Microbial degradation of hydrocarbons in the environment.

Microbial degradation of petroleum hydrocarbons: an environmental perspective.

Hundreds of millions of litres of petroleum enter the environment from both natural and anthropogenic sources every year. The input from natural marine oil seeps alone would be enough to cover all of the world's oceans in a layer of oil 20 molecules thick. That the globe is not swamped with oil is testament to the efficiency and versatility of the networks of microorganisms that degrade hydrocarbons, some of which have recently begun to reveal the secrets of when and how they exploit hydrocarbons as a source of carbon and energy.

Marine microorganisms make a meal of oil

A laboratory study was conducted with the aim of evaluating and optimizing the environmental parameters of "landfarming", i.e., the disposal by biodegradation in soil of oily sludges generated in the refining of crude oil and related operations. Oil sludge biodegradation was monitored by CO2 evolution and by periodic analysis of residual hydrocarbons. The parameters studied were soil moisture, pH, mineral nutrients, micronutrients, organic supplements, treatment rate, teratment frequency, and incubation temperature. Oil sludge biodegradation was optimal at a soil water-holding capacity of 30 to 90%, a pH of 7.5 to 7.8, C:N and C:P ratios of 60:1 and 800:1, respectively, and a temperature of 20 degrees C or above. Addition of micronutrients and organic supplements was not beneficial; sewage sludge interfered with hydrocarbon biodegradation. Breakdown of the saturated hydrocarbon (alkane and cycloalkane) fraction was the highest at low application rates, but higher application rates favored the biodegradation of the aromatic and asphaltic fractions. An application rate of 5% (wt/wt) oil sludge hydrocarbon to the soil (100,000 liters/hectare) achieved a good compromise between high biodegradation rates and efficient land use and resulted in the best overall biodegradation rate of all hydrocarbon classes. Frequent small applications resulted in higher biodegradation than single large applications. Two 100,000-liter/hectare (255 barrels per acre) or four 50,000-liter/hectare oil sludge hydrocarbon applications per growing season seem appropriate for most temperate zone disposal sites.

Effect of environmental parameters on the biodegradation of oil sludge.

Degradation of oil on beaches is, in general, limited by the supply of inorganic nutrients. In order to obtain a more systematic understanding of the effects of nutrient addition on oil spill bioremediation, beach sediment microcosms contaminated with oil were treated with different levels of inorganic nutrients. Oil biodegradation was assessed respirometrically and on the basis of changes in oil composition. Bacterial communities were compared by numerical analysis of denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified 16S rRNA genes and cloning and sequencing of PCR-amplified 16S rRNA genes. Nutrient amendment over a wide range of concentrations significantly improved oil degradation, confirming that N and P limited degradation over the concentration range tested. However, the extent and rate of oil degradation were similar for all microcosms, indicating that, in this experiment, it was the addition of inorganic nutrients rather than the precise amount that was most important operationally. Very different microbial communities were selected in all of the microcosms. Similarities between DGGE profiles of replicate samples from a single microcosm were high (95% ± 5%), but similarities between DGGE profiles from replicate microcosms receiving the same level of inorganic nutrients (68% ± 5%) were not significantly higher than those between microcosms subjected to different nutrient amendments (63% ± 7%). Therefore, it is apparent that the different communities selected cannot be attributed to the level of inorganic nutrients present in different microcosms. Bioremediation treatments dramatically reduced the diversity of the bacterial community. The decrease in diversity could be accounted for by a strong selection for bacteria belonging to the alkane-degrading Alcanivorax/Fundibacter group. On the basis of Shannon-Weaver indices, rapid recovery of the bacterial community diversity to preoiling levels of diversity occurred. However, although the overall diversity was similar, there were considerable qualitative differences in the community structure before and after the bioremediation treatments.

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Robust hydrocarbon degradation and dynamics of bacterial communities during nutrient-enhanced oil spill bioremediation.

Biodegradation and mineralization of petroleum, added at 1% (v/v) to freshly collected sea water, were measured using gas–liquid chromatographic, residual weight, and CO2-evolution techniques. Only 3% of the added petroleum was biodegraded and 1% was mineralized in unamended sea water after 18 days of incubation. Added individually, nitrate (10−2M) or phosphate (3.5 × 10−4M) supplements caused little improvement, but when added in combination, they increased petroleum biodegradation and mineralization to 70% and 42%, respectively. Attempts to clean up oil spills with the aid of microorganisms should take into consideration the nutritional deficiencies of sea water.

Degradation and mineralization of petroleum in sea water: limitation by nitrogen and phosphorous.

Within the framework of a study on the oil biodegradation potential of the sea the ability of a Flavobacterium sp. and Brevibacterium sp. to metabolize a paraffinic crude oil and a chemically defined hydrocarbon mixture was investigated. Major components of the crude oil were identified by combination gas chromatography and mass spectrometry. The rate and extent of total hydrocarbon biodegradation was measured. In addition, CO2 evolution from the crude oil was continuously monitored in a shaker-mounted gas train arrangement. Degradation started after a 2 to 4 day lag period, and reached its maximum within two weeks. At this time up to 60% of the crude oil and 75% of the model hydrocarbon mixture, each added at the level of 1 ml per 100 ml artificial sea water, were degraded. Mineralization(conversion to CO2) was slightly lower due to formation of products and bacterial cell material. n-Paraffins were preferentially degraded as compared to branched chain hydrocarbons. Biodegradation of n-paraffins in the range of C12 to C20 was simultaneous; no diauxie effects were observed.

Degradation and mineralization of petroleum by two bacteria isolated from coastal waters

Abundance, distribution and oil biodegradation potential of micro-organisms in Raritan Bay

: Within the framework of a study on the oil biodegradation potential of the sea the ability of a Flavobacterium sp. and Brevibacterium sp. to metabolize a paraffinic crude oil and a chemically defined hydrocarbon mixture was investigated. Major components of the crude oil were identified by combination gas chromatography and mass spectrometry. The rate and extent of total hydrocarbon biodegradation was measured. Degradation started after a 2 to 4 day lag period, and reached its maximum within two weeks. At this time up to 60% of the crude oil was degraded. n-Paraffins were preferentially degraded as compared to branched chain hydrocarbons. Biodegradation and mineralization of petroleum, added at 1% (v/v) to freshly collected sea water, were measured using gas-liquid chromatographic, residual weight, and CO2-evolution techniques. Only 3% of the added petroleum was biodegraded and 1% was mineralized in unamended sea water after 18 days of incubation. Added nitrate, phosphate supplements in combination increased petroleum biodegradation and mineralization. Attempts to clean up oil spills with the aid of microorganisms should take into consideration the nutritional deficiencies of sea water.

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A. Degradation and Mineralization of Petroleum by Two Bacteria Isolated from Coastal Waters. B. Degradation and Mineralization of Petroleum in Sea Water: Limitation by Nitrogen and Phosphorus

Ronald M. Atlas

Papers

Degradation and mineralization of petroleum in sea water: limitation by nitrogen and phosphorous.

Degradation and mineralization of petroleum by two bacteria isolated from coastal waters

Abundance, distribution and oil biodegradation potential of micro-organisms in Raritan Bay

A. Degradation and Mineralization of Petroleum by Two Bacteria Isolated from Coastal Waters. B. Degradation and Mineralization of Petroleum in Sea Water: Limitation by Nitrogen and Phosphorus