Bioaugmentation as a soil bioremediation approach

Rhizodegradation of petroleum hydrocarbons by Sesbania cannabina in bioaugmented soil with free and immobilized consortium

The present study reports the effect of bioaugmentation by free and immobilized bacterial culture on the rhizodegradation of petroleum-polluted soil using Sesbania cannabina plant. Total petroleum hydrocarbon (TPH), hydrocarbon-degrading bacterial counts, microbial activity and root morphology were assessed during 120 days of plant growth. TPH concentration analyzed by GC-MS showed that bioaugmentation did not improve the TPH degradation. TPH concentration decreased from 2541 mg kg(-1) to 673 mg kg(-1) and 867 mg kg(-1) in the rhizosphere of free (FR) and immobilized bacterial inoculated (IR) soil, respectively at the 120th day while in the rhizosphere of uninoculated soil (CR) concentration decreased to 679 mg kg(-1) only at the 90th day, showing higher and rapid rhizodegradation with indigenous bacteria than bioaugmented bacterial cultures. Various predominant bacterial groups responsible for higher TPH degradation in the rhizosphere of S. cannabina were identified by PCR-DGGE analysis. It is concluded that natural plant-microbe interaction in the rhizosphere of S. cannabina was efficient enough to degrade TPH and plant rhizosphere keeps bacterial community in its surrounding therefore immobilized culture had no obvious effect on petroleum degradation.

Biodegradation of crude oil using an efficient microbial consortium in a simulated marine environment

Ochrobactrum sp. N1, Brevibacillus parabrevis N2, B. parabrevis N3 and B. parabrevis N4 were selected when preparing a mixed bacterial consortium based on the efficiency of crude oil utilization. A crude oil degradation rate of the N-series microbial consortium reached upwards of 79% at a temperature of 25 °C in a 3.0% NaCl solution in the shake flask trial. In the mesocosm experiment, a specially designed device was used to simulate the marine environment. The internal tank size was 1.5 m (L)×0.8 m (W)×0.7 m (H). The microbial growth conditions, nutrient utilization and environmental factors were thoroughly investigated. Over 51.1% of the crude oil was effectively removed from the simulated water body. The escalation process (from flask trials to the mesocosm experiment), which sought to represent removal under conditions more similar to the field, proved the high efficiency of using N-series bacteria in crude oil degradation.

Molinate biodegradation in soils: natural attenuation versus bioaugmentation

The aims of the present study were to assess the potential of natural attenuation or bioaugmentation to reduce soil molinate contamination in paddy field soils and the impact of these bioremediation strategies on the composition of soil indigenous microbiota. A molinate mineralizing culture (mixed culture DC) was used as inoculum in the bioaugmentation assays. Significantly higher removal of molinate was observed in bioaugmentation than in natural attenuation microcosms (63 and 39 %, respectively) after 42 days of incubation at 22 °C. In the bioaugmentation assays, the impact of Gulosibacter molinativorax ON4(T) on molinate depletion was observed since the gene encoding the enzyme responsible for the initial molinate breakdown (harboured by that actinobacterium) was only detected in inoculated microcosms. Nevertheless, the exogenous mixed culture DC did not overgrow as the heterotrophic counts of the bioaugmentation microcosms were not significantly different from those of natural attenuation and controls. Moreover, the actinobacterial clone libraries generated from the bioaugmentation microcosms did not include any 16S rRNA gene sequences with significant similarity to that of G. molinativorax ON4(T). The multivariate analysis of the 16S rRNA DGGE patterns of the soil microcosm suggested that the activity of mixed culture DC did not affect the soil bacterial community structure since the DGGE patterns of the bioaugmentation microcosms clustered with those of natural attenuation and controls. Although both bioremediation approaches removed molinate without indigenous microbiota perturbation, the results suggested that bioaugmentation with mixed culture DC was more effective to treat soils contaminated with molinate.

Natural attenuation is enhanced in previously contaminated and coniferous forest soils

PURPOSE

Prevalence of organic pollutants or their natural analogs in soil is often assumed to lead to adaptation in the bacterial community, which results in enhanced bioremediation if the soil is later contaminated. In this study, the effects of soil type and contamination history on diesel oil degradation and bacterial adaptation were studied.

METHODS

Mesocosms of mineral and organic forest soil (humus) were artificially treated with diesel oil, and oil hydrocarbon concentrations (GC-FID), bacterial community composition (denaturing gradient gel electrophoresis, DGGE), and oil hydrocarbon degraders (DGGE + sequencing of 16S rRNA genes) were monitored for 20 weeks at 16°C.

RESULTS

Degradation was advanced in previously contaminated soils as compared with pristine soils and in coniferous organic forest soil as compared with mineral soil. Contamination affected bacterial community composition especially in the pristine mineral soil, where diesel addition increased the number of strong bands in the DGGE gel. Sequencing of cloned 16S rRNA gene fragments and DGGE bands showed that potential oil-degrading bacteria were found in mineral and organic soils and in both pristine and previously contaminated mesocosms. Fast oil degradation was not associated with the presence of any particular bacterial strain in soil.

CONCLUSIONS

We demonstrate at the mesocosm scale that previously contaminated and coniferous organic soils are superior environments for fast oil degradation as compared with pristine and mineral soil environments. These results may be utilized in preventing soil pollution and planning soil remediation.

Groundwater remediation using an enricher reactor-permeable reactive biobarrier for periodically absent contaminants

A combined enricher reactor (ER)-permeable reactive biobarrier (PRBB) system was developed to treat groundwater with contaminants that appear in batches. An enricher reactor is an offline reactor used to enrich contaminant degraders by supplying necessary growth materials, and the enriched degraders are used to augment PRBB to increase its performance after a period of contaminant absence. Bench-scale experiments on PRBBs with and without bacterial supply from the enricher reactor were conducted to evaluate PRBB removal performances for benzene, which was used as a model contaminant. Benzene absence periods of 10 and 25 days were tested in the presence and absence of ethanol. The PRBBs without the bioaugmentation from the enricher reactor experienced a decrease in performance from approximately 65% to 30% after benzene reappeared. The presence of ethanol accelerated the benzene removal performance recovery of PRBBs. The 25-day benzene absence period caused greater changes in the bacterial community structure, regardless of the ethanol availability.

Characterization of a bacterial strain capable of degrading DDT congeners and its use in bioremediation of contaminated soil

A bacterial strain DDT-6 (D6) capable of utilizing dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE) (DDTs) as its sole carbon and energy source was isolated and identified as Sphingobacterium sp. The degradation of DDTs by strain D6 in mineral salt medium and in field soil was investigated. The half-lives of the degradation of DDTs increased with increasing concentration ranging from 1 to 50 mg L(-1). Favorable degradation conditions for DDTs by strain D6 were found to be pH 7.0 and 30°C. The degradation of DDTs by strain D6 was found to be statistically significantly enhanced (p ≤ 0.05) by the addition of glucose. Based on the metabolites detected, a pathway was proposed for DDT degradation in which it undergoes dechlorination, hydrogenation, dioxygenation, decarboxylation, hydroxylation, and phenyl ring-cleavage reactions to complete the mineralization process. The addition of strain D6 into the contaminated soils was found to statistically significantly enhance (p ≤ 0.05) the degradation of DDTs. The results indicate that the isolate D6 can be used successfully for the removal or detoxification of residues of DDTs in contaminated soil.

Evaluation of bioaugmentation with entrapped degrading cells as a soil remediation technology

Soil augmentation with microbial degraders immobilized on carriers is evaluated as a potential remediation technology using a mathematical model that includes degradation within spatially distributed carriers and diffusion or advection-dispersion as contaminant mass transfer mechanisms. The total volume of carriers is a critical parameter affecting biodegradation performance. In the absence of advection, 320 and 20 000 days are required to mineralize 90% of the herbicide linuron by Variovorax sp. SRS16 encapsulated in 2 mm beads with 5 and 20 mm spacings, respectively. Given that many pesticide degraders have low intrinsic degradation rates and that only limited carrier to soil volume ratios are practically feasible, bioaugmented soils are characterized by low effective degradation rates and can be considered fully mixed. A simple exponential model is then sufficient to predict biodegradation as verified by comparisons with published experimental data. By contrast, the full spatially distributed model is needed to adequately model the degradation of faster degrading contaminants such as naphthalene and benzene which can be mass-transfer limited. Dimensionless Damköhler numbers are proposed to determine whether the spatially distributed model is required. Results show that field scale applications of immobilized degraders will be limited by the amount of carriers required to reach acceptable degradation rates.

Bioaugmentation with Pseudomonas sp. strain MHP41 promotes simazine attenuation and bacterial community changes in agricultural soils

Bioremediation is an important technology for the removal of persistent organic pollutants from the environment. Bioaugmentation with the encapsulated Pseudomonas sp. strain MHP41 of agricultural soils contaminated with the herbicide simazine was studied. The experiments were performed in microcosm trials using two soils: soil that had never been previously exposed to s-triazines (NS) and soil that had >20 years of s-triazine application (AS). The efficiency of the bioremediation process was assessed by monitoring simazine removal by HPLC. The simazine-degrading microbiota was estimated using an indicator for respiration combined with most-probable-number enumeration. The soil bacterial community structures and the effect of bioaugmentation on these communities were determined using 16S RNA gene clone libraries and FISH analysis. Bioaugmentation with MHP41 cells enhanced simazine degradation and increased the number of simazine-degrading microorganisms in the two soils. In highly contaminated NS soil, bioaugmentation with strain MHP41 was essential for simazine removal. Comparative analysis of 16S rRNA gene clone libraries from NS and AS soils revealed high bacterial diversity. Bioaugmentation with strain MHP41 promoted soil bacterial community shifts. FISH analysis revealed that bioaugmentation increased the relative abundances of two phylogenetic groups (Acidobacteria and Planctomycetes) in both soils. Although members of the Archaea were metabolically active in these soils, their relative abundance was not altered by bioaugmentation.

Impact of 4-chlorophenol contamination and/or inoculation with the 4-chlorophenol-degrading strain, Arthrobacter chlorophenolicus A6L, on soil bacterial community structure

The 4-chlorophenol-degrading strain, Arthrobacter chlorophenolicus A6L (chromosomally tagged with the firefly luciferase gene, luc) was inoculated into 4-chlorophenol-contaminated soil to assess the impact of bioaugmentation with a biodegrading strain on the indigenous microbiota. Simultaneously, the impact of 4-chlorophenol alone, or inoculation with A. chlorophenolicus into non-contaminated soil, was addressed. Using terminal restriction fragment length polymorphism (T-RFLP) several significant changes were detected in community fingerprint patterns obtained from soil microcosms treated under the different conditions. The relative abundances of some populations, as judged by the relative intensity of terminal restriction fragments, were significantly impacted by either 4-chlorophenol, A. chlorophenolicus inoculation, or by a combination of both inoculation and 4-chlorophenol contamination. Some populations were significantly stimulated and others were significantly repressed when compared to control soil with no additions. For several peaks, the positive or negative impact imposed by the treatments increased over the 13-day incubation period. Some members of the bacterial community were specifically sensitive to A. chlorophenolicus inoculation or to 4-chlorophenol contamination, whereas other populations remained relatively unaffected by any of the treatments. The A. chlorophenolicus inoculum was also monitored by T-RFLP and was found to have a significantly higher relative abundance in soil contaminated with 4-chlorophenol. These results were substantiated by a high correlation to luciferase activity measurements and the number of colony forming units of the inoculum. Therefore, the A. chlorophenolicus A6L population was positively stimulated by the presence of the 4-chlorophenol substrate (180 microg g(-1) soil) that it catabolized during the first 8 days of the incubation period as a carbon and energy source. Together, these results demonstrate that specific populations in the soil bacterial community rapidly fluctuated in response to specific disturbances and the resulting shifts in the community may therefore represent an adjustment in community structure favoring those populations best capable of responding to novel stress scenarios.

Bioaugmentation as a strategy for cleaning up of soils contaminated with aromatic compounds

The contamination of soil with aromatic compounds is of particular environmental concern as they exhibit carcinogenic and mutagenic properties. One of the methods of their removal from soil is bioaugmentation, defined as a technique for improvement of the degradative capacity of contaminated areas by introduction of specific competent strains or consortia of microorganisms. The efficiency of bioaugmentation is determined by many abiotic and biotic factors discussed in this paper. The first include chemical structure, concentration and availability of pollutants as well as physico-chemical properties of soil. In turn, among biotic factors the most important is the selection of proper microorganisms that can not only degrade contaminants but can also successfully compete with indigenous microflora. Several strategies are being developed to make augmentation a successful technology particularly in soils without degrading indigenous microorganisms. These approaches involve the use of genetically engineered microorganisms and gene bioaugmentation. The enhancement of bioaugmentation may be also achieved by delivering suitable microorganisms immobilized on various carriers or use of activated soil.

Selection of a cold-adapted bacterium for bioremediation of wastewater at low temperatures

Amongst more than 1000 isolates collected in various cold environments, the strain Arthrobacter psychrolactophilus Sp 31.3 has been selected for its ability to grow and to produce exoenzymes at low temperatures, its inability to grow at 37 degrees C, its non-halophilic character and its growth versatility on various media. This non-pathogenic strain displays a strong resistance to desiccation and storage at room temperature and is suitable for the production of freeze-dried bacterial starters. When grown in a synthetic wastewater at 10 degrees C, the strain induces a complete clarification of the turbid medium and efficiently hydrolyses proteins, starch and lipids in the broth. Furthermore, this strain has a remarkable capacity to improve the biodegradability of organic compounds in wastewater as indicated by a BOD(5)/COD ratio of 0.7.

Bioaugmentation of a 4-chloronitrobenzene contaminated soil with Pseudomonas putida ZWL73

The strain Pseudomonas putida ZWL73, which metabolizes 4-chloronitrobenzene (4CNB) by a partial-reductive pathway, was inoculated into lab-scale 4CNB-contaminated soil for bioaugmentation purposes in this study. The degradation of 4CNB was clearly stimulated, as indicated with the gradual accumulation of ammonium and chloride. Simultaneously, the diversity and quantity of cultivable heterotrophic bacteria decreased due to 4CNB contamination, while the quantity of 4CNB-resistant bacteria increased. During the bioaugmentation, denaturing gradient gel electrophoresis analysis showed the changes of diversity in dominant populations of intrinsic soil microbiota. The results showed that Alphaproteobacteria and Betaproteobacteria were not distinctly affected, but Actinobacteria were apparently stimulated. In addition, an interesting dynamic within Acidobacteria was observed, as well as an influence on ammonia-oxidizing bacteria population. These combined findings demonstrate that the removal of 4CNB in soils by inoculating strain ZWL73 is feasible, and that specific populations in soils rapidly changed in response to 4CNB contamination and subsequent bioaugmentation.

Enhanced bioaugmentation of petroleum- and salt-contaminated soil using wheat straw

A new bioaugmentation method for petroleum- and salt-contaminated soil was presented, in which wheat straw was used to enhance salt leaching and subsequent petroleum degradation by a bacteria-fungi consortium of Enterobacter cloacae and Cunninghamella echinulata. The effectiveness of a coarse wheat straw layer in inhibiting capillary-induced upward salt movement and in enhancing growth of E. cloacae and C. echinulata was shown in the laboratory and a 7000-m(2) field study in Henan Province, China. In the field study, the Na(+) concentration in remediated soil at 1-25 cm depth decreased from 1597 ± 394 to 543 ± 217 mg kg(-1), while Cl(-) decreased from 1520 ± 922 to 421 ± 253 mg kg(-1). The wheat straw increased bacterial biomass by 170-fold and fungi 11-fold compared to control soil without wheat straw. The concentration of total petroleum hydrocarbons decreased from 6320 ± 1180 to 2260 ± 420 mg kg(-1) after 45 d of treatment. Wheat was cultivated on remediated soil and grain yield reached 72% of that obtained in normal farmland adjacent to the study site. The results demonstrated the effectiveness of wheat straw in enhancing bioaugmentation of the petroleum- and salt-contaminated soil and indicated a high application potential.

Earthworm assisted bioremediation of organic contaminants

Due to their biological, chemical and physical actions, earthworms can be directly employed within bioremediation strategies to promote biodegradation of organic contaminants. Earthworms have been shown to aerate and bioturbate soils and improve their nutritional status and fertility, which are variables known to limit bioremediation. Earthworms have also been shown to retard the binding of organic contaminants to soils, release previously soil-bound contaminants for subsequent degradation, and promote and disperse organic contaminant degrading microorganisms. This review discusses these earthworm actions upon the soil environment and how they might influence the fate and behaviour of soil associated organic contaminants, subsequently improving bioremediation potential. The latter part of this review considers organic compounds in the following order: agrochemicals, petroleum and crude oil hydrocarbons, PAHs and PCBs.

Bioremediation of anthracene contaminated soil in bio-slurry phase reactor operated in periodic discontinuous batch mode

Bioremediation of soil-bound anthracene was studied in a series of bio-slurry phase reactors operated in periodic discontinuous/sequencing batch mode under anoxic-aerobic-anoxic microenvironment using native soil microflora. Five reactors were operated for a total cycle period of 144 h (6 days) at soil loading rate of 16.66 kg soil/m(3)/day at 30 +/- 2 degrees C temperature. The performance of the bioreactors was studied at various substrate loading rates (volumetric substrate loading rate (SLR), 0.1, 0.2 and 0.3g anthracene/kg soil/day) with and without bioaugmentation (domestic sewage inoculum; 2 x 10(6) CFU/g of soil). Control reactor (without microflora) showed negligible degradation of anthracene due to the absence of biological activity. The performance of the bio-slurry system with respect to anthracene degradation was found to depend on both substrate loading rate and bioaugmentation. Application of bioaugmentation showed positive influence on the rate of degradation of anthracene. Anthracene degradation data was analysed using different kinetic models to understand the mechanism of bioremediation process in the bio-slurry phase system. Variation in pH/oxidation-reduction potential (ORP), soil microflora and oxygen consumption rate correlated well with the substrate degradation pattern observed during soil slurry phase anthracene degradation.

Effectiveness of bacterial inoculum and mangrove plants on remediation of sediment contaminated with polycyclic aromatic hydrocarbons

The remediation of mangrove sediment contaminated with mixed polycyclic aromatic hydrocarbons (PAHs) having 3-, 4- and 5-rings by natural attenuation, bioaugmentation, phytoremediation and its combination was compared by greenhouse microcosm studies. At Days 90 and 154, the decreases of PAHs in contaminated mangrove sediment by phytoremediation, planted with one-year old Aegiceras corniculatum, and bioaugmentation, the inoculation of PAH-degrading bacterial strains isolated from mangrove sediment, either SCSH (Mycobacterium parafortuitum) or SAFY (Sphingobium yanoikuyae), were not better than that by natural attenuation (the non-vegetated and un-inoculated microcosms). The populations of SCSH and SAFY in sediment could not be maintained even with repeated inoculation, suggesting that the two isolates were not able to compete with the indigenous microbes and had little enhancement effect. Although some PAHs were accumulated in roots, root uptake only accounted for <15% of the spiked PAHs and the effect of plants on remediation were also insignificant. At the end of the 154-day experiment, the mass balance calculation revealed that the overall losses of PAHs by phytoremediation were comparable to that by bioaugmentation but were lower than that by natural attenuation, especially for the high molecular weight PAHs. Under natural attenuation, around 90% fluorene, 80% phenanthrene, 70% fluoranthene, 68% pyrene and 32% benzo[a]pyrene in contaminated sediment were removed. These results demonstrated that the mangrove sediment itself had sufficient indigenous microorganisms capable of naturally remedying PAH contamination.

Hydrophobised sawdust as a carrier for immobilisation of the hydrocarbon-oxidizing bacterium Rhodococcus ruber

Pine sawdust treated by a series of hydrophobising agents (drying oil, organosilicon emulsion, n-hexadecane and paraffin) was examined as carrier for adsorption immobilisation of hydrocarbon-oxidizing bacterial cells Rhodococcus ruber. It was shown that hydrophobising agents based on drying oil turned out to be optimal (among the other modifiers examined) for the preparation of sawdust carriers suitable for the efficient immobilisation. The results obtained demonstrate promising possibilities in developing a wide range of available and cheap, biodegradable cellulose-containing carriers that possess varying surface hydrophobicity.

Remediation technologies for organochlorine-contaminated sites in developing countries

Despite its importance in human life, until recently the relationship between soils and human health has been undervalued, especially in least developed countries. Currently, a holistic approach has been incorporated to identify best practices in soil science, defining it as "the task of all people concerned with the soil to direct their interest, not just towards the physical, chemical, and biological aspects, but also to those environmental, economic, social, legal, and technical aspects that affect soil use" (Abrahams 2002; Fent 2003). Considering this definition, the European Union (EU) as well as most developed countries have recognized organochlorine-contaminated sites as potential threats to the human health, threats that take different forms, such as their influence on water (e.g., drinking water resources), soil, and air as well as their interrelationships, which can directly affect human health (EC 2002; EP 2002; Bezama et al. 2004). Moreover, economic expansion and industrial growth are linked with growing lack of "greenfields" (a term that defines all areas without previous history of development): the supply of new building sites is limited and must contend with other competing uses, such as housing, recreation, nature, traffic, or agriculture (De Sousa 2001; Tedd et al. 2001). Thus, cleaning and reusing contaminated sites can be a meaningful alternative to address this issue, because most contaminated sites are located in metropolitan centres and are, therefore, prime candidates for urban development (Lorber et al. 2004).

Multi-factors on biodegradation kinetics of polycyclic aromatic hydrocarbons (PAHs) by Sphingomonas sp. a bacterial strain isolated from mangrove sediment

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated sediment is an attractive remediation technique and its success depends on biodegradation kinetics, and the optimal condition for the PAH-degrading isolates; however, information on this aspect is still scarce. The effects of multi-factors on biodegradation of phenanthrene, a 3-ring model PAH, in contaminated sediment slurry by Sphingomonas sp. a bacterial strain isolated from surface mangrove sediment, were investigated using the orthogonal experimental design (form L(16)(4(5))). The most significant factors were salinity and inoculum size, while the effects of phenanthrene concentrations, nutrient addition and temperatures were insignificant. The optimal biodegradation condition in contaminated mangrove sediment slurry was 30 degrees C, 15 ppt salinity, a carbon/nitrogen ratio of 100:1 (the background ratio in sediment) and an inoculum size of 10(6) most probable number g(-1) sediment. The phenanthrene biodegradation could be best described by the first order rate model, C=C(0)e(-kt), where k (the rate constant) is equaled to 0.1185, under the optimal condition. The kinetic model was verified and its validity in predicting biodegradation by Sphingomonas sp. at various phenanthrene concentrations was proved by experimental data.

Anaerobic BTEX degradation in soil bioaugmented with mixed consortia under nitrate reducing conditions

Different concentrations of BTEX, including benzene, toluene, ethylbenzene, and three xylene isomers, were added into soil samples to investigate the anaerobic degradation potential by the augmented BTEX-adapted consortia under nitrate reducing conditions. All the BTEX substrates could be anaerobically biodegraded to non-detectable levels within 70 d when the initial concentrations were below 100 mg/kg in soil. Toluene was degraded faster than any other BTEX compounds, and the high-to-low order of degradation rates were toluene > ethylbenzene > m-xylene > o-xylene > benzene > p-xylene. Nitrite was accumulated with nitrate reduction, but the accumulation of nitrite had no inhibitory effect on the degradation of BTEX throughout the whole incubation. Indigenous bacteria in the soil could enhance the BTEX biodegradation ability of the enriched mixed bacteria. When the six BTEX compounds were simultaneously present in soil, there was no apparent inhibitory effect on their degradation with lower initial concentrations. Alternatively, benzene, o-xylene, and p-xylene degradation were inhibited with higher initial concentrations of 300 mg/kg. Higher BTEX biodegradation rates were observed in soil samples with the addition of sodium acetate compared to the presence of a single BTEX substrate, and the hypothesis of primary-substrate stimulation or cometabolic enhancement of BTEX biodegradation seems likely.

Bioslurry phase remediation of chlorpyrifos contaminated soil: process evaluation and optimization by Taguchi design of experimental (DOE) methodology

Design of experimental (DOE) methodology using Taguchi orthogonal array (OA) was applied to evaluate the influence of eight biotic and abiotic factors (substrate-loading rate, slurry phase pH, slurry phase dissolved oxygen (DO), soil water ratio, temperature, soil microflora load, application of bioaugmentation and humic substance concentration) on the soil bound chlorpyrifos bioremediation in bioslurry phase reactor. The selected eight factors were considered at three levels (18 experiments) in the experimental design. Substrate-loading rate showed significant influence on the bioremediation process among the selected factors. Derived optimum operating conditions obtained by the methodology showed enhanced chlorpyrifos degradation from 1479.99 to 2458.33microg/g (over all 39.82% enhancement). The proposed method facilitated systematic mathematical approach to understand the complex bioremediation process and the optimization of near optimum design parameters, only with a few well-defined experimental sets.

Microbe-aliphatic hydrocarbon interactions in soil: implications for biodegradation and bioremediation

Aliphatic hydrocarbons make up a substantial portion of organic contamination in the terrestrial environment. However, most studies have focussed on the fate and behaviour of aromatic contaminants in soil. Despite structural differences between aromatic and aliphatic hydrocarbons, both classes of contaminants are subject to physicochemical processes, which can affect the degree of loss, sequestration and interaction with soil microflora. Given the nature of hydrocarbon contamination of soils and the importance of bioremediation strategies, understanding the fate and behaviour of aliphatic hydrocarbons is imperative, particularly microbe-contaminant interactions. Biodegradation by microbes is the key removal process of hydrocarbons in soils, which is controlled by hydrocarbon physicochemistry, environmental conditions, bioavailability and the presence of catabolically active microbes. Therefore, the aims of this review are (i) to consider the physicochemical properties of aliphatic hydrocarbons and highlight mechanisms controlling their fate and behaviour in soil; (ii) to discuss the bioavailability and bioaccessibility of aliphatic hydrocarbons in soil, with particular attention being paid to biodegradation, and (iii) to briefly consider bioremediation techniques that may be applied to remove aliphatic hydrocarbons from soil.

TOL plasmid transfer during bacterial conjugation in vitro and rhizoremediation of oil compounds in vivo

Molecular profiling methods for horizontal transfer of aromatics-degrading plasmids were developed and applied during rhizoremediation in vivo and conjugations in vitro. pWW0 was conjugated from Pseudomonas to Rhizobium. The xylE gene was detected both in Rhizobium galegae bv. officinalis and bv. orientalis, but it was neither stably maintained in orientalis nor functional in officinalis. TOL plasmids were a major group of catabolic plasmids among the bacterial strains isolated from the oil-contaminated rhizosphere of Galega orientalis. A new finding was that some Pseudomonas migulae and Pseudomonas oryzihabitans strains harbored a TOL plasmid with both pWW0- and pDK1-type xylE gene. P. oryzihabitans 29 had received the archetypal TOL plasmid pWW0 from Pseudomonas putida PaW85. As an application for environmental biotechnology, the biodegradation potential of oil-polluted soil and the success of bioremediation could be estimated by monitoring changes not only in the type and amount but also in transfer of degradation plasmids.

Bacterial diversity of a cyanobacterial mat degrading petroleum compounds at elevated salinities and temperatures

Cyanobacterial mats of the Arabian Gulf coast of Saudi Arabia experience extreme conditions of temperature and salinity. Because they are exposed to continuous oil pollution, they form ideal models for biodegradation under extreme conditions. We investigated the bacterial diversity of these mats using denaturing gradient gel electrophoresis and 16S rRNA cloning, and tested their potential to degrade petroleum compounds at various salinities (fresh water to 16%) and temperatures (5 to 50 degrees C). Cloning revealed that c. 15% of the obtained sequences were related to unknown, possibly novel bacteria. Bacteria belonging to Beta-, Gamma- and Deltaproteobacteria, Cytophaga-Flavobacterium-Bacteroides group and Spirochetes, were detected. The biodegradation of petroleum compounds at different salinities by mat microorganisms showed that pristine and n-octadecane were optimally degraded at salinities between 5 and 12% (weight per volume NaCl) whereas the optimum degradation of phenanthrene and dibenzothiophene was at 3.5% salinity. The latter compounds were also degradable at 8% salinity. The same compounds were degraded at temperatures between 15 and 40 degrees C but not at 5 and 50 degrees C. The optimum temperature of degradation was 28-40 degrees C for both aliphatics and aromatics. We conclude that the studied microbial mats from Saudi Arabia are rich in novel halotolerant and thermotolerant microorganisms with the potential to degrade petroleum compounds at elevated salinities and temperatures.

Role of autochthonous filamentous fungi in bioremediation of a soil historically contaminated with aromatic hydrocarbons

Nine fungal strains isolated from an aged and heavily contaminated soil were identified and screened to assess their degradative potential. Among them, Allescheriella sp. strain DABAC 1, Stachybotrys sp. strain DABAC 3, and Phlebia sp. strain DABAC 9 were selected for remediation trials on the basis of Poly R-478 decolorization associated with lignin-modifying enzyme (LME) production. These autochthonous fungi were tested for the abilities to grow under nonsterile conditions and to degrade various aromatic hydrocarbons in the same contaminated soil. After 30 days, fungal colonization was clearly visible and was confirmed by ergosterol determination. In spite of subalkaline pH conditions and the presence of heavy metals, the autochthonous fungi produced laccase and Mn and lignin peroxidases. No LME activities were detected in control microcosms. All of the isolates led to a marked removal of naphthalene, dichloroaniline isomers, o-hydroxybiphenyl, and 1,1'-binaphthalene. Stachybotrys sp. strain DABAC 3 was the most effective isolate due to its ability to partially deplete the predominant contaminants 9,10-anthracenedione and 7H-benz[DE]anthracen-7-one. A release of chloride ions was observed in soil treated with either Allescheriella sp. strain DABAC 1 or Stachybotrys sp. strain DABAC 3, suggesting the occurrence of oxidative dehalogenation. The autochthonous fungi led to a significant decrease in soil toxicity, as assessed by both the Lepidium sativum L. germination test and the Collembola mortality test.

Identification and characterization of o-xylene-degrading Rhodococcus spp. which were dominant species in the remediation of o-xylene-contaminated soils

Soils contaminated with o-xylene were more difficult to bioremediate than those contaminated with other BTEX hydrocarbons (benzene, toluene, ethylbenzene, m-xylene and p-xylene). In order to identify microorganisms responsible for o-xylene degradation in soil, microbial community structure analyses were carried out with two soil samples in the presence of o-xylene and mineral nutrients. In two different soil samples, Rhodococcus opacus became abundant. We were also able to isolate o-xylene degrading Rhodococcus species from these soil samples. A primer set was developed to specifically detect a cluster of this Rhodococcus group including isolated Rhodococcus strains, Rhodococcus opacus and Rhodococcus koreensis. The growth of this bacterial group in an o-xylene-contaminated soil was followed by competitive PCR (cPCR). The decrease in o-xylene clearly paralleled the growth of the Rhodococcus group.

Impact of the microscale distribution of a Pseudomonas strain introduced into soil on potential contacts with indigenous bacteria

Soil bioaugmentation is a promising approach in soil bioremediation and agriculture. Nevertheless, our knowledge of the fate and activity of introduced bacteria in soil and thus of their impact on the soil environment is still limited. The microscale spatial distribution of introduced bacteria has rarely been studied, although it determines the encounter probability between introduced cells and any components of the soil ecosystem and thus plays a role in the ecology of introduced bacteria. For example, conjugal gene transfer from introduced bacteria to indigenous bacteria requires cell-to-cell contact, the probability of which depends on their spatial distribution. To quantitatively characterize the microscale distribution of an introduced bacterial population and its dynamics, a gfp-tagged derivative of Pseudomonas putida KT2440 was introduced by percolation in repacked soil columns. Initially, the introduced population was less widely spread at the microscale level than two model indigenous functional communities: the 2,4-dichlorophenoxyacetic acid degraders and the nitrifiers (each at 10(6) CFU g(-1) soil). When the soil was percolated with a substrate metabolizable by P. putida or incubated for 1 month, the microscale distribution of introduced bacteria was modified towards a more widely dispersed distribution. The quantitative data indicate that the microscale spatial distribution of an introduced strain may strongly limit its contacts with the members of an indigenous bacterial community. This could constitute an explanation to the low number of indigenous transconjugants found most of time when a plasmid-donor strain is introduced into soil.

Low temperature bioremediation of oil-contaminated soil using biostimulation and bioaugmentation with a Pseudomonas sp. from maritime Antarctica

AIMS

To identify native Antarctic bacteria capable of oil degradation at low temperatures.

METHODS AND RESULTS

Oil contaminated and pristine soils from Signy Island (South Orkney Islands, Antarctica) were examined for bacteria capable of oil degradation at low temperatures. Of the 300 isolates cultured, Pseudomonas strain ST41 grew on the widest range of hydrocarbons at 4 degrees C. ST41 was used in microcosm studies of low temperature bioremediation of oil-contaminated soils. Microcosm experiments showed that at 4 degrees C the levels of oil degradation increased, relative to the controls, with (i) the addition of ST41 to the existing soil microbial population (bioaugmentation), (ii) the addition of nutrients (biostimulation) and to the greatest extent with (iii) a combination of both treatments (bioaugmentation and biostimulation). Addition of water to oil contaminated soil (hydration) also enhanced oil degradation, although less than the other treatments. Analysis of the dominant species in the microcosms after 12 weeks, using temporal temperature gradient gel electrophoresis, showed Pseudomonas species to be the dominant soil bacteria in both bioaugmented and biostimulated microcosms.

CONCLUSIONS

Addition of water and nutrients may enhance oil degradation through the biostimulation of indigenous oil-degrading microbial populations within the soil. However, bioaugmentation with Antarctic bacteria capable of efficient low temperature hydrocarbon degradation may enhance the rate of bioremediation if applied soon after the spill.

SIGNIFICANCE AND IMPACT OF THE STUDY

In the future, native soil bacteria could be of use in bioremediation technologies in Antarctica.

Degradation of aromatic hydrocarbons by white-rot fungi in a historically contaminated soil

Phanerochaete chrysosporium NRRL 6361 and Pleurotus pulmonarius CBS 664.97 were tested for their ability to grow under nonsterile conditions and to degrade various aromatic hydrocarbons in an aged contaminated soil that also contained high concentrations of heavy metals. After 24 days fungal incubation, carbon-CO2 liberated, an indicator of microbial activity, reached a plateau. At the end of the incubation time (30 days), fungal colonization was clearly visible and was confirmed by ergosterol and cell organic carbon determinations. In spite of unfavorable pH (around 7.4) and the presence of heavy metals, both fungi produced Mn-peroxidase activity. In contrast, laccase and aryl-alcohol oxidase were detected only in the soil treated with P. pulmonarius CBS 664.97 and lignin-peroxidase in that with P. chrysosporium NRRL 6361. No lignin-modifying enzyme activities were present in non-inoculated soil incubated for 30 days (control microcosm). Regardless of the fungus employed, a total removal of naphtalene, tetrachlorobenzene, and dichloroaniline isomers, diphenylether and N-phenyl-1-naphtalenamine, was observed. Significant release of chloride ions was also observed in fungal-treated soil, in comparison with that recorded in the control microcosm. Both fungi led to a significant decrease in soil toxicity, as assessed using two different soil contact assays, including the Lepidium sativum L. germination test and the Collembola mortality test.

Development of a PCR method for the detection and quantification of benzoyl-CoA reductase genes and its application to monitored natural attenuation

Benzoyl coenzyme A reductase (BCR) catalyzes dearomatization of benzoyl coenzyme A (benzoyl-CoA), which is the central step in the anaerobic degradative pathways for a variety of aromatic compounds. This study developed a PCR method for the detection and quantification of BCR genes in bacterial strains and environmental samples. PCR primers were designed by aligning known BCR genes in Thauera, Azoarcus and Rhodopseudomonas species, and their utility was assessed by amplifying BCR fragments from aromatic-hydrocarbon degrading anaerobes and other bacteria. BCR fragments with the expected sizes were obtained from denitrifying and phototrophic aromatics degraders. The positive signals were also obtained from Geobacter metallireducens and xylene-degrading sulfate-reducing bacterium (strain mXyS1) but not from other aromatics-degrading sulfate-reducing bacteria and aerobic bacteria. When the PCR was used for analyzing a natural attenuation (NA) site, the positive signal was obtained only from gasoline-contaminated groundwater; sequence analysis of these amplicons revealed that most of them exhibited substantial similarities to the known BCRs. Quantitative competitive PCR analysis estimated BCR-gene copies to account for 10-40% of bacterial 16S rRNA gene copies in the contaminated groundwater, indicating that bacteria possessing BCR genes were highly enriched in the contaminated groundwater. In microcosm bioremediation tests using the contaminated groundwater, the copy number of BCR gene was approximately 10-fold increased in the course of aromatics degradation under denitrifying conditions but not under sulfidogenic conditions. These results suggest the utility of the PCR method for assessing the potential of denitrifying bacteria for aromatic-compound degradation in groundwater.

Isolation and characterization of novel strains of Pseudomonas aeruginosa and Serratia marcescens possessing high efficiency to degrade gasoline, kerosene, diesel oil, and lubricating oil

Bacteria possessing high capacity to degrade gasoline, kerosene, diesel oil, and lubricating oil were screened from several areas of Hokkaido, Japan. Among isolates, two strains, WatG and HokM, which were identified as new strains of Pseudomonas aeruginosa and Serratia marcescens species, respectively, showed relatively high capacity and wide spectrum to degrade the hydrocarbons in gasoline, kerosene, diesel, and lubricating oil. About 90-95% of excess amount of total diesel oil and kerosene added to mineral salts media as a sole carbon source could be degraded by WatG within 2 and 3 weeks, respectively. The same amount of lubricating oil was 60% degraded within 2 weeks. Strain HokM was more capable than WatG in degrading aromatic compounds in gasoline. This strain could also degrade kerosene, diesel, and lubricating oil with a capacity of 50-60%. Thus, these two isolates have potential to be useful for bioremediation of sites highly contaminated with petroleum hydrocarbons.