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PubMed1995

Effect of the local anesthetics phenethyl alcohol and procaine on hns mutants of the acid-induced biodegradative arginine (adi) and lysine (cad) decarboxylases of Escherichia coli.

The environmentally responsive biodegradative arginine (adi) and lysine (cad) decarboxylases are maximally induced when Escherichia coli is cultured under acidic, anaerobic conditions in rich medium. Previously, transposon mutagenesis led to the identification of hns (encoding H-NS, a histone-like DNA binding protein) as being a trans-acting regulatory factor of both systems. The hns mutants show depressed expression of adi or cad (i.e., their expression is increased). The effects of the local anesthetics phenethyl alcohol (PEA) and procaine (both environmental perturbants) were investigated with lacZ operon fusions to either adi or cad and their respective hns mutants. These results indicate that wild-type fusion strains are insensitive to either PEA or procaine, but that hns mutants show decreased beta-galactosidase synthesis in the presence of one or both of the local anesthetics. This is the first report of the effect of local anesthetics on hns mutants in this or any other environmentally responsive system.

Biodegradation, Environmental↗
PubMed2003

Biodegradation of chemicals in a standardized test and in environmental conditions.

The estimation of biodegradation rates is an important source of uncertainty in chemical risk assessment. The existing OECD tests for ready biodegradability have been developed to devise screening methods to determine whether a chemical is potentially easily biodegradable, rather than to predict the actual rate, of biodegradation in the environment. However, risk assessment needs degradation rates. In practice these rates are often estimated (default values) from ready biodegradability tests. These tests have many compromising arbitrary features compared to the situation in the real environment. One important difference is the concentration of the chemical. In wastewater treatment or in the environment many chemicals are present at ng l(-1) to microg l(-1) levels whereas in the tests the concentrations exceed 10-400 mg carbon per litre. These different concentrations of the chemical will lead to different growth kinetics and hence different biodegradation rates. At high concentrations the chemical, if it is degradable, can serve as a primary substrate and competent microorganisms will grow exponentially, resulting in a sigmoid biodegradation curve. At low environmental concentrations the chemical does not serve as a primary substrate, and therefore does not support significant growth of the degraders, and the substrate has a linear biodegradation rate. In this study the biodegradation rates of two reference chemicals, aniline and 4-chloroaniline, were compared in a standard method and in more realistic conditions at low concentrations, using 14C-labelled substances and different sources of inocula. Biomass evolution during the tests was monitored by adenosine triphosphate measurement and also on the basis of the residual 14C-activity in the particulate matter. The results partly support the thesis that low concentrations lead to different biodegradation kinetics compared to the concentrations used in the standard tests. Furthermore the biodegradation rates of the chemicals studied, particularly of 4-chloroaniline, in Finnish natural waters appeared to be lower than those reported in some other countries.

Adenosine Triphosphate↗
PubMed2006

Soft ligands--biodegradable complexants in plant cultivation and environmental protection.

In this paper, the place and role of biodegradable complexants in light of modern plant cultivation criteria is discussed. From this point of view, micro- and macroelement (metal) chelators play a remarkable role. They are widely used in a variety of consumer products and processes, especially in agriculture. The great majority of the traditional chelators (e.g., EDTA) are, however, essentially non-biodegradable. We have systematically investigated some new biodegradable ligands with polyaminopolycarboxylic structure. We conclude that these compounds may be considered as a special group of the soft (safer) chemicals proposed first by Bodor based on retrometabolic concepts. We studied the structural conditions of biodegradability, especially regarding the new ligands, by the physicochemical characterization of their complexes formed with micro- and macroelements. The study of the complicated equilibrium conditions required the prior determination of the stability constants of the metal aqua/hydroxo complexes and the protonation constants of the ligands as well. Knowledge of the pH-dependence of the proper competitive equilibriums allowed the optimization of the investigated complexation reactions. The protonation and stability constants obtained were compared with the adequate values of the traditional, but weakly biodegradable EDTA. Excellent or very good linear correlations have been found between the logarithms of the different ligands' protonation constants, but the slopes of the straight lines were different and generally smaller than EDTA's corresponding values. Presumably, the log stability constants (logK(st)) of complexes formed by different ligands (X(m), X(n)) having analogue structures with a given metal-ion series (M(i), i = 1, 2, ...) are linearly correlated [i.e., log K(X(m)M(i)) = a log K(X(n)M(i)) + b], just as the stability constants of complexes formed by different ions (M(k), M(l)) with a given ligand series (X(j), j = 1, 2, ...). Based on the rich data basis of EDTA, these regression equations allow the calculation of some still unmeasured stability constants of the new biodegradable complexes. In the analysis of structural effects we would like to especially highlight the role of stereochemical relations in addition to the usual structural elements. From this point of view, the eventual presence of chiral nitrogen atoms is of particular importance. The stability of these compounds increases in their complexed form. As a special research field, we have examined the possibility of obtaining metal ion buffers. These systems may get an important role both from theoretical and practical points of view.

Biodegradation, Environmental↗
PubMed2003

A comparison of DNA profiling techniques for monitoring nutrient impact on microbial community composition during bioremediation of petroleum-contaminated soils.

Amplicon length heterogeneity PCR (LH-PCR) and terminal restriction fragment length polymorphisms (TRFLP) were used to monitor the impact that nutrient amendments had on microbial community dynamics and structural diversity during bioremediation of petroleum-contaminated soils. Slurried soils contaminated with petroleum hydrocarbons were treated in airlift bench-scale bioreactors and were either amended with optimal inorganic nutrients or left unamended. Direct DNA extraction and PCR amplification of whole eubacterial community DNA were performed with universal primers that bracketed the first two or three hypervariable regions of the 16S rDNA gene sequences. The LH-PCR method profiled a more diverse microbial community than did the TRFLP method. The LH-PCR method also tracked differences between the communities due to nutrient amendments. An in silico database search for bacterial genera with amplicon lengths represented in the community fingerprints was performed. It was possible to qualitatively identify different groups in the microbial community based on the amplicon length variations. A similar "virtual" search was performed for the TRFLP fragments using the web-based TAP-TRFLP program. Cloning and sequencing of the PCR products confirmed the in silico database matches. The application of the LH-PCR method as a monitoring tool for bioremediation could greatly enhance and extend the current understanding of the microbial community dynamics during the biodegradation of environmental contaminants.

Bacteria↗
PubMed1998

19F NMR study on the biodegradation of fluorophenols by various Rhodococcus species.

Of all NMR observable isotopes 19F is the one perhaps most convenient for studies on biodegradation of environmental pollutants. The reasons underlying this potential of 19F NMR are discussed and illustrated on the basis of a study on the biodegradation of fluorophenols by four Rhodococcus strains. The results indicate marked differences between the biodegradation pathways of fluorophenols among the various Rhodococcus species. This holds not only for the level and nature of the fluorinated biodegradation pathway intermediates that accumulate, but also for the regioselectivity of the initial hydroxylation step. Several of the Rhodococcus species contain a phenol hydroxylase that catalyses the oxidative defluorination of ortho-fluorinated di- and trifluorophenols. Furthermore, it is illustrated how the 19F NMR technique can be used as a tool in the process of identification of an accumulated unknown metabolite, in this case most likely 5-fluoromaleylacetate. Altogether, the 19F NMR technique proved valid to obtain detailed information on the microbial biodegradation pathways of fluorinated organics, but also to provide information on the specificity of enzymes generally considered unstable and, for this reason, not much studied so far.

Biodegradation, Environmental↗
PubMed2024

Comparative genomic analysis and functional investigations for MCs catabolism mechanisms and evolutionary dynamics of MCs-degrading bacteria in ecology.

Microcystins (MCs) significantly threaten the ecosystem and public health. Biodegradation has emerged as a promising technology for removing MCs. Many MCs-degrading bacteria have been identified, including an indigenous bacterium Sphingopyxis sp. YF1 that could degrade MC-LR and Adda completely. Herein, we gained insight into the MCs biodegradation mechanisms and evolutionary dynamics of MCs-degrading bacteria, and revealed the toxic risks of the MCs degradation products. The biochemical characteristics and genetic repertoires of strain YF1 were explored. A comparative genomic analysis was performed on strain YF1 and six other MCs-degrading bacteria to investigate their functions. The degradation products were investigated, and the toxicity of the intermediates was analyzed through rigorous theoretical calculation. Strain YF1 might be a novel species that exhibited versatile substrate utilization capabilities. Many common genes and metabolic pathways were identified, shedding light on shared functions and catabolism in the MCs-degrading bacteria. The crucial genes involved in MCs catabolism mechanisms, including mlr and paa gene clusters, were identified successfully. These functional genes might experience horizontal gene transfer events, suggesting the evolutionary dynamics of these MCs-degrading bacteria in ecology. Moreover, the degradation products for MCs and Adda were summarized, and we found most of the intermediates exhibited lower toxicity to different organisms than the parent compound. These findings systematically revealed the MCs catabolism mechanisms and evolutionary dynamics of MCs-degrading bacteria. Consequently, this research contributed to the advancement of green biodegradation technology in aquatic ecology, which might protect human health from MCs.

Humans↗
PubMed1999

Development and characterization of a lux-modified 2,4-dichlorophenol-degrading Burkholderia sp. RASC.

lux-marked biosensors for assessing the toxicity and bioremediation potential of polluted environments may complement traditional chemical techniques. luxCDABE genes were introduced into the chromosome of the 2,4-dichlorophenol (2,4-DCP)-mineralizing bacterium, Burkholderia sp. RASC c2, by biparental mating using the Tn4431 system. Experiments revealed that light output was constitutive and related to cell biomass concentration during exponential growth. The transposon insertion was stable and did not interrupt 2,4-DCP-degradative genes, and expression of luxCDABE did not constitute a metabolic burden to the cell. A bioluminescence response was detectable at sublethal 2,4-DCP concentrations: at < 10.26 microg ml(-1), bioluminescence was stimulated (e.g. 218% of control), but at concentrations >60 microg ml(-1) it declined to < 1%. Investigating the effect of [14C]-2,4-DCP concentration on the evolution of 14CO2 revealed that, for initial concentrations of 2.5-25 microg ml(-1), approximately equals 55% of the added 14C was mineralized after 24 h compared with <1% at 50 and 100 microg ml(-1). Inhibition of 2,4-DCP mineralization between 25 and 50 microg ml(-1) corresponded well to the EC50 value (33.83 microg ml(-1)) obtained from bioluminescence inhibition studies. lux-marked RASC c2 may therefore be used as a functionally (i.e. 2,4-DCP degrader) and environmentally relevant biosensor of toxicity and biodegradation inhibition.

2,4-Dinitrophenol↗
PubMed2002

Chromate reduction in Serratia marcescens isolated from tannery effluent and potential application for bioremediation of chromate pollution.

Pollution of aquatic systems by heavy metals has resulted in increasing environmental concern because they cannot be biodegraded. One metal that gives reason for concern due to its toxicity is chromium. Cr(VI) and Cr(III) are the principal forms of chromium found in natural waters. A chromate-resistant strain of the bacterium S. marcescens was isolated from tannery effluent. The strain was able to reduce Cr(VI) to Cr(III), and about 80% of chromate was removed from the medium. The reduction seems to occur on the cell surface. Transmission electron microscopic examination of cells revealed that particles were deposited on the outside of bacterial cells. A stable biofilm was formed in less than 10 h, reaching around 1010 cfu attached per milligram of activated carbon. These findings demonstrate that immobilized S. marcescens might be used in industrial waste treatment processes.

Biodegradation, Environmental↗
PubMed1984

Biochemical studies on the fate of monensin in animals and in the environment.

Extensive studies have been conducted with monensin in target animals and laboratory animals to determine monensin concentrations in tissues, route of elimination, metabolism and pharmacokinetics of monensin. These studies indicate that monensin administered orally is absorbed, extensively metabolized, excreted in the bile and eliminated in the feces by the several species examined. Monensin did not accumulate in the tissues of orally dosed animals. When fed to cattle and chickens according to recommended practices, monensin was not detected (less than .05 ppm) in edible tissues. Environmental studies indicate that monensin is biodegradable in manure and soil.

Adipose Tissue↗
PubMed1995

Biodegradation of nitroaromatic compounds.

Nitroaromatic compounds are released into the biosphere almost exclusively from anthropogenic sources. Some compounds are produced by incomplete combustion of fossil fuels; others are used as synthetic intermediates, dyes, pesticides, and explosives. Recent research revealed a number of microbial systems capable of transforming or biodegrading nitroaromatic compounds. Anaerobic bacteria can reduce the nitro group via nitroso and hydroxylamino intermediates to the corresponding amines. Isolates of Desulfovibrio spp. can use nitroaromatic compounds as their source of nitrogen. They can also reduce 2,4,6-trinitrotoluene to 2,4,6-triaminotoluene. Several strains of Clostridium can catalyze a similar reduction and also seem to be able to degrade the molecule to small aliphatic acids. Anaerobic systems have been demonstrated to destroy munitions and pesticides in soil. Fungi can extensively degrade or mineralize a variety of nitroaromatic compounds. For example, Phanerochaete chrysosporium mineralizes 2,4-dinitrotoluene and 2,4,6-trinitrotoluene and shows promise as the basis for bioremediation strategies. The anaerobic bacteria and the fungi mentioned above mostly transform nitroaromatic compounds via fortuitous reactions. In contrast, a number of nitroaromatic compounds can serve as growth substrates for aerobic bacteria. Removal or productive metabolism of nitro groups can be accomplished by four different strategies. (a) Some bacteria can reduce the aromatic ring of dinitro and trinitro compounds by the addition of a hydride ion to form a hydride-Meisenheimer complex, which subsequently rearomatizes with the elimination of nitrite. (b) Monooxygenase enzymes can add a single oxygen atom and eliminate the nitro group from nitrophenols. (c) Dioxygenase enzymes can insert two hydroxyl groups into the aromatic ring and precipitate the spontaneous elimination of the nitro group from a variety of nitroaromatic compounds. (d) Reduction of the nitro group to the corresponding hydroxylamine is the initial reaction in the productive metabolism of nitrobenzene, 4-nitrotoluene, and 4-nitrobenzoate. The hydroxylamines undergo enzyme-catalyzed rearrangements to hydroxylated compounds that are substrates for ring-fission reactions. Potential applications of the above reactions include not only the biodegradation of environmental contaminants, but also biocatalysis and synthesis of valuable organic molecules.

Aerobiosis↗
PubMed1992

Screening methods for assessment of biodegradability of chemicals in seawater--results from a ring test.

An international ring test involving 14 laboratories was organized on behalf of the Commission of the European Economic Communities (EEC) with the purpose of evaluating two proposed screening methods for assessment of biodegradability in seawater: (a) a shake flask die-away test based primarily on analysis of dissolved organic carbon and (b) a closed bottle test based on determination of dissolved oxygen. Both tests are performed with nutrient-enriched natural seawater as the test medium and with no inoculum added other than the natural seawater microflora. The test methods are seawater versions of the modified OECD screening test and the closed bottle test, respectively, adopted by the Organization for Economic Cooperation and Development (OECD) and by the EEC as tests for "ready biodegradability." The following five chemicals were examined: sodium benzoate, aniline, diethylene glycol, pentaerythritol, and 4-nitrophenol. Sodium benzoate and aniline, which are known to be generally readily biodegradable consistently degraded in practically all tests, thus demonstrating the technical feasibility of the methods. Like in previous ring tests with freshwater screening methods variable results were obtained with the other three compounds, which is believed primarily to be due to site-specific differences between the microflora of the different seawater samples used and to some extent also to differences in the applied concentrations of test material. A positive result with the screening methods indicates that the test substance will most likely degrade relatively rapidly in seawater from the site of collection, while a negative test result does not preclude biodegradability under environmental conditions where the concentrations of chemicals are much lower than the concentrations applied for analytical reasons in screening tests. Nevertheless, the screening tests are considered useful and cost-effective tools for an initial assessment of biodegradability in marine environments.

Aniline Compounds↗
PubMed2005

Polycyclic aromatic hydrocarbon biodegradation rates: a structure-based study.

This study was designed to examine the role of molecular structure in determining the biodegradation rates of polycyclic aromatic hydrocarbons (PAHs). Laboratory experiments were performed in aqueous systems, and data were analyzed in a manner that allowed determination of first-order biodegradation rates independent of bioavailability limitations from physical-chemical processes. An aerobic mixed culture was used, which had been enriched on a broad range of PAHs. The 22 PAHs included in this study ranged in size from two to four rings and included compounds with 5-carbon rings and alkyl substituents. The range of observed biodegradation rates was only 1 order of magnitude, which is much less than that which is typically observed in the field. This supports the findings of other types of studies, which conclude that most of the observed variation in environmental PAH biodegradation rates comes from processes controlling the bioavailability of the compounds and not processes controlling uptake or biotransformation. Rate differences that were observed were attributable either to the presence of a 5-carbon ring or an alkyl substituent in an alpha position. Various molecular descriptors that might be expected to correlate with rate-limiting steps in the biodegradation process were used in an attemptto develop a quantitative structure-activity relationship for the PAH biodegradation rates. No significant correlations were found, but rate limitation from interactions with the relevant enzymes remains a possibility.

Aerobiosis↗
PubMed2005

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.

Biodegradation, Environmental↗