SEARCH · PubMed Health

Results for “Biodegradation, Environmental”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49Linked to original sources

PubMed1992

Environmental conditions affect transcription of the pectinase genes of Erwinia chrysanthemi 3937.

To depolymerize plant pectin, the phytopathogenic enterobacterium Erwinia chrysanthemi produces a series of enzymes which include a pectin-methyl-esterase encoded by the pem gene and five isoenzymes of pectate lyases encoded by the five genes pelA, pelB, pelC, pelD, and pelE. We have constructed transcriptional fusions between the pectinase gene promoters and the uidA gene, encoding beta-glucuronidase, to study the regulation of these E. chrysanthemi pectinase genes individually. The transcription of the pectinase genes is dependent on many environmental conditions. All the fusions were induced by pectic catabolic products and responded, to different degrees, to growth phase, catabolite repression, temperature, and nitrogen starvation. Transcription of pelA, pelD, and pelE was also increased in anaerobic growth conditions. High osmolarity of the culture medium increased expression of pelE but decreased that of pelD; the other pectinase genes were not affected. The level of expression of each gene was different. Transcription of pelA was very low under all growth conditions. The expression of the pelB, pelC, and pem genes was intermediate. The pelE gene had a high basal level of expression. Expression of pelD was generally the most affected by changes in culture conditions and showed a low basal level but very high induced levels. These differences in the expression of the pectinase genes of E. chrysanthemi 3937 presumably reflect their role during infection of plants, because the degradation of pectic polymers of the plant cell walls is the main determinant of tissue maceration caused by soft rot erwiniae.

Anaerobiosis↗

PubMed2006

Environmental challenge vis a vis opportunity: the case of water hyacinth.

Water hyacinth (Eichhornia crassipes) is a noxious weed that has attracted worldwide attention due to its fast spread and congested growth, which lead to serious problems in navigation, irrigation, and power generation. On the other hand, when looked from a resource angle, it appears to be a valuable resource with several unique properties. As a result, research activity concerning control (especially biological control) and utilization (especially wastewater treatment or phytoremediation) of water hyacinth has boomed up in the last few decades. Investigations on biogas/compost production from water hyacinth have also come up very well mainly from few research groups in India. This review presents a comprehensive view of the research related to water hyacinth with special emphasis on the recent investigations on water hyacinth control and utilization technologies conducted in the last 2-3 decades. Based on these significant research achievements, now it is desirable to identify a management strategy so that the excessive growth can be controlled and the plant can be used in beneficial ways. In the rural areas, water hyacinth could be used in an integrated manner for decentralized wastewater treatment systems coupled to biogas and compost production from the resulting biomass. There is a need to work out the techno-economic viability of such integrated model systems.

Animals↗

PubMed2005

Pilot-scale demonstration of phytofiltration for treatment of arsenic in New Mexico drinking water.

Arsenic contamination of drinking water poses serious health risks to millions of people worldwide. To reduce such risks, the United States Environmental Protection Agency recently lowered the Maximum Contaminant Level for arsenic in drinking water from 50 to 10 microgL(-1). The majority of water systems requiring compliance are small systems that serve less than 10,000 people. Current technologies used to clean arsenic-contaminated water have significant drawbacks, particularly for small treatment systems. In this pilot-scale demonstration, we investigated the use of arsenic-hyperaccumulating ferns to remove arsenic from drinking water using a continuous flow phytofiltration system. Over the course of a 3-month demonstration period, the system consistently produced water having an arsenic concentration less than the detection limit of 2 microgL(-1), at flow rates as high as 1900 L day(-1) for a total treated water volume of approximately 60,000 L. Our results demonstrate that phytofiltration provides the basis for a solar-powered hydroponic technique to enable small-scale cleanup of arsenic-contaminated drinking water.

Arsenic↗

PubMed2005

Assessment of the energy dissipation parameters inside the draft tube of a liquid spout-fluid bed.

Spouted beds are fluid-particle contactors in which the fluid is introduced centrally through a nozzle instead of a distributor plate, resulting in a regular particle circulation pattern. To assess the suitability of such sytems to environmental engineering applications such as filter backwashing and biofilm systems, a priori knowledge of the energy dissipation parameters is essential. A new model is developed for evaluating the energy dissipation parameters inside the draft tube of spout-fluid beds. The shear stress, velocity gradient, and turbulence fluctuation parameters in the draft tube of a liquid spout-fluid bed are calculated with the help of an energy equation for flows carrying suspensions and the experimentally determined pressure losses inside the draft tube and compared with results for particulately fluidized beds. A spout-fluid bed with a draft tube provides higher shear stress inside the draft tube than a fluidized bed. The mean velocity gradient in the draft tube is comparable to and higher than in a fluidized bed and increases with solids fraction. The turbulence dissipation coefficient decreases very slightlywith increasing solids fraction for both systems. Consequently, according to the model calculations, a spout-fluid bed with a draft tube can be an alternative to the classical fluidized bed filter backwashing system.

Beds↗

PubMed2001

Enzymes and operons mediating xenobiotic degradation in bacteria.

Aromatic hydrocarbons constitute a major group of environmental pollutants. Bioremediation appears to be the only viable alternative for large-scale decontamination. A number of bacteria have been identified that can degrade a variety of xenobiotics. Extensive studies of the enzymes and genes involved in degradation of aromatic hydrocarbons have revealed that the degradative enzymes could be broadly grouped into two major categories, peripheral and ring-cleavage enzymes. The peripheral enzymes are the ones that catabolize the pollutants initially to a metabolite that is further degraded. A majority of peripheral enzymes are oxygenases that hydroxylate the aromatic compounds, rendering them susceptible to the enzymes of ring-cleavage pathway. The genes of ring-cleavage enzymes have been shown to be highly conserved between different bacterial species. Presently, a number of constraints limit the use of available strains for efficient bioremediation. This review describes the enzymes and genes involved in xenobiotic degradation and underscores the importance of understanding the expression and regulation of genes encoding peripheral enzymes and their intelligent manipulation using recombinant DNA technology for efficient degradation of aromatic compounds.

Bacteria↗

PubMed1988

Environmental factors affecting indole metabolism under anaerobic conditions.

The influence of physiological and environmental factors on the accumulation of oxindole during anaerobic indole metabolism was investigated by high-performance liquid chromatography. Under methanogenic conditions, indole was temporarily converted to oxindole in stoichiometric amounts in media inoculated with three freshwater sediments and an organic soil. In media inoculated with methanogenic sewage sludge, the modest amounts of oxindole detected at 35 degrees C reached higher concentrations and persisted longer when the incubation temperature was decreased from 35 to 15 degrees C. Also, decreasing the concentration of sewage sludge used as an inoculum from 50 to 1% caused an increase in the accumulation of oxindole from 10 to 75% of the indole added. Under denitrifying conditions, regardless of the concentration or source of the inoculum, oxindole appeared in trace amounts but did not accumulate during indole metabolism. In addition, denitrifying consortia which previously metabolized indole degraded oxindole with no lag period. Our data suggest that oxindole accumulation under methanogenic, but not under denitrifying conditions is caused by differences between relative rates of oxindole production and destruction.

Anaerobiosis↗

PubMed1997

Sensitive detection of a novel class of toluene-degrading denitrifiers, Azoarcus tolulyticus, with small-subunit rRNA primers and probes.

Azoarcus tolulyticus is a new class of widely distributed toluene-degrading denitrifiers of potential importance in remediating benzene, toluene, ethylbenzene, and xylene (BTEX)-contaminated environments. To detect these organisms in the environment, 16S rRNA gene-based phylogenetic probes were developed. Two sets of specific PCR amplification primers and two oligonucleotide hybridization probes were designed and tested against both closely and distantly related environmental isolates. All of these primers and probes were specific to the species A. tolulyticus. The sensitivity of the PCR amplification primer sets was evaluated with DNA isolated from A. tolulyticus Tol-4 pure culture and from sterile soils seeded with a known number of Tol-4 and Escherichia coli cells. These primer sets were able to detect 1 fg to 1 pg of template DNA from the pure culture and 1.11 x 10(2) to 1.1 x 10(8) Tol-4 cells per g of soil in the presence of 1.56 x 10(10) E. coli cells. These two PCR amplification primers were also successfully tested at two field sites. The primers identified the A. tolulyticus strains among the toluene-degrading bacteria isolated from a low-O2-high-NO(3)- aquifer at Moffett Field, Calif. Also, the presence of A. tolulyticus was detected in the groundwater samples from a BTEX-contaminated aquifer at an industrial site in Detroit, Mich., which showed anaerobic toluene degradation.

Base Sequence↗

PubMed2004

Growth of polychlorinated-biphenyl-degrading bacteria in the presence of biphenyl and chlorobiphenyls generates oxidative stress and massive accumulation of inorganic polyphosphate.

Inorganic polyphosphate (polyP) plays a significant role in increasing bacterial cell resistance to unfavorable environmental conditions and in regulating different biochemical processes. Using transmission electron microscopy of the polychlorinated biphenyl (PCB)-degrading bacterium Pseudomonas sp. strain B4 grown in defined medium with biphenyl as the sole carbon source, we observed large and abundant electron-dense granules at all stages of growth and following a shift from glucose to biphenyl or chlorobiphenyls. Using energy dispersive X-ray analysis and electron energy loss spectroscopy with an integrated energy-filtered transmission electron microscope, we demonstrated that these granules were mainly composed of phosphate. Using sensitive enzymatic methods to quantify cellular polyP, we confirmed that this polymer accumulates in PCB-degrading bacteria when they grow in the presence of biphenyl and chlorobiphenyls. Concomitant increases in the levels of the general stress protein GroEl and reactive oxygen species were also observed in chlorobiphenyl-grown cells, indicating that these bacteria adjust their physiology with a stress response when they are confronted with compounds that serve as carbon and energy sources and at the same time are chemical stressors.

Biodegradation, Environmental↗

PubMed2005

Sulfur, chromium, and selenium accumulated in Chinese cabbage under direct covers.

Currently, pollution of our agricultural soils and waters is increasing and is often associated with many human health ailments. Soils contaminated with low levels of heavy metals and other trace elements are frequently used for growing vegetable crops and in such a situation, these toxic contaminants often accumulate in the edible portions of these agricultural plants and thereby enter the human food chain. In 3 consecutive years of field experiments (1994-1996), two different crop-covering treatments--T (50 microm perforated polyethylene), and T2 (17 gm(-2) non-woven polypropylene)--were used to modify the environmental conditions for the growth of Chinese cabbage 'Nagaoka 50' [Brassica rapa L. (Pekinensis group)]. Open-air plots (T(0)) were used as controls. Analytical determinations of chromium (Cr), selenium (Se), two forms of sulfur (total-S and sulfate-S), and amino acids (Isoleucine, leucine, lysine, methionine, serine, threonine, and valine) were performed utilizing plant shoots for analysis. The T1 and T2 treated plants contained concentrations of lysine, methionine, serine, and threonine higher than in T(0). Under T1, the extent of Cr and Se removal in the field was more favorable. Direct covers could be used in contaminated agricultural zones for a variety of plant species, not just for use with those plants previously reported to be efficient at bio-accumulating toxic elements because the thermal effect created by the covers favors phytoextraction processes. However, it is clear that the accumulation of these toxic substances in the plants (Cr) would deem the plant material unsuitable for human consumption and use as animal fodder.

Amino Acids↗

PubMed1999

In situ, real-time catabolic gene expression: extraction and characterization of naphthalene dioxygenase mRNA transcripts from groundwater.

We developed procedures for isolating and characterizing in situ-transcribed mRNA from groundwater microorganisms catabolizing naphthalene at a coal tar waste-contaminated site. Groundwater was pumped through 0.22-microm-pore-size filters, which were then frozen in dry ice-ethanol. RNA was extracted from the frozen filters by boiling sodium dodecyl sulfate lysis and acidic phenol-chloroform extraction. Transcript characterization was performed with a series of PCR primers designed to amplify nahAc homologs. Several primer pairs were found to amplify nahAc homologs representing the entire diversity of the naphthalene-degrading genes. The environmental RNA extract was reverse transcribed, and the resultant mixture of cDNAs was amplified by PCR. A digoxigenin-labeled probe mixture was produced by PCR amplification of groundwater cDNA. This probe mixture hybridized under stringent conditions with the corresponding PCR products from naphthalene-degrading bacteria carrying a variety of nahAc homologs, indicating that diverse dioxygenase transcripts had been retrieved from groundwater. Diluted and undiluted cDNA preparations were independently amplified, and 28 of the resulting PCR products were cloned and sequenced. Sequence comparisons revealed two major groups related to the dioxygenase genes ndoB and dntAc, previously cloned from Pseudomonas putida NCIB 9816-4 and Burkholderia sp. strain DNT, respectively. A distinctive subgroup of sequences was found only in experiments performed with the undiluted cDNA preparation. To our knowledge, these results are the first to directly document in situ transcription of genes encoding naphthalene catabolism at a contaminated site by indigenous microorganisms. The retrieved sequences represent greater diversity than has been detected at the study site by culture-based approaches.

Bacteria↗

PubMed2003

Conservation of ornamental stone by Myxococcus xanthus-induced carbonate biomineralization.

Increasing environmental pollution in urban areas has been endangering the survival of carbonate stones in monuments and statuary for many decades. Numerous conservation treatments have been applied for the protection and consolidation of these works of art. Most of them, however, either release dangerous gases during curing or show very little efficacy. Bacterially induced carbonate mineralization has been proposed as a novel and environmentally friendly strategy for the conservation of deteriorated ornamental stone. However, the method appeared to display insufficient consolidation and plugging of pores. Here we report that Myxococcus xanthus-induced calcium carbonate precipitation efficiently protects and consolidates porous ornamental limestone. The newly formed carbonate cements calcite grains by depositing on the walls of the pores without plugging them. Sonication tests demonstrate that these new carbonate crystals are strongly attached to the substratum, mostly due to epitaxial growth on preexisting calcite grains. The new crystals are more stress resistant than the calcite grains of the original stone because they are organic-inorganic composites. Variations in the phosphate concentrations of the culture medium lead to changes in local pH and bacterial productivity. These affect the structure of the new cement and the type of precipitated CaCO(3) polymorph (vaterite or calcite). The manipulation of culture medium composition creates new ways of controlling bacterial biomineralization that in the future could be applied to the conservation of ornamental stone.

Biodegradation, Environmental↗

PubMed2005

Degradation and effects of the potential mosquito larvicides methazolamide and acetazolamide in sheepshead minnow (Cyprinodon variegatus).

To test for environmental persistence in order to determine the potential of carbonic anhydrase inhibitors as larvicides, the decomposition and degradation of samples containing methazolamide (MTZ) and acetazolamide (ACZ) in aqueous solution were monitored under different conditions. Additionally, nontarget species impact was assessed in an acute toxicity test using sheepshead minnow (Cyprinodon variegatus). The fish were exposed for 120 h to 10(-3) and 10(-4) M each compound in replicate seawater tanks. In the high-MTZ treatment, all fish died within 48 h, while mortality in the low-MTZ treatment was 27% at 120 h. In the high-ACZ treatment mortality reached 83% at 120 h. We observed no mortality for the lowest dose of ACZ. Tissue samples were collected from the fish to investigate absorption of the compounds. In the gills, MTZ concentrations were around 40 microg g(-1) and ACZ reached concentrations up to 80 microg g(-1). Liver concentrations were low for MTZ probably due to metabolism.

Acetazolamide↗

PubMed2006

Phytoremediation and rehabilitation of municipal solid waste landfills and dumpsites: A brief review.

Environmental problems posed by municipal solid waste (MSW) are well documented. Scientifically designed landfills and/or open dumpsites are used to dispose MSW in many developed and developing countries. Non-availability of land and need to reuse the dumpsite space, especially in urban areas, call for rehabilitation of these facilities. A variety of options have been tried to achieve the goals of rehabilitation. In the last couple of decades, phytoremediation, collectively referring to all plant-based technologies using green plants to remediate and rehabilitate municipal solid waste landfills and dumpsites, has emerged as a potential candidate. Research and development activities relating to different aspects of phytoremediation are keeping the interest of scientists and engineers alive and enriching the literature. Being a subject of multi-disciplinary interest, findings of phytoremediation research has resulted in generation of enormous data and their publication in a variety of journals and books. Collating data from such diverse sources would help understand the dynamics and dimensions of landfill and dumpsite rehabilitation. This review is an attempt in this direction.

Biodegradation, Environmental↗

PubMed2003

Divergence of mobile genetic elements involved in the distribution of xenobiotic-catabolic capacity.

Bacteria adapt rapidly to environmental stimuli, such as exposure to xenobiotics. Mobile genetic elements (MGEs) play a major role in such bacterial adaptation, via the dispersal of catabolic capacity; and, in fact, genes that encode the degradation enzymes for xenobiotics are often located on MGEs. The list of reported catabolic MGEs keeps growing as researchers continue to isolate and characterize xenobiotic degraders and the corresponding catabolic genes. Major catabolic MGEs include (conjugative) plasmids, transposons, and conjugative transposons. Catabolic transposons can be divided into class I elements (composite transposons) and class II elements (Tn 3 family transposons). This review includes a comprehensive list of naturally occurring discrete catabolic MGEs, together with a brief description for each. While MGEs are often rather large, genome-wide or large-scale sequence analyses have provided useful information on the whole genetic structure of MGEs, with clues to their function (transfer, maintenance, catabolism, etc.) and behavior in a complex natural environment. This review also gives an insight into MGE functions, based on the complete sequencing of several catabolic plasmids and two Pseudomonas genomes.

Adaptation, Biological↗

PubMed1997

Indicators of the sustainability of heavy-metal management in agro-ecosystems.

The aim of sustainable heavy-metal management in agro-ecosystems is to ensure that the soil continues to fulfil its function in agricultural production, in environmental processes such as the cycling of elements, and as a habitat of numerous organisms. Assessment of sustainability has to be carried out in time, since metal accumulation in soil is largely irreversible and may cause problems if certain concentration levels are exceeded. In this study, we provide a concept to assess the sustainability of current metal cycles in agro-ecosystems based on dynamic heavy-metal balances for the plough layer. After presenting some general aspects of dynamic metal balances, we introduce 'sustainability indices'. These characteristic numbers can be used as indicators for potentially adverse effects of current agricultural practices, since they account for (ecotoxicologically founded) soil quality standards and for quality standards for produce, groundwater and surface water. They can also be used to assess the effects of different management options that aim to prevent quality standards from being exceeded as they provide insight in the dynamics governing input-output relationships. This is illustrated with a case study on heavy-metal flows in different arable farming systems.

Agriculture↗

PubMed2005

Methyl parathion toxicity to and removal efficiency by Typha latifolia in water and artificial sediments.

Methyl parathion (MeP) is a very hazardous pesticide freely used in agriculture in Mexico. This pesticide and others, arriving through different processes, exert significant effects on water quality with serious consequences for environmental and human health. This study evaluates the removal efficiency of common cattail Typha latifolia L. on MeP in water and artificial sediments. The effects of the pesticide on this macrophyte after 10 days of exposure were determined using a concentration range of 0-200 mg l(-1), 198.1+/-1.79 g average biomass, pH 7.0, 18-22 degrees C temperature and natural daylight/darkness periods, using chlorophyll production as a biomarker. Removal kinetics were conducted under similar conditions on days 0, 3, 7, 9, 11 and 14 of exposure, using 6 mg l(-1) in each system. Pesticide concentration, chlorophyll content and glutathione S-transferase (GST) activity were quantified. Results show a high removal efficiency of cattails on MeP in water and sediments relative to controls. An increase in GST activity and a decline in chlorophyll content in the test systems were not significantly different relative to controls. Cattails may thus be a good candidate for development of a phytoremediation system for MeP-contaminated water and artificial sediments.

Biodegradation, Environmental↗

PubMed2002

Degradation of polyethoxylated nonylphenols in a sewage treatment plant. Quantitative analysis by isotopic dilution-HRGC/MS.

Polyethoxylated alkylphenols (APnEO, where n is the number of ethylene oxide molecules), are non-ionic surfactants widely used for domestic and industrial purposes. Most of APnEO are polyethoxylated nonylphenols (NPnEO). NPnEO are widespread environmental pollutants with relatively low toxicity for mammals and higher toxicity for aquatic organisms. In addition, they have been described as endocrine disrupters in recent publications. One of the main problems related to these surfactants is their uncomplete degradation, even in the most effective sewage treatment plants. Usually, the final products, more toxic and resistant to biological degradation than NPnEO, are nonylphenol (NP), monoethoxylated nonylphenol (NP1EO), diethoxylated nonylphenol (NP2EO), nonylphenoxy acetic acid (NP1EC), and nonylphenoxyethoxy acetic acid (NP2EC). In this paper, the degradation of NPnEO was studied in the different processes of a sewage treatment plant. For this purpose, NP, NP1EO and NP2EO were analysed in composite samples collected at different points along the plant (influent, pre-treatment effluent, primary effluent, plant effluent). Analyses were carried out by isotopic dilution-HRGC/MS, using available labelled nonylphenols (13C6-NP, 13C6-NP1EO, 13C6-NP2EO) as internal standards. Extraction of NPnEO from aqueous samples, previous to analysis, was performed by the Likens-Nickerson method (simultaneous steam distillation/solvent extraction, SDE).

Biodegradation, Environmental↗

PubMed2001

A comparative study of anaerobically digested and undigested sewage sludges in preparation of activated carbons.

Disposal of sewage sludge is an increasingly expensive and environmentally sensitive problem throughout the world. Preparation of activated carbon from sewage sludge offers an attractive re-use alternative to the traditional disposal routes. The objective of this research work was to compare anaerobically digested sewage sludge (DS) and undigested sewage sludge (US) as source materials in the preparation of activated carbons. Prior to the preparation the properties of the two types of sewage sludges were determined and compared. Subsequently the sludge samples were activated with 5 M ZnCl2 solution and thereafter pyrolysed at heating temperature of 650 degrees C for 2 h with the heating rate of 15 degrees C/min under a nitrogen atmosphere. The produced activated carbons were characterised by surface area and porosity analysis, CHN elemental composition and ash contents determination, and aqueous phase phenol adsorption tests. The results indicate that in comparison with the DS, the US had a higher carbon content and lower ash content, and accordingly yielded a better activated carbon with a higher BET surface area, pore volume, carbon content and phenol adsorption capacity.

Adsorption↗