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PubMed2006

Soluble di-iron monooxygenase gene diversity in soils, sediments and ethene enrichments.

Soluble di-iron monooxygenases (SDIMOs) are key enzymes in the bacterial oxidation of hydrocarbons, and have applications in environmental and industrial biotechnology. SDIMOs from pure cultures are unlikely to represent the total diversity of this enzyme family, so we used polymerase chain reaction to survey the diversity of SDIMO alpha subunit genes in environmental samples, ethene enrichments and ethene-degrading bacterial isolates. From 178 cloned amplicons, 98 restriction fragment length polymorphism types were seen, from which 75 representative SDIMO sequences were obtained; 45 from environmental samples, 25 from enrichments and seven from isolates. The sequences were diverse, including genes similar to ethene (etnC), propene (amoC, pmoC), propane (prmA) and butane (bmoX) monooxygenases, in addition to many novel sequences comprising a new SDIMO group (group 6). Environmental samples showed the highest diversity, with strong representation of group 6 SDIMOs and prmA-like genes. Ethene stimulation of samples resulted in increased frequencies of group 4 SDIMOs (etnC-like). Four ethene-utilizing Mycobacterium isolates (NBB1-NBB4) from enrichments all contained etnC; one isolate (NBB4) also contained three additional SDIMO genes (bmoX-like, amoC-like and group 6). The primers, database, clone libraries and strains reported here provide a resource for future bioremediation and biocatalysis studies, with particular relevance for chlorinated alkene and alkane compounds.

Bacteriological Techniques↗

PubMedDate not supplied

Phytoextraction of toxic metals: a review of biological mechanisms.

Remediation of sites contaminated with toxic metals is particularly challenging. Unlike organic compounds, metals cannot be degraded, and the cleanup usually requires their removal. However, this energy-intensive approach can be prohibitively expensive. In addition, the metal removing process often employs stringent physicochemical agents which can dramatically inhibit soil fertility with subsequent negative impacts on the ecosystem. Phytoremediation has been proposed as a cost-effective, environmental-friendly alternative technology. A great deal of research indicates that plants have the genetic potential to remove many toxic metals from the soil. Despite this potential, phytoremediation is yet to become a commercially available technology. Progress in the field is hindered by a lack of understanding of complex interactions in the rhizosphere and plant-based mechanisms which allow metal translocation and accumulation in plants. In this paper, four research areas relevant to metal phytoextraction from contaminated soil are reviewed. The review concludes with an assessment of the current status of technology deployment and suggestions for future phytoremediation research.

Biodegradation, Environmental↗

PubMed2006

Wastewater treatment: a model system for microbial ecology.

Biological wastewater treatment is among the most important biotechnological applications and, as drivers of the key processes, microorganisms are central to its success. Therefore, the study of wastewater microorganisms has obvious applied significance; however, the importance of wastewater treatment reactors as model systems for microbial ecology is often overlooked. Modern molecular techniques, including environmental genomics, have identified unexpected microbial key players for nutrient removal and sludge bulking and/or foaming, and provided many exciting insights into the diversity, functions and niche differentiations of these predominantly uncultivated microorganisms. It is now time for wastewater microbiology to be recognized as a mature and dynamic discipline in its own right, offering much toward a deeper understanding of life in complex microbial communities. Here, we consider selected key findings to illustrate the past and future roles of molecular ecophysiology and genomics in the development of wastewater microbiology as an important subdiscipline of microbial ecology.

Bacteria↗

PubMed2002

Accuracy analysis of a respirometer for activated sludge dynamic modelling.

The aim of the paper is to assess the experimental errors arising from the operation of a closed respirometer using autotrophic biomass. A closed, intermittent-flow device has been set-up for the measurement of oxygen uptake rate (OUR) and parameter calibration. After describing the device structure and operation, the factors affecting accuracy have been assessed. Inaccuracies may be caused by two groups of parameters: design parameters, including flow rate, volume, sampling time, numerical algorithm, sample injection and environmental parameters, concerning the physicochemical conditions of the experiment, such as unwanted oxygen transfer, pH, and the influence of sludge condition on "start-up" behaviour. It is shown to what extent each of them affects the final accuracy of the OUR measurement. In the second part of the paper, the respirometric data are used to calibrate a two-step nitrification model and their impact on the accuracy of the estimation of model parameters is assessed. Confidence limits are derived for the identifiable parameter combinations and the practical identifiability assessed with the aid of trajectory sensitivity analysis.

Biodegradation, Environmental↗

PubMed2001

Phytoremediation of organic contaminants in soils.

Soil pollution, a very important environmental problem, has been attracting considerable public attention over the last decades. Unfortunately, the enormous costs associated with the removal of pollutants from soils by means of traditional physicochemical methods have been encouraging companies to ignore the problem. Phytoremediation is an emerging technology that uses plants to clean up pollutants in the environment. As overwhelmingly positive results have become available regarding the ability of plants to degrade certain organic compounds, more and more people are getting involved in the phytoremediation of organic contaminants. Phytoremediation of organics appears a very promising technology for the removal of these contaminants from polluted sites.

Biodegradation, Environmental↗

PubMed2001

Bioaugmentation of soils by increasing microbial richness: missing links.

It is generally assumed that increased microbial diversity corresponds to increased catabolic potential and, hence, to better removal of metabolites and pollutants. Yet, microbial diversity, more specifically richness of species in environmental samples and sites, is difficult to assess. It is proposed to interpret this diversity more in the framework of Pareto's law, i.e. 20% of the species govern 80% of the energy flux of the ecosystem. Ecological studies should attempt to delineate the main energy fluxes and that group of species playing quantitative key roles in the system. Consequently, bioaugmentation should aim at the rearrangement of the group of organisms dominantly involved in the overall energy flux, so that specific catabolic traits necessary for the clean up of pollutants are part of that active group. For soil ecosystems, the capacity of plant roots as creators of physical and chemical discontinuity should be used more strategically to bring about such rearrangements. Overall, this paper identifies a number of ecological concepts, such as the Pareto law, the Gompertz model and plant community-induced microbial competence, which may, given careful underpinning, open new perspectives for microbial ecology and biodegradation.

Bacteria↗

PubMed2007

Overview of on-farm bioremediation systems to reduce the occurrence of point source contamination.

Contamination of ground and surface water puts pressure on the use of pesticides. Pesticide contamination of water can often be linked to point sources rather than to diffuse sources. Examples of such point sources are areas on farms where pesticides are handled and filled into sprayers, and where sprayers are cleaned. To reduce contamination from these point sources, different kinds of bioremediation system are being researched in various member states of the EU. Bioremediation is the use of living organisms, primarily microorganisms, to degrade the environmental contaminants into less toxic forms. The systems available for biocleaning of pesticides vary according to their shape and design. Up till now, three systems have been extensively described and reported: the biobed, the Phytobac and the biofilter. Most of these constructions are excavations or different sizes of container filled with biological material. Typical overall clean-up efficiency exceeds 95%, realising even more than 99% in many cases. This paper provides an overview of the state of the art of these bioremediation systems and discusses their construction, efficiency and drawbacks.

Agriculture↗

PubMed1990

Degradation of halogenated aromatic compounds.

Due to their persistence, haloaromatics are compounds of environmental concern. Aerobically, bacteria degrade these compounds by mono- or dioxygenation of the aromatic ring. The common intermediate of these reactions is (halo)catechol. Halocatechol is cleaved either intradiol (ortho-cleavage) or extradiol (meta-cleavage). In contrast to ortho-cleavage, meta-cleavage of halocatechols yields toxic metabolites. Dehalogenation may occur fortuitously during oxygenation. Specific dehalogenation of aromatic compounds is performed by hydroxylases, in which the halo-substituent is replaced by a hydroxyl group. During reductive dehalogenation, haloaromatic compounds may act as electron-acceptors. Herewith, the halosubstituent is replaced by a hydrogen atom.

Bacteria↗

PubMed1999

Photocatalytic decomposition of 4-chlorophenol over oxide catalysts.

4-Chlorophenol in the presence of catalysts was decomposed in aqueous solution by a 125 W medium pressure mercury lamp in a thermostated quartz batch photoreactor, and the organic bound chlorine was catalytically converted into the environmentally less harmful inorganic chloride. Differences in the concentration of 4-chlorophenol and of the intermediates, such as hydroquinone and quinone, are followed by HPLC. The best catalyst among a homolog series for the photo-decomposition of 4-chlorophenol was selected as finely dispersed platinum oxide on a TiO2 semiconductor support, and kinetic parameters of the Langmuir-Hinshelwood type decomposition reaction were reported for the selected catalyst. A simple mechanism of substrate degradation in accord with the chosen kinetic model was postulated. The developed process may serve photooxidative removal of chlorophenols in wastewater without using costly oxidants.

Biodegradation, Environmental↗

PubMed1980

Chlorinated phenols: occurrence, toxicity, metabolism, and environmental impact.

Pentachlorophenol and the lower chlorinated phenols, tetra- and trichlorophenols, have gained an increasing use as fungicides, herbicides, insecticides, and precursors in the synthesis of other pesticides since the early 1930s. World-wide production totals about 200,000 tons. Production and use of chlorinated phenols have caused industrial hygiene problems but, otherwise, have not been recognized to create more than limited environmental problems. The introduction of modern analytical techniques, however, has revealed the ubiquitous occurrence of chlorophenols in the environment, and the discovery of chlorinated dimers, such as dibenzo-p-dioxins and dibenzofurans, as impurities in commercial chlorophenol formulations, has made a reevaluation of the chlorinated phenols necessary. The present article reviews recent studies on the toxicity and metabolism in mammals and aquatic organisms and the degradation of the chlorophenols under various conditions in the environment. Finally, the hazards of burning of chlorophenol wastes are discussed, as well as health considerations with regard to humans and the environment.

Animals↗

PubMed2005

Treatment of high strength wastewater with vertical flow constructed wetland filters.

The aim of the present study was to evaluate the behaviour of vertical flow constructed wetlands to treat high strength wastewater. Influents were obtained mixing tap water with different percentages of MSW landfill leachate (5%, 10% and 20%). Phragmites australis seedlings were used as macrophytes. The reeds were nurtured during three spring months, before the start of the experimental period. Three and four days of detention time were adopted. Influent concentrations of 510-2,050 mg L(-1), 180-740 mg L(-1) and 65-260 mg L(-1) were obtained for COD, N-NH4(+) and N-NO3(-), respectively. The environmental temperature averaged around 31.0 +/- 1.4 degrees C. During the experimental period, all parameters showed an increasing removal efficiency trend. Best results in terms of COD removal were obtained for mixtures at lowest rate of landfill leachate; while, denitrification process showed an opposite behaviour; finally, the removal of ammonia nitrogen appeared to be independent upon influent concentrations. Analysis carried out on the reed tissues showed a theoretic maximum storage of TKN in the leaves of about 55 mg/g dry weight. A leachate percentage of about 35% was derived to be able to fully inhibit the growth of macrophytes.

Biodegradation, Environmental↗

PubMed2003

Effects of oil and bioremediation on mussel (Mytilus edulis L.) growth in mudflats.

Mussels (Mytilus edulis L.) were exposed to crude oil during a field experiment to evaluate two bioremediation strategies (nutrient addition and nutrient addition with tilling). The mussels were placed in 4 mesocosms: Control, Oil, Oil + Nutrients, and Oil + Nutrients + Tilled. Tilling appeared to be clearly detrimental to mussel growth. Additionally, this field experiment demonstrated that at temperatures below 5 degrees C, growth was reduced to rates undetectable by the laser diffraction method. The data on mussel shell length show that this technique does offer very sensitive and useful comparative measurements of physiological function. Measurement of shell growth has the advantage over other techniques in that it is non-invasive and non-destructive and thus may be used continuously without disturbing critical physiological and biochemical functions; however, bivalve physiology is strongly linked to environmental conditions, so it is important to include such measures (i.e. seawater temperature and turbidity) in the design of the biomonitoring program. Elevated polycyclic aromatic hydrocarbon (PAH) levels reflected bioaccumulation in mussels from all the oiled mesocosms. This correlated with reduction in growth rate. Maximum reduction in growth was observed in mussels from the tilled mesocosm which contained the lowest phenanthrene and dibenzothiophene concentrations. The tilling caused an increase in suspended solids which inhibited filter feeding activity, and resulted in suppressed growth and slower intake of PAH-laden sediment.

Animals↗

PubMed2001

Technologies to address air quality issues impacting animal agriculture.

The continued productivity, profitability and sustainability of animal production agriculture in most parts of the world will be dependent upon implementation of effective technologies and management practices to mitigate perceived and documented environmental impacts resulting from confined animal operation emissions. North Carolina State University Animal and Poultry Waste Management Center (APWMC) program efforts to identify such technologies through support of research, development and demonstration projects involve collaborative efforts with approximately 20 other universities (nationally and internationally). Many of these projects are well beyond the laboratory developmental stage and some are yielding encouraging results. Performance data, to date, has shown that swine manure treatment systems including a covered in-ground anaerobic digester, a sequencing batch reactor, and an upflow biological aerated filter system significantly improved odor emission variables.

Agriculture↗

PubMed2004

Identification of Chromobacterium violaceum genes with potential biotechnological application in environmental detoxification.

Chromobacterium violaceum is a Gram-negative bacterium found in a wide variety of tropical and subtropical ecosystems. The complete genome sequence of C. violaceum ATCC 12472 is now available, and it has considerable biotechnological potential for various applications, such as environmental detoxification, as well as medical and agricultural use. We examined the biotechnological potential of C. violaceum for environmental detoxification. Three operons, comprising the ars operon, involved in arsenic resistance, the cyn operon, involved in cyanate detoxification, and the hcn operon, encoding a cyanase, responsible for biogenic production of cyanide, as well as an open reading frame, encoding an acid dehalogenase, were analyzed in detail. Probable catalytic mechanisms for the enzymes were determined, based on amino acid sequence comparisons and on published structural information for these types of proteins.

Arsenic↗

PubMed2006

[Characteristics of heavy metals enrichment in algae ano its application prospects].

Using algae to bio-remedy heavy metals-contaminated waters has become an available and practical approach for environmental restoration. Because of its special cell wall structure, high capacity of heavy metal-enrichment, and easy to desorption, algae has been considered as an ideal biological adsorbent. This paper briefly introduced the structural and metabolic characteristics adapted for heavy metals enrichment of algae, including functional groups on cell wall, extracellular products, and intracellular heavy metals-chelating proteins, discussed the enrichment capability of living, dead and immobilized algae as well as the simple and convenient ways for desorption, and analyzed the advantages and disadvantages of using algae for bioremediation of polluted water, and its application prospects.

Biodegradation, Environmental↗

PubMed2006

Photo-induced degradation of diuron in aqueous solution by nitrites and nitrates: kinetics and pathways.

The photo-induced degradation of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) in aqueous solution under simulated solar irradiation has been investigated in the presence of NO3-/NO2- ions. The degradation rates were compared by varying environmental parameters including substrate and inducer concentrations, oxygen content and pH. The photoproducts were identified by extensive LC-ESI-MS and LC-ESI-MS-MS studies after SPE preconcentration on prepacked cartridges. In both NO3- and NO2- conditions, oxidation of the N-(CH3)2 terminus group is the main process leading to the N-monodemethylated (NHCH3), N-formyl (N(CH3)CHO) and the uncommon and unstable carbinolamine (N(CH3)CH2OH) by-products. Cl/OH substituted and nitrated phenylureas are formed minorily. Degradation pathways involving OH* and NO2* (or dimer) radicals as reactive species are proposed.

Biodegradation, Environmental↗

PubMed2006

Microbial degradation of sulfur, nitrogen and oxygen heterocycles.

Sulfur (S), nitrogen (N) and oxygen (O) heterocycles are among the most potent environmental pollutants. Microbial degradation of these pollutants is attracting more and more attention because such bioprocesses are environmentally friendly. The biotechnological potential of these processes is being investigated, for example, to achieve better sulfur removal by immobilized biocatalysts with magnetite nanoparticles or by solvent-tolerant bacteria, and to obtain valuable intermediates from these heterocycles. Other recent advances have demonstrated the mechanisms of angular dioxygenation of nitrogen heterocycles by microbes. However, these technologies are not yet available for large-scale applications so future research must investigate proper modifications for industrial applications of these processes. This review focuses on recent progress in understanding how microbes degrade S, N and O heterocycles.

Bacteria↗

PubMedDate not supplied

Use of genetically engineered microorganisms (GEMs) for the bioremediation of contaminants.

This paper presents a critical review of the literature on the application of genetically engineered microorganisms (GEMs) in bioremediation. The important aspects of using GEMs in bioremediation, such as development of novel strains with desirable properties through pathway construction and the modification of enzyme specificity and affinity, are discussed in detail. Particular attention is given to the genetic engineering of bacteria using bacterial hemoglobin (VHb) for the treatment of aromatic organic compounds under hypoxic conditions. The application of VHb technology may advance treatment of contaminated sites, where oxygen availability limits the growth of aerobic bioremediating bacteria, as well as the functioning of oxygenases required for mineralization of many organic pollutants. Despite the many advantages of GEMs, there are still concerns that their introduction into polluted sites to enhance bioremediation may have adverse environmental effects, such as gene transfer. The extent of horizontal gene transfer from GEMs in the environment, compared to that of native organisms including benefits regarding bacterial bioremediation that may occur as a result of such transfer, is discussed. Recent advances in tracking methods and containment strategies for GEMs, including several biological systems that have been developed to detect the fate of GEMs in the environment, are also summarized in this review. Critical research questions pertaining to the development and implementation of GEMs for enhanced bioremediation have been identified and posed for possible future research.

Bacteria↗