Degradation of fluorene,anthracene, phenanthrene,fluoranthene, and pyrene lacks connection to the production of extracellular enzymes by Pleurotus ostreatus and Bjerkandera adusta

The degradation of polycyclic aromatic hydrocarbons (PAH) was studied in liquid cultures of Bjerkandera adusta and Pleurotus ostreatus during 7 weeks of cultivation. During only 3 days of incubation, B. adusta removed 56% and 38% of fluorene and anthracene, while P. ostreatus degraded 43% and 60% of these compounds; other PAH were degraded to a lower extent. Except for anthracene in cultures of P. ostreatus, all PAH were removed uniformly during the cultivation time but fluorene and anthracene were degraded faster than other PAH. Supplementation of liquid cultures with milled wood decreased the concentration of PAH in the solution and diminished the degradation of PAH. The fungi produced valuable activity of manganese-dependent peroxidase; laccase was secreted only by P. ostreatus and was strongly induced by the addition of milled wood. The production of the oxidative enzymes did not correlate directly to the metabolisation of PAH.     

Strong Impact on the Polycyclic Aromatic Hydrocarbon (PAH)-Degrading Community of a PAH-Polluted Soil but Marginal Effect on PAH Degradation when Priming with Bioremediated Soil Dominated by Mycobacteria

Bioaugmentation of soil polluted with polycyclic aromatic hydrocarbons (PAHs) is often disappointing because of the low survival rate and low activity of the introduced degrader bacteria. We therefore investigated the possibility of priming PAH degradation in soil by adding 2% of bioremediated soil with a high capacity for PAH degradation. The culturable PAH-degrading community of the bioremediated primer soil was dominated by Mycobacterium spp. A microcosm containing pristine soil artificially polluted with PAHs and primed with bioremediated soil showed a fast, 100- to 1,000-fold increase in numbers of culturable phenanthrene-, pyrene-, and fluoranthene degraders and a 160-fold increase in copy numbers of the mycobacterial PAH dioxygenase gene pdo1. A nonpolluted microcosm primed with bioremediated soil showed a high rate of survival of the introduced degrader community during the 112 days of incubation. A nonprimed control microcosm containing pristine soil artificially polluted with PAHs showed only small increases in the numbers of culturable PAH degraders and no pdo1 genes. Initial PAH degradation rates were highest in the primed microcosm, but later, the degradation rates were comparable in primed and nonprimed soil. Thus, the proliferation and persistence of the introduced, soil-adapted degraders had only a marginal effect on PAH degradation. Given the small effect of priming with bioremediated soil and the likely presence of PAH degraders in almost all PAH-contaminated soils, it seems questionable to prime PAH-contaminated soil with bioremediated soil as a means of large-scale soil bioremediation.     

Products from the Incomplete Metabolism of Pyrene by Polycyclic Aromatic Hydrocarbon-Degrading Bacteria

Pyrene is a regulated pollutant at sites contaminated with polycyclic aromatic hydrocarbons (PAH). It is mineralized by some bacteria but is also transformed to nonmineral products by a variety of other PAH-degrading bacteria. We examined the formation of such products by four bacterial strains and identified and further characterized the most apparently significant of these metabolites. Pseudomonas stutzeri strain P16 and Bacillus cereus strain P21 transformed pyrene primarily to cis-4,5-dihydro-4,5-dihydroxypyrene (PYRdHD), the first intermediate in the known pathway for aerobic bacterial mineralization of pyrene. Sphingomonas yanoikuyae strain R1 transformed pyrene to PYRdHD and pyrene-4,5-dione (PYRQ). Both strain R1 and Pseudomonas saccharophila strain P15 transform PYRdHD to PYRQ nearly stoichiometrically, suggesting that PYRQ is formed by oxidation of PYRdHD to 4,5-dihydroxypyrene and subsequent autoxidation of this metabolite. A pyrene-mineralizing organism, Mycobacterium strain PYR-1, also transforms PYRdHD to PYRQ at high initial concentrations of PYRdHD. However, strain PYR-1 is able to use both PYRdHD and PYRQ as growth substrates. PYRdHD strongly inhibited phenanthrene degradation by strains P15 and R1 but had only a minor effect on strains P16 and P21. At their aqueous saturation concentrations, both PYRdHD and PYRQ severely inhibited benzo[a]pyrene mineralization by strains P15 and R1. Collectively, these findings suggest that products derived from pyrene transformation have the potential to accumulate in PAH-contaminated systems and that such products can significantly influence the removal of other PAH. However, these products may be susceptible to subsequent degradation by organisms able to metabolize pyrene more extensively if such organisms are present in the system.     

Biochemical and physiological peculiarities of the interactions between <Emphasis Type="Italic">Sinorhizobium meliloti</Emphasis> and <Emphasis Type="Italic">Sorghum bicolor</Emphasis> in the presence of phenanthrene

The effect of phenanthrene, a polycyclic aromatic hydrocarbon (PAH) at concentrations of 0, 10, and 100 mg/kg and the bacterium Sinorhizobium meliloti P221 on root exudation of Sorghum bicolor L. Moench was studied in laboratory vegetative experiments. Inoculation of the bacterium promoted plant resistance to the pollutant stress and increased their acclimation rate and biomass formation. The ability of this microorganism to produce a phytohormone, indolyl-3-acetic acid, and to degrade phenanthrene, resulted in morphological changes of the plant root system and in the changed intensity of root exudation. In root exudates of sorghum, enzyme activities towards the metabolites formed during microbial degradation of PAH were revealed, which is indicative of a direct involvement of plants in PAH degradation in the rhizosphere as well as of the coupled plant-microbial metabolism in the course of xenobiotic degradation in the root zone. In phenanthrene-contaminated soil, sorghum was found to support selectively the development of the S. meliloti P221 population.     

Effect of rapeseed oil on the degradation of polycyclic aromatic hydrocarbons in soil by Rhodococcus wratislaviensis

The effect of rapeseed oil (0, 0.1 and 1% w/w) on the degradation of polycyclic aromatic hydrocarbons (PAH) by Rhodococcus wratislaviensis was studied in soils artificially contaminated with phenanthrene, anthracene, pyrene and benzo(a)pyrene (50 mg kg⁻¹ each), during 49 days at 30 °C. Without or with 0.1% of rapeseed oil, R. wratislaviensis degraded >90% of phenanthrene and anthracene in 14 days and mineralised approx. 23% of ¹⁴C-phenanthrene. The native microflora degraded pyrene (90% degradation; 75% mineralisation) and benzo(a)pyrene (30% degradation, no mineralisation). With 1% rapeseed oil, R. wratislaviensis degraded only 66% of the phenanthrene and mineralised 12.4%, and had no effect on other PAH, while degradation by the native microflora was inhibited. On the other hand, the addition of 1% oil promoted degradation of benzo(a)pyrene (75%) and anthracene (90%) and anthraquinone was produced at high concentrations and accumulated. Two distinct processes gave degradation of PAH, one biological and one abiotic. Biological processes mainly degraded phenanthrene and pyrene, either by R. wratislaviensis or by the indigenous microflora. Benzo(a)pyrene was degraded mainly by an abiotic process in the presence of 1% rapeseed oil. Anthracene was degraded by a combination of both processes.PAH are often found in contaminated soils and there is the need of developing techniques that can be applied in the remediation of these sites, where PAH, specially those with high molecular weight, pose health and environmental risks. There is a continuous search for efficient microorganisms able to degrade these pollutants and for methods to enhance their degradation and bioavailability, e.g. by the use of vegetable oils. This paper presents a novel process for the degradation of PAH by a combined biological/abiotic system.     

Decontamination of aged creosote polluted soil: the influence of temperature,white rot fungus Pleurotus ostreatus,and pre-treatment

This study investigated the effect of inoculation of white rot fungus, Pleurotus ostreatus, temperature and two pre-treatment methods on PAH degradation in aged creosote contaminated soil. It is shown that Pleurotus ostreatus has an overall positive effect on PAH degradation, and that temperature and soil pre-treatment affect this degradation. In general, adding bark and incubating at 22°C before inoculation with white rot fungi has a better effect on PAH degradation than no pre-treatment, or pre-treatment with fertilizer. At low temperature (8°C) fungal inoculation had best effect when fertilizer was not added, and significant effect on degradation on different groups of PAH compounds, except for the more easily degradable compounds, 3-ring PAHs and heterocyclic compounds was obtained. Pre-treatment with fertilizer stimulated microbial activity at low temperature and enhanced PAH degradation even without addition of fungi.     

Reorganization of gene network for degradation of polycyclic aromatic hydrocarbons (PAHs) in <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> PAO1 under several conditions

Although polycyclic aromatic hydrocarbons (PAHs) are harmful to human health, their elimination from the environment is not easy. Biodegradation of PAHs is promising since many bacteria have the ability to use hydrocarbons as their sole carbon and energy sources for growth. Of various microorganisms that can degrade PAHs, Pseudomonas aeruginosa is particularly important, not only because it causes a series of diseases including infection in cystic fibrosis patients, but also because it is a model bacterium in various studies. The genes that are responsible for degrading PAHs have been identified in P. aeruginosa, however, no gene acts alone as various stresses often initiate different metabolic pathways, quorum sensing, biofilm formation, antibiotic tolerance, etc. Therefore, it is important to study how PAH degradation genes behave under different conditions. In this study, we apply network analysis to investigating how 46 PAH degradation genes reorganized among 5549 genes in P. aeruginosa PAO1 under nine different conditions using publicly available gene coexpression data from GEO. The results provide six aspects of novelties: (i) comparing the number of gene clusters before and after stresses, (ii) comparing the membership in each gene cluster before and after stresses, (iii) defining which gene changed its membership together with PAH degradation genes before and after stresses, (iv) classifying membership-changed-genes in terms of category in Pseudomonas Genome Database, (v) postulating unknown gene’s function, and (vi) proposing new mechanisms for genes of interests. This study can shed light on understanding of cooperative mechanisms of PAH degradation from the level of entire genes in an organism, and paves the way to conduct the similar studies on other genes.     

Uptake and Active Efflux of Polycyclic Aromatic Hydrocarbons by Pseudomonas fluorescens LP6a

The mechanism of transport of polycyclic aromatic hydrocarbons (PAHs) by Pseudomonas fluorescens LP6a, a PAH-degrading bacterium, was studied by inhibiting membrane transport and measuring the resulting change in cellular uptake. Three cultures were used: wild-type LP6a which carried a plasmid for PAH degradation, a transposon mutant lacking the first enzyme in the pathway for PAH degradation, and a cured strain without the plasmid. Washed cells were mixed with aqueous solutions of radiolabelled PAH; then the cells were removed by centrifugation, and the concentrations of PAH in the supernatant and the cell pellet were measured. The change in the pellet and supernatant concentrations after inhibitors of membrane transport (azide, cyanide, or carbonyl cyanide m-chlorophenyl hydrazone) were added indicated the role of active transport. The data were consistent with the presence of two conflicting transport mechanisms: uptake by passive diffusion and an energy-driven efflux system to transport PAHs out of the cell. The efflux mechanism was chromosomally encoded. Under the test conditions used, neither uptake nor efflux of phenanthrene by P. fluorescens LP6a was saturated. The efflux mechanism showed selectivity since phenanthrene, anthracene, and fluoranthene were transported out of the cell but naphthalene was not.     

Bioremediation of PAH-contaminated soil with fungi – From laboratory to field scale

The purpose of this study was to develop a fungal bioremediation method that could be used for soils heavily contaminated with persistent organic compounds, such as polyaromatic hydrocarbons (PAHs). Sawmill soil, contaminated with PAHs, was mixed with composted green waste (1:1) and incubated with or without fungal inoculum. The treatments were performed at the laboratory and field scales. In the laboratory scale treatment (starting concentration 3500 mg kg⁻¹, sum of 16 PAH) the high molecular weight PAHs were degraded significantly more in the fungal-inoculated microcosms than in the uninoculated ones. In the microcosms inoculated with Phanerochaete velutina, 96% of 4-ring PAHs and 39% of 5- and 6-ring PAHs were removed in three months. In the uninoculated microcosms, 55% of 4-ring PAHs and only 7% of 5- and 6-ring PAHs were degraded. However, during the field scale (2 t) experiment at lower starting concentration (1400 mg kg⁻¹, sum of 16 PAH) the % degradation was similar in both the P. velutina-inoculated and the uninoculated treatments: 94% of the 16 PAHs were degraded in three months. In the field scale experiment the copy number of gram-positive bacteria PAH-ring hydroxylating dioxygenase genes was found to increase 1000 fold, indicating that bacterial PAH degradation also played an important role.     

Microbial Diversity and PAH Catabolic Genes Tracking Spatial Heterogeneity of PAH Concentrations

We analyzed the within-site spatial heterogeneity of microbial community diversity, polyaromatic hydrocarbon (PAH) catabolic genotypes, and physiochemical soil properties at a creosote contaminated site. Genetic diversity and community structure were evaluated from an analysis of denaturant gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified sequences of 16S rRNA gene. The potential PAH degradation capability was determined from PCR amplification of a suit of aromatic dioxygenase genes. Microbial diversity, evenness, and PAH genotypes were patchily distributed, and hot and cold spots of their distribution coincided with hot and cold spots of the PAH distribution. The analyses revealed a positive covariation between microbial diversity, biomass, evenness, and PAH concentration, implying that the creosote contamination at this site promotes diversity and abundance. Three patchily distributed PAH-degrading genotypes, NAH, phnA, and pdo1, were identified, and their abundances were positively correlated with the PAH concentration and the fraction of soil organic carbon. The covariation of the PAH concentration with the number and spatial distribution of catabolic genotypes suggests that a field site capacity to degrade PAHs may vary with the extent of contamination.     

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

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

Predictors of mortality in connective tissue disease-associated pulmonary arterial hypertension: a cohort study

Introduction

Pulmonary arterial hypertension (PAH) is a major cause of mortality in connective tissue disease (CTD). We sought to quantify survival and determine factors predictive of mortality in a cohort of patients with CTD-associated PAH (CTD-PAH) in the current era of advanced PAH therapy.

Methods

Patients with right heart catheter proven CTD-PAH were recruited from six specialised PAH treatment centres across Australia and followed prospectively. Using survival methods including Cox proportional hazards regression, we modelled for all-cause mortality. Independent variables included demographic, clinical and hemodynamic data.

Results

Among 117 patients (104 (94.9%) with systemic sclerosis), during 2.6 ± 1.8 (mean ± SD) years of follow-up from PAH diagnosis, there were 32 (27.4%) deaths. One-, two- and three-year survivals were 94%, 89% and 73%, respectively. In multiple regression analysis, higher mean right atrial pressure (mRAP) at diagnosis (hazard ratio (HR) = 1.13, 95% CI: 1.04 to 1.24, P = 0.007), lower baseline six-minute walk distance (HR = 0.64, 95% CI: 0.43 to 0.97, P = 0.04), higher baseline World Health Organization functional class (HR = 3.42, 95% CI: 1.25 to 9.36, P = 0.04) and presence of a pericardial effusion (HR = 3.39, 95% CI: 1.07 to 10.68, P = 0.04) were predictive of mortality. Warfarin (HR = 0.20, 95% CI: 0.05 to 0.78, P = 0.02) and combination PAH therapy (HR = 0.20, 95% CI: 0.05 to 0.83, P = 0.03) were protective.

Conclusions

In this cohort of CTD-PAH patients, three-year survival was 73%. Independent therapeutic predictors of survival included warfarin and combination PAH therapy. Our findings suggest that anticoagulation and combination PAH therapy may improve survival in CTD-PAH. This observation merits further evaluation in randomised controlled trials.     

Degradation of phenanthrene,fluorene and fluoranthene by pure bacterial cultures

Summary Bacterial mixed cultures able to degrade the polycyclic aromatic hydrocarbons (PAH) phenanthrene, fluorene and fluoranthene, were obtained from soil using conventional enrichment techniques. From these mixed cultures three pure strains were isolated:Pseudomonas paucimobilis degrading phenanthrene;P. vesicularis degrading fluorene andAlcaligenes denitrificans degrading fluoranthene. The maximum rates of PAH degradation ranged from 1.0 mg phenanthrene/ml per day to 0.3 mg fluoranthene/ml per day at doubling times of 12 h to 35 h for growth on PAH as sole carbon source. The protein yield during PAH degradation was about 0.25 mg/mg C for all strains. Maximum PAH oxidation rates and optimum specific bacterial growth were obtained near pH 7.0 and 30°C. After growth entered the stationary phase, no dead end-products of PAH degradation could be detected in the culture fluid.     

Biodegradation of phenanthrene and pyrene by Ganoderma lucidum

Biodegradation of two polycyclic aromatic hydrocarbons (PAHs), phenanthrene and pyrene, by a white rot fungus, Ganoderma lucidum, in broth cultures was investigated. It was found that the biomass of the organism decreased with the increase of PAH concentration in the cultures. In the cultures with 2 to 50 mg l⁻¹ PAHs, the degradation rate constants (k₁) increased with the PAH concentration, whereas, at the level of 100 mg l⁻¹, the degradation rate constants decreased. In the presence of 20 mg l⁻¹ PAHs, the highest degradation rates of both PAHs occurred in cultures with an initial pH of 4.0 at 30 °C. The addition of CuSO₄, citric acid, gallic acid, tartaric acid, veratryl alcohol, guaiacol, 2,2′-azino-bis-(3- ethylbenzothazoline-6-sulfonate) (ABTS) enhanced the degradation of both PAHs and laccase activities; whereas the supplement of oxalate, di-n-butyl phthalate (DBP), and nonylphenol (NP) decreased the degradation of both PAHs and inhibited laccase production. In conclusion, G. lucidum is a promising white rot fungus to degrade PAHs such as phenanthrene and pyrene in the environment.     

Bacterial Community Dynamics and Polycyclic Aromatic Hydrocarbon Degradation during Bioremediation of Heavily Creosote-Contaminated Soil

Bacterial community dynamics and biodegradation processes were examined in a highly creosote-contaminated soil undergoing a range of laboratory-based bioremediation treatments. The dynamics of the eubacterial community, the number of heterotrophs and polycyclic aromatic hydrocarbon (PAH) degraders, and the total petroleum hydrocarbon (TPH) and PAH concentrations were monitored during the bioremediation process. TPH and PAHs were significantly degraded in all treatments (72 to 79% and 83 to 87%, respectively), and the biodegradation values were higher when nutrients were not added, especially for benzo(a)anthracene and chrysene. The moisture content and aeration were determined to be the key factors associated with PAH bioremediation. Neither biosurfactant addition, bioaugmentation, nor ferric octate addition led to differences in PAH or TPH biodegradation compared to biodegradation with nutrient treatment. All treatments resulted in a high first-order degradation rate during the first 45 days, which was markedly reduced after 90 days. A sharp increase in the size of the heterotrophic and PAH-degrading microbial populations was observed, which coincided with the highest rates of TPH and PAH biodegradation. At the end of the incubation period, PAH degraders were more prevalent in samples to which nutrients had not been added. Denaturing gradient gel electrophoresis analysis and principal-component analysis confirmed that there was a remarkable shift in the composition of the bacterial community due to both the biodegradation process and the addition of nutrients. At early stages of biodegradation, the α-Proteobacteria group (genera Sphingomonas and Azospirillum) was the dominant group in all treatments. At later stages, the γ-Proteobacteria group (genus Xanthomonas), the α-Proteobacteria group (genus Sphingomonas), and the Cytophaga-Flexibacter-Bacteroides group (Bacteroidetes) were the dominant groups in the nonnutrient treatment, while the γ-Proteobacteria group (genus Xathomonas), the β-Proteobacteria group (genera Alcaligenes and Achromobacter), and the α-Proteobacteria group (genus Sphingomonas) were the dominant groups in the nutrient treatment. This study shows that specific bacterial phylotypes are associated both with different phases of PAH degradation and with nutrient addition in a preadapted PAH-contaminated soil. Our findings also suggest that there are complex interactions between bacterial species and medium conditions that influence the biodegradation capacity of the microbial communities involved in bioremediation processes.     

The degradation of three-ringed polycyclic aromatic hydrocarbons by wood-inhabiting fungus Pleurotus ostreatus and soil-inhabiting fungus Agaricus bisporus

The degradation of two isomeric three-ringed polycyclic aromatic hydrocarbons by the white rot fungus Pleurotus ostreatus D1 and the litter-decomposing fungus Agaricus bisporus F-8 was studied. Despite some differences, the degradation of phenanthrene and anthracene followed the same scheme, forming quinone metabolites at the first stage. The further fate of these metabolites was determined by the composition of the ligninolytic enzyme complexes of the fungi. The quinone metabolites of phenanthrene and anthracene produced in the presence of only laccase were observed to accumulate, whereas those formed in presence of laccase and versatile peroxidase were metabolized further to form products that were further included in basal metabolism (e.g. phthalic acid). Laccase can catalyze the initial attack on the PAH molecule, which leads to the formation of quinones, and that peroxidase ensures their further oxidation, which eventually leads to PAH mineralization.A. bisporus, which produced only laccase, metabolized phenanthrene and anthracene to give the corresponding quinones as the dominant metabolites. No products of further utilization of these compounds were detected. Thus, the fungi's affiliation with different ecophysiological groups and their cultivation conditions affect the composition and dynamics of production of the ligninolytic enzyme complex and the completeness of PAH utilization.     

Indigenous PAH-degrading bacteria from oil-polluted sediments in Caleta Cordova,Patagonia Argentina

Indigenous bacteria with the capability to degrade polycyclic aromatic hydrocarbons (PAH) were isolated from polluted sediment samples recovered from Caleta Cordova by using selective enrichment cultures supplemented with phenanthrene. Bacterial communities were evaluated by denaturing gradient gel electrophoresis (DGGE) in order to detect changes along enrichment culture and relationships with the representative strains subsequently isolated. Members of these communities included marine bacteria such as Lutibacter, Polaribacter, Arcobacter and Olleya, whose degradation pathway of PAH has not been studied yet. However, isolated bacteria obtained from this enrichment comprised the genus Pseudomonas, Marinobacter, Salinibacterium and Brevibacterium. The ability of isolates to grow and degrade naphthalene, phenanthrene and pyrene was demonstrated by detection of the residual substrate by HPLC. Archetypical naphthalene and catechol dioxygenase genes were found in two isolates belonging to genus Pseudomonas (Pseudomonas monteilii P26 and Pseudomonas xanthomarina N12), suggesting biodegradation potential in these sediments. The successful bacterial isolation with the ability to degrade PAH in pure culture suggest the possibility to study and further consider strategies like growth stimulation in situ, in order to increase the intrinsic bioremediation opportunities in the polluted Caleta Cordova harbor.     

Bioremediation of a polyaromatic hydrocarbon contaminated soil by native soil microbiota and bioaugmentation with isolated microbial consortia

Biodegradation of a mixture of PAHs was assessed in forest soil microcosms performed either without or with bioaugmentation using individual fungi and bacterial and a fungal consortia. Respiratory activity, metabolic intermediates and extent of PAH degradation were determined. In all microcosms the low molecular weight PAH’s naphthalene, phenanthrene and anthracene, showed a rapid initial rate of removal. However, bioaugmentation did not significantly affect the biodegradation efficiency for these compounds. Significantly slower degradation rates were demonstrated for the high molecular weight PAH’s pyrene, benz[a]anthracene and benz[a]pyrene. Bioaugmentation did not improve the rate or extent of PAH degradation, except in the case of Aspergillus sp. Respiratory activity was determined by CO₂ evolution and correlated roughly with the rate and timing of PAH removal. This indicated that the PAHs were being used as an energy source. The native microbiota responded rapidly to the addition of the PAHs and demonstrated the ability to degrade all of the PAHs added to the soil, indicating their ability to remediate PAH-contaminated soils.     

Effect of surfactants on fluoranthene degradation by <Emphasis Type="Italic">Pseudomonas alcaligenes</Emphasis> PA-10

Two surfactants, Tween 80 and JBR, were investigated for their effect on fluoranthene degradation by a Pseudomonad. Both surfactants enhanced fluoranthene degradation by Pseudomonas alcaligenes PA-10 in shake flask culture. This bacterium was capable of utilising the synthetic surfactant and the biosurfactant as growth substrates and the critical micelle concentration of neither compound inhibited bacterial growth. The biosurfactant JBR significantly increased polycyclic aromatic hydrocarbon (PAH) desorption from soil. Inoculation of fluoranthene-contaminated soil microcosms with P. alcaligenes PA-10 resulted in the removal of significant amounts (45 ± 5%) of the PAH after 28 days compared to an uninoculated control. Addition of the biosurfactant increased the initial rate of fluoranthene degradation in the inoculated microcosm. The presence of a lower molecular weight PAH, phenanthrene, had a similar effect on the rate of fluoranthene removal.     

Impact of Inoculation Protocols, Salinity, and pH on the Degradation of Polycyclic Aromatic Hydrocarbons (PAHs) and Survival of PAH-Degrading Bacteria Introduced into Soil

Degradation of polycyclic aromatic hydrocarbons (PAHs) and survival of bacteria in soil was investigated by applying different inoculation protocols. The soil was inoculated with Sphingomonas paucimobilis BA 2 and strain BP 9, which are able to degrade anthracene and pyrene, respectively. CFU of soil bacteria and of the introduced bacteria were monitored in native and sterilized soil at different pHs. Introduction with mineral medium inhibited PAH degradation by the autochthonous microflora and by the strains tested. After introduction with water (without increase of the pore water salinity), no inhibition of the autochthonous microflora was observed and both strains exhibited PAH degradation.