Showing papers by "Pedro J. J. Alvarez published in 2004"

Repression of Pseudomonas putida phenanthrene‐degrading activity by plant root extracts and exudates

Abstract: The phenanthrene-degrading activity (PDA) of Pseudomonas putida ATCC 17484 was repressed after incubation with plant root extracts of oat (Avena sativa), osage orange (Maclura pomifera), hybrid willow (Salix alba x matsudana), kou (Cordia subcordata) and milo (Thespesia populnea) and plant root exudates of oat (Avena sativa) and hybrid poplar (Populus deltoides x nigra DN34). Total organic carbon content of root extracts ranged from 103 to 395 mg l(-1). Characterization of root extracts identified acetate (not detectable to 8.0 mg l(-1)), amino acids (1.7-17.3 mg l(-1)) and glucose (1.6-14.0 mg l(-1)), indicating a complex mixture of substrates. Repression was also observed after exposure to potential root-derived substrates, including organic acids, glucose (carbohydrate) and glutamate (amino acid). Carbon source regulation (e.g. catabolite repression) was apparently responsible for the observed repression of P. putida PDA by root extracts. However, we showed that P. putida grows on root extracts and exudates as sole carbon and energy sources. Enhanced growth on root products may compensate for partial repression, because larger microbial populations are conducive to faster degradation rates. This would explain the commonly reported increase in phenanthrene removal in the rhizosphere.

Enhanced Anaerobic Biodegradation of Benzene-Toluene-Ethylbenzene-Xylene-Ethanol Mixtures in Bioaugmented Aquifer Columns

Abstract: Methanogenic flowthrough aquifer columns were used to investigate the potential of bioaugmentation to enhance anaerobic benzene-toluene-ethylbenzene-xylene (BTEX) degradation in groundwater contaminated with ethanol-blended gasoline. Two different methanogenic consortia (enriched with benzene or toluene and o-xylene) were used as inocula. Toluene was the only hydrocarbon degraded within 3 years in columns that were not bioaugmented, although anaerobic toluene degradation was observed after only 2 years of acclimation. Significant benzene biodegradation (up to 88%) was observed only in a column bioaugmented with the benzene-enriched methanogenic consortium, and this removal efficiency was sustained for 1 year with no significant decrease in permeability due to bioaugmentation. Benzene removal was hindered by the presence of toluene, which is a more labile substrate under anaerobic conditions. Real-time quantitative PCR analysis showed that the highest numbers of bssA gene copies (coding for benzylsuccinate synthase) occurred in aquifer samples exhibiting the highest rate of toluene degradation, which suggests that this gene could be a useful biomarker for environmental forensic analysis of anaerobic toluene bioremediation potential. bssA continued to be detected in the columns 1 year after column feeding ceased, indicating the robustness of the added catabolic potential. Overall, these results suggest that anaerobic bioaugmentation might enhance the natural attenuation of BTEX in groundwater contaminated with ethanol-blended gasoline, although field trials would be needed to demonstrate its feasibility. This approach may be especially attractive for removing benzene, which is the most toxic and commonly the most persistent BTEX compound under anaerobic conditions.

Effect of root-derived substrates on the expression of nah-lux genes in Pseudomonas fluorescens HK44: implications for PAH biodegradation in the rhizosphere.

Abstract: The bioluminescent reporter strain Pseudomonas fluorescens HK44 with a nah-lux fusion, was used to investigate the effect of root material (from hybrid poplars, willow, kou, milo, Osage orange, mulberry, and switch grass) and potential root-derived substrates (e.g., sugars, carboxylic acids, amino acids, and phenolics) on the expression of nahG, one of the genes responsible for naphthalene dioxygenase transcription. Whereas nahG was induced by some phenolic substrates that could be released by plants (i.e., salicylate, methyl salicylate, and acetyl salicylate), no induction by root extracts was observed. Rather, increasing root extract concentrations (50 to 275 mg L(-1) as total organic carbon) inhibited nahG expression in assays with cells concurrently exposed to naphthalene. Root extracts also decreased nahG expression at the individual cell level during naphthalene degradation assays. However, treatments with root extracts exhibited significantly higher microbial growth and overall bioluminescence, indicating a higher level of nahG expression by the resulting larger microbial population. This generally resulted in faster naphthalene degradation rates, suggesting that plant-promoted proliferation of competent genotypes could compensate for the interference that labile substrates exert on the expression of genes that code for the degradation of polynuclear aromatic hydrocarbons (PAHs). This could explain the faster PAH degradation commonly reported in planted than in unplanted soils.

Chapter 16 Phytoremediation of hydrocarbon-contaminated soils: principles and applications

Abstract: Publisher Summary This chapter provides a strong foundation for understanding phytoremediation of petroleum hydrocarbon contaminated sites from principles to practice Phytoremediation has developed into a more acceptable technology for the remediation of soils and groundwater polluted with residual concentrations of petroleum hydrocarbons Phytoremediation is an emerging technology that is based on sound ecological engineering principles Phytoremediation is a practical and cost-effective approach with aesthetical and atmospheric-carbon-sequestration ancillary benefits and is particularly attractive for rural areas with residual and shallow contamination Phytoremediation holds great potential to manage a wide variety of environmental pollution problems, including the cleanup of soils and groundwater contaminated with hydrocarbons and other hazardous substances; the attenuation of pollutants dispersing through the environment in agricultural drainage, landfill leachates, and other forms of surface runoff or sub-surface migration; and the assimilation of industrial wastewater effluents to support efforts to move toward a zero-discharge policy from industrial facilities

Nitrate and Nitrite Reduction by Fe0: Influence of Mass Transport, Temperature, and Denitrifying Microbes

Abstract: To evaluate how mass transport, temperature, and denitrifying micro-organisms affect the relative kinetics of nitrate and nitrite reduction by iron metal (Fe0), nitrate and nitrite reduction rates were measured over a range of mixing rates and temperatures. The effect of mixing rate was studied at a polished Fe0 rotating disk electrode (RDE) in an electrochemical cell, and the effect of temperature was studied in batch reactors with granular Fe0 in the absence and presence of Paracoccus denitrificans. Electrode rotation rate had little influence on the cathodic current measured in the presence of nitrate, whereas higher rotation rates resulted in significant increases in current in the presence of nitrite. The heterogeneous reaction rate coefficient (krxn) for nitrite reduction at the Fe0 RDE is several orders of magnitude faster than the surface-area normalized rate coefficient (kSA) for nitrite reduction by granular Fe0. Activation energies for nitrate and nitrite reduction by granular Fe0 were similar ...

Effect of ethanol, acetate, and phenol on toluene degradation activity and tod–lux expression in Pseudomonas putida TOD102: evaluation of the metabolic flux dilution model

Abstract: The reporter strain Pseudomonas putida TOD102 (with a tod-lux fusion) was used in chemostat experiments with binary substrate mixtures to investigate the effect of potentially occurring cosubstrates on toluene degradation activity. Although toluene was simultaneously utilized with other cosubstrates, its metabolic flux (defined as the toluene utilization rate per cell) decreased with increasing influent concentrations of ethanol, acetate, or phenol. Three inhibitory mechanisms were considered to explain these trends: (1) repression of the tod gene (coding for toluene dioxygenase) by acetate and ethanol, which was quantified by a decrease in specific bioluminescence; (2) competitive inhibition of toluene dioxygenase by phenol; and (3) metabolic flux dilution (MFD) by all three cosubstrates. Based on experimental observations, MFD was modeled without any fitting parameters by assuming that the metabolic flux of a substrate in a mixture is proportional to its relative availability (expressed as a fraction of the influent total organic carbon). Thus, increasing concentrations of alternative carbon sources “dilute” the metabolic flux of toluene without necessarily repressing tod, as observed with phenol (a known tod inducer). For all cosubstrates, the MFD model slightly overpredicted the measured toluene metabolic flux. Incorporating catabolite repression (for experiments with acetate or ethanol) or competitive inhibition (for experiments with phenol) with independently obtained parameters resulted in more accurate fits of the observed decrease in toluene metabolic flux with increasing cosubstrate concentration. These results imply that alternative carbon sources (including inducers) are likely to hinder toluene utilization per unit cell, and that these effects can be accurately predicted with simple mathematical models. © 2004 Wiley Periodicals, Inc.

Fe(0)-Based-Bioremediation of RDX-Contaminated Groundwater

Abstract: : RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) is an explosive compound that is gaining notoriety as a recalcitrant and toxic groundwater contaminant at many military installations. Batch and flow-through column studies suggest that permeable reactive iron barriers (PRBs) should effectively intercept and degrade RDX plumes, and that treatment efficiency could be enhanced by some biogeochemical interactions. This project addresses the potential to enhance RDX degradation by bioaugmentation of an Fe(0) permeable reactive barrier, with focus on investigating RDX mechanisms and the sustainability and robustness of an integrated microbial-Fe(0) treatment system. Activities completed this year included chemical characterization including assessing the subsequent degradability of unknown soluble metabolites formed during RDX transformation. Such byproducts were mineralized faster and to a greater extent to carbon dioxide than the parent RDX compound. A significant fraction of carbon from RDX formed under abiotic conditions was confirmed to be formaldehyde. We also continued to run flow-through column studies to investigate the sustainability of these systems. The RDX degradation profile for columns containing aged iron was determined and these columns were characterized with respect to their microbial communities and iron oxides formed along the length of the simulated Fe(0) barrier. Lastly, our investigation with the homoacetogen Acetobacterium paludosum has indicated that RDX can serve as a nitrogen source for this bacterium. This report details the importance, relevance, and scope of this work and the achievement of milestones for this research in 2003.