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A wide range of microbial taxa are active in hydrocarbon-contaminated Arctic soils, and many are capable of hydrocarbon metabolism. The most effective hydrocarbon degraders may not naturally dominate following contamination events, so shifts in microbial abundance could potentially increase hydrocarbon biodegradation. In this study, we contaminated an Arctic soil with diesel and used gentamicin and vancomycin to inhibit distinct portions of the microbial community. We measured diesel loss using gas chromatography, bacterial and fungal abundance with qPCR, and assessed bacterial diversity and community composition through Ion Torrent sequencing of 16S rRNA gene amplicons. The combined addition of both antibiotics increased diesel biodegradation significantly relative to the no-antibiotic treatment, despite reduced bacterial and fungal abundance; however, this effect was not observed when nutrients were also added. All treatments produced unique bacterial communities, and both Xanthomonadaceae and Micrococcineae were dominant in the dual antibiotic treatment. The bacterial communities resulting from dual gentamicin and vancomycin addition were similar both with and without nutrients, although nutrient addition produced a much larger fungal population, which may partly explain the differences in biodegradation between these two treatments. These results suggest that the most efficient hydrocarbon-degrading community may not always be promoted naturally in contaminated soils., (© Her Majesty the Queen in Right of Canada 2013.)

Aims: To explore rhizospheric microbial communities from Arctic native plant species evaluating their bacterial hydrocarbon-degrading capacities., Methods and Results: Eriophorum scheuchzeri, Potentilla cf. rubricaulis, Oxyria digyna, Salix arctica and Puccinellia angustata plant species were collected at Eureka (Canadian high Arctic) along with their rhizospheric soil samples. Their bacterial community fingerprints (16S rRNA gene, DGGE) were distinctive encompassing members from the phyla: Bacteroidetes, Firmicutes, Actinobacteria and Proteobacteria. Isolated diesel-degrading bacteria belonged to the phyla Actinobacteria and Proteobacteria. Strains of Mycobacterium, Nocardia, Rhodococcus, Intrasporangiaceae, Leifsoni and Arthrobacter possessed alkB and Pseudomonas possessed both ndoB and xylE gene sequences. Two Rhodococcus strains mineralized [1-(14) C] hexadecane at 5 and -5°C. From the rhizosphere of P. angustata, larger numbers of hydrocarbon-degrading bacteria were isolated than from other plant rhizosphere samples and all three genes alkB (from Actinobacteria), ndoB and xylE (from Pseudomonas) were detected by PCR., Conclusions: (i) Arctic plants have unique rhizospheric bacterial communities. (ii) P. angustata has potential for phytoremediation research at high Arctic soils. (iii) Isolated bacteria mineralized hydrocarbons at ambient low temperatures., Significance and Impact of the Study: To the best of our knowledge, this is the first rhizospheric exploration examining the phytoremediation potential of five Arctic plants and evaluating their microbial hydrocarbon-degrading capacities., (© 2012 The Society for Applied Microbiology.)

Temporal atmospheric temperature changes during summers at sub-Arctic sites often cause periodic fluctuations in shallow landfarm and surface soil temperatures. However, little information is available on the effect of site-relevant variations on biodegradation performance in cold climates. This study compares the rate and extents of biodegradation of petroleum hydrocarbons at variable site temperatures (1-10 °C) representative of summers at a sub-Arctic site reported previously with those obtained under a constant average temperature of 6 °C. The biodegradation was evaluated in pilot-scale landfarming experiments with field-aged petroleum-contaminated soils shipped from Resolution Island (61°30'N, 65°00'W), Nunavut, Canada. Under the variable site temperature conditions biodegradation rate constants of semi- (F2) and non-volatile (F3) hydrocarbon fractions were enhanced by over a factor of two during the 60-d experiment, compared to the constant temperature mode. The decrease in total petroleum hydrocarbons (TPH) under the variable site temperature mode was 55% compared to only 19% under the constant average temperature mode. The enhanced biodegradation is attributable to the non-linear acceleration of microbial activity between 4.7 and 10°C and faster growth of indigenous hydrocarbon-degrading microbial populations. The first-order biodegradation rate constants of 0.018, 0.024 and 0.016 d(-1) for TPH, F2 and F3 fractions at the variable site temperature were in agreement with those determined by an on-site experiment at the same site., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Several studies have shown that biostimulation in ex situ systems such as landfarms and biopiles can facilitate remediation of petroleum hydrocarbon contaminated soils at sub-Arctic sites during summers when temperatures are above freezing. In this study, we examine the biodegradation of semivolatile (F2: C10-C16) and nonvolatile (F3: C16-C34) petroleum hydrocarbons and microbial respiration and population dynamics at post- and presummer temperatures ranging from -5 to 14 °C. The studies were conducted in pilot-scale tanks with soils obtained from a historically contaminated sub-Arctic site in Resolution Island (RI), Canada. In aerobic, nutrient-amended, unsaturated soils, the F2 hydrocarbons decreased by 32% during the seasonal freeze-thaw phase where soils were cooled from 2 to -5 °C at a freezing rate of -0.12 °C d(-1) and then thawed from -5 to 4 °C at a thawing rate of +0.16 °C d(-1). In the unamended (control) tank, the F2 fraction only decreased by 14% during the same period. Biodegradation of individual hydrocarbon compounds in the nutrient-amended soils was also confirmed by comparing their abundance over time to that of the conserved diesel biomarker, bicyclic sesquiterpanes (BS). During this period, microbial respiration was observed, even at subzero temperatures when unfrozen liquid water was detected during the freeze-thaw period. An increase in culturable heterotrophs and 16S rDNA copy numbers was noted during the freezing phase, and the (14)C-hexadecane mineralization in soil samples obtained from the nutrient-amended tank steadily increased. Hydrocarbon degrading bacterial populations identified as Corynebacterineae- and Alkanindiges-related strains emerged during the freezing and thawing phases, respectively, indicating there were temperature-based microbial community shifts.

This study evaluates the feasibility of landfarming biotreatment of petroleum-contaminated soils obtained from a sub-Arctic site at Resolution Island, Nunavut, Canada, and evaluates the changes in composition of the semi- and non-volatile petroleum hydrocarbon fractions during the biotreatment. Pilot-scale landfarming experiments were conducted in a laboratory in soil tanks under temperature profiles representative of the 3-year site air temperatures in July and August where temperature varied uniformly between 1 degrees C and 10 degrees C over 10 d. The site soils were acidic and N-deficient, but contained indigenous populations of hydrocarbon-degrading microorganisms. Biostimulation with nitrogen and phosphorus nutrient amendments to achieve C(TPH):N:P molar ratio of 100:9:1, and CaCO(3) amendment at 2000 mg Kg(-1) for maintaining neutral pH, and periodic 10-day tilling, reduced total petroleum hydrocarbon (TPH) concentrations by up to 64% over a 60-day period. The rate and extent of semi-volatile (F2: >C10-C16) and non-volatile (F3: >C16-C34) petroleum hydrocarbon fractions in the landfarms containing higher initial TPH levels ( approximately 2000 mg Kg(-1)) and lower TPH levels ( approximately 1000 mg Kg(-1)) were compared. Significant biodegradation of the F2 and F3 fractions occurred in both of those systems. First-order biodegradation rate constants of up to 0.019+/-0.001 d(-1) were determined for the F3 hydrocarbon fraction and were similar to the F2 fraction biodegradation rate constants of up to 0.024+/-0.005 d(-1). Biodegradation profiles of the C14, C16 and C18 alkanes revealed that at TPH concentrations above 1000 mg Kg(-1) these compounds are degraded concurrently, whereas below 1000 mg Kg(-1) the higher-molecular weight alkanes are preferentially degraded. After the 60-day treatment period, the TPH concentration was approximately 500 mg Kg(-1), and the residual TPH mass was largely associated with particles and aggregated particles with diameters of 0.6-2 mm, rather than the larger or finer particles and aggregates., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Biodegradation of petroleum hydrocarbons in cold environments, including Alpine soils, is a result of indigenous cold-adapted microorganisms able to degrade these contaminants. In the present study, the prevalence of seven genotypes involved in the degradation of n-alkanes (Pseudomonas putida GPo1 alkB; Acinetobacter spp. alkM; Rhodococcus spp. alkB1, and Rhodococcus spp. alkB2), aromatic hydrocarbons (P. putida xylE), and polycyclic aromatic hydrocarbons (P. putida ndoB and Mycobacterium sp. strain PYR-1 nidA) was determined in 12 oil-contaminated (428 to 30,644 mg of total petroleum hydrocarbons [TPH]/kg of soil) and 8 pristine Alpine soils from Tyrol (Austria) by PCR hybridization analyses of total soil community DNA, using oligonucleotide primers and DNA probes specific for each genotype. The soils investigated were also analyzed for various physical, chemical, and microbiological parameters, and statistical correlations between all parameters were determined. Genotypes containing genes from gram-negative bacteria (P. putida alkB, xylE, and ndoB and Acinetobacter alkM) were detected to a significantly higher percentage in the contaminated (50 to 75%) than in the pristine (0 to 12.5%) soils, indicating that these organisms had been enriched in soils following contamination. There was a highly significant positive correlation (P < 0.001) between the level of contamination and the number of genotypes containing genes from P. putida and Acinetobacter sp. but no significant correlation between the TPH content and the number of genotypes containing genes from gram-positive bacteria (Rhodococcus alkB1 and alkB2 and Mycobacterium nidA). These genotypes were detected at a high frequency in both contaminated (41.7 to 75%) and pristine (37.5 to 50%) soils, indicating that they are already present in substantial numbers before a contamination event. No correlation was found between the prevalence of hydrocarbon-degradative genotypes and biological activities (respiration, fluorescein diacetate hydrolysis, lipase activity) or numbers of culturable hydrocarbon-degrading soil microorganisms; there also was no correlation between the numbers of hydrocarbon degraders and the contamination level. The measured biological activities showed significant positive correlation with each other, with the organic matter content, and partially with the TPH content and a significant negative correlation with the soil dry-mass content (P < 0.05 to 0.001).

Plant-bacterial combinations can increase contaminant degradation in the rhizosphere, but the role played by indigenous root-associated bacteria during plant growth in contaminated soils is unclear. The purpose of this study was to determine if plants had the ability to selectively enhance the prevalence of endophytes containing pollutant catabolic genes in unrelated environments contaminated with different pollutants. At petroleum hydrocarbon contaminated sites, two genes encoding hydrocarbon degradation, alkane monooxygenase (alkB) and naphthalene dioxygenase (ndoB), were two and four times more prevalent in bacteria extracted from the root interior (endophytic) than from the bulk soil and sediment, respectively. In field sites contaminated with nitroaromatics, two genes encoding nitrotoluene degradation, 2-nitrotoluene reductase (ntdAa) and nitrotoluene monooxygenase (ntnM), were 7 to 14 times more prevalent in endophytic bacteria. The addition of petroleum to sediment doubled the prevalence of ndoB-positive endophytes in Scirpus pungens, indicating that the numbers of endophytes containing catabolic genotypes were dependent on the presence and concentration of contaminants. Similarly, the numbers of alkB- or ndoB-positive endophytes in Festuca arundinacea were correlated with the concentration of creosote in the soil but not with the numbers of alkB- or ndoB-positive bacteria in the bulk soil. Our results indicate that the enrichment of catabolic genotypes in the root interior is both plant and contaminant dependent.

Three hydrocarbon-degrading psychrotrophic bacteria were isolated from petroleum-contaminated Arctic soils and characterized. Two of the strains, identified as Pseudomonas spp., degraded C5 to C12 n-alkanes, toluene, and naphthalene at both 5 and 25 degrees C and possessed both the alk catabolic pathway for alkane biodegradation and the nah catabolic pathway for polynuclear aromatic hydrocarbon biodegradation. One of these strains contained both a plasmid slightly smaller than the P. oleovorans OCT plasmid, which hybridized to an alkB gene probe, and a NAH plasmid similar to NAH7, demonstrating that both catabolic pathways, located on separate plasmids, can naturally coexist in the same bacterium.