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).     

Degradation of phenanthrene on plant leaves by phyllosphere bacteria

The activity of phyllosphere bacteria in the degradation of phenanthrene was investigated as a mechanism for the removal of atmospheric phenanthrene after its deposition on plant leaves. Initially, leaf samples of six plant species were collected from two roadsides in Bangkok to determine the presence of phenanthrene-degrading bacteria. The numbers of phenanthrene-degrading phyllosphere bacteria were varied and ranged from 3.5 x 10(4) to 1.95 x 10(7) CFU/g, in which the highest number was found from Ixora sp. Further studies were carried out in the laboratory by spraying phenanthrene on Ixora sp. leaves and then monitoring the amount of deposited phenanthrene and number of phenanthrene-degrading bacteria after incubation. The results showed that the amount of phenanthrene was significantly reduced on leaves containing phenanthrene-degrading bacteria. These were detected along with a rapid increase in the number of bacteria on leaves. The results indicated that many phyllosphere bacteria could utilize phenanthrene to support their growth and thereby reduce the amount of deposited phenanthrene on leaf surfaces. Several phenanthrene-degrading bacteria were later isolated from the leaves and identified with a high 16S rDNA sequence similarity to the genera Pseudomonas, Microbacterium, Rhizobium, and Deinococcus.     

Repeated inoculation as a strategy for the remediation of low concentrations of phenanthrene in soil

Phenanthrene, a polycyclic aromatic hydrocarbon, becomes increasingly unavailable to microorganisms for degradation as it ages in soil. Consequently, many bioaugmentation efforts to remediate polycyclic aromatic hydrocarbons in soil have failed. We studied theeffect of repeatedly inoculating a soil with a phenanthrene-degrading Arthrobacter sp. on the mineralization kinetics of low concentrations of phenanthrene. After the first inoculation, the initial mineralization rate of 50 ng/g phenanthrene declined in a biphasicexponential pattern. By three hundred hours after inoculation, there was no difference in mineralization rates between the inoculated and uninoculated treatments even though a large fraction of the phenanthrene had not yet been mineralized. A second and third inoculation significantly increased the mineralization rate, suggesting that, though themineralization rate declined, phenanthrene remained bioavailable. Restirring the soil, without inoculation, did not produce similar increases in mineralization rates, suggesting absence of contact between cells and phenanthrene on a larger spatial scale (>mm) is not the cause of the mineralization decline. Bacteria inoculated into soil 280 hours beforethe phenanthrene was added could not maintain phenanthrene degradation activity. We suggest sorption lowered bioavailability of phenanthrene below an induction threshold concentration for metabolic activity of phenanthrene-degrading bacteria.     

Temporal change in culturable phenanthrene degraders in response to long-term exposure to phenanthrene in a soil column system

Widespread environmental contamination by polycyclic aromatic hydrocarbons (PAH) has led to increased interest in the use of natural attenuation as a clean-up strategy. However, few bioremediation studies have investigated the behaviour of the indigenous PAH-degrading community after long-term exposure to a PAH. In this study, a column packed with sandy loam soil was exposed to a solution saturated with phenanthrene ( approximately 1.2 mg l-1) for a 6-month period to examine the temporal response of the indigenous phenanthrene-degrading community. Initial soil, effluent, and final soil samples were collected and analysed for phenanthrene concentration and culturable phenanthrene degraders. Phenanthrene-degrading isolates were grouped by colony morphology. For each unique group, 16S rDNA polymerase chain reaction was performed, and then sequencing analysis was used to identify the isolate at the genus level. Twenty-five phenanthrene-degrading isolates, potentially representing 19 genera, were obtained from this analysis. Of these, eight genera have not been reported previously to degrade phenanthrene, including Afipia, Janthinobacterium, Leptothrix, Massilia, Methylobacterium, Rhizobium, Sinorhizobium and Thiobacillus. Results indicate that the dominant phenanthrene-degrading population changed over the course of this 6-month experiment. Specifically, the isolates obtained initially from the soil were not subsequently found in either effluent samples or the soil at the end of the experiment. Furthermore, several isolates that were found in the soil at the end of the experiment were not observed in the soil initially or in the effluent samples. This study confirms earlier findings indicating that a diverse community participates in phenanthrene degradation in the environment, and also suggests that the composition of this community is temporally variable.     

Enumeration and phylogenetic analysis of polycyclic aromatic hydrocarbon-degrading marine bacteria from Puget sound sediments.

Naphthalene- and phenanthrene-degrading bacteria in Puget Sound sediments were enumerated by most-probable-number enumeration procedures. Sediments from a creosote-contaminated Environmental Protection Agency Superfund Site (Eagle Harbor) contained from 10(4) to 10(7) polycyclic aromatic hydrocarbon (PAH)-degrading bacteria g (dry weight) of sediment-1, whereas the concentration at an uncontaminated site ranged from 10(3) to 10(4) g of sediment(-1). Isolates of PAH-degrading bacteria were obtained from these most-probable-number tubes as well as from sediment samples from noncontaminated sites and from bioreactors enriched with PAHs. The 18 resulting strains were grouped by whole-cell fatty acid analysis into two subgroups. The larger group of strains belonged to the newly described genus Cycloclasticus, whereas the other group contained members of the genus Vibrio. The Cycloclasticus group seems to be widespread in noncontaminated sediments. PAH degradation was confirmed in selected strains on the basis of removal of phenanthrene from growing cultures.     

The effect of soil: water ratios on the mineralisation of phenanthrene: LNAPL mixtures in soil

Contamination of soil by polycyclic aromatic hydrocarbons is frequently associated with non-aqueous-phase liquids. Measurement of the catabolic potential of a soil or determination of the biodegradable fraction of a contaminant can be done using a slurried soil respirometric system. This work assessed the impact of increasing the concentration of transformer oil and soil:water ratio on the microbial catabolism of [(14)C]phenanthrene to (14)CO(2) by a phenanthrene-degrading inoculum. Slurrying (1:1, 1:2, 1:3 and 1:5 soil:water ratios) consistently resulted in statistically higher rates and extents of mineralisation than the non-slurried system (2:1 soil:water ratio; P<0.01). The maximum extents of mineralisation observed occurred in the 1:2-1:5 soil:water ratio microcosms irrespective of transformer oil concentration. Transformer oil concentrations investigated displayed no statistically significant effect on total mineralisation (P>0.05). Soil slurries 1:2 or greater, but less than 1:5 (soil:water), are recommended for bioassay determinations of total contaminant bioavailability due to greater overall mineralisation and improved reproducibility.     

Effect of copper on the degradation of phenanthrene by soil micro-organisms

AIMS: The effect of copper on the degradation by soil micro-organisms of phenanthrene, a polycyclic aromatic hydrocarbon, was investigated. METHODS AND RESULTS: Inert nylon filters were incubated in the soil for 28 days at 25 degrees C. Each filter was inoculated with a soil suspension, phenanthrene (400 ppm), copper (0, 70, 700 or 7000 ppm) and nitrogen/phosphorus sources. The filters were assessed for phenanthrene degradation, microbial respiration and colonization. Phenanthrene degradation proceeded even at toxic copper levels (700/7000 ppm), indicating the presence of phenanthrene-degrading, copper-resistant and/or -tolerant microbes. However, copper at these high levels reduced microbial activity (CO2 evolution). CONCLUSION: High levels of copper caused an incomplete mineralization of phenanthrene and possible accumulation of its metabolites. SIGNIFICANCE AND IMPACT OF THE STUDY: The presence of heavy metals in soils could seriously affect the bioremediation of PAH-polluted environments.     

Linking of microorganisms to phenanthrene metabolism in soil by analysis of (13)C-labeled cell lipids

Phenanthrene-metabolizing soil microbial communities were characterized by examining mineralization of [(14)C]phenanthrene, by most-probable-number (MPN) counting, by 16S-23S spacer DNA analysis of the numerically dominant, culturable phenanthrene-degrading isolates, and by examining incorporation of [(13)C]phenanthrene-derived carbon into sterols and polar lipid fatty acids (PLFAs). An unpolluted agricultural soil, a roadside soil diffusely polluted with polycyclic aromatic hydrocarbons (PAHs), and two highly PAH-polluted soils from industrial sites were analyzed. Microbial phenanthrene degraders were not detected by MPN counting in the agricultural soil and the roadside soil. In the industrial soils, phenanthrene degraders constituted 0.04 and 3.6% of the total number of CFU. 16S-23S spacer DNA analysis followed by partial 16S DNA sequencing of representative isolates from one of the industrial soils showed that one-half of the isolates belonged to the genus Sphingomonas and the other half were closely related to an unclassified beta-proteobacterium. The (13)C-PLFA profiles of the two industrial soils were relatively similar and resembled the profiles of phenanthrene-degrading Sphingomonas reference strains and unclassified beta-proteobacterium isolates but did not match the profiles of Pseudomonas, Mycobacterium, or Nocardia reference strains. The (13)C-PLFA profiles of phenanthrene degraders in the agricultural soil and the roadside soil were different from each other and different from the profiles of the highly polluted industrial soils. Only in the roadside soil were 10me/12me18:0 PLFAs enriched in (13)C, suggesting that actinomycetes metabolized phenanthrene in this soil. The (13)C-PLFA profiles of the unpolluted agricultural soil did not resemble the profiles of any of the reference strains. In all of the soils investigated, no excess (13)C was recovered in the 18:2omega6,9 PLFA, suggesting that fungi did not contribute significantly to assimilation of [(13)C]phenanthrene.     

The potential of established turf cover for cleaning oily desert soil using rhizosphere technology

The rhizosphere of two turf cover sorts; Bermuda grass and American grass contained high numbers, 8.1 to 16.8 x 10(6) g(-1) of cultivable oil-utilizing and diazotrophic bacteria belonging predominantly to the genera Agrobacterium, Arthrobacter, Pseudomonas, Gordonia, and Rhodococcus. Those bacteria also grew on a nitrogen-free medium and demonstrated the ability to reduce acetylene to ethylene. These isolates grew on a wide range of n-alkanes (C9 to C40) and aromatic hydrocarbons, as sole sources of carbon. Quantitative determinations revealed that predominant bacteria consumed crude oil and representative aliphatic (n-octadecane) and aromatic (phenanthrene) hydrocarbons efficiently. The fact that those organisms had the combined activities of hydrocarbon-utilization and nitrogen-fixation makes them suitable tools for bioremediating oily desert areas that are normally poor in nitrogenous compounds. Phytoremediation experiments showed that spreading turf cover on oily desert soil inhibited oil volatilization and enhanced oil loss in soil by about 15%. Oil loss was also enhanced in turf free soil samples fertilized with NH4NO3. In conclusion, covering this oil-polluted soil with turf cover minimized atmospheric pollution, increased the numbers of the oil-utilizing/nitrogen-fixing bacteria by about 20 to 46% thus, encouraging oil attenuation.     

Pyrene and Phenanthrene Influence on Soil Microbial Populations

Two studies were conducted to evaluate microbial populations in polycyclic aromatic hydrocarbon-contaminated soil. Captina silt loam was freshly exposed to (1) 0 or 2000 mg pyrene/kg and sampled after 10- and 61-wk incubation and (2) 0 or 505 mg pyrene + 445 mg phenanthrene/kg and sampled after a 21-wk incubation. Microbial numbers were determined by plate-count techniques. Isolated bacteria, selected degraders, and wholesoil extracts were analyzed by fatty acid methyl ester analysis (FAME). In the pyrene experiment, pyrene did not affect total bacterial or fungal numbers, but pyrene degraders increased from undetectable levels to 7.09 log₁₀ degraders/g in the contaminated soil. The FAME analysis of bacterial isolates detected no pyrene effect, but wholesoil FAME indicated an increase in the contaminated soil of a fatty acid characteristic of protozoa and a major fatty acid detected in isolated degraders. In the pyrene + phenanthrene experiment, the contaminants had no impact on bacterial, fungal, or actinomycete numbers but increased degrader numbers. No effect of pyrene + phenanthrene was detected by isolate FAME, but whole-soil FAME indicated an effect similar to that in the pyrene experiment. The results indicate that pyrene, although not impacting microbial numbers, may have altered the soil microbial composition and that Captina silt loam can develop an effective degrader population under tested conditions.     

Pyrene and Phenanthrene Influence on Soil Microbial Populations

Two studies were conducted to evaluate microbial populations in polycyclic aromatic hydrocarbon-contaminated soil. Captina silt loam was freshly exposed to (1) 0 or 2000?mg pyrene/kg and sampled after 10- and 61-wk incubation and (2) 0 or 505?mg pyrene + 445?mg phenanthrene/kg and sampled after a 21-wk incubation. Microbial numbers were determined by plate-count techniques. Isolated bacteria, selected degraders, and wholesoil extracts were analyzed by fatty acid methyl ester analysis (FAME). In the pyrene experiment, pyrene did not affect total bacterial or fungal numbers, but pyrene degraders increased from undetectable levels to 7.09 log₁₀ degraders/g in the contaminated soil. The FAME analysis of bacterial isolates detected no pyrene effect, but wholesoil FAME indicated an increase in the contaminated soil of a fatty acid characteristic of protozoa and a major fatty acid detected in isolated degraders. In the pyrene + phenanthrene experiment, the contaminants had no impact on bacterial, fungal, or actinomycete numbers but increased degrader numbers. No effect of pyrene + phenanthrene was detected by isolate FAME, but whole-soil FAME indicated an effect similar to that in the pyrene experiment. The results indicate that pyrene, although not impacting microbial numbers, may have altered the soil microbial composition and that Captina silt loam can develop an effective degrader population under tested conditions.     

Measuring growth of a phenanthrene-degrading bacterial inoculum in soil with a quantitative competitive polymerase chain reaction method

We measured growth of a phenanthrene-degrading bacterium, Arthrobacter, strain RP17, in Forbes soil, amended with 500 μg g(-1) phenanthrene using a quantitative competitive polymerase chain reaction method. The inoculum, which was not indigenous to Forbes soil, grew from 5.55x10(5) colony forming units (cfu) g(-1) to 1.97x10(7) cfu g(-1) within 100 h after the cells were added to the soil. Maximum population density was reached before the highest degradation rate was observed 150 h after the cells were added to soil. Population density remained stable even after 56% of the phenanthrene had mineralized. This study is one of the few documented examples of growth by a non-indigenous bacterium in a non-sterile soil amended with a pollutant.     

Mineralization of phenanthrene by a Mycobacterium sp.

A Mycobacterium sp., designated strain BG1, able to utilize the polycyclic aromatic hydrocarbon phenanthrene as the sole carbon and energy source was isolated from estuarine sediment following enrichment with the hydrocarbon. Unlike other phenanthrene degraders, this bacterium degraded phenanthrene via 1-hydroxy-2-naphthoic acid without accumulating this or other aromatic intermediates, as shown by high-performance liquid chromatography. Degradation proceeded via meta cleavage of protocatechuic acid. Different nonionic surfactants (Tween compounds) solubilized the phenanthrene to different degrees and enhanced phenanthrene utilization. The order of enhancement, however, did not correlate perfectly with increased solubility, suggesting physiological as well as physicochemical effects of the surfactants. Plasmids of approximately 21, 58, and 77 megadaltons were detected in cells grown with phenanthrene but not in those which, after growth on nutrient media, lost the phenanthrene-degrading phenotype. Given that plasmid-mediated degradations of aromatic hydrocarbons generally occur via meta cleavages, it is of interest that the addition of pyruvate, a product of meta cleavage, supported rapid mineralization of phenanthrene in broth culture; succinate, a product of ortho cleavage, supported growth but completely repressed the utilization of phenanthrene. The involvement of plasmids may have given rise to the unusual degradation pattern that was observed.     

Kinetics and key enzyme activities of phenanthrene degradation by Pseudomonas mendocina

Phenanthrene degradation by Pseudomonas mendocina CGMCC 1.766, a new phenanthrene-degrading strain, was investigated in this work. When cells were grown on 20, 50, 100 and 200 mg l⁻¹ of phenanthrene, the doubling time was 18.3, 19.8, 21.0 and 20.3 h and the growth yield during exponential phase was 242, 271, 221 and 206 mg protein (g phenanthrene)⁻¹, respectively. High level accumulation of the intermediate metabolite 1-hydroxy-2-naphthoic acid (1H2N) up to ≈94% of its theoretical yield was observed. Dynamic profiles of the activities of two key enzymes, i.e. polycyclic aromatic hydrocarbon (PAH) dioxygenase (PDO) and catechol-2,3-oxygenase (C23O), during the biodegradation were revealed and the results suggest a delicate mechanism in the regulation of these phenanthrene-degrading enzymes in this strain.     

Diversity and Activity of PAH-Degrading Bacteria in the Phyllosphere of Ornamental Plants

Phyllosphere bacteria on ornamental plants were characterized based on their diversity and activity towards the removal of polycyclic aromatic hydrocarbons (PAHs), the major air pollutants in urban area. The amounts of PAH-degrading bacteria were about 1–10% of the total heterotrophic phyllosphere populations and consisted of diverse bacterial species such as Acinetobacter, Pseudomonas, Pseudoxanthomonas, Mycobacterium, and uncultured bacteria. Bacterial community structures analyzed by polymerase chain reaction–denaturing gradient gel electrophoresis from each plant species showed distinct band patterns. The uniqueness of these phyllosphere bacterial communities was partly due to the variation in leaf morphology and chemical properties of ornamental plants. The PAH degradation activity of these bacteria was monitored in gas-tight systems containing sterilized or unsterilized leaves. The results indicated that phyllosphere bacteria on unsterilized leaves were able to enhance the activity of leaves for phenanthrene removal. When compared between plant species, phenanthrene removal efficiency corresponded to the size of phenanthrene-degrading bacteria. In addition, phyllosphere bacteria on Wrightia religiosa were able to reduce other PAHs such as acenaphthylene, acenaphthene, and fluorine in 60-ml glass vials and in a 14-l glass chamber. Thus, phyllosphere bacteria on ornamental plants may play an important role in natural attenuation of airborne PAHs in urban areas.     

Involvement of a rhamnolipid-producing strain of Pseudomonas aeruginosa in the degradation of polycyclic aromatic hydrocarbons by a bacterial community

A rhamnolipid-producing strain of Pseudomonas aeruginosa GL1 was isolated from a bacterial community growing on a mixture of polycyclic aromatic hydrocarbons (PAH) as sole carbon source. Strain GL1 did not grow on PAH but grew on known degradation metabolites of phenanthrene ( o -phthalic acid) and of naphthalene (salicylic acid). In co-culture with a phenanthrene-degrading strain, Ps. aeruginosa GL1 accelerated the degradation of phenanthrene. Strain GL1 was resistant to toxic amphiphilic compounds such as cationic and anionic detergents. Rhamnolipid production took place in a late stage growth in cultures of strain GL1 on glycerol or n -hexadecane. It coincided with a substantial decrease in cell hydrophobicity and with morphological changes of the outer membrane as observed by transmission electronic microscopy. The rhamnolipids produced inhibited the growth of bacteria such as Rhodococcus erythropolis , Bacillus cereus and Ps. fluorescens . The overall results suggested an outer membrane origin for the rhamnolipids. They also indicate that the utilization of PAH metabolites by strain GL1 is important for the stability of the PAH-degrading community.     

Staphylococcus sp. KW-07 contains nahH gene encoding catechol 2,3-dioxygenase for phenanthrene degradation and a test in soil microcosm

We isolated three species of phenanthrene-degrading bacteria from oil-contaminated soils and marine sediment, and assessed the potential use of these bacteria for bioremediation of soils contaminated by polycyclic aromatic hydrocarbons (PAHs). Based on 16S rDNA sequences, these bacteria were Staphylococcus sp. KW-07 and Pseudomonas sp. CH-11 from soil, and Ochrobactrum sp. CH-19 from the marine sediment. By PCR amplification, catechol 2,3-dioxygenase genes (nahH genes) mediating PAH degradation in the chromosome of Staphylococcus sp. KW-07 and Ochrobactrum sp. CH-19, and in plasmid DNA of Pseudomonas sp. CH-11 were detected. All isolates had a similar optimal growth temperature (25 °C) and optimal growth pH (7.0) in a minimal salt medium (MSM) with 0.1% (w/v) phenanthrene as the sole source of carbon and energy. Pseudomonas sp. CH-11 and Staphylococcus sp. KW-07 degraded 90% of added phenanthrene in 3 days and Ochrobactrum sp. CH-19 degraded 90% of the phenanthrene in 7 days under laboratory batch culture conditions. However, Staphylococcus sp. KW-07 was the most effective among the three strains in degradation of phenanthrene in soil. After inoculation of 1 × 10¹¹ cells of Staphylococcus sp. KW-07, over 90% degradation of 0.1% phenanthrene (0.1 g/100 g soil) was achieved after 1 month at 25 °C. The results collectively suggest that the Staphylococcus sp. KW-07 strain isolated may be useful in bioremediation of PAH-contaminated soils.     

两株多环芳烃降解菌协同对菲-镉污染的去除特性北大核心

【目的】从污染土壤中分离筛选一株多环芳烃降解菌,并探究其与Pseudomonas aeruginosa B6-2构建的混菌体系对菲-镉复合污染的修复效能,以及微生物代谢特性对不同镉浓度赋存的响应特性,以期为复合污染的生物修复提供优良菌株资源及应用技术参考。【方法】采用富集驯化、筛选纯化方法得到一株多环芳烃降解菌,通过生理生化特征和16S rRNA基因序列分析进行鉴定。利用高效液相色谱法和电感耦合等离子体质谱法评估不同镉浓度赋存下各反应体系对菲和镉的去除效能;通过菌体细胞形态的扫描电镜观测及菌株代谢活性检测,探讨镉胁迫对菲生物降解过程的影响机制。【结果】筛选得到一株具有重金属耐受性和多环芳烃高效降解菌SZ-3,经鉴定为节杆菌属;降解菌协同体系(M)具有良好的菲降解效能和抗镉胁迫优势。镉胁迫浓度为0.5、10 mg/L时,M对菲和镉的去除率分别高于85%、80%;镉胁迫浓度为25、50 mg/L时,2种污染物的去除率均大于65%。扫描电镜分析表明,镉胁迫导致菌体表面粗糙且出现不同程度变形,菌体间黏附性和聚集性提高。反应周期内,邻苯二酚1,2-双加氧酶活性与电子传递体系活性随镉浓度增加而降低,两者变化与菲降解速率变化一致。【结论】Arthrobacter sp.SZ-3是一株PAHs高效降解菌,能与Pseudomonas aeruginosa B6-2协同高效修复菲-镉复合污染,随着初始镉胁迫浓度增加,混菌协同对目标污染物去除的优势显著。     

低分子有机酸对土壤中菲降解及细菌群落结构的影响

多环芳烃是一类普遍存在于环境中的持久性有机污染物,其通过食物链进入生态系统,直接危害人类健康和整个生态系统的安全。为探讨低分子有机酸对土壤中菲降解及细菌群落结构的影响,通过室内培养的方式研究了在添加不同种类有机酸处理下第0—180天土壤中菲含量的变化状况,并采用高通量Illumina Miseq技术分析了土壤细菌群落种类和数量的变化特征。结果表明,低分子有机酸对于土壤中菲的降解有明显的促进作用,由一级动力学方程得出乙酸对菲降解的促进作用最明显。从细菌群落结构来看,土壤细菌的数量及其多样性或许不是导致土壤菲降解的主要因素,反而特定的菲降解菌的丰度对菲降解有重要影响。添加低分子有机酸减少了细菌OTU数及细菌菌群多样性,但增加了PAHs降解菌的丰度。随着时间推移细菌总OTU数呈现下降趋势,独有种类数均呈现出先增长后下降的趋势。检测到了6种典型的菲降解菌,分别为:Bacillus、鞘氨醇单胞菌属、Massilia、Azospirillum、Burkholderia-paraburkholderia、红球菌。研究结果可为多环芳烃污染土壤的植物修复提供基础数据和科学参考。     

Microbial degradation of polycyclic aromatic hydrocarbons in soil by bacterium-fungus co-cultures

Two fungi and the phenanthrene-degrading bacterial strainRhodococcus sp. IC10 were used as inocula for the bioremediation of petroleum hydrocarbon-contaminated soil from a manufactured gas plant area. The two fungi, which were previously isolated from different hydrocarbon-contaminated soil samples, were identified asAspergillus terreus andPenicillium sp. In addition, two types of co-cultures which consist of fungal species includingA. terreus orPenicilium sp. withRhodococcus sp. IC10 were applied. After a 10-week incubation period, the concentrations of anthracene, phenanthrene, and pyrene were totally biodegraded by days 68, 54, and 64, for the 16 polycyclic aromatic hydrocarbons (PAH's) tested. The ecotoxicity of the soil after bioremediation did not show any effect on the survival ofDaphnia magna (24 h-old-daphnids). However, the toxicity on seed germination ofBrassica alba and the oxidoreductase activity ofBacillus cereus declined after 5- and 10-weeks of incubation, respectively. Co-cultures ofPenicillium sp. andRhodococcus sp. IC 10 revealed the best efficiency at reducing ecotoxicity.