Degradation of 1,4-dichlorobenzene by a Pseudomonas sp

A Pseudomonas species able to degrade p-dichlorobenzene as the sole source of carbon and energy was isolated by selective enrichment from activated sludge. The organism also grew well on chlorobenzene and benzene. Washed cells released chloride in stoichiometric amounts from o-, m-, and p-dichlorobenzene, 2,5-dichlorophenol, 4-chlorophenol, 3-chlorocatechol, 4-chlorocatechol, and 3,6-dichlorocatechol. Initial steps in the pathway for p-dichlorobenzene degradation were determined by isolation of metabolites, simultaneous adaptation studies, and assay of enzymes in cell extracts. Results indicate that p-dichlorobenzene was initially converted by a dioxygenase to 3,6-dichloro-cis-1,2-dihydroxycyclohexa-3,5-diene, which was converted to 3,6-dichlorocatechol by an NAD+-dependent dehydrogenase. Ring cleavage of 3,6-dichlorocatechol was by a 1,2-oxygenase to form 2,5-dichloro-cis, cis-muconate. Enzymes for degradation of haloaromatic compounds were induced in cells grown on chlorobenzene or p-dichlorobenzene, but not in cells grown on benzene, succinate, or yeast extract. Enzymes of the ortho pathway induced in cells grown on benzene did not attack chlorobenzenes or chlorocatechols.     

Degradation of 1,4-dichlorobenzene by a Pseudomonas sp.

A Pseudomonas species able to degrade p-dichlorobenzene as the sole source of carbon and energy was isolated by selective enrichment from activated sludge. The organism also grew well on chlorobenzene and benzene. Washed cells released chloride in stoichiometric amounts from o-, m-, and p-dichlorobenzene, 2,5-dichlorophenol, 4-chlorophenol, 3-chlorocatechol, 4-chlorocatechol, and 3,6-dichlorocatechol. Initial steps in the pathway for p-dichlorobenzene degradation were determined by isolation of metabolites, simultaneous adaptation studies, and assay of enzymes in cell extracts. Results indicate that p-dichlorobenzene was initially converted by a dioxygenase to 3,6-dichloro-cis-1,2-dihydroxycyclohexa-3,5-diene, which was converted to 3,6-dichlorocatechol by an NAD+-dependent dehydrogenase. Ring cleavage of 3,6-dichlorocatechol was by a 1,2-oxygenase to form 2,5-dichloro-cis, cis-muconate. Enzymes for degradation of haloaromatic compounds were induced in cells grown on chlorobenzene or p-dichlorobenzene, but not in cells grown on benzene, succinate, or yeast extract. Enzymes of the ortho pathway induced in cells grown on benzene did not attack chlorobenzenes or chlorocatechols.     

Degradation of 1,4-dichlorobenzene by Alcaligenes sp. strain A175

An organism, identified as an Alcaligenes sp., was isolated from an enrichment culture in which 1,4-dichlorobenzene served as the sole carbon and energy source. During growth with 1,4-dichlorobenzene in pure culture, stoichiometric amounts of chloride were released. Growth experiments and oxygen uptake rates with other chlorinated aromatic compounds revealed a high degree of specificity of the initial dioxygenase. cis-1,2-Dihydroxycyclohexa-3,5-diene oxidoreductase and 1,2-pyrocatechase, but not 2,3-pyrocatechase, were found in cell extracts, while 3,6-dichlorocatechol and (2,5-dichloro)muconic acid could be detected as intermediates during degradation of 1,4-dichlorobenzene. It is proposed that dioxygenases are involved in the initial steps of 1,4-dichlorobenzene degradation, while ring opening proceeds via ortho cleavage.     

Degradation of 1,4-dichlorobenzene by Xanthobacter flavus 14p1.

Xanthobacter flavus 14p1 was isolated from sludge of the river Mulde by selective enrichment with 1,4-dichlorobenzene as the sole source of carbon and energy. The bacterium did not use other aromatic or chloroaromatic compounds as growth substrates. During growth on 1,4-dichlorobenzene, stoichiometric amounts of chloride ions were released. Degradation products of 1,4-dichlorobenzene were identified by gas chromatography-mass spectrometry analysis. 3,6-Dichloro-cis-1,2-dihydroxycyclohexa-3,5-diene and 3,6-dichlorocatechol were isolated from culture fluid. 2,5-Dichloromuconic acid and 2-chloromaleylacetic acid as well as the decarboxylation product 2-chloroacetoacrylic acid were identified after enzymatic conversion of 3,6-dichlorocatechol by cell extract. 1,4-Dichlorobenzene dioxygenase, dihydrodiol dehydrogenase, and catechol 1,2-dioxygenase activity were induced in cells grown on 1,4-dichlorobenzene. The results demonstrate that 1,4-dichlorobenzene degradation is initiated by dioxygenation and that ring opening proceeds via ortho cleavage.     

Degradation of 1,4-dichlorobenzene by Alcaligenes sp. strain A175.

An organism, identified as an Alcaligenes sp., was isolated from an enrichment culture in which 1,4-dichlorobenzene served as the sole carbon and energy source. During growth with 1,4-dichlorobenzene in pure culture, stoichiometric amounts of chloride were released. Growth experiments and oxygen uptake rates with other chlorinated aromatic compounds revealed a high degree of specificity of the initial dioxygenase. cis-1,2-Dihydroxycyclohexa-3,5-diene oxidoreductase and 1,2-pyrocatechase, but not 2,3-pyrocatechase, were found in cell extracts, while 3,6-dichlorocatechol and (2,5-dichloro)muconic acid could be detected as intermediates during degradation of 1,4-dichlorobenzene. It is proposed that dioxygenases are involved in the initial steps of 1,4-dichlorobenzene degradation, while ring opening proceeds via ortho cleavage.     

Degradation of 1,2-dichlorobenzene by a Pseudomonas sp

A Pseudomonas sp. that was capable of growth on 1,2-dichlorobenzene (o-DCB) or chlorobenzene as a sole source of carbon and energy was isolated by selective enrichment from activated sludge. The initial steps involved in the degradation of o-DCB were investigated by isolation of metabolites, respirometry, and assay of enzymes in cell extracts. Extracts of o-DCB-grown cells converted radiolabeled o-DCB to 3,4-dichloro-cis-1,2-dihydroxycyclohexa-3,5-diene (o-DCB dihydrodiol). 3,4-Dichlorocatechol and o-DCB dihydrodiol accumulated in culture fluids of cells exposed to o-DCB. The results suggest that o-DCB is initially converted by a dioxygenase to a dihydrodiol, which is converted to 3,4-dichlorocatechol by an NAD+-dependent dehydrogenase. Ring cleavage of 3,4-dichlorocatechol is by a catechol 1,2-oxygenase to form 2,3-dichloro-cis,cis-muconate. Preliminary results indicate that chloride is eliminated during subsequent lactonization of the 2,3-dichloro-cis,cis-muconate, followed by hydrolysis to form 5-chloromaleylacetic acid.     

Degradation of 1,2-dichlorobenzene by a Pseudomonas sp.

A Pseudomonas sp. that was capable of growth on 1,2-dichlorobenzene (o-DCB) or chlorobenzene as a sole source of carbon and energy was isolated by selective enrichment from activated sludge. The initial steps involved in the degradation of o-DCB were investigated by isolation of metabolites, respirometry, and assay of enzymes in cell extracts. Extracts of o-DCB-grown cells converted radiolabeled o-DCB to 3,4-dichloro-cis-1,2-dihydroxycyclohexa-3,5-diene (o-DCB dihydrodiol). 3,4-Dichlorocatechol and o-DCB dihydrodiol accumulated in culture fluids of cells exposed to o-DCB. The results suggest that o-DCB is initially converted by a dioxygenase to a dihydrodiol, which is converted to 3,4-dichlorocatechol by an NAD+-dependent dehydrogenase. Ring cleavage of 3,4-dichlorocatechol is by a catechol 1,2-oxygenase to form 2,3-dichloro-cis,cis-muconate. Preliminary results indicate that chloride is eliminated during subsequent lactonization of the 2,3-dichloro-cis,cis-muconate, followed by hydrolysis to form 5-chloromaleylacetic acid.     

Degradation of alkanes by bacteria

Pollution of soil and water environments by crude oil has been, and is still today, an important problem. Crude oil is a complex mixture of thousands of compounds. Among them, alkanes constitute the major fraction. Alkanes are saturated hydrocarbons of different sizes and structures. Although they are chemically very inert, most of them can be efficiently degraded by several microorganisms. This review summarizes current knowledge on how microorganisms degrade alkanes, focusing on the biochemical pathways used and on how the expression of pathway genes is regulated and integrated within cell physiology.     

Degradation of 1,4-naphthoquinones by Pseudomonas putida

Pseudomonas putida J1 and J2, enriched from soil with juglone, are capable of a total degradation of 1,4-naphthoquinone, 2-hydroxy-1,4-naphthoquinone, and 2-chloro-1,4-naphthoquinone. Naphthazerin and plumbagin are only converted into the hydroxyderivatives 2-hydroxynaphthazerin and 3-hydroxyplumbagin, respectively, whereas 2-amino-1,4-naphthoquinone is not attacked at all. The degradation of 1,4-naphthoquinone begins with a hydroxylation of the quinoid ring, yielding 2-hydroxy-1,4-naphthoquinone (lawsone). Lawsone is reduced to 1,2,4-trihydroxynaphthalene with consumption of NADH. The fission product of the quinol could not be detected by direct means because of its instability. However, the presence of 2-chromonecarboxylic acid, a secondary product of lawsone degradation, leads to the conclusion, that the cleavage of the quinol takes place in the meta-position. The resulting ring fission product is converted into salicylic acid by removal of the side chain, presumably as pyruvate. Further degradation of salicyclic acid leads to the formation of catechol, which is then cleaved in the ortho-position and then metabolized via the 3-oxoadipate pathway. The initial steps in the degradation of 2-chloro-1,4-naphthoquinone, namely, the hydroxylation of the quinone to 2-chloro-3-hydroxy-1,4-naphthoquinone, followed by the elimination of the chlorine substituent lead to lawsone, which is further degraded through the pathway described. The degradation steps could be verified by the accumulation products of mutant strains blocked in different steps of lawsone metabolism. Generation of mutants was carried out by chemical and by transposon mutagenesis. The regulation of the first steps of the pathway catalysed by juglone hydroxylase and lawsone reductase, was investigated by induction experiments.     

Biodegradation of naphthalene by enriched marine denitrifying bacteria

Numerous studies have been investigated on the PAHs biodegradation in aerobic and anaerobic environments; however, the biodegradation of PAHs under anoxic conditions, especially denitrifying conditions, has drawn less attention. In this study, four series of batch experiments were conducted to investigate the effect of temperature, pH, naphthalene concentration and nitrate concentration on the naphthalene degradation under denitrification condition. Our results showed that the degradation of naphthalene was most favorable at pH 7 and 25 °C. Results also indicated that 30 mg/l naphthalene inhibited the biodegradation and the removal efficiency was only 20.2%. Significant degradation (91.7% and 96.3%) of naphthalene occurred when nitrate concentrations were 1.0 and 5.0 mM. Moreover, the maximum degradation rates were 0.13 and 0.18 mg-NAP/(l h) depending on the concentration of nitrate. Based on 16S rDNA analysis, the denitrifying enriched culture was mainly composed of ??-Proteobacteria (19 clones out of a total of 23 clones) and Actinobacteria (4 clones). Using a primer set specific for naphthalene degrading functional gene nahAc, two operational taxonomy units were obtained in the clone library of nahAc. Both of them were closely related to nahAc genes of known species of Pseudomonas. Quantitative polymerase chain reaction (qPCR) was employed to quantify the change of naphthalene-degrading population during the degradation of naphthalene using nahAc gene as the biomarker. The maximum degradation rate and removal efficiency were strongly correlated with nahAc gene copy number, with R² of 0.69 and 0.79, respectively.     

Degradation of cellulose by thermophilic bacteria

Degradation of 1—.10% crystalline cellulose and concentration of:free reducing sugars in the medium, were studied during cultivation of a wild coculture of obligately thermphilic bacteria in 3-L fermentors at 60^°C and pH 7.0 under anaerobic conditions. The coculture was composed of five different species ofBacillus and a single cellulolytic species lof Clostridium. The proportion of degraded substrate was inversely proportional to the initial concentration of cellulose. The higher the initial substrate concentration the lower the proportion of its.degradation. Cellulose at 1 — 2 % concentration is best degraded (98 % in:5.d). The fermentation time increases with increasing cellulose concentration, the level of reducing saccharides increases together with the initial rate of substrate degradation. In the presence of 10 %) cellulose the rate of degradation within a period of a 1-d fermentation is close toV, being 0.455 g L^-1 h^-1withK _m of 12.5 g/L. However, during further cultivation (1—3 d) the rate of degradation of 4—10 % cellulose decreases, probably due to the effect of accumulated reducing saccharides whose levels reach 55—60 mg/L.     

Degradation of lactoferrin by periodontitis-associated bacteria

Abstract The degradation of human lactoferrin by putative periodontopathogenic bacteria was examined. Fragments of lactoferrin were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and measured by densitometry. The degradation of lactoferrin was more extensive by Porphyromonas gingivalis and Capnocytophaga sputigena , slow by Capnocytophaga ochracea , Actinobacillus actinomycetemcomitans and Prevotella intermedia , and very slow or absent by Prevotella nigrescens , Campylobacter rectus, Campylobacter sputorum, Fusobacterium nucleatum ssp. nucleatum, Capnocytophaga gingivalis, Bacteroides forsythus and Peptostreptococcus micros . All strains of P. gingivalis tested degraded lactoferrin. The degradation was sensitive to protease inhibitors, cystatin C and albumin. The degradation by C. sputigena was not affected by the protease inhibitors and the detected lactoferrin fragments exhibited electrophoretic mobilities similar to those ascribed to deglycosylated forms of lactoferrin. Furthermore a weak or absent reactivity of these fragments with sialic acid-specific lectin suggested that they are desialylated. The present data indicate that certain bacteria colonizing the periodontal pocket can degrade lactoferrin. The presence of other human proteins as specific inhibitors and/or as substrate competitors may counteract this degradation process.     

Biodegradation of 4-chloroaniline by bacteria enriched from soil

4-Chloroaniline has been released into the environment due to extensive use in chemical industries and intensive agriculture; hence, it becomes one of the hazardous pollutants in the priority pollutant list. In this study, three gram-negative bacteria were enriched and isolated from agricultural soil as 4-chloroaniline-degrading bacteria. They were identified as Acinetobacter baumannii CA2, Pseudomonas putida CA16 and Klebsiella sp. CA17. They were able to utilize 4-chloroaniline as a sole carbon and nitrogen source without stimulation or cocultivation with aniline or another cosubstrate. The biodegradation in these bacteria was occurred via a modified ortho-cleavage pathway of which the activity of chlorocatechol 1, 2-dioxygenase was markedly induced. They grew well on 0.2-mM 4-chloroaniline exhibiting a 60-75% degradation efficiency and equimolar liberation of chloride. The isolates were able to survive in the presence of 4-chloroaniline at higher concentrations (up to 1.2 mM). 2-Chloroaniline, 3-chloroaniline and aniline, but not 3, 4-dichloroaniline, were also growth substrates for these isolates. The results of cosubstrate supplementation illustrated the suitable conditions of each isolate to improve growth rate and 4-chloroaniline biodegradation efficiency. These results suggest that these isolates have a potential use for bioremediation of the site contaminated with 4-chloroaniline.     

Metal removal by sulphate-reducing bacteria from natural and constructed wetlands

The use of wetlands is a promising technology to treat acid mine drainage, yet there is little understanding of the fundamental biological processes involved. They are considered to centre on the complex anaerobic ecology within sediments and involve the removal of metals by sulphate-reducing bacteria (SRB). These bacteria generate hydrogen sulphide and cause precipitation of metals from solution as the insoluble metal sulphide. Sulphate-reducing bacteria have been isolated from natural and constructed wetlands receiving acid mine drainage. Sulphide production by isolates and removal of the metals iron, manganese and zinc were measured, as well as utilization of a range of carbon sources. Marked ecological differences between the wetlands were reflected in population composition of SRB enrichments, and these consortia displayed significant differences in sulphide generation and rates of metal removal from solution. Rates of metal removal did not correlate with sulphide generation in all cultures, suggesting the involvement of other biological mechanisms of metal removal. Differences in substrate utilization have highlighted the need for further investigation of carbon flow and potential carbon sources within constructed wetlands.     

Degradation of 2-chlorobenzoate by in vivo constructed hybrid pseudomonads

Abstract 5-Chlorosalicylate degrading bacteria were obtained from the mating between Pseudomonas sp. strain WR401 and Pseudomonas sp. strain B13. Further selection of the hybrid organisms for growth on 2-chlorobenzoate allowed the isolation of strains such as JH230. During growth on 2-chlorobenzoate stoichiometric amounts of chloride were released. Steps in the pathway for 2-chlorobenzoate degradation were determined by simultaneous adaptation studies, assays of enzymes in cell extracts and cooxidation of the analogous substrate 2-methylbenzoate. Results indicate that 2-chlorobenzoate was degraded to 3-chlorocatechol. Ring cleavage of 3-chlorocatechol was by a catechol 1,2-dioxygenase to from 2-chloro- cis, cis - muconate. Further degradation runs via 4-carboxymethylenebut-2-en-4-olide.     

Anaerobic biodegradation of 1,4-dioxane by sludge enriched with iron-reducing microorganisms

The potential on anaerobic biodegradation of 1,4-dioxane was evaluated by use of enriched Fe(III)-reducing bacterium sludge from Hangzhou municipal wastewater treatment plant. The soluble Fe(III) supplied as Fe(III)-EDTA was more available for the Fe(III)-reducing bacterium in the sludge compared to insoluble Fe(III) oxide. The addition of humic acid (HA) further stimulated the anaerobic degradation of 1,4-dioxane accompanying with apparent reduction of Fe(III) which is believed that HA could stimulate the activity of Fe(III)-reducing bacterium by acting as an electron shuttle between Fe(III)-reducing bacterium and Fe(III), especially for insoluble Fe(III) oxides. After 40-day incubation, the concentration of 1,4-dioxane dropped up to 90% in treatment of Fe(III)-EDTA+HA. Further study proved that more than 50% of the carbon from 1,4-dioxane was converted to CO2 and no organic products other than biomass accumulated in the growth medium. The results demonstrated that, under the appropriate conditions, 1,4-dioxane could be biodegraded while serving as a sole carbon substrate for the growth of Fe(III)-reducing bacterium. It might be possible to design strategies for anaerobic remediation of 1,4-dioxane in contaminated subsurface environments.     

Degradation of 3-chlorobiphenyl by in vivo constructed hybrid pseudomonads

Abstract 3-Chlorobiphenyl-degrading bacteria were obtained from the mating between Pseudomonas putida strain BN10 and Pseudomonas sp. strain B13. Strains such as BN210 resulted from the transfer of the genes coding the enzyme sequence for the degradation of chlorocatechols from B13 into BN10, whereas B13 derivatives such as B131 have acquired the biphenyl degradation sequence from BN10. During growth of the hybrid strains on 3-chlorobiphenyl 90% chloride was released. Activities of phenylcatechol 2,3-dioxygenase, benzoate dioxygenase, catechol 1,2-dioxygenase, chloromuconate cyloisomerase and 4-carboxymethyl-enebut-2-en-4-olide hydrolase were found in 3-chlorobiphenyl-grown cells. The hybrid strains were found to convert some congeners of the Aroclor 1221 mixture such as mono- and dichloro-substituted biphenyls.     

Degradation and biosynthesis of L-phenylalanine by chloridazon-degrading bacteria]

Incubating chloridazon-degrading bacteria with L-phenylalanine leads to the accumulation of L-2,3-dihydroxyphenylalanine, o-tyrosine and m-tyrosine in the medium. Incubating the bacteria with N-acetyl-L-phenylalanine leads to N-acetyl-(2,3-dihydroxyphenyl)alanine. Using phenylacetic acid as substrate leads to the accumulation of malonic acid. The products are isolated by gel chromatography and high performance liquid chromatography. 2,3-Dihydroxy-L-phenylalanine is attacked by a catechol 2,3-dioxygenase in the presence of Fe2. An unstable yellow compound is formed in this reaction. This meta-cleavage-product is again cleaved by a hydrolase, leading to aspartic acid and 4-hydroxy-2-oxovaleric acid. Both products were isolated fromthe reaction buffer by amino acid analysis and high performance liquid chromatography. The dioxygenase and hydrolase were partially purified and characterized. A new degradation pathway for phenylalanine is discussed and compared with known pathways. The enzymes chorismate mutase, prephenate dehydratase and prephenate dehydrogenase are characterized and inhibition as well as repression are investigated. Only prephenate dehydrogenase is inhibited by phenylalanine, tyrosine and tryptophane. Chorismate mutase is repressed by phenylalanine, prephenate dehydrogenase by phenylalanine and tyrosine. Prephenate dehydratase is not repressed by aromatic amino acids. Regulation of aromatic amino acid biosynthesis in connection with phenylalanine degradation is discussed.     

Degradation of 1,4-Dioxane and Cyclic Ethers by an Isolated Fungus

By using 1,4-dioxane as the sole source of carbon, a 1,4-dioxane-degrading microorganism was isolated from soil. The fungus, termed strain A, was able to utilize 1,4-dioxane and many kinds of cyclic ethers as the sole source of carbon and was identified as Cordyceps sinensis from its 18S rRNA gene sequence. Ethylene glycol was identified as a degradation product of 1,4-dioxane by the use of deuterated 1,4-dioxane-d₈ and gas chromatography-mass spectrometry analysis. A degradation pathway involving ethylene glycol, glycolic acid, and oxalic acid was proposed, followed by incorporation of the glycolic acid and/or oxalic acid via glyoxylic acid into the tricarboxylic acid cycle.