Showing papers in "Biodegradation in 1992"
TL;DR: In this paper, the authors provide an outline of the microbial degradation of polycyclic aromatic hydrocarbons, including bacteria, fungi and algae, and the biochemical principles underlying the degradation.
Abstract: The intent of this review is to provide an outline of the microbial degradation of polycyclic aromatic hydrocarbons. A catabolically diverse microbial community, consisting of bacteria, fungi and algae, metabolizes aromatic compounds. Molecular oxygen is essential for the initial hydroxylation of polycyclic aromatic hydrocarbons by microorganisms. In contrast to bacteria, filamentous fungi use hydroxylation as a prelude to detoxification rather than to catabolism and assimilation. The biochemical principles underlying the degradation of polycyclic aromatic hydrocarbons are examined in some detail. The pathways of polycyclic aromatic hydrocarbon catabolism are discussed. Studies are presented on the relationship between the chemical structure of the polycyclic aromatic hydrocarbon and the rate of polycyclic aromatic hydrocarbon biodegradation in aquatic and terrestrial ecosystems.
1,839 citations
TL;DR: The use of bioremediation as a supplemental cleanup technology in the Exxon Valdez oil spill, in Prince William Sound, Alaska, has proven to be a good example of the problems and successes associated with the practical application of this technology as discussed by the authors.
Abstract: The use of bioremediation as a supplemental cleanup technology in the Exxon Valdez oil spill, in Prince William Sound, Alaska, has proven to be a good example of the problems and successes associated with the practical application of this technology. Field studies conducted by scientists from the U.S. Environmental Protection Agency have demonstrated that oil degradation by indigenous microflora on the beaches of Prince William Sound was accelerated by adding fertilizer directly to the surfaces of oil-contaminated beaches. Although several types of fertilizers were used in the studies, only the results from the application of an oleophilic fertilizer are presented. The fertilizer enhanced biodegradation of the oil, as measured by changes in hydrocarbon composition and bulk oil weight per unit of beach material, by approximately two-fold relative to untreated controls. Laboratory studies verified the usefulness of the oleophilic fertilizer as a nutrient source, but the contribution of its oleophilic components towards enhancing biodegradation is still unclear. These studies supported bioremediation as a useful cleanup strategy that was subsequently used by Exxon on a large scale. The Exxon Valdez experience has also provided a number of informative lessons that have significant relevance to future oil bioremediation efforts. This paper discusses these lessons and the difficulties in assessing the effectiveness of bioremediation in the field.
203 citations
TL;DR: The list of toxic compounds that can be degraded or transformed in media of high salinity is growing as mentioned in this paper, including saturated and aromatic hydrocarbons, organophosphorus compounds, and formaldehyde.
Abstract: Though our knowledge on microbial degradation of organic pollutants at high salt concentrations is still limited, the list of toxic compounds shown to be degraded or transformed in media of high salinity is growing. Compounds transformed aerobically include saturated and aromatic hydrocarbons (by certain archaeobacteria), certain aromatic compounds, organophosphorus compounds, and formaldehyde (by halotolerant eubacteria). Anaerobic microbial transformations of toxic compounds occurring at high salt concentrations include reduction of nitroaromatic compounds, and possibly transformation of chlorinated aromatic compounds.
177 citations
TL;DR: Bacteria have developed two general strategies for enhancing contact with water-insoluble hydrocarbons: specific adhesion mechanisms and production of extracellular emulsifying agents.
Abstract: Microbial degradation of hydrocarbons is a multiphase reaction, involving oxygen gas, water-insoluble hydrocarbons, water, dissolved salts and microorganisms. The fact that the first step in hydrocarbon catabolism involves a membrane-bound oxygenase makes it essential for microorganisms to come into direct contact with the hydrocarbon substrate. Growth then proceeds on the hydrocarbon/water interface. Bacteria have developed two general strategies for enhancing contact with water-insoluble hydrocarbons: specific adhesion mechanisms and production of extracellular emulsifying agents. Since petroleum is a complex mixture of many different classes of hydrocarbons, of which any particular microorganism has the potential to degrade only part, it follows that the microorganisms must also have a mechanism for desorbing from used' oil droplets.
166 citations
TL;DR: The enzymes which utilize cyanide as a substrate can be categorized into the following reaction types: substitution/addition, hydrolysis, oxidation, and reduction, which are reviewed with respect to the known biochemistry and feasibility for use in treatment of cyanide containing wastes.
Abstract: Cyanide is an important industrial chemical produced on a grand scale each year. Although extremely toxic to mammalian life, cyanide is a natural product generated by fungi and bacteria, and as a result microbial systems have evolved for the degradation of cyanide to less toxic compounds. The enzymes which utilize cyanide as a substrate can be categorized into the following reaction types: substitution/addition, hydrolysis, oxidation, and reduction. Each of these categories is reviewed with respect to the known biochemistry and feasibility for use in treatment of cyanide containing wastes.
137 citations
TL;DR: Findings show that the pMMO is capable of TCE oxidation; although the rates are lower than those observed for the sMMO.
Abstract: Trichloroethylene (TCE) oxidation was examined in 9 different methanotrophs grown under conditions favoring expression of the membrane associated methane monooxygenase. Depending on the strain, TCE oxidation rates varied from 1 to 677 pmol/min/mg cell protein. Levels of TCE in the reaction mixture were reduced to below 40 nmolar in some strains. Cells incubated in the presence of acetylene, a selective methane monooxygenase inhibitor, did not oxidize TCE.
119 citations
TL;DR: The detoxification of organophosphate chemical agents focuses on the investigation of organo-nitro degrading enzymes from bacteria, and the relationship of this research to the critical concerns of the agricultural industry regarding detoxified pesticides is discussed.
Abstract: Hazardous energetic organo-nitro compounds are found as contaminants in many environments. A series of nitro aromatics, nitrate esters and nitro amines, all characteristic of this class, has been studied for their susceptibility to biological transformation. Biotransformation pathways for each of these compounds have been identified and are summarized. Implications for these findings in light of current contamination issues is discussed. The detoxification of organophosphate chemical agents focuses on the investigation of organophosphate degrading enzymes from bacteria. Certain of these enzymes, active both in solution and when immobilized onto a solid surface, are very successful in hydrolyzing and detoxifying various organophosphate chemical agents. The relationship of this research to the critical concerns of the agricultural industry regarding detoxification of organophosphorous pesticides is discussed.
107 citations
TL;DR: The utilization of carbon monoxide as energy and/or carbon source by different physiological groups of bacteria is described and compared and the little information available on the nutritional and physicochemical requirements determining the sink strength is summarized.
Abstract: The utilization of carbon monoxide as energy and/or carbon source by different physiological groups of bacteria is described and compared. Utilitarian CO oxidation which is coupled to the generation of energy for growth is achieved by aerobic and anaerobic eu- and archaebacteria. They belong to the physiological groups of aerobic carboxidotrophic, facultatively anaerobic phototrophic, and anaerobic acetogenic, methanogenic or sulfate-reducing bacteria. The key enzyme in CO oxidation is CO dehydrogenase which is a molybdo iron-sulfur flavoprotein in aerobic CO-oxidizing bacteria and a nickel-containing iron-sulfur protein in anaerobic ones. In carboxidotrophic and phototrophic bacteria, the CO-born CO2 is fixed by ribulose bisphosphate carboxylase in the reductive pentose phosphate cycle. In acetogenic, methanogenic, and probably in sulfate-reducing bacteria, CODH/acetyl-CoA synthase directly incorporates CO into acetyl-CoA.
106 citations
TL;DR: Three new isolates obtained by conventional enrichment technics which show significant degradation capabilities for Aroclor 1242 are details and it is concluded that the described strains may be of future bioremediation use in processes which have an initial anaerobic dechlorination stage.
Abstract: The environment has become polluted with a variety of xenobiotics, including PCBs, as a result of the industrial development of useful halogenated compounds. While the PCBs may not exhibit the acute toxicity originally ascribed to them, they and their attendant byproducts remain as significant factors for adverse effects in the ecological food-chain. The use of microorganisms for bioremediation of PCBs is reviewed. This paper further details three new isolates obtained by conventional enrichment technics which show significant degradation capabilities for Aroclor 1242. These were identified by morphology, staining, and fatty acid analysis as Comamonas testosteroni, Rhodococcus rhodochrous, and a strain of Pseudomonas putida. These isolates demonstrated somewhat selective degradations of the congeners within Aroclor 1242; comprising total losses of 13.8, 19.1, and 24.6%, respectively. Each organism can attack dichloro-through tetrachlorobiphenyls. Analysis of chromatographic patterns from anaerobically digested Aroclor 1242 samples treated by these bacteria demonstrated decreases in di- through penta-substituted biphenyls. Each of these isolates, with discrete specificities, showed preferences for ‘open’ 2,3-sites, indicative of the action of 2,3-dioxygenase enzymes. The identification of many intermediates in the foregoing transformations was established by GC-MS analyses. Several variations in metabolic pathways, centering on the meta cleavage product 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) were suggested from these data. It is concluded that the described strains may be of future bioremediation use in processes which have an initial anaerobic dechlorination stage.
99 citations
TL;DR: The various aspects of cellulose as a pollutant are considered in view of its lack of toxicity on the one hand and its recalcitrant durable nature on the other, and the microbial degradation of cellulosics is discussed.
Abstract: The various aspects of cellulose as a pollutant are considered in view of its lack of toxicity on the one hand and its recalcitrant durable nature on the other. The microbial degradation of cellulosics is discussed, and the contrast between its success in handling natural cellulosic wastes versus its failure to cope with man-made refuse is described. Research carried out in the past decade has demonstrated that cellulolytic organisms are provided with cell surface multifunctional multienzyme conglomerates, called cellulosomes, which are capable of solubilizing solid cellulosic substrates. The intriguing properties of such complexes include their cohesive nature, their many enzymatic components, and a characteristic glycosylated cellulose-binding, ‘scaffolding’ component. The latter appears to serve as a substrate-targeting carrier, which delivers the other (hydrolytic) components to the cellulose. Progress in establishing efficient model systems for in vitro solubilization of purified cellulose or natural cellulosic substrates has been achieved using purified cellulosome preparations, fortified with β-glucosidase and pectinase. The latter enzymes were required in order to alleviate the phenomenon of product inhibition which reduces the efficiency of the free cellulosome. Such combined enzyme systems are proposed as examples of future tailor-made cellulolytic systems for the degradation of natural cellulosics.
77 citations
TL;DR: In this paper, the current knowledge of fluxes and conversions of C1 organic sulfides in different ecosystems is presented, and the role of these compounds in the global sulfur budget at their climatic role is discussed.
Abstract: C1 organic sulfides are part of many ecosystems and play an important role in the global sulfur budget and climate regulation. At this point, fluxes and conversions of these compounds are only superficially understood. Understanding of the regulating mechanisms will be necessary to quantify the role of these compounds in the global sulfur budget at their climatic role. In this review, the current knowledge of fluxes and conversions of C1 organic sulfides in different ecosystems is presented.
TL;DR: In cell-free extracts of S. rochei, the activity of hydroxyquinol 1,2-dioxygenase was found and the enzyme was induced with chlorophenols, enabling a wider range of chlorinated phenols as the sole sourse of carbon and energy.
Abstract: The strain Streptomyces rochei 303 (VKM Ac-1284D) is capable of utilizing 2-chloro-,2,4-,2,6-dichloro- and 2,4,6-trichlorophenols as the sole source of carbon. Its resting cells completely dechlorinated and degraded 2-, 3-chloro-; 2,4-, 2,6-, 2,3-, 2,5-, 3,4-, 3,5-dichloro-; 2,4-, 2,6-dibromo-; 2,4,6-, 2,4,5-, 2,3,4-, 2,3,5-, 2,3,6-trichlorophenols; 2,3,5,6-tetrachloro- and pentachlorophenol. During chlorophenol degradation, a stoichiometric amount of chloride ions was released and chlorohydroquinols were formed as intermediates. In cell-free extracts of S. rochei, the activity of hydroxyquinol 1,2-dioxygenase was found. The enzyme was induced with chlorophenols. Of all so far described strains degrading polychlorophenols, S. rochei 303 utilized a wider range of chlorinated phenols as the sole sourse of carbon and energy.
TL;DR: In this article, a set of shampoo bottles were attached to a buoy in order to incubate poly(3-hydroxyalkanoates) (PHA) in an aquatic ecosystem under natural conditions.
Abstract: Experiments have been carried out in Lake Lugano, Switzerland, in order to study the biodegradation of poly(3-hydroxyalkanoates) (PHA) in an aquatic ecosystem under natural conditions. Commercially available plastic articles made from PHA, such as bottles and films, were incubated for 254 days in a water depth of 85 m. Shampoo bottles were positioned precisely on the sediment surface by the use of a small manned submarine. A set of bottles was attached to a buoy in order to incubate plastic material in diffent water depths. When incubated in the water column or on the sediment surface, a life span of five to ten years for this specific bottle type was calculated. In situ degradation rates of 10 to 20 mg/d were determined. PHA films were completely degraded when incubated in the top 20 cm of the sediment. The results clearly demonstrate that in an aquatic ecosystem (water column as well as sediment) under in situ conditions (i.e. low temperatures, seasonal variations of the oxygen concentration) plastic goods made from PHA are degraded.
TL;DR: In this article, the potential utilization of edible mushrooms of the genus Pleurotus via solid state fermentation, using cotton plant stalks as a substrate was discussed, and the degradation of cotton stalks by white rot fungi was described using chemical analyses and scanning electron microscopy.
Abstract: Lignocellulosic waste represents huge amounts of unutilized renewable resource. The use of the polysaccharides in the lignocellulosic complex is limited due to their high lignin content. White rot fungi are capable of selectively degrading lignin, thereby upgrading it. The focus of this article is on the potential utilization of edible mushrooms of the genus Pleurotus, via solid state fermentation, using cotton plant stalks as a substrate. This material poses agrotechnical problems since the stalks have a fibrous structure similar to that of hardwood. Potential uses for this material are as a fuel in rural areas, a substrate for mushrooms, an animal feed and substrate for paper making. In this study, degradation of cotton stalks by Pleurotus is described using chemical analyses and scanning electron microscopy. During four weeks of solid state fermentation, lignin content significantly decreased and in vitro digestibility was increased. The fermentation product was consumed by ruminants at a level of up to 40% of their diet.
TL;DR: Xylanase T-6 was shown to partially remove lignin from unbleached pulp at 65 °C and pH 9.0, without loss in pulp viscosity, and was used to make handsheets that had higher brightness than untreated pulp.
Abstract: During the bleaching of wood pulp for the paper industry, large amounts of chlorinated aromatic compounds are produced and released into the environment. These compounds are extremely toxic and are a major source of pollution. The paper and pulp industry is seeking for alternative methods for bleaching pulp. One such method involves the use of hemicellulases to release the colored lignohemicellulose. We have isolated and characterized several thermophilic bacteria which produce xylanases. One such strain, T-6, produced high levels of extracellular xylanase, free of cellulase and proteinase activities. Strain T-6 was classified as a strain of Bacillus stearothermophilus and was able to grow on defined medium containing xylose, methionine and asparagine at 65 °C. Xylanase activity was induced by either xylose or xylan; no activity was detected with other carbon sources, such as glycerol, acetate, lactose, glucose, maltose, fructose, mannose, galactose or sucrose. Xylanase constitutive mutants were obtained following mutagenesis and detection on p-nitrophenol β-d-xylopyranoside containing agar plates. Xylanase T-6 was produced on large scale, and was purified and concentrated by a single adsorption-desorption step from a cation exchanger. The overall purification yield of a 1000 liter fermentation was 45%, resulting in a 98% pure enzyme. Xylanase T-6 was shown to partially remove lignin from unbleached pulp at 65 °C and pH 9.0, without loss in pulp viscosity. The enzyme-treated pulp was used to make handsheets that had higher brightness than untreated pulp.
TL;DR: Unless the structure and function of the various components of the process are worked out, progress in developing means for controlling nitrification will depend mainly on laborious trial and error and not on knowledgeable manipulation of this group of bacteria.
Abstract: In the sequence of events leading from ammonia to N2 during the process of biotransformation of inorganic nitrogen compounds, the weakest link, with respect to our knowledge and understanding of the organisms involved, is nitrification. In particular, this is true for the oxidation of ammonia to nitrite. The enzymes have not been thoroughly studied, and the enzymatic mechanisms have not been identified. Almost any biochemical and physiological aspect studied proved to be controversial, and major ecological questions still remain unanswered. Unless the structure and function of the various components of the process are worked out, progress in developing means for controlling nitrification will depend mainly on laborious trial and error and not on knowledgeable manipulation of this group of bacteria.
TL;DR: Bacterially mediated ionic mercury reduction to volatile Hg0 was shown to play an important role in the geochemical cycling of mercury in a contaminated freshwater pond as discussed by the authors, which could be stimulated to reduce the concentration of methylmercury that is available for accumulation by biota.
Abstract: Bacterially mediated ionic mercury reduction to volatile Hg0 was shown to play an important role in the geochemical cycling of mercury in a contaminated freshwater pond. This process, and the degradation of methylmercury, could be stimulated to reduce the concentration of methylmercury that is available for accumulation by biota. A study testing the utility of this approach is described.
TL;DR: In this paper, the transformations of 14CCl4 by whole cells of Acetobacterium woodii suspended in phosphate buffer containing reducing agents, and by the cobalt corrinoid aquocobalamin in the same solution, were compared.
Abstract: The transformations of 14CCl4 by whole cells of Acetobacterium woodii suspended in phosphate buffer containing reducing agents, and by the cobalt corrinoid aquocobalamin in the same solution, were compared. Each catalyst transformed 14CCl4 not only to reduced products (CHCl3 and CH2Cl2) but also to CO and CO2 as well as non-volatile products. The mass balance for radioactive carbon was complete in each case. Thus, the reactions of the pure cobalt corrinoid resemble the reactions in vivo. The proton in CHCl3, formed from CCl4 by A. woodii, was derived from water. Extracts of A. woodii were fractionated into large and small molecules, and each of the two fractions was separated chromatographically. Fractions of proteins demonstrated poor correlation between content of the corrinoid vitamin B12 and rates of transformation of CCl4. The correlation was somewhat improved if the fractions were autoclaved, but dechlorination in the absence of vitamin B12 was observed. Separation of the small molecules yielded only one fraction containing vitamin B12, and this fraction catalyzed dechlorination, whereas several other fractions were able to dechlorinate CCl4 in the absence of vitamin B12. We presume there to be unrecognized dechlorinative factors in anaerobic bacteria.
TL;DR: These studies with purified enzymes are beginning to reveal more detailed mechanistic features of bacterial chlorinated methane metabolism.
Abstract: Chlorinated methanes are important environmental pollutants, which can be metabolized by bacteria. The biotransformation of chlorinated methanes by bacteria has been shown to be due either to gratuitous metabolism (cometabolism) or their use as a source of carbon and energy. The reactions which result in carbon-halogen bond cleavage include substitutive, reductive, oxygenative, and gem-elimination mechanisms. Certain methylotrophic bacteria can use dichloromethane as a source of carbon and energy. Dichloromethane dehalogenase catalyzes the first substitutive reaction in this metabolism. The enzyme shows a 1010-fold rate enhancement over the reaction of the bisulfide anion with dichloromethane in water. Pseudomonas putida G786 synthesizes cytochrome P-450CAM which catalyzes the gratuitous reduction of chlorinated methanes. These studies with purified enzymes are beginning to reveal more detailed mechanistic features of bacterial chlorinated methane metabolism.
TL;DR: The nature of the environment dictates to a large extent the biodegradability of synthetic compounds by modulating the evolutionary processes in microorganisms for new degradative genes.
Abstract: Microorganisms in nature are largely responsible for the biodegradation and removal of toxic and non-toxic chemicals. Many organisms are also known to have specific ecological niches for proliferation and colonization. The nature of the environment dictates to a large extent the biodegradability of synthetic compounds by modulating the evolutionary processes in microorganisms for new degradative genes. Similarly, environmental factors often determine the extent of microbial gene expression by activating or repressing specific gene or sets of genes through a sensory signal transduction process. Understanding how the environment modulates microbial activity is critical for successful bioremediative applications.
TL;DR: Cleavage of 3-chlorocatechol by catechol 1,2-dioxygenase seems to be the critical step in the metabolism of chlorobenzene, and metabolites also seem to function as toxic compounds.
Abstract: Pseudomonas sp. strain RHO1 able to use chloro- and 1,4-dichlorobenzene as growth substrates was tested towards sensitivity against chlorobenzene. Concentrations of chlorobenzene higher than 3.5 mM were found to be toxic to cells independent of pregrowth with chlorobenzene or nutrient broth. Below this concentration, sensitivity towards chlorobenzene depended on the precultivation of the cells, i.e. type of growth substrate (chlorobenzene or nutrient broth) and the concentration of chlorobenzene as the growth substrate. Cells grown in continuous culture were especially sensitive with a threshold concentration of 2.5 mM chlorobenzene. In addition to chlorobenzene, metabolites also seem to function as toxic compounds. 2-Chlorophenol and 3-chlorocatechol were isolated from cell extracts. Cleavage of 3-chlorocatechol by catechol 1,2-dioxygenase seems to be the critical step in the metabolism of chlorobenzene.
TL;DR: In this article, the authors present a review of the natural and anthropogenic sources of sulphur pollution, its consequences and possible solutions, as well as the appropriate reactor design based on this type of study is essential if such bacterial communities are to function efficiently.
Abstract: Pollution by inorganic and organic sulphur compounds is increasing and, because of the many environmental hazards associated with these compounds (e.g. toxicity, acidification of rain and freshwater, increase of COD, the greenhouse effect), must be taken seriously. There is a wide variety of sulphur oxidizing bacteria available in nature, and these can be used for the effective control of such pollution. The best way to break the sulphur cycle is to stop it at sulphur which, being insoluble, can be easily recovered (e.g. SO4 2− → S2− → S0). (Eco)physiological knowledge about the sulphur oxidizing bacteria has proved very useful in the prediction of the performance of sulphur oxidizing communities in actual wastewater treatment systems. Appropriate reactor design, based on this type of study, is essential if such bacterial communities are to function efficiently, especially when toxic sulphides must be treated. This paper reviews the natural and anthropogenic sources of sulphur pollution, its consequences and possible solutions.
TL;DR: The usual situation is of large volumes of soil and water that are contaminated with low, but significant, concentrations of cadmium, and detoxification of the polluted water and soil involves the concentration of the metal, or binding it in a way that makes it biologically inert as mentioned in this paper.
Abstract: Cadmium pollution arises mainly from contamination of minerals used in agriculture and from industrial processes. The usual situation is of large volumes of soil and water that are contaminated with low — but significant — concentrations of cadmium. Therefore, detoxification of the polluted water and soil involves the concentration of the metal, or binding it in a way that makes it biologically inert.
TL;DR: The linear or the logarithmic form of a three-half-order model were found to be the most appropriate models for describing 2,4-D mineralization in soil and a significant growth of the inoculated strains was found in accordance with the assumptions of the model.
Abstract: Mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) by two Alcaligenes eutrophus strains and one Pseudomonas cepacia strain containing the 2,4-D degrading plasmids pJP4 or pRO101 (=pJP4::Tn1721) was tested in 50 g (wet wt) samples of non-sterile soil. Mineralization was measured as 14C-CO2evolved during degradation of uniformly-ring-labelled 14C-2,4-D. When the strains were inoculated to a level of approximately 108 CFU/g soil, between 20 and 45% of the added 2,4-D (0.05 ppm, 10 ppm or 500 ppm) was mineralized within 72 h. Mineralization of 0.05 ppm and 10 ppm, 2,4-D by the two A. eutrophus strains was identical and rapid whereas mineralization by P. cepacia DBO1(pRO101) occurred more slowly. In contrast, mineralization of 500 ppm 2,4-D by the two A. eutrophus strains was very slow whereas mineralization by P. cepacia DBO1 was more rapid. Comparison of 2,4-D mineralization at different levels of inoculation with P. cepacia DBO1(pRO101) (6×104, 6×106 and 1×108 CFU/g soil) revealed that the maximum mineralization rate was reached earlier with the high inoculation levels than with the low level. The kinetics of mineralization were evaluated by nonlinear regression analysis using five different models. The linear or the logarithmic form of a three-half-order model were found to be the most appropriate models for describing 2,4-D mineralization in soil. In the cases in which the logarithmic form of the three-half-order model was the most appropriate model we found, in accordance with the assumptions of the model, a significant growth of the inoculated strains.
TL;DR: Molecular methods have been developed based upon recovery of DNA from environmental samples and gene probe hybridization to specific diagnostic gene sequences for the specific detection of genetically engineered microorganisms.
Abstract: Plans to introduce genetically engineered microorganisms into the environment has led to concerns over safety and has raised questions about how to detect and to contain such microorganisms. Specific gene sequences, such as lacZ, have been inserted into genetically engineered microorganisms to permit their phenotypic detection. Molecular methods have been developed based upon recovery of DNA from environmental samples and gene probe hybridization to specific diagnostic gene sequences for the specific detection of genetically engineered microorganisms. DNA amplification using the polymerase chain reaction has been applied to enhance detection sensitivity so that single gene targets can be detected. Detection of messenger RNA has permitted the monitoring of gene expression in the environment. The use of reporter genes, such as the lux gene for bioluminescence, likewise has permitted the observation of gene expression. Conditional lethal constructs have been developed as models for containment of genetically engineered microorganisms. Suicide vectors, based upon the hok gene have been developed as model containment systems.
TL;DR: Information is still severely lacking regarding the biochemical pathways involved in haloalkane degradation, as well as their genetic control.
Abstract: Halogenated alkanes constitute a significant group among the organic pollutants of environmental concern. Their industrial and agricultural uses are extensive, but until 1978 they were considered to be non-biodegradable. In recent years, microorganisms were described that could degrade, partially or fully, singly or in consortia, many of the compounds tested. The first step in haloalkane degradation appears to be universal: removal of the halogen atom(s). This is mediated by a group of enzymes, generally known as dehalogenases, acting in most cases either as halidohydrolases or oxygenases. Nevertheless, information is still severely lacking regarding the biochemical pathways involved in these processes, as well as their genetic control.
TL;DR: In this article, molecular structures and properties were calculated using the semi-empirical Modified Neglect of Differential Overlap method at the Cornell Supercomputing Facility, which correlated with observed reductive dechlorination pathways by unacclimated consortia.
Abstract: Electronic properties were correlated with observed reductive dechlorination pathways by unacclimated consortia for chlorinated phenols, dihydroxybenzenes, benzoic acids, and anilines. Molecular structures and properties were calculated using the semi-empirical Modified Neglect of Differential Overlap method at the Cornell Supercomputing Facility. Observed preferential positions for reductive dechlorination by unacclimated consortia correlate well with the largest negative value for the carbon-chlorine bond charge. Of 16 dechlorination pathways observed for unacclimated bacteria, the most negative carbon-chlorine bond charge correlated with 15 pathways. This correlation between the observed dechlorination position and the parent compound's electronic properties is consistent with the observed reductive dechlorination of chlorophenols and chlorinated dihydroxybenzenes at the ortho position, and the meta dechlorination of chlorobenzoic acids. Net carbonchlorine bond charges also correlate with the preferred dechlorination position for two of three known chloroaniline pathways, suggesting preferential removal of chlorines from the ortho position of chloroanilines.
TL;DR: It was found that microbes could adapt to using chlorinated benzenes by evolution of new enzyme specificities and by exchange of genetic material to improve biodegradability of halogenated compounds.
Abstract: Soil column experiments were performed to obtain insight in the different biological and physico-chemical processes affecting biodegradation of halogenated compounds under natural conditions in a water infiltration site. Lower chlorinated aromatic compounds could be degraded under aerobic conditions, whereas highly chlorinated compounds and chlorinated aliphatic compounds were mainly transformed under anaerobic conditions. Microorganisms which derive energy from reductive dechlorination were enriched and characterized. It was found that microbes could adapt to using chlorinated benzenes by evolution of new enzyme specificities and by exchange of genetic material. For halogenated pollutants, which are generally hydrophobic, sorption processes control the concentration available for biodegradation. The effects of very low concentrations of halogenated compounds on their biodegradability are described. The use of isolated bacterial strains to enhance biodegradation was evaluated with respect to their temperature-related activity and to their adhesion properties.
TL;DR: The dehalogenation step in the chlorophenol degradation is the cycloisomerization of the cis,cis-chloromuconic acid to 4-carboxymethylenebut-2-en-4-olide in the ortho fission pathway.
Abstract: The phenol-assimilating yeast Candida maltosa is able to degrade monochlorophenols but cannot grow on these substrates. 3- and 4-chlorophenol were broken down very rapidly by phenol-grown cells under the formation of 4-chlorocatechol, 5-chloropyrogallol and 4-carboxymethylenebut-2-en-4-olide with concomitant release of chloride. 2-Chlorophenol was partially converted into cis,cis-2-chloromuconic acid via 3-chlorocatechol which was also obtained from 3-chlorophenol in low amounts. No further metabolites containing chloride were found. The dehalogenation step in the chlorophenol degradation is the cycloisomerization of the cis,cis-chloromuconic acid to 4-carboxymethylenebut-2-en-4-olide in the ortho fission pathway.
TL;DR: In this paper, two materials of different structure, sepiolite and bentonite, evaluated as supports for the microorganisms effecting anaerobic fermentation, behaved differently towards condensation water from thermally concentrated olive mill wastewater from a kinetic point of view.
Abstract: Two materials of different structure, sepiolite and bentonite, evaluated as supports for the microorganisms effecting anaerobic fermentation, behaved differently towards condensation water from thermally concentrated olive mill wastewater from a kinetic point of view. Assuming the overall anaerobic digestion process to conform to first-order kinetics, the apparent kinetic constant for the digester including sepiolite as support was 1.12 day-1, while that of the digester using the bentonite support was 0.73 day-1. Thus, the apparent kinetic constant of the process was increased by 35% with the use of sepiolite. The yield coefficient, Yp/s, was 0.344 and 0.318 litres CH4 STP/g COD for the sepiolite and bentonite supports respectively.