PLFA Analyses of Microbial Communities Associated with PAH-Contaminated Riverbank Sediment

Sediment contaminated with polycyclic aromatic hydrocarbons (PAHs) is widely distributed in aquatic ecosystems. The microbial community structure of riverbank PAH-contaminated sediments was investigated using phospholipid-derived fatty acid (PLFA) analysis. Surface and subsurface riverbank sediment was collected from a highly contaminated site and from an uncontaminated site along the Mahoning River, OH. PAH concentrations, physical sediment characteristics, and other microbial community parameters (biomass as phospholipid phosphate (PLP) and activity) were also measured. PAHs were detected in all samples but were only quantifiable in the contaminated (250?μg/g?g(-1)) subsurface sediment. Subsurface samples from both locations showed very similar PLP values and distribution of PLFAs, with 27-37?% of the microbial community structure being composed of sulfate reducing and other anaerobic bacteria. Principal components analysis indicated no correlation between PAH contamination and PLFA diversity. Although PLP and phospholipid fatty acid measurements of bacterial communities did not reflect the environmental differences among sites, the highly PAH-contaminated sediment showed the highest measured microbial activity (reduction of 1,200?nmol?INT?g(-1)?h(-1)), likely from a population adapted to environmental pollutants, rates that are much higher than measured in many uncontaminated soil and sediment systems. These data warrant further investigation into community structure at the genetic level and indicate potential for bioremediation by indigenous microbes.     

Microbiological characterization of a coke oven contaminated site and evaluation of its potential for bioremediation

The soil microbial population of a coke oven site was investigated in order to evaluate its potential for bioremediation. The study was carried out in soil samples with distinct polynuclear aromatic hydrocarbon (PAH) contamination levels, comparing the population profiles constituted by total heterotrophic and PAH-utilizing strains. Isolation of degrading strains was performed with phenanthrene or pyrene as sole carbon sources. The ability to degrade other PAHs, such as anthracene, fluorene and fluoranthene was also investigated. The results showed a reduction of 30% in species diversity and microbial density drops one order of magnitude in contaminated samples. Furthermore, the number of PAH-utilizing colonies was higher in the contaminated area and about 20% of the isolates were able to degrade phenanthrene and pyrene, while this value decreased to 0.15% in uncontaminated samples. Three PAH-degrader strains were identified as: CDC gr. IV C-2, Aeromonas sp. and Pseudomonas vesicularis. The ability of these strains to degrade other PAHs was also investigated.     

A comparison of microbial community characteristics among petroleum-contaminated and uncontaminated subsurface soil samples

Measurements of microbial community size, including total cell counts and specific degrader enumerations, were conducted on subsurface soil samples from both petroleum-contaminated and pristine aquifers. Samples were collected from both uncontaminated and contaminated areas of the petroleum-contaminated sites. In pristine and uncontaminated samples, total cell counts (acridine orange direct counts) were related to depth. The deeper samples contained smaller total microbial populations. However, indices of microbial activity varied considerably from sample to sample and probably reflect soil and site heterogeneity. Exposure to petroleum contamination apparently altered the microbial community structure. In samples exposed to low levels of contaminants as vapors and/or dissolved phases (ppb concentrations), and not free product, the toluene-specific degrader populations were larger at greater depths, and the numbers of amino acid-specific degraders were highly correlated to the numbers of decane-specific degraders, indicating that petroleum-adapted microbial communities were present in the contaminated samples. In highly contaminated samples, total microbial population densities decreased with increasing depth; however, microbial activity tended to increase with depth. These results indicate that petroleum contaminants exert toxic effects on the active microbial community at high exposures and enrich specific degraders at ppb levels of dissolved contaminants. Correspondence to: S.C. Long     

Isolation and Molecular Characterization of Heavy Metal-Resistant Azotobacter chroococcum from Agricultural Soil and Their Potential Application in Bioremediation

Pollution of soil with heavy metals, herbicides, antibiotics and other chemicals is known to have a negative effect on microbial activities. Therefore, the aim of this study was to isolate cultures of Azotobacter sp. from polluted and unpolluted soils and to study the effect of these pollutants on their growth. A total of 120 Azotobacter sp. were isolated from soils irrigated with wastewater (contaminated soils) and groundwater (uncontaminated soils). These isolates were screened for resistance to heavy metals, herbicide and antibiotics. Also, the soils from which the cultures were isolated were analyzed for the concentrations of Zn²⁺, Cd²⁺, Cu²⁺, Pb²⁺ and Mn²⁺ they contained. Contaminated soil showed high levels of heavy metals as compared to uncontaminated soil. The size of the Azotobacter population in contaminated soil was lower than that in uncontaminated soil. Of the Azotobacter isolates, 64 that were recovered from contaminated soil exhibited high resistance to heavy metals (Hg²⁺, Cd²⁺, Cu²⁺, Cr³⁺, Co²⁺, Ni²⁺, Zn²⁺ and Pb²⁺) and herbicide 2,4-D compared to 56 isolates from uncontaminated soil. Also, isolates from contaminated soil showed high resistance to chloramphenicol, nitrofurantoin and co-trimoxazole compared to those isolated from uncontaminated soil. The majority of Azotobacter isolates from contaminated soil showed multiple-resistance to different metal ions and antibiotics. All isolates failed to grow at pH less than 6. Salt concentration (5%) was found to be inhibitory to all isolates. The most potent isolates from contaminated soil that showed multiresistance to all substances tested were identified on the basis of morphological and biochemical characteristics, and 16S rRNA as A. chroococcum. These resistant isolates could be employed in contaminated soils and/or bioremediation.     

The effect of Piriformospora indica on the root development of maize (Zea mays L.) and remediation of petroleum contaminated soil

As the depth of soil petroleum contamination can vary substantially under field conditions, a rhizotron experiment was performed to investigate the influence of endophyte, P. indica, on maize growth and degradation of petroleum components in a shallow and a deep-reaching subsurface layer of a soil. For control, a treatment without soil contamination was also included. The degree in contamination and the depth to which it extended had a strong effect on the growth of the plant roots. Contaminated soil layers severely inhibited root growth thus many roots preferred to bypass the shallow contaminated layer and grow in the uncontaminated soil. While the length and branching pattern of these roots were similar to those of uncontaminated treatment. Inoculation of maize with P. indica could improve root distribution and root and shoot growth in all three contamination treatments. This inoculation also enhanced petroleum degradation in soil, especially in the treatment with deep-reaching contamination, consequently the accumulation of petroleum hydrocarbons (PAHs) in the plant tissues were increased.     

Characterisation of biodegradation capacities of environmental microflorae for diesel oil by comprehensive two-dimensional gas chromatography

In contaminated soils, efficiency of natural attenuation or engineered bioremediation largely depends on biodegradation capacities of the local microflorae. In the present study, the biodegradation capacities of various microflorae towards diesel oil were determined in laboratory conditions. Microflorae were collected from 9 contaminated and 10 uncontaminated soil samples and were compared to urban wastewater activated sludge. The recalcitrance of hydrocarbons in tests was characterised using both gas chromatography (GC) and comprehensive two-dimensional gas chromatography (GC×GC). The microflorae from contaminated soils were found to exhibit higher degradation capacities than those from uncontaminated soil and activated sludge. In cultures inoculated by contaminated-soil microflorae, 80% of diesel oil on an average was consumed over 4-week incubation compared to only 64% in uncontaminated soil and 60% in activated sludge cultures. As shown by GC, n-alkanes of diesel oil were totally utilised by each microflora but differentiated degradation extents were observed for cyclic and branched hydrocarbons. The enhanced degradation capacities of impacted-soil microflorae resulted probably from an adaptation to the hydrocarbon contaminants but a similar adaptation was noted in uncontaminated soils when conifer trees might have released natural hydrocarbons. GC×GC showed that a contaminated-soil microflora removed all aromatics and all branched alkanes containing less than C₁₅. The most recalcitrant compounds were the branched and cyclic alkanes with 15–23 atoms of carbon.     

Distribution of aerobic bacteria,protozoa, algae,and fungi in deep subsurface sediments

The distribution of microorganisms in deep subsurface profiles was determined at three sites at the Savannah River Plant, Aiken, South Carolina. Acridine orange direct counts (AODC) of bacteria were highest in surface soil samples and declined to the 10⁶ to 10⁷ per gram range in the subsurface, but then did not decline further with depth. In the subsurface, AODC values varied from layer to layer, the highest being found in samples from sandy aquifer formations and the lowest in clayey interbed layers. Sandy aquifer sediments also contained the highest numbers of viable bacteria as determined by aerobic spread plate counts (CFU) on a dilute heterotrophic medium. In some of these samples bacterial CFU values approached 100% of the AODC values. Viable protozoa (amoebae and flagellates, but no ciliates) were found in samples with high bacterial CFU values. A variety of green algae, phytoflagellates, diatoms, and a few cyanobacteria were found at low population densities in samples from two of the three boreholes. Low numbers of fungi were evenly distributed throughout the profiles at all three sites. Microbial population density estimates correlated positively with sand content and pore‐water pH, and negatively with clay content and pore‐water metal concentration. A large diversity of prokaryotic and eukaryotic microorganisms was found in samples with high population densities. A survey of bacterial strains isolated from subsurface samples revealed associations of gram‐positive bacteria with high clay sediments and gram‐negative bacteria with sandy sediments. The ability to deposit lipophilic storage material (presumably poly‐ß‐hydroxybutyrate) was found in a high proportion of isolates from sandy sediments, but only rarely in isolates from high clay sediments.     

Hydrochemical,bacteriological assessment,and classification of groundwater quality in Thulamela Municipality,South Africa: potential health risk

Abstract

Potential effects of anthropogenic activities on different boreholes around Thulamela Municipality, South Africa, were evaluated by quantifying the bacteria indicators and physicochemical parameters during summer, autumn, and winter. The purpose was to determine whether the borehole water in this region is safe for domestic use across the seasons. The concentrations of physicochemical (Temperature, pH, electrical conductivity (EC), turbidity, and nitrate) and bacteriological (both Escherichia coli and Enterococcus faecalis) contaminants in the borehole water samples were determined using standard microbiology methods. The mean concentration of NO₃ for most of the boreholes failed to comply with the recommended guidelines throughout the season. High microbial load of E. coli (2.0?×?10¹ – 4.6?×?10³ CFU/100?ml) and E. faecalis (2.0?×?10° – 6.0?×?10² CFU/100?ml) was recorded in the wet season than in the dry season (0.0 – 7.0?×?10² and 0.0 – 1.0?×?10¹ CFU/100?ml, respectively). Sanitary inspection and water source classification showed that most boreholes are prone to chemical contaminants during summer and autumn due to rainfall and this correlates with the measured microbial contamination. The result is significantly important because water from these boreholes is used for domestic purposes without treatment and could pose major public health risks to the consumers.     

Aerobic metabolic potential of microbial populations indigenous to deep subsurface environments

Subsurface sediment samples, collected from three boreholes ranging in depths from 0.1 to 260 m, were used in substrate mineralization studies to examine the aerobic metabolic potential of microbial populations indigenous to the deep subsurface. Mineralization was measured by quantifying the amount of ¹⁴CO₂ released from radiolabeled acetate, phenol, or 4‐methoxybenzoate added to subsurface sediments at 10 μg g^‐1. Mineralization of the three compounds was observed in all but a few of the subsurface samples and did not decrease with depth. In addition, mineralization data collected from similar geologic formations from the different boreholes indicated that there was significant lateral continuity of microbial activity. Regression analyses were performed to determine which environmental factors were related to microbial metabolic potential. Mineralization was positively correlated with heterotrophic abundance as measured by plate counts. Other parameters that appeared to influence metabolic potential included pH and clay content.     

Rhizosphere microbial community and hexachlorocyclohexane degradative potential in contrasting plant species

The organochlorine 1,2,3,4,5,6 hexachlorocyclohexane (HCH) is a broad-spectrum insecticide that was used on a large-scale worldwide. The soil–plant–microbe system and its influence on HCH biodegradation are evaluated. A greenhouse experiment was designed to evaluate HCH dissipation and several microbial parameters among rhizosphere and bulk soil of two contrasting plants, Cytisus striatus (Hill) Rothm and Holcus lanatus L. Plants were grown for 180 days in three treatments: uncontaminated soil (control), uncontaminated soil inoculated with soil (3% w/w) from a HCH-contaminated site (INOC), and uncontaminated soil inoculated with soil (3% w/w) from the HCH-contaminated site and artificially contaminated to obtain 100 mg HCH kg⁻¹ dry soil (100HCH-INOC). At harvest, plant biomass, soil water-extractable organic C, pH and Cl concentration, rhizosphere microbial densities (total heterotrophs, ammonifiers, amylolytics) and C substrate utilization patterns, and degradation of α-, β-, δ- and γ-HCH isomers were determined in bulk and rhizosphere soils. Soil solution Cl concentration was determined every 30 days throughout the entire growth period. Results demonstrate that both Cytisus striatus and Holcus lanatus can grow in soils with up to 100 mg HCH kg⁻¹. An enhanced degradation of α-HCH, but not β- or δ-HCH, was observed in the rhizosphere. Significant changes in the microbial densities were observed between bulk and rhizosphere soils of Cytisus, and an increase in C source utilization indicated changes in community level physiological profiles (CLPP) in the rhizosphere of this species when grown in contaminated soils. HCH dissipation was also greater in soils planted with this species. In accordance, increases in soil extractable C, Cl concentration and acidity were greater at the rhizosphere of Cytisus. Concentration of Cl in soil solutions also indicates greater HCH dechlorination in soils planted with Cytisus than Holcus. Results suggest that phytostimulation of bacteria present or added to soil is a promising approach to cleaning HCH-contaminated sites, and especially for biodegradation of α-HCH.     

Shifts in alkane-degrading bacteria genotypes during bioremediation of a vegetated coastal soil

The effect of plants (milo, oleander and buffelgrass) and hexadecane (1 g/kg of soil) on the diversity of hexadecane-degraders in a coastal soil was investigated. Hexadecane was rapidly degraded during the first 56 days. Its depletion was not plant-enhanced but was slightly retarded by milo and buffelgrass. The diversity of the dominant cultured hexadecane-degrading bacteria was based on sequencing of the V6-8 region of 16S rDNA. On day 0, Alphaproteobacteria prevailed. By day 56, Gammaproteobacteria dominated the contaminated samples whereas similar numbers of Alphaproteobacteria and Gammaproteobacteria genotypes occurred in the uncontaminated samples. Bacteria related to Alcanivorax, a specialized alkane-degrading marine bacterium, were found in all contaminated samples except for buffelgrass rhizospheres, which solely harbored Pseudomonas indica. On day 114, when hexadecane was highly depleted in the contaminated treatments, similar numbers of Alpha- and Gammaproteobacteria genotypes occurred in contaminated and uncontaminated samples. At this stage Alcanivorax had virtually disappeared. Thus in this coastal soil the prevalence of the alkane-dependent Alcanivorax may be a useful indicator of bioremediation progress provided the plant cover favors the dominance of Alcanivorax.     

Biodegradation of trichloroethylene and toluene by indigenous microbial populations in vadose sediments

The unsaturated subsurface (vadose zone) receives significant amounts of hazardous chemicals, yet little is known about its microbial communities and their capacity to biodegrade pollutants. Trichloroethylene (TCE) biodegradation occurs readily in surface soils; however, the process usually requires enzyme induction by aromatic compounds, methane, or other cosubstrates. The aerobic biodegradation of toluene and TCE by indigenous microbial populations was measured in samples collected from the vadose zone at unpolluted and gasoline-contaminated sites. Incubation at field moisture levels showed little activity on either TCE or toluene, so samples were tested in soil suspensions. No degradation occurred in samples suspended in water or phosphate buffer solution; however, both toluene and TCE were degraded in samples suspended in mineral salts medium. TCE degradation depended on toluene degradation, and little loss occurred under sterile conditions. Studies with specific nutrients showed that addition of ammonium sulfate was essential for degradation, and addition of other mineral nutrients further enhanced the rate. Additional studies with vadose sediments amended with nutrients showed similar trends to those observed in sediment suspensions. Initial rates of biodegradation in suspensions were faster in uncontaminated samples than in gasolinecontaminated samples, but the same percentages of chemicals were degraded. Biodegradation was slower and less extensive in shallower samples than deeper samples from the uncontaminated site. Two toluene-degrading organisms isolated from a gasoline-contaminated sample were identified as Corynebacterium variabilis SVB74 and Acinetobacter radioresistens SVB65. Inoculation with 10⁶ cells of C. variabilis ml^–1 of soil solution did not enhance the rate of degradation above that of the indigenous population. These results indicate that mineral nutrients limited the rate of TCE and toluene degradation by indigenous populations and that no additional benefit was derived from inoculation with a toluene-degrading bacterial strain. Correspondence to: K.M. Scow     

Copper complexation by natural organic matter in contaminated and uncontaminated ground water

Abstract

Ground-water samples were collected from an uncontaminated and a contaminated site. Copper complexation was characterized by ion- selective electrode (ISE), fluorescence quenching (FQ), and cathodic stripping voltammetric (CSV) titrations. All of the samples were titrated at their natural pH values and some of the samples were also titrated at other pH values. For a total Cu concentration of 10^?6 M, the free Cu²⁺ concentrations in the samples from the uncontaminated site were all less than 10^?7 M, while free Cu²⁺ in the samples from the contaminated site were all less than 10^?8 M. For a particular sample and total Cu concentration, the free Cu²⁺ concentration decreased as the pH increased. Relative to ISE, FQ underestimated and CSV overestimated the degree of Cu²⁺ binding. The Cu²⁺ -complexing properties of the ground waters are similar to many published results for the same pH and for ligand concentrations normalized to T.O.C. Chemical equilibrium computations indicate that organic complexes would dominate Cu speciation in the uncontaminated ground waters for 10^?7 to 10^?5 M total Cu. In the contaminated ground waters, sulfide complexes would be the predominant Cu species for total Cu less than the total S(?11) concentration. Organic complexes would dominate Cu speciation for total Cu greater than total S(?11).     

Lithotrophic and Heterotrophic Bacteria in Deep Subsurface Sediments and Their Relation to Sediment Properties

Subsurface sediments obtained from three cores drilled to depths of 260 m below the surface in South Carolina were analyzed for heterotrophic bacteria; N₂‐fixing microaerophiles; and nitrifying, sulfur‐oxidizing, and H₂‐oxidizing lithotrophic bacteria. In addition, pore waters were extracted for chemical analysis of inorganic nitrogen species, sulfate, dissolved organic carbon, pH, and Eh. Autotroph populations were generally less than 10³ most probable number (MPN) g^‐1 dry sediment with sulfur‐oxidizing bacteria, detected in 60% of the sediment samples, being the most frequently encountered group. Nitrifying bacteria were detected mainly in sediments from one borehole (P28), and their populations in those sediments were correlated with pore‐water ammonium concentrations. Populations of heterotrophic bacteria in 60% of the sediments were greater than 10⁶ colony forming units (CFU) g^‐1 dry sediment and were typically lower in sediments of high clay content and low pH. Microaerophilic N₂‐fixing bacteria were cultured from >50% and bacteria capable of growth on H₂ were cultured from 35% of the subsurface sediments examined. Sediment texture, which controls porosity, water potential, and hydraulic conductivity, appears to be a major factor influencing microbial populations in coastal plain subsurface sediments.     

Toxicity and Bioaccumulation of Petroleum Mixtures with Alkyl PAHs in Earthworms

The toxicities of three oil products with boiling-point ranges representative of petroleum hydrocarbons were tested on earthworms (Eisenia fetida) to investigate the correlation between bioaccumulated concentrations of polycyclic aromatic hydrocarbons (PAHs) and toxicity. The toxicities to earthworms were in the sequence: kerosene > diesel > bunker-C. After 14 days, the LC50s of the soils contaminated with kerosene, diesel, and bunker-C were 1079, 9135, and 15,609 mg/kg, respectively. Analysis of the body residue concentrations of PAHs in the earthworms showed that the accumulation of alkyl PAHs predominated that of the 16 priority PAHs. Principal component analysis (PCA) identified 12 PAHs, including four alkylated naphthalenes, as the oil constituents that affected mortality in the kerosene-contaminated soil. For the diesel-contaminated soil, eight PAHs were identified, including dibenzothiophene. It was not clear which compounds affected mortality in the bunker-C soil. Across the three series, biota-to-soil accumulation factors (BSAFs) ranged from 10^–2.05 to 10^3.98, and generally increased as the hydrophobicity (K_ow) or molecular weight of the alkyl PAHs increased. The toxicity endpoints of each oil product can be used as reference values in the risk assessment of soils contaminated with petroleum, and individual PAHs screened out have implications for future toxicity assessment of petroleum hydrocarbons.     

Horizontal Gene Transfer of PIB-Type ATPases among Bacteria Isolated from Radionuclide- and Metal-Contaminated Subsurface Soils

Aerobic heterotrophs were isolated from subsurface soil samples obtained from the U.S. Department of Energy's (DOE) Field Research Center (FRC) located at Oak Ridge, Tenn. The FRC represents a unique, extreme environment consisting of highly acidic soils with cooccurring heavy metals, radionuclides, and high nitrate concentrations. Four hundred isolates obtained from contaminated soil were assayed for heavy metal resistance, and a smaller subset was assayed for tolerance to uranium. The vast majority of the isolates were gram-positive bacteria and belonged to the high-G+C- and low-G+C-content genera Arthrobacter and Bacillus, respectively. Genomic DNA from a randomly chosen subset of 50 Pb-resistant (Pb^r) isolates was amplified with PCR primers specific for P_IB-type ATPases (i.e., pbrA/cadA/zntA). A total of 10 pbrA/cadA/zntA loci exhibited evidence of acquisition by horizontal gene transfer. A remarkable dissemination of the horizontally acquired P_IB-type ATPases was supported by unusual DNA base compositions and phylogenetic incongruence. Numerous Pb^r P_IB-type ATPase-positive FRC isolates belonging to the genus Arthrobacter tolerated toxic concentrations of soluble U(VI) (UO₂²⁺) at pH 4. These unrelated, yet synergistic, physiological traits observed in Arthrobacter isolates residing in the contaminated FRC subsurface may contribute to the survival of the organisms in such an extreme environment. This study is, to the best of our knowledge, the first study to report broad horizontal transfer of P_IB-type ATPases in contaminated subsurface soils and is among the first studies to report uranium tolerance of aerobic heterotrophs obtained from the acidic subsurface at the DOE FRC.     

Polycyclic aromatic hydrocarbons in traffic soil and Pinus needles of Beijing,China

Abstract

This study was conducted to examine the impact of vehicular traffic on the contamination status of urban traffic sites in Beijing with respect to polycyclic aromatic hydrocarbons (PAHs). The soil and Pinus pinea needle samples were collected at 12 sites on Three Ring Road in Beijing, China, from July 2009 to March 2010. Total PAH concentrations at traffic sites ranged from 113.86 to 2226.24 ng g^?1 with an average value of 658.71 ± 742.41 ng g^?1 in soil samples and 112.03 to 2016.80ng g^?1 with an average value of 680.29 ± 485.61 ng g^?1 in needle samples. The PAH pattern was dominated by two- and three-ring PAHs (contributing >80% to the total PAHs) at all the 12 traffic sites. Seasonal variations of PAHs compounds indicated the PAHs concentrations in autumn and winter were higher than those in spring and summer due to temperature effects. This work indicates that the low ring PAHs were the major profile at the roadside of a busy street with heavy traffic in Beijing.     

Uptake and distribution of several inorganic ions in Nephrolepis cordifolia (L.) C. Presl grown on contaminated soil

Plants of Nephrolepis cordifolia (L.) C. Presl were grown on soil samples collected in a mine site located in Central Italy and on soil samples from uncontaminated soils to test the ability of this species to accumulate inorganic contaminants under semi-natural conditions. The plants were kept under observation for monitoring the growth and the appearance of any stress symptoms. The concentrations of inorganic ions were determined in the substrates and in different plant organs. The results indicated that N. cordifolia is able to grow vigorously on soils contaminated by inorganic ions that are potentially toxic for living organisms and that this species is able to accumulate several inorganic contaminants mainly in its underground parts. Concentrations of aluminium, iron and lead >1000 mg/kg in the underground parts were detected in plants grown on the contaminated substrate. N. cordifolia is, therefore, potentially useful as a tool for phytostabilization of contaminated soils.     

Isolation and characterization of heavy polycyclic aromatic hydrocarbon-degrading bacteria adapted to electrokinetic conditions

Polycyclic aromatic hydrocarbon (PAH)-degrading bacteria capable of growing under electrokinetic conditions were isolated using an adjusted acclimation and enrichment procedure based on soil contaminated with heavy PAHs in the presence of an electric field. Their ability to degrade heavy PAHs under an electric field was individually investigated in artificially contaminated soils. The results showed that strains PB4 (Pseudomonas fluorescens) and FB6 (Kocuria sp.) were the most efficient heavy PAH degraders under electrokinetic conditions. They were re-inoculated into a polluted soil from an industrial site with a PAH concentration of 184.95 mg kg^?1. Compared to the experiments without an electric field, the degradation capability of Pseudomonas fluorescens and Kocuria sp. was enhanced in the industrially polluted soil under electrokinetic conditions. The degradation extents of total PAHs were increased by 15.4 and 14.0 % in the electrokinetic PB4 and FB6 experiments (PB4 + EK and FB6 + EK) relative to the PB4 and FB6 experiments without electrokinetic conditions (PB4 and FB6), respectively. These results indicated that P. fluorescens and Kocuria sp. could efficiently degrade heavy PAHs under electrokinetic conditions and have the potential to be used for the electro-bioremediation of PAH-contaminated soil, especially if the soil is contaminated with heavy PAHs.     

The Impact of Bioaugmentation on Metal Cyanide Degradation and Soil Bacteria Community Structure

Metal cyanides are significant contaminants of many soils found at the site of former industrial activity. In this study we isolated bacteria capable of degrading ferric ferrocyanide and K₂Ni(CN)₄. One of these bacteria a Rhodococcus spp. was subsequently used to bioaugment a minimal medium broth, spiked with K₂Ni(CN)₄, containing 1 g of either an uncontaminated topsoil or a former coke works site soil. Degradation of the K₂Ni(CN)₄ was observed in both soils, however, bioaugmentation did not significantly impact the rate or degree of K₂Ni(CN)₄ removal. Statistical analysis of denaturing gradient gel electrophoresis profiles showed that the topsoil bacterial community had a higher biodiversity, and its structure was not significantly affected by either K₂Ni(CN)₄ or bioaugmentation. In contrast, profiles from the coke works site indicated significant changes in the bacterial community in response to these additions. Moreover, in both soils although bioaugmentation did not affect rates of biodegradation the Rhodococcus spp. did become established in the communities in broths containing both top and coke works soil. We conclude that bacterial communities from contaminated soils with low biodiversity are much more readily perturbed through interventions such as contamination events or bioaugmentation treatments and discuss the implications of these findings for bioremediation studies.