 biosurfactant producing bacteria were isolated from the crude oil-contaminated soil samples of Isfahan refinery, and the activity of the produced biosurfactants was measured in terms of surface tension reduction and emulsification E24 test. Then, the isolates screened for the biodegradation of kerosene hydrocarbons and chemical structure of the purified biosurfactants produced by the most efficient isolates were partially characterized. Next, the isolates were sorted based on their surfactant activity and biodegradation efficiency, and the higher ranked bacteria thus selected were utilized to form an efficient consortium removing hydrocarbons from the oil-contaminated soil samples in a slurry phase system. The consortium consisted of Bacillus subtilis tb1 and Pseudomonas aeruginosa species having the highest biodegradation capabilities and surface activities. The results revealed that the hydrocarbon removal efficiency of the consortium was at least 25 % higher than single species, and the final removal efficiency for the consortium could be reached in a considerably shorter time.

Effect of yeast extract on fluoranthene degradation and aromatic ring dioxygenase expressing bacterial community structure of a fluoranthene degrading bacterial consortium

Fluoranthene (Fla) is a high molecular weight polycyclic aromatic hydrocarbon that exerts hazardous effects on living organisms. An efficient Fla degrading bacterial consortium LP was enriched from an oil contaminated soil sample, with and without yeast extract as a supplement. Objective of the present study was to see if there was any differential effect of yeast extract addition on Fla degradation potential and aromatic ring dioxygenase expressing bacteria (ARDB) of the enrichments. Primary enrichment of the soil sample was carried out in minimal salt medium (MSM) added with 500 mg l−1 Fla and 0.05% yeast extract (YMSM). Secondary, tertiary and subsequent enrichments were prepared in YMSM and MSM after every sixteen days of incubation. Fla was efficiently degraded by YMSM enriched culture than MSM enriched culture. However, when MSM enrichment was incubated longer instead of further subculturings, it also degraded Fla efficiently. All three enrichments exhibited growth of bacterial colonies on Fla sprayed minimal agar plates however only YMSM enrichment showed clear zone forming bacterial colonies. A positive effect was observed of yeast extract on ARDB population of LP consortium. To our limited knowledge this is first time that effect of yeast extract on ARDB population was studied.

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.

Molecular characterization of the alpha subunit of multicomponent phenol hydroxylase from 4-chlorophenol-degrading Pseudomonas sp. strain PT3

Multicomponent phenol hydroxylases (mPHs) are diiron enzymes that use molecular oxygen to hydroxylate a variety of phenolic compounds. The DNA sequence of the alpha subunit (large subunit) of mPH from 4-chlorophenol (4-CP)-degrading bacterial strain PT3 was determined. Strain PT3 was isolated from oil-contaminated soil samples adjacent to automobile workshops and oil stations after enrichment and establishment of a chlorophenol-degrading consortium. Strain PT3 was identified as a member of Pseudomonas sp. based on sequence analysis of the 16S rRNA gene fragment. The 4-CP catabolic pathway by strain PT3 was tentatively proposed to proceed via a meta-cleavage pathway after hydroxylation to the corresponding chlorocatechol. This hypothesis was supported by polymerase chain reaction (PCR) detection of the LmPH encoding sequence and UV/VIS spectrophotometric analysis of the culture filtrate showing accumulation of 5-chloro-2-hydroxymuconic semialdehyde (5-CHMS) with λmax 380. The detection of catabolic genes involved in 4-CP degradation by PCR showed the presence of both mPH and catechol 2,3-dioxygenase (C23DO). Nucleotide sequence analysis of the alpha subunit of mPH from strain PT3 revealed specific phylogenetic grouping to known mPH. The metal coordination encoding regions from strain PT3 were found to be conserved with those from the homologous dinuclear oxo-iron bacterial monooxygenases. Two DE(D)XRH motifs was detected in LmPH of strain PT3 within an approximate 100 amino acid interval, a typical arrangement characteristic of most known PHs.

Dynamic extraction in microcolumn as a method for the sample preparation of oil-contaminated soils

A method is proposed for the sample preparation of oil-contaminated soils based on the dynamic extraction of petroleum products in a microcolumn of special design. By an example of the analysis of GSO (State Standard Sample) 8673-2005 of an oil-contaminated soil and model soil samples, a comparative evaluation of the efficiency of dynamic and batch (shaking in a shaker) extraction for the sample preparation of oil-polluted soils is carried out. The concentration of petroleum products in the extracts was determined by IR spectrometry. It was shown that the recovery of petroleum products into carbon tetrachloride in extraction in a microcolumn is, on the average, 50% higher than that in mixing the sample and reagent in a shaker. The rapid and efficient extraction of petroleum products in a microcolumn is possible because of dynamic extraction occurring at a constant renewal of the reagent.

Screening, purification and characterization of a novel cold-active and organic solvent-tolerant lipase from Stenotrophomonas maltophilia CGMCC 4254

An extracellular organic solvent-tolerant and cold-active lipase producing bacterium was isolated from oil-contaminated soil samples, and identified taxonomically as Stenotrophomonas maltophilia. The lipase from S. maltophilia CGMCC 4254 (SML) was purified 60.5-fold to homogeneity with 38.9 U/mg specific activity. Partially purified SML displayed remarkable stability in 50% and 100% (v/v) hydrophobic organic solvents after incubation for 7 days. The enzyme also retained more than 50% of its residual activity in several pure hydrophilic organic solvents after incubation for 7 days. SML showed 57% maximum activity at 5°C, and had optimal activity at 35°C. These unique properties of SML make it promising as a biocatalyst for industrial processes.

Evaluation of Total Petroleum Hydrocarbons (TPH) Measurement Methods for Assessing Oil Contamination in Soil

The most commonly used total petroleum hydrocarbons (TPH) analysis method measures petroleum hydrocarbon concentrations in soil by carbon range that can be detected by gas chromatography/flame ionization detection (GC/FID). Different cleanup procedures have been performed for removing some naturally occurring organics from petrogenic hydrocarbons prior to GC/FID analysis. To evaluate the different pre-treatment methods, more than 60 samples (including background soil and plant samples, as well as oil contaminated soil samples) were sampled from 2008 to 2010 in Canada. TPH values without cleanup (TPH-T), with column cleanup (TPH-F 3) and with in-situ cleanup (TPH-F) were compared to evaluate the effects of different pre-treatment methods on the TPH analysis values. Different total solvent extractable materials (TSEM) loading amounts were applied for in-situ silica gel cleanup method to evaluate the effect of the TSEM loading amount on the measured TPH-F values. The column cleanup method was evaluated by comparing the representative polar biogenic organic compounds (BOCs) and TPH in polar fraction (designated as TPH-F 4). Qualitatively, cleanup procedures removed most of the BOCs for background samples with high content of BOCs, but the GC/FID chromatograms did not show significant alteration for samples with heavy oil contamination. The quantified TPH-T, TPH-F 3 and TPH-F showed good agreement for oil contaminated samples, even though the loading dosage exceeded the maximum TSEM limits of silica gel (16.7 mg TSEM on per gram silica gel). For background samples, the measured TPH values were ranked as: TPH-T > TPH-F > TPH-F 3 when the TSEM loading amount exceeded 16.7 mg/g of silica gel, but no obvious difference was observed when the TSEM loading amount was less than 16.7 mg/g. Therefore, the TSEM loading capacity played an important role for the cleanup of background samples. The comparison of the measured TPH-T and TPH-F 3 obtained from background soil and plant samples did not show an obvious relationship, thus TPH values of soil samples can not be replaced by those from plants grown in the soil sampled area. The evaluation of column cleanup method showed that this method can effectively remove most of the BOCs, but the removal of the hydrocarbons which contribute to the measured TPH-F 3 can be negligible.

Molecular Characterization of 2-Chlorobiphenyl Degrading Stenotrophomonas maltophilia GS-103

The catabolic potential of transformer oil contaminated soil bacteria in aerobic degradation of polychlorinated biphenyls (PCB) were assessed. Transformer oil contaminated soil sample was subjected to microcosm enrichment experiments (PAS medium/biphenyl as sole carbon source). PCB-degrading activity of the enrichment cultures in PAS medium with the addition of 2-chlorobiphenyl were analysed by GC-MS indicated that, although the isolates differed in PCB-degrading capabilities, all of the enrichment cultures expressed activity toward at least some of the lower chlorinated congeners. Biphenyl-utilizing bacteria isolated from the most active PCB-degrading mixed cultures showed little taxonomic diversity and identified as Stenotrophomonas maltophilia GS-103.

Modeling the Effect of Crude Oil Impacted Sand on the Properties of Concrete Using Artificial Neural Networks

A network of the feedforward-type artificial neural networks (ANNs) was used to predict the compressive strength of concrete made from crude oil contaminated soil samples at 3, 7, 14, 28, 56, 84, and 168 days at different degrees of contamination of 2.5%, 5%, 10%, 15%, 20% and 25%. A total of 49 samples were used in the training, testing, and prediction phase of the modeling in the ratio 32 : 11 : 7. The TANH activation function was used and the maximum number of iterations was limited to 20,000 the model used a momentum of 0.6 and a learning rate of 0.031056. Twenty (20) different architectures were considered and the most suitable one was the 2-2-1. Statistical analysis of the output of the network was carried out and the correlation coefficient of the training and testing data is 0.9955712 and 0.980097. The result of the network has shown that the use of neural networks is effective in the prediction of the compressive strength of concrete made from crude oil impacted sand.

Isolation and characterization of Staphylococcus hominis JX961712 from oil contaminated soil

BackgroundOnly about 2% of the world's microorganisms have been tested as enzyme sources. Enormous biodiversity of organisms improves alternative biotechnological processes justifies the search for new lipases. Enzymes are considered as nature's catalysts. Lipids constitute a large part of the earth's biomass and lipolytic enzymes play an important role in the turnover of these water insoluble compounds. Most enzymes today are produced by fermentation. The benefits offered by enzymes are specificity, mild conditions and reduced waste. It may be possible, by choosing the right enzyme, to control the product production and also unwanted side reactions are minimized due to specificity of enzymes. ObjectivesTo screen, isolate and identify lipase producing organism from oil contaminated soil sample at Salem District, Tamil Nadu, India, in order to optimize the growth conditions and to assess the activity of lipase as an attempt to produce wealth from waste. MethodologyMorphological, Biochemical characterization of the isolate was evaluated and final confirmation was done by 16S rRNA gene sequencing. Optimization of different parameters were carried out to find the lipase activity. Results16S rRNA gene sequencing confirms the organism as Staphylococcus hominis MTCC 8980 and the strain was named as MK-1. The sequence was submitted in GenBank under the accession number JX961712. The G + C content was found to be 51.5%.Maximum lipase production was found to be 17.8 U/ml at 48hr incubation period and 14.7 U/ml at pH7 and at 40 °C it was found to be 22.3 U/ml. Among the oil sources selected, olive oil was found to be a best lipase producer, as it produces 13.5 U/ml. Among the organic nitrogen sources selected yeast extract showed 19.5 U/ml, 22 U/ml in Triton X100 and 14.6 U/ml in Hexane.Ca2+induces lipase activity up to 21.5 U/ml whereas Hg2+, Ni2+ inhibits lipase activity. ConclusionS. hominis was effective in producing lipase in moderate amount with the provided nutritional factors in the lipase production medium.

Isolation and identification of petroleum degrading bacteria from oil contaminated soil & water and assessment of their potentiality in bioremediation

Oil spillage has become a global environmental problem. Natural bioremediation is the only eco- friendly solution to resist its devastating environmental and economic damage damage. In this investigation, petroleum tolerant and degrading bacteria were isolated from different oil-contaminated soil and water samples. Bushnell Haas media supplemented with petrol, kerosene, and diesel as sole carbon sources was used for isolation of bacteria capable of degrading these petroleum fractionates. From three soil samples and two water samples, a total of nine bacterial strains were isolated capable of degrading petrol, kerosene and diesel with varying tolerance capacities. The isolates were identified by using standard biochemical tests and morphological studies, and it was determined that these strains belong to six bacterial genera e.g., Staphylococcus, Micrococcus, Streptococcus, Bacillus, Klebsiella and Corynebacterium. The isolated Staphylococcus spp. were found to be the most tolerant isolate withstanding as high as 7% petroleum. The others also exhibit tolerance to varying concentrations of petroleum. All these isolates were able to degrade petroleum completely and produced CO2 within 7 days, with a few exceptions for Bacillus sp. and Klebsiella sp. which required 15 days for complete degradation of kerosene. These isolates seemed to have potential for bioremediation of oil contaminated soil and water. Keywords : Bioremediation, Degradation, Petroleum, Staphylococcus spp., Tolerance

Rhamnolipids Increase the Phytotoxicity of Diesel Oil Towards Four Common Plant Species in a Terrestrial Environment

The study focused on assessing the influence of rhamnolipids on the phytotoxicity of diesel oil-contaminated soil samples. Tests evaluating the seed germination and growth inhibition of four terrestrial plant species (alfalfa, sorghum, mustard and cuckooflower) were carried out at different rhamnolipid concentrations (ranging from 0 to 1.200 mg/kg of wet soil). The experiments were performed in soil samples with a different diesel oil content (ranging from 0 to 25 ml/kg of wet soil). It was observed that the sole presence of rhamnolipids may be phytotoxic at various levels, which is especially notable for sorghum (the germination index decreased to 41 %). The addition of rhamnolipids to diesel oil-contaminated soil samples contributed to a significant increase of their phytotoxicity. The most toxic effect was observed after a rhamnolipid-supplemented diesel oil biodegradation, carried out with the use of a hydrocarbon-degrading bacteria consortium. The supplemention of rhamnolipids (600 mg/kg of wet soil) resulted in a decrease of seed germination of all studied plant species and an inhibition of microbial activity, which was measured by the 2,3,5-triphenyltetrazolium chloride tests. These findings indicate that the presence of rhamnolipids may considerably increase the phytotoxicity of diesel oil. Therefore, their use at high concentrations, during in situ bioremediation processes, should be avoided in a terrestrial environment.

Production and Characterization of Bioemulsifiers by Thermotolerant Bacteria for Enhanced Oil Recovery Potential

Three bacterial strains were isolated from oil contaminated soil samples in Yumen oilfield of China and selected due to their capacity of growing under extreme conditions and production of bioemulsifier. The isolates were identified as Brevibacillus sp. XS1, Geobacillus sp. XS2 and Geobacillus sp. XS3 according to 16S rDNA sequence and physiological methods, respectively. The isolates XS1, XS2 and XS3 were thermotolerant with the optimum growth temperature of 50 °C, 60 °C and 55 °C, respectively. All the three isolates were able to produce bioemulsifiers which had little effect on surface tension reduction. The bioemusifiers produced by the three isolates were purified with a production yield of 2.98g/L, 4.24g/L and 3.82 g/L, respectively. The bioemulsifiers were identified as anionic heteropolysaccharides by FTIR analysis and their average molecular weight and polydispersity were investigated by GPC method. The bioemulsifiers produced by Geobacillus sp. XS2 and XS3 exhibited a perfect stability over various temperature (up to 100 °C), pH (range from 2.0 to 12.0) and salinity (up to 30.0% of NaCl concentration) and were considered to be ideal candidates in MEOR process.

Production and Characterization of Bioemulsifiers by Thermotolerant Bacteria for Enhanced Oil Recovery Potential

Three bacterial strains were isolated from oil contaminated soil samples in Yumen oilfield of China and selected due to their capacity of growing under extreme conditions and production of bioemulsifier. The isolates were identified as Brevibacillus sp. XS1, Geobacillus sp. XS2 and Geobacillus sp. XS3 according to 16S rDNA sequence and physiological methods, respectively. The isolates XS1, XS2 and XS3 were thermotolerant with the optimum growth temperature of 50 °C, 60 °C and 55 °C, respectively. All the three isolates were able to produce bioemulsifiers which had little effect on surface tension reduction. The bioemusifiers produced by the three isolates were purified with a production yield of 2.98g/L, 4.24g/L and 3.82 g/L, respectively. The bioemulsifiers were identified as anionic heteropolysaccharides by FTIR analysis and their average molecular weight and polydispersity were investigated by GPC method. The bioemulsifiers produced by Geobacillus sp. XS2 and XS3 exhibited a perfect stability over various temperature (up to 100 °C), pH (range from 2.0 to 12.0) and salinity (up to 30.0% of NaCl concentration) and were considered to be ideal candidates in MEOR process.

Fingerprinting of petroleum hydrocarbons (PHC) and other biogenic organic compounds (BOC) in oil-contaminated and background soil samples

Total petroleum hydrocarbons (TPH) or petroleum hydrocarbons (PHC) are one of the most widespread soil contaminants in Canada, the United States and many other countries worldwide. Clean-up of PHC-contaminated soils costs the Canadian economy hundreds of millions of dollars annually. In Canada, most PHC-contaminated site evaluations are based on the methods developed by the Canadian Council of the Ministers of the Environment (CCME). However, the CCME method does not differentiate PHC from BOC (the naturally occurring biogenic organic compounds), which are co-extracted with petroleum hydrocarbons in soil samples. Consequently, this could lead to overestimation of PHC levels in soil samples. In some cases, biogenic interferences can even exceed regulatory levels (300 μg g(-1) for coarse soils and 1300 μg g(-1) for fine soils for Fraction 3, C(16)-C(34) range, in the CCME Soil Quality Level). Resulting false exceedances can trigger unnecessary and costly cleanup or remediation measures. Therefore, it is critically important to develop new protocols to characterize and quantitatively differentiate PHC and BOC in contaminated soils. The ultimate objective of this PERD (Program of Energy Research and Development) project is to correct the misconception that all detectable hydrocarbons should be regulated as toxic petroleum hydrocarbons. During 2009-2010, soil and plant samples were collected from over forty oil-contaminated and paired background sites in various provinces. The silica gel column cleanup procedure was applied to effectively remove all target BOC from the oil-contaminated sample extracts. Furthermore, a reliable GC-MS method in combination with the derivatization technique, developed in this laboratory, was used for identification and characterization of various biogenic sterols and other major biogenic compounds in these oil-contaminated samples. Both PHC and BOC in these samples were quantitatively determined. This paper reports the characterization results of this set of 21 samples. In general, the presence of petroleum-characteristic alkylated PAH homologues and biomarkers can be used as unambiguous indicators of the contamination of oil and petroleum product hydrocarbons; while the absence of petroleum-characteristic alkylated PAH homologues and biomarkers and the presence of abundant BOC can be used as unambiguous indicators of the predominance of natural organic compounds in soil samples.

The Effect of Compactive Efforts on the Hydraulic Conductivity Behaviour of Oil Contaminated Lateritic Soils

Large quantities of oil contaminated soils result from pipeline vandalization, onshore and offshore oil spills every year in Nigeria. An extensive laboratory program was carried out to determine the effect of varying compactive efforts on the hydraulic conductivity behaviour of oil contamination lateritic soils. Hydraulic conductivity tests were carried out on both the natural and oil contaminated soil samples at the Reduced British Standard Light (RBSL), British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH) compaction energies. Contaminated specimens were prepared by mixing the lateritic soil with maximum 6 % oil concentration by weight of dry soil. The results obtained indicated a decrease in the hydraulic conductivity of the contaminated soil samples with increasing compactive efforts.

Multi-System Phytoremediation on Oil-Contaminated Alkaline Soil in Daqing Oilfield

Daqing oilfield; oil-contaminated soil; alkaline soil; multi-plant system; phytoremediation Abstract: Daqing oil-contaminated alkaline soil and high concentrations oil-pollutant samples were mixed at the ratio of 4:1, 2:1, 1:1 and 1:2 (vsoil/voil), respectively. Then the oil content of the mixed samples were detected and analyzed after phytoremediation experiment with multi-plant systems. The research results showed that Salsola collina Pall-Chinese wildrye-Thistle Herb-Medicago-Artemisia ordosica multi-plant system had a good degradation effect on oily-pollutants. During the 105-day experiment, the degradation rate of oil-pollutants could be up to 80.5% in the mixed soil (4:1, vsoil/voil). During the whole experiment, removal rate of total petroleum hydrocarbons (TPHs) could raise up 65.5% in the Coronilla varia-Lolium perenne-Amaranthus hypochondriacus multi-plant system mixed soil (2:1, vsoil/voil). Experimental results proved that the degradation effect on TPHs could be improved by the multi-plant systems and they could be reasonably matched to cure and restore the ecological environment of oil-contaminated soils.

Indigenous soil bacteria with the combined potential for hydrocarbon consumption and heavy metal resistance

Transconjugant bacteria with combined potential for hydrocarbon utilization and heavy metal resistance were suggested by earlier investigators for bioremediation of soils co-contaminated with hydrocarbons and heavy metals. The purpose of this study was to offer evidence that such microorganisms are already part of the indigenous soil microflora. Microorganisms in pristine and oily soils were counted on nutrient agar and a mineral medium with oil as a sole carbon source, in the absence and presence of either sodium arsenate (As V), sodium arsenite (As III) or cadmium sulfate, and characterized via 16S rRNA gene sequencing. The hydrocarbon-consumption potential of individual strains in the presence and absence of heavy metal salts was measured. Pristine and oil-contaminated soil samples harbored indigenous bacteria with the combined potential for hydrocarbon utilization and As and Cd resistance in numbers up to 4 × 10⁵ CFU g⁻¹. Unicellular bacteria were affiliated to the following species arranged in decreasing order of predominance: Bacillus subtilis, Corynebacterium pseudotuberculosis, Brevibacterium linens, Alcaligenes faecalis, Enterobacter aerogenes, and Chromobacterium orangum. Filamentous forms were affiliated to Nocardia corallina, Streptomyces flavovirens, Micromonospora chalcea, and Nocardia paraffinea. All these isolates could grow on a wide range of pure aliphatic and aromatic hydrocarbons, as sole sources of carbon and energy, and could consume oil and pure hydrocarbons in batch cultures. Low As concentrations, and to a lesser extent Cd concentrations, enhanced the hydrocarbon-consumption potential by the individual isolates. There is no need for molecularly designing microorganisms with the combined potential for hydrocarbon utilization and heavy metal resistance, because they are already a part of the indigenous soil microflora.

C–S Targeted Biodegradation of Dibenzothiophene by Stenotrophomonas sp. NISOC-04

Crude oil-contaminated soil samples were gathered across Khuzestan oilfields (National Iranian South Oil Company, NISOC) consequently experienced a screening procedure for isolating C-S targeted dibenzothiophene-biodegrading microorganisms with previously optimized techniques. Among the isolates, a bacterial strain was selected due to its capability of biodegrading dibenzothiophene in a C-S targeted manner in aqueous phases and medium mostly consisting of separately biphasic water-gasoline. The 16S rDNA of the isolate was amplified using eubacterial-specific primers and then sequenced. Based on sequence data analysis, the microorganism, designated NISOC-04, clustered most closely with the members of the genus Stenotrophomonas. Gas chromatography indicated that Stenotrophomonas sp. NISOC-04 utilizes 82% of starting 0.8 mM dibenzothiophene within a 48-h-long exponential growth phase. Growth curve analysis revealed the inability of Stenotrophomonas sp. NISOC-04 to utilize dibenzothiophene (DBT) as the exclusive carbon or carbon/sulfur source. Gibbs' assay showed no 2-hydroxy biphenyl accumulation, but HPLC confirmed the presence of 2-hydroxy biphenyl as the final product of DBT desulfurization. Under sulfur starvation, Stenotrophomonas sp. NISOC-04 produced a huge biomass with untraceable sulfur and utilized atmospheric insignificant sulfur levels.

Hydrocarbon degradation and bioemulsifier production by thermophilic Geobacillus pallidus strains

Geobacillus pallidus XS2 and XS3 were isolated from oil contaminated soil samples in Yumen oilfield, China, and were able to produce bioemulsifiers on different hydrocarbons. Biodegradation assays exhibited that approximately 70% of PAH (250mg/L) or 85% of crude oil (500mg/L) was removed by the thermophilic bacteria after 20days. The bioemulsifiers of the two strains were isolated and obtained a productive yield of 4.24±0.08 and 3.82±0.11g/L, respectively. GPC analysis revealed that the number-average molecular weights (Mn) of the two bioemulsifiers were 271,785Da and 526,369Da, with PDI values of 1.104 and 1.027, respectively. Chemical composition studies exhibited that the bioemulsifier XS2 consisted of carbohydrates (68.6%), lipids (22.7%) and proteins (8.7%) while the bioemulsifier XS3 was composed by carbohydrates (41.1%), lipids (47.6%) and proteins (11.3%). Emulsification assays approved the effectiveness of bioemulsifiers over a wide range of temperature, pH and salinity.