Enumeration of phenanthrene-degrading bacteria by an overlayer technique and its use in evaluation of petroleum-contaminated sites.

Bacteria that are capable of degrading polycyclic aromatic hydrocarbons were enumerated by incorporating soil and water dilutions together with fine particles of phenanthrene, a polycyclic aromatic hydrocarbon, into an agarose overlayer and pouring the mixture over a mineral salts underlayer. The phenanthrene-degrading bacteria embedded in the overlayer were recognized by a halo of clearing in the opaque phenanthrene layer. Diesel fuel- or creosote-contaminated soil and water that were undergoing bioremediation contained 6 x 10(6) to 100 x 10(6) phenanthrene-degrading bacteria per g and ca. 5 x 10(5) phenanthrene-degrading bacteria per ml, respectively, whereas samples from untreated polluted sites contained substantially lower numbers. Unpolluted soil and water contained no detectable phenanthrene degraders (desert soil) or only very modest numbers of these organisms (garden soil, municipal reservoir water).     

Enumeration of phenanthrene-degrading bacteria by an overlayer technique and its use in evaluation of petroleum-contaminated sites.

Bacteria that are capable of degrading polycyclic aromatic hydrocarbons were enumerated by incorporating soil and water dilutions together with fine particles of phenanthrene, a polycyclic aromatic hydrocarbon, into an agarose overlayer and pouring the mixture over a mineral salts underlayer. The phenanthrene-degrading bacteria embedded in the overlayer were recognized by a halo of clearing in the opaque phenanthrene layer. Diesel fuel- or creosote-contaminated soil and water that were undergoing bioremediation contained 6 x 10(6) to 100 x 10(6) phenanthrene-degrading bacteria per g and ca. 5 x 10(5) phenanthrene-degrading bacteria per ml, respectively, whereas samples from untreated polluted sites contained substantially lower numbers. Unpolluted soil and water contained no detectable phenanthrene degraders (desert soil) or only very modest numbers of these organisms (garden soil, municipal reservoir water).     

Apparent contradiction: psychrotolerant bacteria from hydrocarbon-contaminated arctic tundra soils that degrade diterpenoids synthesized by trees.

Resin acids are tricyclic terpenoids occurring naturally in trees. We investigated the occurrence of resin acid-degrading bacteria on the Arctic tundra near the northern coast of Ellesmere Island (82 degrees N, 62 degrees W). According to most-probable-number assays, resin acid degraders were abundant (10(3) to 10(4) propagules/g of soil) in hydrocarbon-contaminated soils, but they were undetectable (<3 propagules/g of soil) in pristine soils from the nearby tundra. Plate counts indicated that the contaminated and the pristine soils had similar populations of heterotrophs (10(6) to 10(7) propagules/g of soil). Eleven resin acid-degrading bacteria belonging to four phylogenetically distinct groups were enriched and isolated from the contaminated soils, and representative isolates of each group were further characterized. Strains DhA-91, IpA-92, and IpA-93 are members of the genus Pseudomonas. Strain DhA-95 is a member of the genus Sphingomonas. All four strains are psychrotolerant, with growth temperature ranges of 4 degrees C to 30 degrees C (DhA-91 and DhA-95) or 4 degrees C to 22 degrees C (IpA-92 and IpA-93) and with optimum temperatures of 15 to 22 degrees C. Strains DhA-91 and DhA-95 grew on the abietanes, dehydroabietic and abietic acids, but not on the pimaranes, isopimaric and pimaric acids. Strains IpA-92 and IpA-93 grew on the pimaranes but not the abietanes. All four strains grew on either aliphatic or aromatic hydrocarbons, which is unusual for described resin acid degraders. Eleven mesophilic resin acid degraders did not use hydrocarbons, with the exception of two Mycobacterium sp. strains that used aliphatic hydrocarbons. We conclude that hydrocarbon contamination in Arctic tundra soil indirectly selected for resin acid degraders, selecting for hydrocarbon degraders that coincidentally use resin acids. Psychrotolerant resin acid degraders are likely important in the global carbon cycle and may have applications in biotreatment of pulp and paper mill effluents.     

Effects of oil spills on microbial heterotrophs in Antarctic soils

Oil spillage on the moist coastal soils of the Ross Sea region of Antarctica can impact on populations of microbial heterotrophs in these soils, as determined by viable plate counts and a most probable number technique. Elevated numbers of culturable hydrocarbon degraders, bacteria and fungi were detected in surface and subsurface soils from oil-contaminated sites, compared with nearby control sites. Culturable yeasts were not detected in soil from coastal control sites, yet reached >10⁵ organisms g^-1 dry weight in contaminated soils. The presence of hydrocarbons in soils resulted in a shift in the genera of culturable filamentous fungi. Chrysosporium dominated control soils, yet Phialophora was more abundant in oil-contaminated soils. Hydrocarbon degraders are most likely bacteria; however, fungi could play a role in degradation of hydrocarbons or their metabolites. Depleted levels of nitrate detected in some contaminated soils and decreased pH may be the result of growth of hydrocarbon degraders. Numbers and diversity of culturable microbes from Antarctic soil varied depending on whether a pristine site or a human-impacted (in this case, by fuel spills) site is studied.     

Development of a Microbial Consortium from a Contaminated Soil That Degrades Pentachlorophenol and Wood-Preserving Oil

An indigenous microbial consortium capable of degrading pentachlorophenol (PCP) and petroleum hydrocarbons (C₁₀-C₅₀) was produced from a soil contaminated with wood-preserving oil. Two 10-L stainless steel soil slurry (10% w/v) bioreactors were operated in fed-batch mode. To verify the growth and efficiency of PCP degraders in the presence of other contaminants, one bioreactor was fed with a PCP-based wood-preserving mixture (WPM) and a second reactor was fed with technical-grade NaPCP. During the 90-day period of activation, PCP, C₁₀-C₅₀, Cl^-, pH, and dissolved oxygen levels were monitored. The microbial community was monitored using specific most probably number (MPN) bacterial counts and mineralization tests. PCP degradation rates increased similarly in both reactors, from 19 to 132 mg/L-d in the NaPCP reactor, and from 41 to 112 mg/L-d in the WPM reactor. Contaminant loss calculations showed that 99.5% of PCP and 92.5% of C₁₀-C₅₀ added to the WPM reactor were biodegraded. It also revealed that 83% of polychlorinated dioxins and furans were removed. PCP-degrading bacteria increased from 7×10² to 1.6×10⁶ bacteria/mL in both reactors, and petroleum hydrocarbon degraders increased from 1.7×102 to 3.4×108 bacteria/mL in the WPM reactor, indicating that the activity of PCP degraders was not inhibited by the presence of microorganisms growing on petroleum hydrocarbons.     

Characterization of a Polycyclic Aromatic Hydrocarbon-Degrading Microbial Consortium from a Petrochemical Sludge Landfarming Site

Anthracene, phenanthrene, and pyrene are polycyclic aromatic hydrocarbon (PAHs) that display both mutagenic and carcinogenic properties. They are recalcitrant to microbial degradation in soil and water due to their complex molecular structure and low solubility in water. This study presents the characterization of an efficient PAH (anthracene, phenanthrene, and pyrene)-degrading microbial consortium, isolated from a petrochemical sludge landfarming site. Soil samples collected at the landfarming area were used as inoculum in Warburg flasks containing soil spiked with 250 mg kg^-1 of anthracene. The soil sample with the highest production of CO₂-C in 176 days was used in liquid mineral medium for further enrichment of anthracene degraders. The microbial consortium degraded 48%, 67%, and 22% of the anthracene, phenanthrene, and pyrene in the mineral medium, respectively, after 30 days of incubation. Six bacteria, identified by 16S rRNA sequencing as Mycobacterium fortuitum, Bacillus cereus, Microbacterium sp., Gordonia polyisoprenivorans, two Microbacteriaceae bacteria, and a fungus identified as Fusarium oxysporum were isolated from the enrichment culture. The consortium and its monoculture isolates utilized a variety of hydrocarbons including PAHs (pyrene, anthracene, phenanthrene, and naftalene), monoaromatics hydrocarbons (benzene, ethylbenzene, toluene, and xylene), aliphatic hydrocarbons (1-decene, 1-octene, and hexane), hydrocarbon mixtures (gasoline and diesel oil), intermediary metabolites of PAHs degradation (catechol, gentisic acid, salicylic acid, and dihydroxybenzoic acid) and ethanol for growth. Biosurfactant production by the isolates was assessed by an emulsification index and reduction of the surface tension in the mineral medium. Significant emulsification was observed with the isolates, indicating production of high-molecular-weigh surfactants. The high PAH degradation rates, the wide spectrum of hydrocarbons utilization, and emulsification capacities of the microbial consortium and its member microbes indicate that they can be used for biotreatment and bioaugumentation of soils contaminated with PAHs.     

Identification and catabolic activity of well-derived gasoline-degrading bacteria from a contaminated aquifer.

Approximately 300 gasoline-degrading bacteria were isolated from well water and core material from a shallow coastal aquifer contaminated with unleaded gasoline. Identification of 244 isolates revealed four genera: Pseudomonas, Alcaligenes, Nocardia, and Micrococcus, with pseudomonads making up 86.9% of bacteria identified. A total of 297 isolates was sorted into 111 catabolic groups on the basis of aerobic growth responses on 15 gasoline hydrocarbons. Each test hydrocarbon was degraded by at least one isolate. Toluene, p-xylene, ethylbenzene, and 1,2,4-trimethylbenzene were most frequently utilized as growth substrates, whereas cyclic and branched alkanes were least utilized. Most isolates were able to grow on 2 or 3 different hydrocarbons, and nearly 75% utilized toluene as a sole source of carbon and energy. Isolates were remarkably specific for hydrocarbon usage, often catabolizing only one of several closely related compounds. A subset of 220 isolates was sorted into 51 groups by polyacrylamide gel electrophoresis. Pseudomonas aeruginosa was partitioned into 16 protein-banding groups (i.e., subspecies) whose catabolic activities were largely restricted to substituted aromatics. Different members of subspecies groups defined by protein-banding pattern analysis often exhibited different growth responses on the same hydrocarbon, implying marked strain diversity. The catabolic activities of well-derived, gasoline-degrading bacteria associated with this contaminated aquifer are consonant with in situ adaptation at the site.     

Enhancing the biodegradation of total petroleum hydrocarbons in oily sludge by a modified bioaugmentation strategy

The effect of successive inoculation with hydrocarbon-degrading bacteria on the dynamics of petroleum hydrocarbons degradation in soil was investigated in this study. Oily sludge was used as a source of mixed hydrocarbons pollutant. Two bacterial consortia composed of alkanes and polycyclic aromatic hydrocarbon degraders were constructed from bacteria isolated from soil and oily sludge. These consortia were applied to incubated microcosms either in one dose at the onset of the incubation or in two doses at the beginning and at day 62 of the incubation period, which lasted for 198 days. During this period, carbon mineralization was evaluated by respirometry while total petroleum hydrocarbons and its fractions were gravimetrically evaluated by extraction from soil and fractionation. Dosing the bacterial consortia resulted in more than 30% increase in the overall removal of total petroleum hydrocarbons from soil. While alkane removal was only slightly improved, aromatic and asphaltic hydrocarbon fraction removal was significantly enhanced by the addition of the second consortium. Polar compounds (resins) were enriched only as a result of aromatics and asphaltene utilization. Nonetheless, their concentration declined back to the original level by the end of the incubation period.     

Apparent Contradiction: Psychrotolerant Bacteria from Hydrocarbon-Contaminated Arctic Tundra Soils That Degrade Diterpenoids Synthesized by Trees

Resin acids are tricyclic terpenoids occurring naturally in trees. We investigated the occurrence of resin acid-degrading bacteria on the Arctic tundra near the northern coast of Ellesmere Island (82°N, 62°W). According to most-probable-number assays, resin acid degraders were abundant (10³ to 10⁴ propagules/g of soil) in hydrocarbon-contaminated soils, but they were undetectable (<3 propagules/g of soil) in pristine soils from the nearby tundra. Plate counts indicated that the contaminated and the pristine soils had similar populations of heterotrophs (10⁶ to 10⁷ propagules/g of soil). Eleven resin acid-degrading bacteria belonging to four phylogenetically distinct groups were enriched and isolated from the contaminated soils, and representative isolates of each group were further characterized. Strains DhA-91, IpA-92, and IpA-93 are members of the genus Pseudomonas. Strain DhA-95 is a member of the genus Sphingomonas. All four strains are psychrotolerant, with growth temperature ranges of 4°C to 30°C (DhA-91 and DhA-95) or 4°C to 22°C (IpA-92 and IpA-93) and with optimum temperatures of 15 to 22°C. Strains DhA-91 and DhA-95 grew on the abietanes, dehydroabietic and abietic acids, but not on the pimaranes, isopimaric and pimaric acids. Strains IpA-92 and IpA-93 grew on the pimaranes but not the abietanes. All four strains grew on either aliphatic or aromatic hydrocarbons, which is unusual for described resin acid degraders. Eleven mesophilic resin acid degraders did not use hydrocarbons, with the exception of two Mycobacterium sp. strains that used aliphatic hydrocarbons. We conclude that hydrocarbon contamination in Arctic tundra soil indirectly selected for resin acid degraders, selecting for hydrocarbon degraders that coincidentally use resin acids. Psychrotolerant resin acid degraders are likely important in the global carbon cycle and may have applications in biotreatment of pulp and paper mill effluents.     

Determining the identity and roles of oil-metabolizing marine bacteria from the Thames estuary, UK

Crude oil is a complex mixture of different hydrocarbons. While diverse bacterial communities can degrade oil, the specific roles of individual members within such communities remain unclear. To identify the key bacterial taxa involved in aerobic degradation of specific hydrocarbons, microcosm experiments were established using seawater from Stanford le Hope, Thames estuary, UK, adjacent to a major oil refinery. In all microcosms, hydrocarbon degradation was significant within 10 weeks, ranging from > 99% of low-molecular-weight alkanes (C(10)-C(18)), 41-84% of high-molecular-weight alkanes (C(20)-C(32)) and pristane, and 32-88% of polycyclic aromatic hydrocarbons (PAHs). Analysis of 16S rRNA sequences from clone libraries and denaturing gradient gel electrophoresis (DGGE) indicated that, except when incubated with fluorene, PAH-degrading communities were dominated by Cycloclasticus. Moreover, PAH-degrading communities were distinct from those in microcosms containing alkanes. Degradation of the branched alkane, pristane, was carried out almost exclusively by Alcanivorax. Bacteria related to Thalassolituus oleivorans (99-100% identity) were the dominant known alkane degraders in n-alkane (C(12)-C(32)) microcosms, while Roseobacter-related bacteria were also consistently found in these microcosms. However, in contrast to previous studies, Thalassolituus, rather than Alcanivorax, was dominant in crude oil-enriched microcosms. The communities in n-decane microcosms differed from those in microcosms supplemented with less volatile alkanes, with a phylogenetically distinct species of Thalassolituus out-competing T. oleivorans. These data suggest that the diversity and importance of the genus Thalassolituus is greater than previously established. Overall, these experiments demonstrate how degradation of different petroleum hydrocarbons is partitioned between different bacterial taxa, which together as a community can remediate petroleum hydrocarbon-impacted estuarine environments.     

Potential for biodegradation of hydrocarbons by microorganisms isolated from Antarctic soils

Seventeen pure aerobic microbial isolates were obtained from soil samples of three regions of Antarctica: Casey Station, Dewart Island and Terra Nova Bay. Most of them were gram positive coryneform bacteria. Isolates were tested for their ability to grow on mineral salt agar plates supplemented with one of the following model n-alkanes or aromatic hydrocarbons: hexane, heptane, paraffin, benzene, toluene, naphthalene and kerosene. Cell hydrophobicity, the ability to produce anionic glycolipids and extracellular emulsifying activity were also determined and assessed on the basis of growth of soil isolates on hydrocarbons. This study revealed degraders with broader abilities to grow on both types of hydrocarbons, good production of glycolipids and emulsifying activity. On this basis, a mixed culture of strains is proposed, which may find application for bioremediation at temperate temperature of soil environments polluted with different hydrocarbons.     

Effects of Jet Fuel Spills on the Microbial Community of Soil

Hydrocarbon residues, microbial numbers, and microbial activity were measured and correlated in loam soil contaminated by jet fuel spills resulting in 50 and 135 mg of hydrocarbon g of soil⁻¹. Contaminated soil was incubated at 27°C either as well-aerated surface soil or as poorly aerated subsurface soil. In the former case, the effects of bioremediation treatment on residues, microbial numbers, and microbial activity were also assessed. Hydrocarbon residues were measured by quantitative gas chromatography. Enumerations included direct counts of metabolically active bacteria, measurement of mycelial length, plate counts of aerobic heterotrophs, and most probable numbers of hydrocarbon degraders. Activity was assessed by fluorescein diacetate (FDA) hydrolysis. Jet fuel disappeared much more rapidly from surface soil than it did from subsurface soil. In surface soil, microbial numbers and mycelial length were increased by 2 to 2.5 orders of magnitude as a result of jet fuel contamination alone and by 3 to 4 orders of magnitude as a result of the combination of jet fuel contamination and bioremediation. FDA hydrolysis was stimulated by jet fuel and bioremediation, but was inhibited by jet fuel alone. The latter was traced to an inhibition of the FDA assay by jet fuel biodegradation products. In subsurface soil, oxygen limitation strongly attenuated microbial responses to jet fuel. An increase in the most probable numbers of hydrocarbon degraders was accompanied by a decline in other aerobic heterotrophs, so that total plate counts changed little. The correlations between hydrocarbon residues, microbial numbers, and microbial activity help in elucidating microbial contributions to jet fuel elimination from soil.     

Dynamics of phreatophyte root growth relative to a seasonally fluctuating water table in a Mediterranean-type environment

While seasonal redistribution of fine root biomass in response to fluctuations in groundwater level is often inferred in phreatophytic plants, few studies have observed the in situ growth dynamics of deep roots relative to those near the surface. We investigated the root growth dynamics of two Banksia species accessing a seasonally dynamic water table and hypothesized that root growth phenology varied with depth, i.e. root growth closest to the water table would be influenced by water table dynamics rather than surface micro-climate. Root in-growth bags were used to observe the dynamics of root growth at different soil depths and above-ground growth was also assessed to identify whole-plant growth phenology. Root growth at shallow depths was found to be in synchrony with above-ground growth phenophases, following increases in ambient temperature and soil water content. In contrast, root growth at depth was either constant or suppressed by saturation. Root growth above the water table and within the capillary fringe occurred in all seasons, corresponding with consistent water availability and aerobic conditions. However, at the water table, a seasonal cycle of root elongation with drawdown in summer followed by trimming in response to water table rise and saturation in winter, was observed. The ability to grow roots year-round at the capillary fringe and redistribute fine root biomass in response to groundwater drawdown is considered critical in allowing phreatophytes, in seasonally water-limited environments, to maintain access to groundwater throughout the year.     

First investigation of the microbiology of the deepest layer of ocean crust

The gabbroic layer comprises the majority of ocean crust. Opportunities to sample this expansive crustal environment are rare because of the technological demands of deep ocean drilling; thus, gabbroic microbial communities have not yet been studied. During the Integrated Ocean Drilling Program Expeditions 304 and 305, igneous rock samples were collected from 0.45-1391.01 meters below seafloor at Hole 1309D, located on the Atlantis Massif (30 °N, 42 °W). Microbial diversity in the rocks was analyzed by denaturing gradient gel electrophoresis and sequencing (Expedition 304), and terminal restriction fragment length polymorphism, cloning and sequencing, and functional gene microarray analysis (Expedition 305). The gabbroic microbial community was relatively depauperate, consisting of a low diversity of proteobacterial lineages closely related to Bacteria from hydrocarbon-dominated environments and to known hydrocarbon degraders, and there was little evidence of Archaea. Functional gene diversity in the gabbroic samples was analyzed with a microarray for metabolic genes ("GeoChip"), producing further evidence of genomic potential for hydrocarbon degradation--genes for aerobic methane and toluene oxidation. Genes coding for anaerobic respirations, such as nitrate reduction, sulfate reduction, and metal reduction, as well as genes for carbon fixation, nitrogen fixation, and ammonium-oxidation, were also present. Our results suggest that the gabbroic layer hosts a microbial community that can degrade hydrocarbons and fix carbon and nitrogen, and has the potential to employ a diversity of non-oxygen electron acceptors. This rare glimpse of the gabbroic ecosystem provides further support for the recent finding of hydrocarbons in deep ocean gabbro from Hole 1309D. It has been hypothesized that these hydrocarbons might originate abiotically from serpentinization reactions that are occurring deep in the Earth's crust, raising the possibility that the lithic microbial community reported here might utilize carbon sources produced independently of the surface biosphere.     

Oil-oxidizing activity of bacteria isolated from south Sakhalin coastal waters

Ability of bacteria isolated from the southern coastal waters of the Sakhalin Island to degrade various hydrocarbons was studied. The population of marine microorganisms grown on oil was heterogeneous in terms of hydrocarbon degradation. The rate of bacterial degradation of oil hydrocarbons was shown to correlate with their growth rate on the model medium. The degradation rates were higher for aromatic hydrocarbons than for alkanes. Based on our data, the studied bacteria were conditionally assigned to three groups: active, intermediately active, and passive degraders. Ability to oxidize oil was previously not reported for members of the genus Cobetia.     

Aerobic bacteria degrading both <Emphasis Type="Italic">n</Emphasis>-alkanes and aromatic hydrocarbons: an undervalued strategy for metabolic diversity and flexibility

Environmental pollution with petroleum toxic products has afflicted various ecosystems, causing devastating damage to natural habitats with serious economic implications. Some crude oil components may serve as growth substrates for microorganisms. A number of bacterial strains reveal metabolic capacities to biotransform various organic compounds. Some of the hydrocarbon degraders are highly biochemically specialized, while the others display a versatile metabolism and can utilize both saturated aliphatic and aromatic hydrocarbons. The extended catabolic profiles of the latter group have been subjected to systematic and complex studies relatively rarely thus far. Growing evidence shows that numerous bacteria produce broad biochemical activities towards different hydrocarbon types and such an enhanced metabolic potential can be found in many more species than the already well-known oil-degraders. These strains may play an important role in the removal of heterogeneous contamination. They are thus considered to be a promising solution in bioremediation applications. The main purpose of this article is to provide an overview of the current knowledge on aerobic bacteria involved in the mineralization or transformation of both n-alkanes and aromatic hydrocarbons. Variant scientific approaches enabling to evaluate these features on biochemical as well as genetic levels are presented. The distribution of multidegradative capabilities between bacterial taxa is systematically shown and the possibility of simultaneous transformation of complex hydrocarbon mixtures is discussed. Bioinformatic analysis of the currently available genetic data is employed to enable generation of phylogenetic relationships between environmental strain isolates belonging to the phyla Actinobacteria, Proteobacteria, and Firmicutes. The study proves that the co-occurrence of genes responsible for concomitant metabolic bioconversion reactions of structurally-diverse hydrocarbons is not unique among various systematic groups.     

Taxonomic diversity of aerobic organotrophic bacteria from clean vietnamese soils and their capacity for oxidation of petroleum hydrocarbons

The dominant species and abundance of the cultured aerobic organotrophic bacteria were determined in the clean soils of the Republic of Vietnam. The total number of organotrophs varied from 2.0 × 10⁵ to 5.8 × 10⁸ CFU/g soil. A considerable fraction of the bacterial population (1.1 × 10⁵–9.5 × 10⁶ CFU/g soil) was able to utilize petroleum hydrocarbons as the sole carbon and energy source. Most of the organisms obtained in pure cultures were gram-positive bacteria; over 70% were hydrocarbon-oxidizing organisms. Analysis of 16S rRNA gene sequences resulted in tentative determination of the taxonomic position of 22 strains, with 12 belonging to the Firmicutes, 4, to the Proteobacteria, and 6 to the Actinobacteria. The most common bacteria capable of hydrocarbon oxidation belonged to the genera Acinetobacter, Bacillus, Brevibacillus, Chromobacterium, Cupriavidus, Gordonia, Microbacterium, Mycobacterium, and Rhodococcus. Some of the isolated Bacillus and Staphylococcus strains, as well as one Pseudomonas and one Sinomonas strain, did not utilize hydrocarbons. Gram-positive degraders, especially members of the order Actinomycetales, which exhibited high hydrocarbon-oxidizing activity, gained competitive advantage in the presence of hydrocarbons. This microbial group probably plays an important role in hydrocarbon degradation in tropical soils. Thus, Vietnamese soils, which had no history of petroleum contamination, support numerically significant and taxonomically diverse populations of h ydrocarbon-oxidizing bacteria.     

Microbial analysis of soil and groundwater from a gasworks site and comparison with a sequenced biological reactive barrier remediation process

AIMS: To investigate the distribution of a polymicrobial community of biodegradative bacteria in (i) soil and groundwater at a former manufactured gas plant (FMGP) site and (ii) in a novel SEquential REactive BARrier (SEREBAR) bioremediation process designed to bioremediate the contaminated groundwater. METHODS AND RESULTS: Culture-dependent and culture-independent analyses using denaturing gradient gel electrophoresis (DGGE) and polymerase chain reaction (PCR) for the detection of 16S ribosomal RNA gene and naphthalene dioxygenase (NDO) genes of free-living (planktonic groundwater) and attached (soil biofilm) samples from across the site and from the SEREBAR process was applied. Naphthalene arising from groundwater was effectively degraded early in the process and the microbiological analysis indicated a dominant role for Pseudomonas and Comamonas in its degradation. The microbial communities appeared highly complex and diverse across both the sites and in the SEREBAR process. An increased population of naphthalene degraders was associated with naphthalene removal. CONCLUSION: The distribution of micro-organisms in general and naphthalene degraders across the site was highly heterogeneous. Comparisons made between areas contaminated with polycyclic aromatic hydrocarbons (PAH) and those not contaminated, revealed differences in the microbial community profile. The likelihood of noncultured bacteria being dominant in mediating naphthalene removal was evident. SIGNIFICANCE AND IMPACT OF THE STUDY: This work further emphasizes the importance of both traditional and molecular-based tools in determining the microbial ecology of contaminated sites and highlights the role of noncultured bacteria in the process.     

Influence of adhesion on aerobic biodegradation and bioremediation of liquid hydrocarbons

Biodegradation of poorly water-soluble liquid hydrocarbons is often limited by low availability of the substrate to microbes. Adhesion of microorganisms to an oil–water interface can enhance this availability, whereas detaching cells from the interface can reduce the rate of biodegradation. The capability of microbes to adhere to the interface is not limited to hydrocarbon degraders, nor is it the only mechanism to enable rapid uptake of hydrocarbons, but it represents a common strategy. This review of the literature indicates that microbial adhesion can benefit growth on and biodegradation of very poorly water-soluble hydrocarbons such as n-alkanes and large polycyclic aromatic hydrocarbons dissolved in a non-aqueous phase. Adhesion is particularly important when the hydrocarbons are not emulsified, giving limited interfacial area between the two liquid phases. When mixed communities are involved in biodegradation, the ability of cells to adhere to the interface can enable selective growth and enhance bioremediation with time. The critical challenge in understanding the relationship between growth rate and biodegradation rate for adherent bacteria is to accurately measure and observe the population that resides at the interface of the hydrocarbon phase.     

Biostimulation and Phytoremediation Treatment Strategies of Gasoline-Nickel Co-Contaminated Soil

This study investigated the potential effect of poultry dung (biostimulation) and stubborn grass (Sporobolus pyramidalis) (phytoremediation) on microbial biodegradation of gasoline and nickel uptake in gasoline-nickel-impacted soil. In addition, the potential stimulatory effects of nickel on hydrocarbon utilization were investigated over a small range of nickel concentrations (2.5–12.5 mg/kg). The results showed that an increase in nickel concentration increased hydrocarbon degraders in soil by a range of 8.4–17.2% and resulted in a relative increase in gasoline biodegradation (57.5–62.4%). Also, under aerobic conditions, total petroleum hydrocarbons’ (TPH) removal was 62.4% in the natural gasoline-nickel microcosm (natural attenuation), and a maximum of 78.5%, 85.7%, and 95.8% TPH removal was obtained in phytoremediation, biostimulation, and a combination of biostimulation- and phytoremediation-treated microcosms, respectively. First-order kinetics described the biodegradation of gasoline and nickel uptake very well. Half-life times obtained were 28.88, 18.24, 14.44, and 8.56 days for gasoline degradation under natural attenuation, phytoremediation, biostimulation, and combined biostimulation and phytoremediation treatment methods, respectively. The results indicate that these remediation methods have promising potential for effective remediation of soils co-contaminated with petroleum hydrocarbons and heavy metals.