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Stuart E Strand

Publications and source records attributed to Stuart E Strand.

11 recordsLinked to original sources
PubMed2006

An explosive-degrading cytochrome P450 activity and its targeted application for the phytoremediation of RDX.

The widespread presence in the environment of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), one of the most widely used military explosives, has raised concern owing to its toxicity and recalcitrance to degradation. To investigate the potential of plants to remove RDX from contaminated soil and water, we engineered Arabidopsis thaliana to express a bacterial gene xplA encoding an RDX-degrading cytochrome P450 (ref. 1). We demonstrate that the P450 domain of XplA is fused to a flavodoxin redox partner and catalyzes the degradation of RDX in the absence of oxygen. Transgenic A. thaliana expressing xplA removed and detoxified RDX from liquid media. As a model system for RDX phytoremediation, A. thaliana expressing xplA was grown in RDX-contaminated soil and found to be resistant to RDX phytotoxicity, producing shoot and root biomasses greater than those of wild-type plants. Our work suggests that expression of xplA in landscape plants may provide a suitable remediation strategy for sites contaminated by this class of explosives.

Arabidopsis↗
PubMed2004

Fate of carbon tetrachloride during phytoremediation with poplar under controlled field conditions.

The fate of carbon tetrachloride (CT) during phytoremediation with poplar was assessed by examining the transpiration of CT from leaves, diffusion from soil, tree trunks, and surface roots, and accumulation of chloride ion in soil and plant tissues. Feedwater containing 12-15 mg/L CT was added to the field test beds planted with poplar, and over 99% of the CT was removed. No significant amount of CT was transpired or diffused into the air, and no significant amount of CT-chlorine accumulated in the tree tissues. Chloride ion accumulated in the soil accounted for all of the CT-chlorine removed. When soils from the root zones were compared to unvegetated soils, microbial mineralization of CT was not enhanced in soils from the root zones as compared to unvegetated soils. Thus, we conclude that uptake and dechlorination of CT by plant tissues is likely the primary mechanism for phytoremediation by poplar.

Carbon Tetrachloride↗
PubMed2004

Analysis and comparison of the microbial community structures of two enrichment cultures capable of reductively dechlorinating TCE and cis-DCE.

In order to study the effect of different chloroethenes (electron acceptors) on the bacterial composition of dechlorinating communities, two reductive dechlorinating enrichment cultures were developed that were able to reduce trichloroethene (TCE) and cis-1,2-dichloroethene (cis-DCE) to ethene using hydrogen as electron donor, respectively. The inoculum for the cultures was material from a methanogenic fluidized bed reactor (FBR), which was originally seeded with digester sludge and showed a stable capacity for tetrachloroethene (PCE) reduction to ethene for over six years. Molecular methods were used to determine and compare the microbial communities of these two enrichment cultures. A clone library of bacterial 16S rRNA genes was generated for each enrichment. The clones were screened into different groups by restriction fragment length polymorphism (RFLP) analysis using two different four base pair recognition restriction enzymes. A total of 12 sequence types were identified by phylogenetic analysis of nearly complete 16S rDNA sequences ( approximately 1450 bp). The sequences were affiliated with six recognized phyla of the domain Bacteria: Firmicutes (low G+C Gram-positives), Chloroflexi (green non-sulphur bacteria), Actinobacteria (high G+C Gram-positives), Bacteroidetes (Cytophaga-Flexibacter-Bacteroides), Nitrospira and Spirochaetes. The results led to the identification of an organism closely related to Dehalococcoides ethenogenes to be the presumptive dechlorinator in both enrichments. Different electron acceptors affected the bacterial diversity and the community profiles of the two enrichments. Most of the sequences identified in our dechlorinating enrichments shared high similarities with sequences previously obtained from other enriched dechlorinating cultures and chlorinated-compound-contaminated sediments or aquifers, suggesting these bacteria may have direct or indirect roles in reductive dechlorination.

Anaerobiosis↗
PubMed2004

Pseudonocardia chloroethenivorans sp. nov., a chloroethene-degrading actinomycete.

A bacterial strain, SL-1T, capable of degrading trichloroethene was isolated from a laboratory enrichment in the Department of Civil and Environmental Engineering, University of Washington, USA. The material in the enrichments was derived from a soil sample from Seattle, WA, USA. Strain SL-1T was capable of using phenol as a source of carbon and energy. Chemotaxonomic, morphological, physiological and phylogenetic analyses showed that strain SL-1T is a member of the genus Pseudonocardia. The ability of strain SL-1T to utilize phenol and degrade trichloroethene, as well as other phenotypic properties and the results from a 16S rRNA phylogenetic analysis, led to the proposal of a novel species, Pseudonocardia chloroethenivorans sp. nov. The type strain is SL-1T (=ATCC BAA-742T=DSM 44698T). Trichloroethene and other chloroethenes are major pollutants at many environmental sites, and P. chloroethenivorans has biodegradation properties that should be of interest to environmental microbiologists and engineers.

Actinomycetales↗
PubMed2003

Vinyl bromide as a surrogate for determining vinyl chloride reductive dechlorination potential.

Site evaluation for bioremediation of chlorinated ethenes may need treatability studies to assess the reductive dechlorination potential of vinyl chloride (VC). Dehalogenation of vinyl bromide (VB) was investigated as a surrogate measurement for the dechlorination potential of VC. VB dehalogenation rates and kinetics were studied and compared with those of VC by a methanogenic reductive dechlorinating enrichment culture that was dominated by Dehalococcoides species and by microcosms from two chloroethene-contaminated sites. The enrichment culture dehalogenated VB to ethene at higher rates than VC at similar concentrations. VB was dehalogenated with a higher enzyme affinity than was VC, as indicated by their half-velocity constants, 240 +/- 150 and 21 +/- 8 microM, for VC and VB, respectively. Cross-inhibition study exhibited some evidence for competitive inhibition between VC and VB, suggesting that their degradation might be catalyzed by the same enzyme in the culture. Laboratory microcosm studies using subsurface soil and groundwater from two contaminated sites demonstrated that the production of the reductive dehalogenation product (ethene) could be detected faster with VB as a substrate than with VC. As a result, a substantially shorter (up to 5-10 times) incubation time would be required to detect the same level of reductive dehalogenation activity using VB as a surrogate for VC in treatability assessments.

Bacteria↗
PubMed2003

Amplification of marine methanotrophic enrichment DNA with 16S rDNA PCR primers for type II alpha proteobacteria methanotrophs.

Type II alpha proteobacteria methanotrophs are capable of a wide range of cometabolic transformations of chlorinated solvents and polycyclic aromatic hydrocarbons (PAHs), and this activity has been exploited in many terrestrial bioremediation systems. However, at present, all known obligately marine methanotrophic isolates are Type I gamma proteobacteria which do not have this activity to the extent of Type II methanotrophs. In previous work in our laboratory, determining the presence of Type II alpha proteobacteria methanotrophs in marine enrichment cultures that co-metabolized PAHs required a more sensitive assay. 16S rDNA PCR primers were designed based on oligonucleotide probes for serine pathway methanotrophs and serine pathway methylotrophs with an approximate amplification fragment size of 870 base pairs. Comparison of the primers using double primer BLAST searches in established nucleotide databases showed potential amplification with all Methylocystis and Methylosinus spp., as well as potential amplification with Methylocella palustrus. DNA from Methylosinus trichosporium OB3b, a Type II methanotroph, amplified with the primers with a fragment size of approximately 850 base pairs, whereas DNA extracted from Methylomonas methanica, a Type I methanotroph, did not. The primers were used to amplify DNA extracted from two marine methanotrophic enrichment cultures: a low nitrogen/low copper enrichment to select for Type II methanotrophs and a high nitrogen/high copper enrichment to select for Type I methanotrophs. Although DNA from both cultures amplified with the PCR primers, amplification was stronger in cultures that were specifically enriched for Type II methanotrophs, suggesting the presence of higher numbers of Type II methanotrophs. These results provide further evidence for the existence of Type II marine methanotrophs, suggesting the possibility of exploiting cometabolic activity in marine systems.

Biodegradation, Environmental↗
PubMed2002

Expression of functional mammalian P450 2E1 in hairy root cultures.

P450 2E1 is an important mammalian liver enzyme known to metabolize a wide range of compounds including several common environmental pollutants. The medicinal plant, Atropa belladonna, was transformed with Agrobacterium rhizogenes containing a binary vector with rabbit P450 2E1 in either the sense or antisense orientation. The resulting "hairy roots" were isolated and grown in liquid medium. Production of P450 2E1 protein was verified in the roots containing the 2E1 gene in the sense orientation. Transgenic and control root cultures were dosed with the environmental pollutant, trichloroethylene (TCE), and were analyzed for the TCE metabolites, chloral and trichloroethanol. The root cultures expressing the mammalian P450 2E1 had increased levels of the metabolites compared to the levels in the control roots. This method represents a quick way to screen transformants for expression of foreign genes before regeneration of whole plants, and also as a possible source of foreign protein for purification.

Animals↗
PubMed2002

Mechanism of aerobic transformation of carbon tetrachloride by poplar cells.

The biochemical mechanism of carbon tetrachloride transformation by poplar cells was investigated using an axenic poplar cell culture. After one-day incubations of poplar cells under aerobic conditions, about 1.5% of dosed carbon tetrachloride was transformed to carbon dioxide, about 0.001% to chloroform and about 3% of the carbon was bound to insoluble poplar cellular materials. The production of carbon dioxide increased under aerobic conditions while the formation of chloroform and cell binding of carbon tetrachloride-carbon was enhanced under anaerobic conditions. Both carbon dioxide production and cell binding were significantly inhibited by a general inhibitor of cytochrome P-450 activity (carbon monoxide) and by specific P-450 2E1 inhibitors (chlorzoxazone, isoniazid, 4-methylpyrazole and 1-phenylimidazole). However, no inhibitory effects were observed when the cells were incubated in the presence of lignin peroxidase inhibitors (NaVO3 and 3-amino-1,2,4-triazole). These results suggest that an enzyme similar to mammalian cytochrome P450-2E1 is involved in the metabolism of carbon tetrachloride by poplar cells. This study demonstrates an environmental biodegradative process for carbon tetrachloride that operates under aerobic conditions.

Aerobiosis↗
PubMedDate not supplied

Influence of aquifer properties on phytoremediation effectiveness.

Recent research has shown that planting deep-rooted trees, such as poplar, can take up and degrade important ground water pollutants such as trichloroethylene (TCE) as they transpire water from the capillary fringe of shallow contaminated aquifers. The effect of hydrogeologic factors on the minimum plantation area needed to prevent downgradient migration of contaminated ground water is not well known. Accordingly, the objective of this research was to identify the hydrogeologic parameters that control phytoremediation effectiveness. We used a numerical ground water flow model to evaluate the effect that natural variations in hydrogeologic parameters and growing season duration have on the minimum plantation area required for capture. We found that the plantation area that was needed to completely capture a ground water contamination plume was directly proportional to aquifer horizontal hydraulic conductivity, saturated thickness, and ground water gradient. The plantation area needed for capture increased nonlinearly with increasing plume width, aquifer anisotropy, and decreasing growing season duration. The plantation area needed for capture was generally insensitive to aquifer-specific yield and storativity. Steady-state simulations can be used to predict the plantation area needed for capture in many applications. A particularly important finding of this work is that evapotranspiration fluxes through plantations appropriately sized to contain the plume substantially exceeded the ground water flux through the plume itself.

Biodegradation, Environmental↗
PubMedDate not supplied

Mass balance studies of volatile chlorinated hydrocarbon phytoremediation.

In field-scale mass balance studies of poplar remediation of carbon tetrachloride (CT), more than 95% of the mass of CT was degraded with all of the CT chlorine accountable as chloride ion accumulation in the soil. Atmospheric loss of CT through leaf transpiration and trunk diffusion was insignificant. These findings are consistent with previously reported uptake and degradation of trichloroethylene (TCE) by poplar. Poplar phytoremediation of CT and TCE results in little decrease in aqueous concentration, since water is taken up at about the same rate as the chlorinated compounds. From this result we predict that phytoirrigation--the application of pumped contaminated groundwater to planted systems--will result in concentrations of the pollutants at the bottom of the root zone that are higher than permitted regulatory levels. Such plantations will be susceptible to loss of contaminants during rainfall events, possibly resulting in pollution of uncontaminated soil. Greenhouse studies of pollutant profiles in the media beneath poplar trees that were surface irrigated with TCE and CT confirmed that regulatory concentrations of these pollutants were not achieved in the root zone of the poplar; rather concentrations fell by less than 50%.

Biodegradation, Environmental↗