Effect of dispersed oil on heterotrophic bacterial communities in cold marine waters

Natural attenuation of oil in marine environments: A review

Natural attenuation is an important process for oil spill management in marine environments. Natural attenuation affects the fate of oil by physical, chemical, and biological processes, which include evaporation, dispersion, dissolution, photo-oxidation, emulsification, oil particle aggregation, and biodegradation. This review examines the cumulative knowledge regarding these natural attenuation processes as well as their simulation and prediction using modelling approaches. An in-depth discussion is provided on how oil type, microbial community and environmental factors contribute to the biodegradation process. It describes how our understanding of the structure and function of indigenous oil degrading microbial communities in the marine environment has been advanced by the application of next generation sequencing tools. The synergetic and/or antagonist effects of oil spill countermeasures such as the application of chemical dispersants, in-situ burning and nutrient enrichment on natural attenuation were explored. Several knowledge gaps were identified regarding the synergetic and/or antagonistic effects of active response countermeasures on the natural attenuation/biodegradation process. This review highlighted the need for field data on both the effectiveness and potential detrimental effects of oil spill response options to support modelling and decision-making on their selection and application.

Effects of oil spill response technologies on marine microorganisms in the high Arctic

We studied how exposure to oil spill response technologies affect marine microorganisms during Arctic winter and spring. Microorganisms were exposed to chemically dispersed oil (DISP), in situ burnt oil (ISB), and natural attenuated oil (NATT) in mesocosms from February to May. We subsampled the mesocosms and studied the effects of oil in laboratory incubations as changes in biomass of the major functional groups: bacteria, heterotrophic-nanoflagellates, dinoflagellates, ciliates, pico- and nanophytoplankton, and diatoms over two 14-day periods. In winter, the majority of polycyclic aromatic hydrocarbons (PAHs) remained encapsulated in the ice, and the low concentrations of PAHs in water led to minute changes in biomass of the investigated groups. In spring, however, when the PAHs were partially released from the melting ice, the biomass of many functional groups in DISP and NATT decreased significantly, while the changes in ISB were less pronounced. The overall biomass reduction, as observed in this study, could lead to a disrupted transfer of energy from the primary producers to the higher trophic levels in oil affected areas.

Responses of microbial communities in Arctic sea ice after contamination by crude petroleum oil

Microbial communities associated with Arctic fjord ice polluted with petroleum oils were investigated in this study. A winter field experiment was conducted in the Van Mijen Fjord (Svalbard) from February to June 2004, in which the ice was contaminated with a North Sea paraffinic oil. Holes were drilled in the ice and oil samples frozen into the ice at the start of the experiment. Samples, including cores of both oil-contaminated and clean ice, were collected from the field site 33, 74, and 112 days after oil application. The sampled cores were separated into three sections and processed for microbiological and chemical analyses. In the oil-contaminated cores, enumerations of total prokaryotic cells by fluorescence microscopy and colony-forming units (CFU) counts of heterotrophic prokaryotes both showed stimulation of microbial growth, while concentrations of oil-degrading prokaryotes remained at similar levels in contaminated and clean ice. Analysis of polymerase chain reaction (PCR)-amplified bacterial 16S rRNA gene fragments by denaturing gradient gel electrophoresis (DGGE) revealed that bacterial communities in oil-contaminated ice generated fewer bands than communities in clean ice, although banding patterns changed both in contaminated and clean ice during the experimental period. Microbial communities in unpolluted ice and in cores contaminated with the paraffinic oil were examined by cloning and sequence analysis. In the contaminated cores, the communities became predominated by Gammaproteobacteria related to the genera Colwellia, Marinomonas, and Glaciecola, while clean ice included more heterogeneous populations. Chemical analysis of the oil-contaminated ice cores with determinations of n-C17/Pristane and naphthalene/phenanthrene ratios indicated slow oil biodegradation in the ice, primarily in the deeper parts of the ice with low hydrocarbon concentrations.

Simultaneous enumeration of different bacteria using reverse sample genome probing technique

Quantitative reverse sample genome probing (RSGP) with lambdaDNA as an internal standard was used to enumerate the total numbers of Rhizobium sp. CCRC 13560, Rhizobium meliloti CCRC 13516 and Bradyrhizobium sp. CCRC 13585. K(lambda)/Kx ratios varied between the three species but also in response to the amounts of lambdaDNA or genomic DNA used in the labeling mixture or fixed upon the membrane. Comparative enumerations of pure cultures revealed higher counts using genomic probing as compared with growth-based colony forming units (CFU; 3.4+/-1.7-fold higher for R. meliloti, 6.4+/-7.8-fold higher for Rhizobium sp. and 0.34+/-0.17-fold higher for Bradyrhizobium sp.). In mixed cultures, the estimated cell numbers using genomic probing were 126+/-172-, 85+/-83- and 4.0+/-3.4-fold higher (same respective order) than the growth-based assay. By replacing the klambda/kx ratio with k'lambda/k'x (slope from signal intensity of differently diluted lambdaDNA/slope from signal intensity of differently diluted target DNAxf(x)/flambda), significant improvement in the accuracy of the estimation was achieved. The calculated cell numbers via the genomic probe technique were 0.99+/-0.13-, 1.25+/-0.23- and 0.18+/-0.11-fold higher than the respective CFUs in pure cultures of R. meliloti, Rhizobium sp. and Bradyrhizobium sp. In samples containing mixed populations, the estimated numbers from genomic probing were 1.25+/-0.51-, 45.9+/-14.8- and 0.27+/-0.07-fold higher than the CFU-derived cell count (same respective order).

Crude oil bioremediation in sub-Antarctic intertidal sediments: chemistry and toxicity of oiled residues

The effectiveness of fertilizers for crude oil bioremediation in sub-Antarctic intertidal sediments was tested over a one-year period in a series of ten (10) experimental enclosures. Chemical, microbial and toxicological parameters demonstrated the effectiveness of various fertilizers in a pristine environment where hydrocarbon degrading bacteria (HDB) had not been stimulated by previous accidental spills or human activities. The low temperature of seawater (3-4 degrees C) had no obvious effects on the HDB community and the bioremediation process. Over 90% of n-alkanes were degraded in the first six months and most light aromatics (2-3 rings) disappeared during the first year of observation. The toxicity of oiled residues (Microtox(R) SP) was significantly reduced in the first 6 months of the process, but it increased again in the last months of the experiment. One of the fertilizers containing fishbone compost enriched with urea, inorganic phosphorus and a lipidic surfactant reduced significantly the toxicity of oil residues in the last 3 months of the experiment. Interstitial waters collected below the oil slicks during the remediation showed no toxicity, and even stimulated Vibrio fischeri. When comparing all fertilizers to the control plots, a good correlation (r(2)=0.82) was found between the growth rate of HDB and the degradation rate of n-alkanes in the first 90 days of the experiment only indicating that fertilizers were efficient for at least 3 months but their beneficial effects were lost after 6 months.

Field observations on the variability of crude oil impact on indigenous hydrocarbon-degrading bacteria from sub-Antarctic intertidal sediments

Oil pollution of the oceans has been a problem ever since man began to use fossil fuels. Biodegradation by naturally occurring populations of micro-organisms is a major mechanism for the removal of petroleum from the environment. To examine the effects of crude oil pollution on intertidal bacteria, we repeated the same contamination experiments on nine different sub-Antarctic intertidal beaches using specifically built enclosures (PVC pipe, 15 cm in inner diameter and 30 cm in height). Despite the pristine environmental conditions, significant numbers of indigenous hydrocarbon-degrading bacteria were observed in all the studied beaches. Introduction of oil into these previously oil-free environments resulted in several orders of magnitude of increase in hydrocarbon-degrading micro-organisms within a few days in some of the studied sites but has no obvious effects on two others. The physical environment of the bacterial assemblage seems to play a major role in the biodegradation capacities. After 3 months of contamination, both remaining oil concentrations and biodegradation indexes differ strongly between the different stations. Thus, chemical and biological parameters reveal a strong heterogeneity of biodegradation capacities between the different sites.