Microbial degradation of chlorinated phenols

The chlorinated phenols comprise a large group of toxic, man-made chemicals that are serious environmental pollutants. Microorganisms can degrade many, but not all, of the chlorinated phenols, often using chlorophenol-specific catabolic enzymes. Novel technologies are evolving for using specific microorganisms to clean contaminated soils and waters of chlorophenols.     

Microbial degradation of chlorinated benzenes

Chlorinated benzenes are important industrial intermediates and solvents. Their widespread use has resulted in broad distribution of these compounds in the environment. Chlorobenzenes (CBs) are subject to both aerobic and anaerobic metabolism. Under aerobic conditions, CBs with four or less chlorine groups are susceptible to oxidation by aerobic bacteria, including bacteria (Burkholderia, Pseudomonas, etc.) that grow on such compounds as the sole source of carbon and energy. Sound evidence for the mineralization of CBs has been provided based on stoichiometric release of chloride or mineralization of (14)C-labeled CBs to (14)CO(2). The degradative attack of CBs by these strains is initiated with dioxygenases eventually yielding chlorocatechols as intermediates in a pathway leading to CO(2) and chloride. Higher CBs are readily reductively dehalogenated to lower chlorinated benzenes in anaerobic environments. Halorespiring bacteria from the genus Dehalococcoides are implicated in this conversion. Lower chlorinated benzenes are less readily converted, and mono-chlorinated benzene is recalcitrant to biotransformation under anaerobic conditions.     

Microbial degradation of chlorinated phenols

Chlorophenols have been introduced into the environment through their use as biocides and as by-products of chlorine bleaching in the pulp and paper industry. Chlorophenols are subject to both anaerobic and aerobic metabolism. Under anaerobic conditions, chlorinated phenols can undergo reductive dechlorination when suitable electron-donating substrates are available. Halorespiring bacteria are known which can use both low and highly chlorinated congeners of chlorophenol as electron acceptors to support growth. Many strains of halorespiring bacteria have the capacity to eliminate ortho-chlorines; however only bacteria from the species Desulfitobacterium hafniense (formerly frappieri) can eliminate para- and meta-chlorines in addition to ortho-chlorines. Once dechlorinated, the phenolic carbon skeletons are completely converted to methane and carbon dioxide by other anaerobic microorganisms in the environment. Under aerobic conditions, both lower and higher chlorinated phenols can serve as sole electron and carbon sources supporting growth. The best studied strains utilizing pentachlorophenol belong to the genera Mycobacterium and Sphingomonas. Two main strategies are used by aerobic bacteria for the degradation of chlorophenols. Lower chlorinated phenols for the most part are initially attacked by monooxygenases yielding chlorocatechols as the first intermediates. On the other hand, polychlorinated phenols are converted to chlorohydroquinones as the initial intermediates. Fungi and some bacteria are additionally known that cometabolize chlorinated phenols.     

Kinetic Modeling of cometabolic degradation of ethanethiol and phenol by Ralstonia eutropha

Cometabolism, as a complex phenomenon in microbial world, is a special mechanism for transformation of many compounds of environmental and toxicological significance. Several models have been proposed to describe the cometabolic transformations of non-growth substrates in the absence or presence of growth substrates. In this study, a model was proposed to simulate the degradation kinetics of phenol and ethanethiol (ET) by a pure culture of Ralstonia eutropha, including the effects of cell growth, endogenous cell decay, loss of transformation activity, competitive inhibition between growth and non-growth substrates, and self-inhibition of non-growth substrate. The model parameters were determined independently and were then used for evaluating the applicability of the model by comparing experimental data with model predictions. The model successfully predicted ET transformation and phenol utilization for a wide range of concentrations of ET (0 ～ 40 mg/L) and phenol (0 ～ 100 mg/L).     

Microbial degradation of chlorinated acetophenones.

A defined mixed culture, consisting of an Arthrobacter sp. and a Micrococcus sp. and able to grow with 4-chloroacetophenone as a sole source of carbon and energy, was isolated. 4-Chlorophenyl acetate, 4-chlorophenol, and 4-chlorocatechol were identified as metabolites through comparison of retention times and UV spectra with those of standard substances. The proposed pathway was further confirmed by investigation of enzymes. The roles of the two collaborating strains were studied by growth experiments and on the level of enzymes. If transient accumulation of 4-chlorophenol was avoided either by the use of phenol-absorbing substances or by careful supplement of 4-chloroacetophenone, the Arthrobacter sp. was able to grow as a pure culture with 4-chloroacetophenone as a sole source of carbon and energy. Several mono-, di-, and trichlorinated acetophenones were mineralized by the Arthrobacter sp.     

Cometabolic degradation of chlorinated aromatic compounds

The degradation of chlorobenzene was investigated with the specially chosen strain Methylocystis sp. GB 14 DSM 12955, using 23 ml headspace vials and in a soil column filled with quaternary aquifer material from a depth of 20 m. A long-term experiment was carried out in this column, situated in a mobile test unit at a contaminated location in Bitterfeld (Germany). Groundwater polluted by chlorobenzene was continuously fed through the column, through which a mixture comprising 4% CH(4) and 96% air was bubbled. Chlorobenzene was oxidized by up to 80% under pure culture conditions in the model experiments and was completely degraded under the mixed culture conditions of the column experiments. Over a period of 4 months, the stability of the biological system was monitored regularly by analyzing the sMMO activity as well as by classical microbiological and molecular biological methods.     

Facilitation of cometabolic degradation of 4-chlorophenol using glucose as an added growth substrate

This paper reports on the feasibility of using glucose as an added substrate for cometabolic transformation of 4-chlorophenol (4-cp). When glucose was fed as the added growth substrate, only 78% and 43% of the initial 4-cp concentrations of 100 and 200 mg l^–1, respectively, were transformed before the pH dropped to below 4.5 and stopped all reactions. By maintaining the medium pH, complete removal of 4-cp was achieved even at the high initial concentration of 200 mg l^–1. Phenol induction prior to inoculation was not a prerequisite to ensure transformation of 4-cp when glucose was the added growth substrate. Compared with phenol as the added growth substrate, cells grown on glucose displayed a longer acclimation phase and, in general, a lower specific transformation rate. The volumetric transformation rate of 4-cp, however, was greatly enhanced due to the increased cell density. The results of this work suggest that 4-cp itself induced the enzymes necessary for its cometabolism. With NADH regenerated effectively through metabolism of glucose, 4-cp was transformed in the absence of added phenol. Consequently, the competitive inhibition involved in cometabolism was avoided and the risks associated with addition of toxic growth substrates such as phenol were eliminated     

Bacterial degradation of riboflavin

Summary Studies on the degradation of 6,7-dimethylquinoxaline-2,3-diol-(methyl-¹⁴C) by Pseudomonas RF are described. Evidence is presented that this degradation product of riboflavin is assimilated by at least two different pathways which are affected by growth conditions. One leads to the previously identified 3,4-dimethyl-6-carboxy--pyrone and the other to intermediates which in turn are metabolized to various cell constituents.Analyses of amino acids from protein hydrolysates and organic acids excreted into the medium disclosed the presence of ¹⁴C-labelled alanine, butyrate, propionate and acetate, all predominantly labelled in the terminal methyl group. Results of studies with various inhibitors of the two pathways are given and the data are compared with previous work on this organism. A scheme for bacterial degradation of 6,7-dimethylquinoxaline-2,3-diol is postulated.     

Bacterial degradation of benzalphthalide

APseudomonas sp., isolated by an enrichment culture technique, grew on benzalphthalide at up to 1 g/l as sole carbon source. Cells oxidized both benzalphthalide ando-phthalate at enhanced rates compared with glucose-grown cells, but catechol, gentisate and protocatechuate were oxidized slowly and equally by benzalphthalide-and glucose-grown cells.     

异养同化降解氯代烃的研究现状、微生物代谢特性及展望

氯代烃(Chlorinated hydrocarbons,CAHs)污染遍布全球,其三致效应和遗传毒性对人类健康和生态环境构成重大威胁。CAHs异养同化具有降解彻底、无二次污染和降解效率高的特点,全面认识CAHs异养同化过程,对于强化和应用异养同化降解,扩大CAHs的修复途径具有重要的推动作用。文中首先分析了微生物细胞异养同化降解CAHs主要方式,阐述了异养同化的两大优势;针对CAHs异养同化的研究现状进行了系统性的总结,明确了可发生异养同化作用的CAHs种类及特征;基于氯代烷烃、氯代烯烃和氯代芳烃分类,概述了异养同化微生物的主要菌属及代谢特征;针对典型氯代烃,系统分析了参与代谢过程关键酶及特征基因,归纳了异养同化代谢途径;最后,根据当前研究现状对异养同化研究存在的问题进行了综述并对未来的发展方向进行了展望。     

Bacterial degradation of emulsan

Emulsan is a polyanionic heteropolysaccharide bioemulsifier produced by Acinetobacter calcoaceticus RAG-1. A mixed bacterial population was obtained by enrichment culture that was capable of degrading emulsan and using it as a carbon source. From this mixed culture, an emulsan-degrading bacterium, termed YUV-1, was isolated. Strain YUV-1 is an aerobic, gram-negative, non-spore-forming, rod-shaped bacterium which grows best in media containing yeast extract. When placed on preformed lawns of A. calcoaceticus RAG-1, strain YUV-1 produced translucent plaques which grew in size until the entire plate was covered. Plaque formation was due to solubilization of the emulsan capsule of RAG-1. Plaque formation was not observed on emulsan-negative mutants of RAG-1. As a consequence of the solubilization of the emulsan capsule, RAG-1 cells became more hydrophobic, as determined by adherence to hexadecane. Growth of YUV-1 on a medium containing yeast extract and emulsan was biphasic. During the initial 24 h, cell concentration increased 10-fold, but emulsan was not degraded; during the lag in growth (24 to 48 h), emulsan was inactivated and depolymerized but not consumed; during the second growth phase (48 to 70 h) the depolymerized emulsan products were consumed.     

Bacterial degradation of EDTA

Degradation of EDTA (ethylenediaminetetraacetic acid) or metal-EDTA complexes by cell suspensions of the bacterial strain DSM 9103 was studied. The activity of EDTA degradation was the highest in the phase of active cell growth and decreased considerably in the stationary phase, after substrate depletion in the medium. Exponential-phase cells were incubated in HEPES buffer (pH 7.0) with 1 mM of uncomplexed EDTA or EDTA complexes with Mg2+, Ca2+, Mn2+, Pb2+, Co2+, Cd2+, Zn2+, Cu2+, or Fe3+. The metal-EDTA complexes (Me-EDTA) studied could be divided into three groups according to their degradability. EDTA complexes with stability constants K below 10(16) (lg K < 16), such as Mg-EDTA, Ca-EDTA, and Mn-EDTA, as well as uncomplexed EDTA, were degraded by the cell suspensions at a constant rate to completion within 5-10 h of incubation. Me-EDTA complexes with lg K above 16 (Zn-EDTA, Co-EDTA, Pb-EDTA, and Cu-EDTA) were not completely degraded during a 24-hour incubation, which was possibly due to the toxic effect of the metal ions released. No degradation of Cd-EDTA or Fe(III)-EDTA by cell suspensions of strain DSM 9103 was observed under the conditions studied.     

Trichloroethylene cometabolic degradation by Rhodococcus sp. L4 induced with plant essential oils

Cometabolic degradation of TCE by toluene-degrading bacteria has the potential for being a cost-effective bioremediation technology. However, the application of toluene may pose environmental problems. In this study, several plant essential oils and their components were examined as alternative inducer for TCE cometabolic degradation in a toluene-degrading bacterium, Rhodococcus sp. L4. Using the initial TCE concentration of 80 muM, lemon and lemongrass oil-grown cells were capable of 20 +/- 6% and 27 +/- 8% TCE degradation, which were lower than that of toluene-grown cells (57 +/- 5%). The ability of TCE degradation increased to 36 +/- 6% when the bacterium was induced with cumin oil. The induction of TCE-degrading enzymes was suggested to be due to the presence of citral, cumin aldehyde, cumene, and limonene in these essential oils. In particular, the efficiency of cumin aldehyde and cumene as inducers for TCE cometabolic degradation was similar to toluene. TCE transformation capacities (T (c)) for these induced cells were between 9.4 and 15.1 mug of TCE mg cells(-1), which were similar to the known toluene, phenol, propane or ammonia degraders. Since these plant essential oils are abundant and considered non-toxic to humans, they may be applied to stimulate TCE degradation in the environment.     

Bacterial bioconcentration of chlorinated hydrocarbon insecticides from aqueous systems

The prevalence of chlorinated hydrocarbon insecticide uptake by chemoorganotrophic bacteria has been investigated. Thirteen bacterial species were observed to sorb and concentrate (bioconcentratc)α-chlordane,β-chlordane, dieldrin, heptachlor epoxide, and lindane from aqueous systems. Bioconcentration, as expressed by the ratio of cellular insecticide in ng/mg (dry wt) to supernatant insecticide in ng/μl, ranged from 10 for lindane byEnterobacter aerogenes to a high of 55,900 forβ-chlordane byCaulobacter vibrioides var.limonus. Amounts of cellular chlorinated hydrocarbon insecticides (CHI) detected and the bioconcentration ratios were observed to have the following order in magnitude:α- orβ-chlordane > dieldrin > heptachlor epoxide > lindane. This decreasing order was the inverse of reported water solubilities for the CHI and the inverse relationship was mathematically defined. The CHI were not easily removed from cells by washing (desorbing) and desorption was directly proportional to insecticide water solubility. Uptake of the CHI was rapid, near-maximum amounts being sorbed within 15 min, and pH 7 appeared optimal for bioconcentration as examined over the range pH 6 to 8. Implications of this investigation are that bioconcentration of CHI by bacteria might serve as a means of introducing these toxic compounds into aquatic food chains and that the bioconcentration phenomenon might lend itself as a treatment procedure for the intentional removal of residual CHI from water supplies and wastewater.     

Bacterial degradation of ammonium lignosulfonate

Bacterial strains were selected for their capacity to assimilate and to transform ammonium-lignosulfonate. Modification of the methyl content and of low molecular weight alkyl functions were demonstrated by gas-chromatography and HLPC analysis. Most of these strains completely degraded simple phenolic compounds related to lignosulfonate without inhibition by the carbohydrates present in the liquor. Further investigation suggested that the enzymes involved in the fission of the aromatic nuclei were constitutive in the strains tested.     

Bacterial degradation of emulsan.

Emulsan is a polyanionic heteropolysaccharide bioemulsifier produced by Acinetobacter calcoaceticus RAG-1. A mixed bacterial population was obtained by enrichment culture that was capable of degrading emulsan and using it as a carbon source. From this mixed culture, an emulsan-degrading bacterium, termed YUV-1, was isolated. Strain YUV-1 is an aerobic, gram-negative, non-spore-forming, rod-shaped bacterium which grows best in media containing yeast extract. When placed on preformed lawns of A. calcoaceticus RAG-1, strain YUV-1 produced translucent plaques which grew in size until the entire plate was covered. Plaque formation was due to solubilization of the emulsan capsule of RAG-1. Plaque formation was not observed on emulsan-negative mutants of RAG-1. As a consequence of the solubilization of the emulsan capsule, RAG-1 cells became more hydrophobic, as determined by adherence to hexadecane. Growth of YUV-1 on a medium containing yeast extract and emulsan was biphasic. During the initial 24 h, cell concentration increased 10-fold, but emulsan was not degraded; during the lag in growth (24 to 48 h), emulsan was inactivated and depolymerized but not consumed; during the second growth phase (48 to 70 h) the depolymerized emulsan products were consumed.     

Bacterial degradation of p-methoxybenzoic acid

Summary A cell-free system from a Pseudomonas sp., strain PM3, catalysed the oxidative demethylation, hydroxylation and subsequent ring cleavage of p-methoxybenzoate. Demethylation, to yield p-hydroxybenzoate, involved absorption of 1.0 mole of oxygen/mole of p-methoxybenzoate, and required reduced pyridine nucleotide (either NADH or NADPH) as cofactor. p-Hydroxybenzoate was hydroxylated to yield protocatechuate with the absorption of 1 mole of oxygen/mole of substrate, and required NADPH as cofactor. Protocatechuate was oxidized, with absorption of 1 mole of oxygen/mole of substrate, to 3-oxoadipate. The methyl group of p-methoxybenzoate was removed as formaldehyde, and oxidized to formate and carbon dioxide by formaldehyde dehydrogenase, which required GSH and NAD⁺, and formate dehydrogenase, which required NAD⁺.     

Bacterial degradation of vinyl chloride

Summary Mycobacterium L1 can grow on vinyl chloride as sole carbon and energy source. Application of this bacterium to remove vinyl chloride from waste gases is proposed. From air containing 1% vinyl chloride 93% of the vinyl chloride was removed by passing the air through a fermentor containing a growing population ofMycobacterium L1.