Bioavailability of solid and non-aqueous phase liquid (NAPL)-dissolved phenanthrene to the biosurfactant-producing bacterium Pseudomonas aeruginosa 19SJ

Design and construction of an artificial labor-division consortium for phenanthrene degradation with three-functional modules

Polycyclic Aromatic Hydrocarbons (PAHs) are highly toxic organic pollutants. Phenanthrene often serves as a model compound for studying PAHs biodegradation. In this work, we firstly engineered Escherichia coli M01 containing seven phenanthrene degradation genes and combined it with existing engineered strains E. coli M2 and M3 to form an artificial three-bacteria consortium, named M0123, which exhibited a degradation ratio of 64.66% for 100 mg/L of phenanthrene over 8 days. Subsequently, we constructed engineered Pseudomonas putida KTRL02 which could produce 928.49 mg/L rhamnolipids and integrated it with M0123, forming a four-bacteria consortium with an impressive 81.62% phenanthrene degradation ratio. Assessment of extracellular adenosine levels during the degradation process indicated high cellular energy demand in the four-bacteria consortium. Then, we introduced Bacillus subtilis RH33, a riboflavin-producing strain, as an energy-supplying bacterium, to create a five-bacteria consortium, which exhibited an 88.19% degradation ratio for phenanthrene. The NADH/NAD+ ratio in the five-bacteria consortium during the degradation process was monitored, which was consistently higher than that of the four-bacteria consortium over the eight-day period, indicating a higher overall intracellular reduction capacity. Furthermore, the five-bacteria consortium displayed good tolerance to phenanthrene, even achieving a degradation ratio of 79.38% for 500 mg/L of phenanthrene. This study demonstrates that designing and constructing artificial consortia from the functional perspective and various angles can effectively enhance the degradation of phenanthrene after the addition of the energy-supplying bacterium. This study demonstrates that designing and constructing artificial labor-division consortia from the functional perspective and various angles can effectively enhance the degradation of phenanthrene.

From Antagonism to Enhancement: Triton X-100 Surfactant Affects Phenanthrene Interfacial Biodegradation by Mycobacteria through a Shift in Uptake Mechanisms

Polycyclic aromatic hydrocarbons (PAHs), as persistent environmental pollutants, often reside in nonaqueous-phase liquids (NAPLs). Mycobacterium sp. WY10, boasting highly hydrophobic surfaces, can adsorb to the oil-water interface, stabilizing the Pickering emulsion and directly accessing PAHs for biodegradation. We investigated the impact of Triton X-100 (TX100) on this interfacial uptake of phenanthrene (PHE) by Mycobacteria, using n-tetradecane (TET) and bis-(2-ethylhexyl) phthalate (DEHP) as NAPLs. Interfacial tension, phase behavior, and emulsion stability studies, alongside confocal laser scanning microscopy and electron microscope observations, unveiled the intricate interplay. In surfactant-free systems, Mycobacteria formed stable W/O Pickering emulsions, directly degrading PHE within the NAPLs because of their intimate contact. Introducing low-dose TX100 disrupted this relationship. Preferentially binding to the cells, the surfactant drastically increased the cell hydrophobicity, triggering desorption from the interface and phase separation. Consequently, PAH degradation plummeted due to hindered NAPL access. Higher TX100 concentrations flipped the script, creating surfactant-stabilized O/W emulsions devoid of interfacial cells. Surprisingly, PAH degradation remained efficient. This paradox can be attributed to NAPL emulsification, driven by the surfactant, which enhanced mass transfer and brought the substrate closer to the cells, despite their absence at the interface. This study sheds light on the complex effect of surfactants on Mycobacteria and PAH uptake, revealing an antagonistic effect at low concentrations that ultimately leads to enhanced degradation through emulsification at higher doses. These findings offer valuable insights into optimizing bioremediation strategies in PAH-contaminated environments.

Biodegradation of Crystalline and Nonaqueous Phase Liquid-Dissolved ATRAZINE by Arthrobacter sp. ST11 with Cd2+ Resistance

A newly isolated cadmium (Cd)-resistant bacterial strain from herbicides-polluted soil in China could use atrazine as the sole carbon, nitrogen, and energy source for growth in a mineral salt medium (MSM). Based on 16S rRNA gene sequence analysis and physiochemical tests, the bacterium was identified as Arthrobacter sp. and named ST11. The biodegradation of atrazine by ST11 was investigated in experiments, with the compound present either as crystals or dissolved in di(2-ethylhexyl) phthalate (DEHP) as a non-aqueous phase liquid (NAPL). After 48 h, ST11 consumed 68% of the crystalline atrazine in MSM. After being dissolved in DEHP, the degradation ratio of atrazine was reduced to 55% under the same conditions. Obviously, the NAPL-dissolved atrazine has lower bioavailability than the crystalline atrazine. Cd2+ at concentrations of 0.05–1.5 mmol/L either had no effect (<0.3 mmol/L), slight effects (0.5–1.0 mmol/L), or significantly (1.5 mmol/L) inhibited the growth of ST11 in Luria-Bertani medium. Correspondingly, in the whole concentration range (0.05–1.5 mmol/L), Cd2+ promoted ST11 to degrade atrazine, whether crystalline or dissolved in DEHP. Refusal to adsorb Cd2+ may be the main mechanism of high Cd resistance in ST11 cells. These results may provide valuable insights for the microbial treatment of arable soil co-polluted by atrazine and Cd.

Interfacial biodegradation of phenanthrene in bacteria-carboxymethyl cellulose-stabilized Pickering emulsions

The limited bioavailability of PAHs in non-aqueous phase liquid (NAPL) limits their degradation. The biodegradation of phenanthrene in n-tetradecane by hydrophilic bacterium Moraxella sp. CFP312 was studied with the assistance of two polymers, chitosan and carboxymethyl cellulose (CMC). Both chitosan and CMC improved the cell hydrophobicity of CFP312 and increased the contact angle of CFP312 cells from 30.4 to 78.5 and 88.5, respectively. However, CMC increased the degradation ratio of phenanthrene from 45 to nearly 100%, while chitosan did not cause any improvement. We found that CMC was more effective than chitosan in promoting CFP312 to stabilize Pickering emulsion. In the bacteria-CMC complex system, oil was dispersed into small droplets to obtain a high emulsification index and large specific surface area. Moreover, according to the microscopic image of the bacteria-CMC emulsion droplet, we observed that the droplet surface was tightly covered by the CFP312 cells. Therefore, CFP312 cells joined with CMC can utilize phenanthrene in oil phase at the oil-water interface. This study will offer a new strategy for effective microbial degradation of hydrophobic compounds in NAPLs by hydrophilic bacteria. KEY POINTS: • Biodegradation of phenanthrene in Pickering emulsions • Pickering emulsions stabilized by hydrophilic CFP312 joined with CMC. • Phenanthrene was degraded by CFP312 at oil-water interface.

Low molecular weight organic acids enhance the high molecular weight polycyclic aromatic hydrocarbons degradation by bacteria

The biodegradation potential of three bacterial cultures isolated from the rhizosphere of maize (Zea mays) and Sudan grass (Sorghum sudanense) grown in PAHs contaminated soils to degrade benzo[a]pyrene (BaP) and pyrene (PYR) was assessed. Of the three bacterial cultures isolated, two belonged to Gram-positive bacteria of phylum Actinobacteria namely Arthrobacter sp. MAL3 and Microbacterium sp. MAL2. The Gram-negative bacterial culture was Stenotrophomonas sp. MAL1, from the phylum Proteobacteria. The cultures were grown in the presence of BaP and PYR as sole carbon sources and with the addition of low molecular weight organic acids (LMWOAs) mixture. After 10-14 days of exposure, all the bacterial isolates exhibited a complete degradation of PYR with the addition of LMWOAs mixture, whereas only 38.7% of BaP was degraded by Stenotrophomonas sp. MAL1 with the addition of LMWOAs mixture. In addition, enhanced PAHs biodegradation by bacterial culture was observed when the PAHs present as mixture (BaP + PYR) with the addition of LMWOAs. Dioxygenase genes were detected in Stenotrophomonas sp. MAL1 (phnAC), and Arthrobacter sp. MAL3 (nidA and PAH-RHDα). Therefore, this study provides new insights on the influence of LMWOAs in enhancing the degradation of high molecular weight (HMW) PAHs in soil by rhizosphere bacterial cultures.

Advances in applications of rhamnolipids biosurfactant in environmental remediation: A review

The objective of this review is to provide a comprehensive overview of the advances in the applications of rhamnolipids biosurfactants in soil and ground water remediation for removal of petroleum hydrocarbon and heavy metal contaminants. The properties of rhamnolipids associated with the contaminant removal, that is, solubilization, emulsification, dispersion, foaming, wetting, complexation, and the ability to modify bacterial cell surface properties, were reviewed in the first place. Then current remediation technologies with integration of rhamnolipid were summarized, and the effects and mechanisms for rhamnolipid to facilitate contaminant removal for these technologies were discussed. Finally rhamnolipid-based methods for remediation of the sites co-contaminated by petroleum hydrocarbons and heavy metals were presented and discussed. The review is expected to enhance our understanding on environmental aspects of rhamnolipid and provide some important information to guide the extending use of this fascinating chemical in remediation applications.

Mycelium-Enhanced Bacterial Degradation of Organic Pollutants under Bioavailability Restrictions

This work examines the role of mycelia in enhancing the degradation by attached bacteria of organic pollutants that have poor bioavailability. Two oomycetes, Pythium oligandrum and Pythium aphanidermatum, were selected as producers of mycelial networks, while Mycobacterium gilvum VM552 served as a model polycyclic aromatic hydrocarbon (PAH) degrading bacterium. The experiments consisted of bacterial cultures exposed to a nondisturbed nonaqueous phase liquid (NAPL) layer containing a heavy fuel spiked with ¹⁴C-labeled phenanthrene that were incubated in the presence or absence of the mycelia of the oomycetes in both shaking and static conditions. At the end of the incubation, the changes in the total alkane and PAH contents in the NAPL residue were quantified. The results revealed that with shaking and the absence of mycelia, the strain VM552 grew by utilizing the bulk of alkanes and PAHs in the fuel; however, biofilm formation was incipient and phenanthrene was mineralized following zero-order kinetics, due to bioavailability limitations. The addition of mycelia favored biofilm formation and dramatically enhanced the mineralization of phenanthrene, up to 30 times greater than the rate without mycelia, possibly by providing a physical support to bacterial colonization and by supplying nutrients at the NAPL/water interface. The results in the static condition were very different because the bacterial strain alone degraded phenanthrene with sigmoidal kinetics but could not degrade alkanes or the bulk of PAHs. We suggest that bacteria/oomycete interactions should be considered not only in the design of new inoculants in bioremediation but also in biodegradation assessments of chemicals present in natural environments.

Phytoremediation effect of Scirpus triqueter inoculated plant-growth-promoting bacteria (PGPB) on different fractions of pyrene and Ni in co-contaminated soils

At present, few reveal the mechanism of inoculation plants with PGPB to remediate PAH-metal co-contaminated soil by analyzing the chemical speciations of contaminants. This study investigated the influence of inoculation plants with PGPB on different fractions of pyrene and Ni in rhizospheric and non-rhizospheric soil. The results demonstrated that the addition of PGPB brought the extensive increase of FDA activities in pyrene-Ni co-contaminated soil. PGPB increased the resistance of plants in nickel and pyrene-Ni contaminated soil, but decreased the plant biomass in single pyrene contaminated soil. The addition of PGPB efficiently decreased bioaccessible fractions of pyrene and increased the bioavailability of Ni in both rhizospheric and non-rhizospheric soil. Although inoculation plants with PGPB significantly increased the accumulation of Ni in single Ni and pyrene-Ni co-contaminated soil, the poor bioavailability of Ni in rhizospheric soil still restricted the phytoremediation of the heavy metal. The presence of pyrene hindered the inoculated plant from accumulating Ni to some extent. On the contrary, the presence of Ni significantly promoted the degradation of pyrene in both rhizospheric and non-rhizospheric soil after inoculation plants with PGPB.

Biodegradation and dissolution of polyaromatic hydrocarbons by Stenotrophomonas sp

The aim of this work was to study the biodegradation capabilities of a locally isolated bacterium, Stenotrophomonas sp. strain IITR87 to degrade the polycyclic aromatic hydrocarbons and also check the preferential biodegradation of polycyclic aromatic hydrocarbons (PAHs). From preferential substrate degradation studies, it was found that Stenotrophomonas sp. strain IITR87 first utilized phenanthrene (three membered ring), followed by pyrene (four membered ring), then benzo[α]pyrene (five membered ring). Dissolution study of PAHs with surfactants, rhamnolipid and tritonX-100 showed that the dissolution of PAHs increased in the presence of surfactants.

Anoxic biodegradation of petroleum hydrocarbons in saline media using denitrifier biogranules

The total petroleum hydrocarbons (TPH) biodegradation was examined using biogranules at different initial TPH concentration and contact time under anoxic condition in saline media. The circular compact biogranules having the average diameter between 2 and 3mm were composed of a dense population of Bacillus spp. capable of biodegrading TPH under anoxic condition in saline media were formed in first step of the study. The biogranules could biodegrade over 99% of the TPH at initial concentration up to 2g/L at the contact time of 22h under anoxic condition in saline media. The maximum TPH biodegradation rate of 2.6 gTPH/gbiomass.d could be obtained at initial TPH concentration of 10g/L. Accordingly, the anoxic biogranulation is a possible and promising technique for high-rate biodegradation of petroleum hydrocarbons in saline media.

Extractive biodegradation and bioavailability assessment of phenanthrene in the cloud point system by Sphingomonas polyaromaticivorans

The biological treatment of polycyclic aromatic hydrocarbons is an important issue. Most microbes have limited practical applications because of the poor bioavailability of polycyclic aromatic hydrocarbons. In this study, the extractive biodegradation of phenanthrene by Sphingomonas polyaromaticivorans was conducted by introducing the cloud point system. The cloud point system is composed of a mixture of (40 g/L) Brij 30 and Tergitol TMN-3, which are nonionic surfactants, in equal proportions. After phenanthrene degradation, a higher wet cell weight and lower phenanthrene residue were obtained in the cloud point system than that in the control system. According to the results of high-performance liquid chromatography, the residual phenanthrene preferred to partition from the dilute phase into the coacervate phase. The concentration of residual phenanthrene in the dilute phase (below 0.001 mg/L) is lower than its solubility in water (1.18 mg/L) after extractive biodegradation. Therefore, dilute phase detoxification was achieved, thus indicating that the dilute phase could be discharged without causing phenanthrene pollution. Bioavailability was assessed by introducing the apparent logP in the cloud point system. Apparent logP decreased significantly, thus indicating that the bioavailability of phenanthrene increased remarkably in the system. This study provides a potential application of biological treatment in water and soil contaminated by phenanthrene.

Development of eukaryotic zoospores within polycyclic aromatic hydrocarbon (PAH)-polluted environments: a set of behaviors that are relevant for bioremediation

In this study, we assessed the development (formation, taxis and settlement) of eukaryotic zoospores under different regimes of exposure to polycyclic aromatic hydrocarbons (PAHs), which imitated environmental scenarios of pollution and bioremediation. With this aim, we used an oomycete, Pythium aphanidermatum, as a source of zoospores and two PAH-degrading bacteria (Mycobacterium gilvum VM552 and Pseudomonas putida G7). The oomycete and both bacteria were not antagonistic, and zoospore formation was diminished only in the presence of the highest bacterial cell density (10(8)-10(10) colony-forming units mL(-1)). A negative influence of PAHs on zoospore formation and taxis was observed when PAHs were exposed in combination with organic solutions and polar solvents. Co-exposure of PAHs with non-polar solvents [hexadecane (HD) and 2,2,4,4,6,8,8-heptamethylnonane (HMN)] did not affect zoospore settlement at the interfaces of the organic solvents and water. However, zoospores settled and created mycelial networks only at HD-water interfaces. Both bacteria diminished the toxic influence of PAHs on zoospore formation and taxis, and they did not interrupt zoospore settlement. The results suggest that zoospore development could be applicable for toxicity assessment of PAHs and enhancement of their bioavailability. Microbial interactions during both swimming modes and community formation at pollutant interfaces were revealed as major factors that have potential relevance to bioremediation.

Role of desorption kinetics in the rhamnolipid-enhanced biodegradation of polycyclic aromatic hydrocarbons

The main aim of this study was to investigate the effect of a rhamnolipid biosurfactant on biodegradation of (14)C-labeled phenanthrene and pyrene under desorption-limiting conditions. The rhamnolipid caused a significant solubilization and enhanced biodegradation of PAHs sorbed to soils. The enhancement was, however, negatively influenced by experimental conditions that caused an enrichment of slow desorption fractions. These conditions included aging, a higher organic matter content in soil, and previous extraction with Tenax to remove the labile-desorbing chemical. The decline in bioavailability caused by aging on sorbed (14)C-pyrene was partially reversed by rhamnolipids, which enhanced mineralization of the aged compound, although not so efficiently like with the unaged chemical. This loss in biosurfactant efficiency in promoting biodegradation can be explained by intra-aggregate diffusion of the pollutant during aging. We suggest that rhamnolipid can enhance biodegradation of soil-sorbed PAHs by micellar solubilization, which increase the cell exposure to the chemicals in the aqueous phase, and partitioning into soil organic matter, thus enhancing the kinetics of slow desorption. Our study show that rhamnolipid can constitute a valid alternative to chemical surfactants in promoting the biodegradation of slow desorption PAHs, which constitutes a major bottleneck in bioremediation.

Low occurrence of Pseudomonas aeruginosa in agricultural soils with and without organic amendment

The occurrence of Pseudomonas aeruginosa was monitored at a broad spatial scale in French agricultural soils, from various soil types and under various land uses to evaluate the ability of soil to be a natural habitat for that species. To appreciate the impact of agricultural practices on the potential dispersion of P. aeruginosa, we further investigated the impact of organic amendment at experimental sites in France and Burkina Faso. A real-time quantitative PCR (qPCR) approach was used to analyze a set of 380 samples selected within the French RMQS (“Réseau de Mesures de la Qualité des Sols”) soil library. In parallel, a culture-dependent approach was tested on a subset of samples. The results showed that P. aeruginosa was very rarely detected suggesting a sporadic presence of this bacterium in soils from France and Burkina Faso, whatever the structural and physico-chemical characteristics or climate. When we analyzed the impact of organic amendment on the prevalence of P. aeruginosa, we found that even if it was detectable in various manures (at levels from 10³ to 10⁵ CFU or DNA targets (g drywt)⁻¹ of sample), it was hardly ever detected in the corresponding soils, which raises questions about its survival. The only case reports were from a vineyard soil amended with a compost of mushroom manure in Burgundy, and a few samples from two fields amended with raw urban wastes in the sub-urban area of Ouagadougou, Burkina Faso. In these soils the levels of culturable cells were below 10 CFU (g drywt)⁻¹.

Is it possible to increase bioavailability but not environmental risk of PAHs in bioremediation?

The current poor predictability of end points associated with the bioremediation of polycyclic aromatic hydrocarbons (PAHs) is a large limitation when evaluating its viability for treating contaminated soils and sediments. However, we have seen a wide range of innovations in recent years, such as an the improved use of surfactants, the chemotactic mobilization of bacterial inoculants, the selective biostimulation at pollutant interfaces, rhizoremediation and electrobioremediation, which increase the bioavailability of PAHs but do not necessarily increase the risk to the environment. The integration of these strategies into practical remediation protocols would be beneficial to the bioremediation industry, as well as improve the quality of the environment.

Chemotaxis in polycyclic aromatic hydrocarbon-degrading bacteria isolated from coal-tar- and oil-polluted rhizospheres

Abstract The limited mass transfer in polycyclic aromatic hydrocarbon (PAH)-contaminated soils during bioremediation treatments often impedes the achievement of regulatory decontamination end-points. Little is known about bioavailability of these hydrophobic pollutants in phytoremediation systems. This work attempts to evaluate, for the first time, chemotaxis as a bioavailability-promoting trait in PAH-degrading bacteria from the rhizosphere. For this aim, 20 motile strains capable of degrading different PAHs were isolated from rhizosphere soils contaminated with coal tar and oil. Three representative Pseudomonas strains were selected, on the basis of their faster growth and/or range of PAHs degraded, for detailed chemotaxis studies with PAHs (naphthalene, phenanthrene, anthracene, and pyrene), bacterial lipopolysaccharide and root exudates from seven different plants. The chemotactic response was quantified with a new densitometric method. The results indicate that chemotaxis is a relevant mobilizing factor for PAH-degrading rhizosphere bacteria.

Emulsifying agent production during PAHs degradation by the white rot fungus Pleurotus ostreatus D1

For the first time the production of an emulsifying agent during phthalic, 2,2'-diphenic and alpha-hydroxy-beta-naphthoic acids, phenanthrene, anthracene, fluorene, pyrene, fluoranthene, and chrysene degradation by white rot fungus Pleurotus ostreatus was found. The emulsifying activity of the cultivation medium after degradation of these compounds was assessed. Maximal activities were found in the presence of chrysene (48.4%) and alpha-hydroxy-beta-naphthoic acid (52.2%). Emulsifying activity inversely dependent on the water solubility of the compounds used. Versatile peroxidase was produced concurrently with the emulsifying agent.

Bacterial metabolism of polycyclic aromatic hydrocarbons: strategies for bioremediation

Polycyclic aromatic hydrocarbons (PAHs) are compounds of intense public concern due to their persistence in the environment and potentially deleterious effects on human, environmental and ecological health. The clean up of such contaminants using invasive technologies has proven to be expensive and more importantly often damaging to the natural resource properties of the soil, sediment or aquifer. Bioremediation, which exploits the metabolic potential of microbes for the clean-up of recalcitrant xenobiotic compounds, has come up as a promising alternative. Several approaches such as improvement in PAH solubilization and entry into the cell, pathway and enzyme engineering and control of enzyme expression etc. are in development but far from complete. Successful application of the microorganisms for the bioremediation of PAH-contaminated sites therefore requires a deeper understanding of the physiology, biochemistry and molecular genetics of potential catabolic pathways. In this review, we briefly summarize important strategies adopted for PAH bioremediation and discuss the potential for their improvement.

Chemoeffectors decrease the deposition of chemotactic bacteria during transport in porous media

Bacterial chemotaxis enables motile cells to move along chemical gradients and to swim toward optimal places for biodegradation. However, its potentially positive effects on subsurface remediation rely on the efficiency of bacterial movement in porous media, which is often restricted by high deposition rates and adhesion to soil surfaces. In well-controlled column systems, we assessed the influence of the chemo-effectors naphthalene, salicylate, fumarate, and acetate on deposition of chemotactic, naphthalene-degrading Pseudomonas putida G7 in selected porous environments (sand, forest soil, and clay aggregates). Our data showed that the presence of naphthalene in the pore water decreased deposition of strain 67 (but not of a derivative strain, P. putida 67.C1 (pHG100), nonchemotactic to naphthalene) by 50% in sand-filled columns, as calculated by the relative adhesion efficiency (at). Similar effects were observed with P. putida G7 strain for the other chemoeffectors. Deposition, however, depended on the chemoeffector's chemical structure, its interaction with the column packing material, and concomitantly its pore-water concentration. As the presence of the chemoeffectors had no influence on the physicochemical surface properties of the bacteria, we suggest that chemotactic sensing, combined with changed swimming modes, is likely to influence the deposition of bacteria in the subsurface, provided that the chemoeffector is dissolved at sufficient concentration in the pore water.

Characterization of a moderate thermophilic Nocardia species able to grow on polycyclic aromatic hydrocarbons

AIMS

Our goal was the characterization of a new moderate thermophilic polycyclic aromatic hydrocarbon (PAH)-utilizing Nocardia strain.

METHODS AND RESULTS

A thermophilic bacterium, strain TSH1, was isolated from a contaminated soil. The macroscopic and microscopic features fit well with the description of Nocardia species. The results of 16S rRNA gene analysis showed 100% match to the type strain of N. otitidiscaviarum DSM 43242(T). Strain TSH1 showed the same mycolic acid pattern as the type strain of N. otitidiscaviarum but its fatty acid profile did not permit identification to the species level. The carbon utilization profile of strain TSH1 was different from N. otitidiscaviarum. The results of hydrophobicity measurements showed that PAHs-grown cells were significantly more hydrophobic than LB-grown cells. Furthermore, biosurfactant production was detected during bacterial growth on different culture media.

CONCLUSIONS

Strain TSH1 is capable of growing on a range of PAHs. When grown in PAHs-supplemented media, strain TSH1 showed a high affinity for the organic phase, suggesting that it can develop a hydrophobic surface.

SIGNIFICANCE AND IMPACT OF THE STUDY

High cell surface hydrophobicity and capability of strain TSH1 to degrade different PAHs at 50 degrees C may make it an ideal candidate to treat PAH-contaminated desert soils.

Differential responses of eubacterial, Mycobacterium, and Sphingomonas communities in polycyclic aromatic hydrocarbon (PAH)-contaminated soil to artificially induced changes in PAH profile

Recent reports suggest that Mycobacterium is better adapted to soils containing poorly bioavailable polycyclic aromatic hydrocarbons (PAHs) compared to Sphingomonas. To study this hypothesis, artificial conditions regarding PAH profile and PAH bioavailability were induced in two PAH-contaminated soils and the response of the eubacterial, Mycobacterium, and Sphingomonas communities to these changed conditions was monitored during laboratory incubation. Soil K3663 with a relatively high proportion of high molecular weight PAHs was amended with phenanthrene or pyrene to artificially change the soil into a soil with a relatively increased bioavailable PAH contamination. Soil AndE with a relatively high proportion of bioavailable low molecular weight PAHs was treated by a single-step Tenax extraction to remove the largest part of the easily bioavailable PAH contamination. In soil K3663, the added phenanthrene or pyrene compounds were rapidly degraded, concomitant with a significant increase in the number of phenanthrene and pyrene degraders, and minor and no changes in the Mycobacterium community and Sphingomonas community, respectively. However, a transient change in the eubacterial community related to the proliferation of several gamma-proteobacteria was noted in the phenanthrene-amended soil. In the extracted AndE soil, the Sphingomonas community initially developed into a more diverse community but finally decreased in size below the detection limit. Mycobacterium in that soil never increased to a detectable size, while the eubacterial community became dominated by a gamma-proteobacterial population. The results suggest that the relative bioavailability of PAH contamination in soil affects bacterial community structure but that the behavior of Mycobacterium and Sphingomonas in soil is more complex than prospected from studies on their ecology and physiology.

Influence of a nonaqueous phase liquid (NAPL) on biodegradation of phenanthrene

A series of batch reactor experiments was carried out to examine the effect of a nonaqueous phase liquid (NAPL) on the biodegradation of a hydrophobic solute. A mathematical program model that describes physical processes of solute solubilization and partitioning between the NAPL and aqueous phases as well as microbial degradation and oxygen utilization was used to analyze the test data. The model calculates the cumulative changes in concentration of substrate, cell mass, carbon dioxide, and dissolved oxygen as a function of time. The equations incorporate the effects of solute solubilization, partitioning, biodegradation, as well as oxygen availability. Hexadecane was used as the model NAPL and was not biodegraded in the timeframe of the experiments performed. The model solute was the polyaromatic hydrocarbon, phenanthrene. In agreement with several previous studies, experimental measurements showed that hexadecane increased rates of mineralization of 15 mg phenanthrene when present at low mass but decreased rates at high mass. Model results suggest that partitioning of the phenanthrene into the hexadecane phase limits bioavailability at high NAPL mass. Further the model suggests that mineralization rates were higher with the low NAPL mass because aqueous phenanthrene concentrations were higher in those treatments from ca. 20 to 40 h than in other treatments. Finally, experiments showed that the presence of hexadecane, at all masses tested, resulted in a lower cell yield, effectively increasing the amount of CO(2) produced during the experiment. Model results suggest that this is due to changes in phenanthrene metabolism that are induced by the presence of the hexadecane phase. Model studies aimed at increasing rates of biodegradation by modifying operating conditions are described along with practical approaches to implementing these modifications.

Environmental applications for biosurfactants

Biosurfactants are surfactants that are produced extracellularly or as part of the cell membrane by bacteria, yeasts and fungi. Examples include Pseudomonas aeruginosa which produces rhamnolipids, Candida (formerly Torulopsis) bombicola, one of the few yeasts to produce biosurfactants, which produces high yields of sophorolipids from vegetable oils and sugars and Bacillus subtilis which produces a lipopeptide called surfactin. This review includes environmental applications of these biosurfactants for soil and water treatment. Biosurfactant applications in the environmental industries are promising due to their biodegradability, low toxicity and effectiveness in enhancing biodegradation and solubilization of low solubility compounds. However, more information is needed to be able to predict and model their behaviour. Full scale tests will be required. The role of biosurfactants in natural attenuation processes has not been determined. Very little information is available concerning the influence of soil components on the remediation process with biosurfactants. As most of the research until now has been performed with rhamnolipids, other biosurfactants need to be investigated as they may have more promising properties.

Characterization of two Pseudomonas putida lipopeptide biosurfactants, putisolvin I and II, which inhibit biofilm formation and break down existing biofilms

Pseudomonas putida strain PCL1445 was isolated from roots of plants, grown on a site polluted with polycyclic aromatic hydrocarbons. PCL1445 produces biosurfactant activity at the end of the exponential growth phase. High-performance liquid chromatography (HPLC) analysis of supernatant extracts of PCL1445 showed two peaks with surface-tension reducing activity, tentatively assigned as biosurfactants putisolvin I and putisolvin II and was followed by structural analyses. A transposon mutant of PCL1445, strain PCL1436, which lacks the two surface-active peaks appeared to be mutated in an open reading frame (ORF) with amino acid homology to various lipopeptide synthetases. Structural analyses of the two biosurfactants of PCL1445 revealed that both are novel cyclic lipodepsipeptides with a hexanoic lipid chain connected to the N-terminus of a 12-amino-acid peptide moiety, in which the C-terminal carboxylic acid group forms an ester with the hydroxyl side-chain of Ser9. The difference between the two structures is located in the second amino acid from the C-terminus, being valine for putisolvin I, and leucine/isoleucine for putisolvin II. We show that these novel compounds lower the surface tension and influence the biofilm development on polyvinyl chloride (PVC). Biofilm formation of the bio-synthetic mutant PCL1436 was strongly increased containing more cells, which formed aggregates earlier as compared with wild-type PCL1445 biofilms. Using purified putisolvin I and II it was shown that biofilm formation of different Pseudomonas strains was inhibited and most interestingly, that both putisolvins are also able to break down existing Pseudomonas biofilms.

Saturable, energy-dependent uptake of phenanthrene in aqueous phase by Mycobacterium sp. strain RJGII-135

The mechanism of uptake of phenanthrene by Mycobacterium sp. strain RJGII-135, a polycyclic hydrocarbon-degrading bacterium, was examined with cultures grown on phenanthrene (induced for phenanthrene metabolism) and acetate (uninduced). Washed cells were suspended in aqueous solutions of [9-(14)C]phenanthrene, and then the cells were collected by filtration. Low-level steady-state (14)C concentrations in uninduced cells were achieved within the first 15 s of incubation. This immediate uptake did not show saturation kinetics and was not susceptible to inhibitors of active transport, cyanide and carbonyl cyanide m-chlorophenylhydrazone. These results indicated that phenanthrene enters rapidly into the cells by passive diffusion. However, induced cells showed cumulative uptake over several minutes. The initial uptake rates followed saturation kinetics, with an apparent affinity constant (K(t)) of 26 +/- 3 nM (mean +/- standard deviation). Uptake of phenanthrene by induced cells was strongly inhibited by the inhibitors. Analysis of cell-associated (14)C-labeled compounds revealed that the concurrent metabolism during uptake was rapid and was not saturated at the substrate concentrations tested, suggesting that the saturable uptake observed reflects membrane transport rather than intracellular metabolism. These results were consistent with the presence of a saturable, energy-dependent mechanism for transport of phenanthrene in induced cells. Moreover, the kinetic data for the cumulative uptake suggested that phenanthrene is specifically bound by induced cells, based on its saturation with an apparent dissociation constant (K(d)) of 41 +/- 21 nM (mean +/- standard deviation). Given the low values of K(t) and K(d), Mycobacterium sp. strain RJGII-135 may use a high-affinity transport system(s) to take up phenanthrene from the aqueous phase.

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.