Higher Hydrocarbon Degradation Research Articles

Microbial enrichment, functional characterization and isolation from a cold seep yield piezotolerant obligate hydrocarbon degraders.

Deep-sea environments can become contaminated with petroleum hydrocarbons. The effects of hydrostatic pressure (HP) in the deep sea on microbial oil degradation are poorly understood. Here, we performed long-term enrichments (100 days) from a natural cold seep while providing optimal conditions to sustain high hydrocarbon degradation rates. Through enrichments performed at increased HP and ambient pressure (AP) and by using control enrichments with marine broth, we demonstrated that both pressure and carbon source can have a big impact on the community structure. In contrast to previous studies, hydrocarbonoclastic operational taxonomic units (OTUs) remained dominant at both AP and increased HP, suggesting piezotolerance of these OTUs over the tested pressure range. Twenty-three isolates were obtained after isolation and dereplication. After recultivation at increased HP, an Alcanivorax sp. showed promising piezotolerance in axenic culture. Furthermore, preliminary co-cultivation tests indicated synergistic growth between some isolates, which shows promise for future synthetic community construction. Overall, more insights into the effect of increased HP on oil-degrading communities were obtained as well as several interesting isolates, e.g. a piezotolerant hydrocarbonoclastic bacterium for future deep-sea bioaugmentation investigation.

Characterization of Mesophilic Bacteria Degrading Crude Oil from Different Sites of Aramco, Saudi Arabia

ABSTRACTThe present study was designed to isolate petroleum hydrocarbon degrading bacterial strains from crude oil contaminated sites near the ARAMCO (Jazan, Saudi Arabia). The main aim was to identify a novel microbial comminutes that possess high degradation potential under variant environmental conditions. Total 43 crude oil degrading bacterial consortiums were isolated and six strains were selected based on high growth rate and hydrocarbon degradation ability. The results of 16S rRNA gene sequences analysis showed that these isolated strains were belonged to genus Pseudomonas, Nitratireductor, Bacillus, Staphylococcus and Erwinia. All isolates bacterial strains showed high degradation potential, however, strain 2-IV (Pseudomonas stutzeri) was the most effective for all parameters. The strain 2-IV showed high degradation rate (77%), emulsifying activity (54.5%), and hydrophobicity (65.5%). Moreover, the production of bio-surfactants and great decrease in surface tension (30.5 mN m−1) was also observed for strain 2-IV compared to the other isolates. On the basis of current research it was concluded that these bacterial strain 2-II and 2-IV can be used for cleaning the environment, respectively. However, further study is needed for identification of fungi and actinomycetes that can act on long-chain hydrocarbons in the studied area.

Role of nutrients in bacterial biosurfactant production and effect of biosurfactant production on petroleum hydrocarbon biodegradation

Petroleum hydrocarbons’ insolubility (due to hydrophobic nature) remains an important factor in microbial degradation of these compounds. The use of microbial biosurfactants significantly decreases the hydrophobicity and increases the rate of hydrocarbon biodegradation. Four bacterial strains, Pseudomonas poae BA1, Acinetobacter bouvetii BP18, Bacillus thuringiensis BG3, and Stenotrophomonas rhizophila BG32, isolated from petroleum hydrocarbon-contaminated soil, were used to test biosurfactant production capacities under different nutrient conditions. The hydrocarbon degradation by biosurfactant producing strains was compared with a non biosurfactant producing hydrocarbon degrading Pseudomonas rhizosphaerae BP3 strain. The percentage increase in biosurfactant production in nutrient rich medium, which was nutrient broth (NB), as compared to nutrient deprive medium, which was Bushnell-Haas broth (BHB), was BA1=20.48%, BP18=24.81%, BG3=16.71% and BG32=14.55%. The biosurfactant producing strains showed 16–28% increase in hydrocarbon degradation, as compared to non biosurfactant producing strain. The highest hydrocarbon degradation (96.07%) was exhibited by BA1, followed by BP18 (93.53%), BG3 (89.97%), BG32 (87.10%), and BP3 (74.60%). We concluded that biosurfactant production is influenced by the availability of nutrients. Cell hydrophobicity, surface tension and biosurfactant production influence hydrocarbon degradation, which can be enhanced with the use of biosurfactant producing bacteria.

Effects of Aquifer Heterogeneity and Geochemical Variation on Petroleum-Hydrocarbon Biodegradation at a Gasoline Spill Site

In subsurface environment, small-scale heterogeneities usually cause the reduction of the applicability of in situ remedial techniques. Biogeochemical heterogeneities and preferential groundwater flow paths create complex hydrogeologic conditions at most contaminated sites. A thorough understanding of the resulting three-dimensional distribution of contaminants is a necessity prior to determining a need for remediation. In this study, a gasoline spill site was selected to examine the effects of aquifer heterogeneities and geochemical variations on petroleum hydrocarbon biodegradation via different oxidation-reduction process. At this site, two multilevel sampling wells were installed to delineate the lateral (5 m) and vertical (0.5 m) distribution of contaminant concentrations and different biogeochemical parameters. Two 5-cm (I.D.) continuous soil cores [from 4 to 8 m below land surface (bls)] were collected within the gasoline plume to evaluate the distribution of the microbial population in soils. Results show that high microbial activities were observed in soil samples based on the following evidences: (1) high petroleum hydrocarbon degradation rate, and (2) high microbial biomass. Each soil section was used for chemical extraction, microbial enumeration, and grain size distribution. Results show that the soil sections with more permeable sediment materials corresponded with higher biomass (total anaerobes > 2 x 106cells/g) and significant contaminant degradation. However, those sections with less permeable sediments contained lower microbial population. Results indicate that the subsurface microorganisms were distributed unevenly in the aquifer, and some regions were devoid of microorganisms and biodegradation activities. Spatial distribution of microorganisms, soil materials, and biogeochemical characteristics in the subsurface soils control the extent and kinetics of contaminant biodegradation. Thus, using blended aquifer materials for measurement of in situ biodegradation rates may not achieve representative results.

The Inoculation Method Affects Colonization and Performance of Bacterial Inoculant Strains in the Phytoremediation of Soil Contaminated with Diesel Oil

Plants in combination with microorganisms can remediate soils, which are contaminated with organic pollutants such as petroleum hydrocarbons. Inoculation of plants with degrading bacteria is one approach to improve remediation processes, but is often not successful due to the competition with resident microorganisms. It is therefore of high importance to address the persistence and colonization behavior of inoculant strains. The objective of this study was to determine whether the inoculation method (seed imbibement and soil inoculation) influences bacterial colonization, plant growth promotion and hydrocarbon degradation. Italian ryegrass was grown in non-sterilized soil polluted with diesel and inoculated with different alkane-degrading strains Pantoea sp. ITSI10, Pantoea sp. BTRH79 and Pseudomonas sp. MixRI75 individually as well as in combination. Inoculation generally had a beneficial effect on plant biomass production and hydrocarbon degradation, however, strains inoculated in soil performed better than applied by seed imbibement. Performance correlated with the colonization efficiency of the inoculated strains. The highest hydrocarbon degradation was observed in the treatment, in which all three strains were inoculated in combination into soil. Our study revealed that besides the degradation potential and competitive ability of inoculant strains the inoculation method plays an important role in determining the success of microbial inoculation.

Bioremediation of volatile oil hydrocarbons by epiphytic bacteria associated with American grass ( Cynodon sp.) and broad bean ( Vicia faba) leaves

Fresh leaves of American grass and broad beans grown in pristine soil were naturally colonized with cultivable volatile oil hydrocarbon-utilizing bacteria, whose numbers increased significantly in plants grown in oily soil. According to their 16S rRNA gene sequences those bacteria were affiliated to various species of the genera Rhodococcus and Pseudomonas. Qualitative growth studies revealed that pure cultures of these phyllospheric bacteria could grow successfully on a solid mineral medium containing individual alkanes with chain lengths of C 9 through C 40 and the aromatics phenanthrene, naphthalene, and biphenyl as sole sources of carbon and energy. Quantitative measurements showed that the individual pure bacterial isolates degraded between about 20 and 30% of crude oil, n-hexadecane, or phenanthrene in batch culture after a one-week incubation. These results reflect the high hydrocarbon degradation potential of those bacteria. The isolates were diazotrophic (nitrogen fixers), meaning that they were self-dependent in covering their nitrogen requirements. Incubating fresh leaves in closed microcosms containing volatile oil hydrocarbons resulted in up to more than 80% attenuation of these compounds after two weeks. Experimental evidence was provided that the leaf tissues did not contribute to this attenuation, which was exclusively due to the bacterial activity.

Biodegradation of aliphatic and aromatic hydrocarbons at high temperatures

In this paper, the high temperature (65-75 degrees C) biodegradation of aliphatic and aromatic hydrocarbons is investigated and kinetic parameters are derived. The shift of the physico-chemical system properties with rising temperature will be discussed in detail. For example, the solubility of naphthalene is increased by a factor of about ten if the temperature is increased from 20 to 75 degrees C. This effect is essential to increase the bioavailability of sparingly soluble hydrocarbons. It is also demonstrated in experiments that very high oxygen transfer rates can be obtained at high temperatures in the presence of hydrocarbons. It is shown that efficient phenol biodegradation is essential for high temperature hydrocarbon degradation because some microorganisms tend to transform phenols into polyphenols which are very inhibitory for microbial growth. A defined mixed culture adapted to phenol converted more than 90% of a mixture of phenol, hexadecane and pyreno and a very high maximal growth rate of 0.19 h(-1) was determined. A yield coefficient Y(X/S) of about 0.8 g (biomass)/g (hydrocarbons) was calculated in this experiment. In a separate experiment the influence of the hydrocarbon droplet size on the biodegradation is investigated at 70 degrees C using a newly isolated Thermus sp. In this case, the growth on a hexadecane/pyrene mixture was described by a model based on the Monod equation and the corresponding kinetic parameters are derived. A mixed culture was used for the bioremediation of soil in a slurry reactor. The initial contamination of 11 g/kg was lowered to about 2 g in a reactor inoculated by an immobilized culture of extreme thermophilic microorganisms, while 9 g/kg remained in a sterile control.

Higher oil biodegradation potential at the Arabian Gulf coast than in the water body

Littoral materials collected from the intertidal zone along the coast of Kuwait City were associated with much higher numbers of oil-utilizing microorganisms than inshore and offshore water samples. Animate materials viz. epilithic biomass, cyanobacterial mats and roots of higher plants were richer in such microorganisms than inanimate materials, e.g. littoral sand, rock pieces, shells and others. Those numbers remained highest during the autumn, winter and spring and decreased dramatically during the hot summer. By far, the predominant indigenous oil-utilizing bacterium in the marine environment of Kuwait was Acinetobacter calcoaceticus. Less dominant organisms included Micrococcus sp., nocardioforms and others. Coast-immobilized strains of A. calcoaceticus and Micrococcus sp. had a higher hydrocarbon degradation potential than planktonic strains of the same organisms. It was concluded that marine coasts have a much higher potential for oil biodegradation than the water body.