Enzymatic degradation of dibutyl phthalate and toxicity of its degradation products

Dibutyl phthalate (DBP) was more efficiently degraded by cutinase compared to yeast esterase; i.e. almost 80% of initial DBP (500 mg l⁻¹) was decomposed within 7.5 h, and nearly 50% of the degraded DBP disappeared within the initial 30 min. The toxicity of the final DBP degradation products were investigated using various recombinant bioluminescent bacteria. Butyl methyl phthalate, the major product of degradation by the esterase, was an oxidative toxic hazard that damaged protein synthesis.     

Kinetics and pathway of biodegradation of dibutyl phthalate by Pleurotus ostreatus

Dibutyl phthalate (DBP) is a plasticizer, whose presence in the environment as a pollutant has attained a great deal of attention due to its reported association with endocrine system disturbances on animals. Growth parameters, glucose uptake, percentage of removal efficiency (%E) of DBP, biodegradation constant of DBP (k) and half-life of DBP biodegradation (t_1/2) were evaluated for Pleurotus ostreatus grown on media containing glucose and different concentrations of DBP (0, 500 and 1000 mg l^?1). P. ostreatus degraded 99.6 % and 94 % of 500 and 1000 mg of DBP l^?1 after 312 h and 504 h, respectively. The k was 0.0155 h^?1 and 0.0043 h^?1 for 500 and 1000 mg of DBP l^?1, respectively. t_1/2 was 44.7 h and 161 h for 500 and 1000 mg of DBP l^?1, respectively. Intermediate compounds of biodegraded DBP were identified by GC-MS and a DBP biodegradation pathway was proposed using quantum chemical calculation. DBP might be metabolized to benzene and acetyl acetate, the first would be oxidated to muconic acid and the latter would enter into the Krebs cycle. P. ostreatus has the ability to degrade DBP and utilizes it as source of carbon and energy.     

Enhanced degradation and toxicity reduction of dihexyl phthalate by Fusarium oxysporum f. sp. pisi cutinase

AIMS: This research aims to investigate the efficiency of two lipolytic enzymes--fungal cutinase and yeast esterase--upon the biodegradation of dihexyl phthalate (DHP). METHOD AND RESULTS: During the enzymatic degradation of DHP dissolved in methanol, several degradation products were detected and their time-course changes were monitored using GC/MS. The DHP-degradation rate of cutinase was surprisingly high; i.e. almost 70% of the initial DHP (500 mg l(-1)) was decomposed within 4.5 h. Although the same amount of esterase was employed, more than 85% of the DHP remained after 3 days. Almost all the DHP was converted by cutinase into 1,3-isobenzofurandione (IBF), whereas hexyl methyl phthalate and IBF were abundantly produced by esterase. In addition, the toxicities of the DHP-degraded products by esterase were evaluated using various recombinant bioluminescent bacteria, which caused oxidative and protein damage, whereas the hydrolysis products from cutinase never caused any cellular damage in the methanol-containing reaction system. CONCLUSIONS: Cutinase starts to act as a DHP-degrader much earlier and faster than esterase, with high stability in ester-hydrolytic activity, therefore a plausible approach to the practical application of cutinase for DHP degradation in the DHP-contaminated environments may be possible. SIGNIFICANCE AND IMPACT OF THE STUDY: This study describes the enhanced degradation and detoxification of DHP using Fusarium oxysporum f. sp. pisi cutinase.     

节杆菌(Arthrobacter sp.)降解阿魏酸的效能

[背景]蓄积在土壤中的阿魏酸类化感自毒物质对农作物生长产生危害,利用有益微生物分解该类物质是一项有效的治理措施.[目的]从自然界土壤分离获得能高效降解阿魏酸的菌株,并评估典型环境因子对降解效能的影响,以期为该菌在阿魏酸类自毒物质降解领域中的应用提供理论依据.[方法]采用一次性投加高浓度化合物的驯化方法分离筛选得到能有效...     

Malathion biodegradation by a psychrotolerant bacteria Ochrobactrum sp. M1D and metabolic pathway analysis

An organophosphorus pesticide malathion biodegradation was investigated by using the bacteria Ochrobactrum sp. M1D isolated from a soil sample of peach orchards in Palampur, District Kangra, Himachal Pradesh (India). The bacterium was able to utilize malathion as the sole source of carbon and energy. The isolated bacterium was found psychrotolerant and could degrade 100% of 100 mg l⁻¹ malathion in minimal salt medium at 20°C, pH 7·0 within 12 days with no major significant metabolites left at the end of the study. Through GCMS analysis, methyl phosphate, diethyl maleate, and diethyl 2-mercaptosuccinate were detected and identified as the major pathway metabolites. Based on the GCMS profile, three probable degradation pathways were interpreted. The present study is the first report of malathion biodegradation at both the psychrophilic and mesophilic conditions by any psychrotolerant strain and also through multiple degradation pathways. In the future, the strain can be explored to bio-remediate the malathion contaminated soil in the cold climatic region and to utilize the enzymatic systems for advanced biotechnology applications.     

Oxidative Degradation of 4-Hydroxyacetophenone in Arthrobacter sp. TGJ4

The 4-hydroxyacetophenone assimilating bacterium Arthrobacter sp. TGJ4 was isolated from a soil sample. The resting cell reaction suggested that the strain cleaved 4-hydroxyacetophenone and its 3-methoxy derivative to the corresponding carboxylic acids and formaldehyde. Some properties of the enzyme catalyzing the cleavage reaction were examined.     

Metabolism of butyl benzyl phthalate by Gordonia sp. strain MTCC 4818

The microbial degradative characteristics of butyl benzyl phthalate (BBP) were investigated by the Gordonia sp. strain MTCC 4818 isolated from creosote-contaminated soil. The test organism can utilize a number of phthalate esters as sole sources of carbon and energy, where BBP was totally degraded within 4 days under shake culture conditions. High performance liquid chromatography profile of the metabolites isolated from spent culture indicated the accumulation of two major products apart from phthalic acid (PA), which were characterized by gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy as mono-n-butyl phthalate (MBuP) and monobenzyl phthalate (MBzP). Neither of the metabolites, MBuP, MBzP or PA, supported growth of the test organism, while in resting cell transformation, the monoesters were hydrolyzed to PA to a very minor extent, which was found to be a dead-end product in the degradation process. On the other hand, the test organism grew well on benzyl alcohol and butanol, the hydrolyzed products of BBP. The esterase(s) was found to be inducible in nature and can hydrolyze in vitro the seven different phthalate diesters tested to their corresponding monoesters irrespective of their support to the growth of the test organism.     

A critical analysis of the biological impacts of plasticizers on wildlife

This review provides a critical analysis of the biological effects of the most widely used plasticizers, including dibutyl phthalate, diethylhexyl phthalate, dimethyl phthalate, butyl benzyl phthalate and bisphenol A (BPA), on wildlife, with a focus on annelids (both aquatic and terrestrial), molluscs, crustaceans, insects, fish and amphibians. Moreover, the paper provides novel data on the biological effects of some of these plasticizers in invertebrates, fish and amphibians. Phthalates and BPA have been shown to affect reproduction in all studied animal groups, to impair development in crustaceans and amphibians and to induce genetic aberrations. Molluscs, crustaceans and amphibians appear to be especially sensitive to these compounds, and biological effects are observed at environmentally relevant exposures in the low ng l⁻¹ to µg l⁻¹ range. In contrast, most effects in fish (except for disturbance in spermatogenesis) occur at higher concentrations. Most plasticizers appear to act by interfering with the functioning of various hormone systems, but some phthalates have wider pathways of disruption. Effect concentrations of plasticizers in laboratory experiments coincide with measured environmental concentrations, and thus there is a very real potential for effects of these chemicals on some wildlife populations. The most striking gaps in our current knowledge on the impacts of plasticizers on wildlife are the lack of data for long-term exposures to environmentally relevant concentrations and their ecotoxicity when part of complex mixtures. Furthermore, the hazard of plasticizers has been investigated in annelids, molluscs and arthropods only, and given the sensitivity of some invertebrates, effects assessments are warranted in other invertebrate phyla.     

Biodegradation of dimethyl phthalate with high removal rates in a packed-bed reactor

Biological treatment of a dimethyl phthalate (DMP)-containing waste stream was evaluated in packed-bed bioreactors using an acclimated mixed bacterial culture. The passive immobilization start-up strategy was successful in the development of a stable biofilm on the packing material in the reactor. Nutrient supplementation significantly improved the removal efficiency. High removal rates with 100% efficiencies of DMP removal were achieved up to the phthalate-loading rate of 560 g/m³ h.     

Biodegradation of diethyl phthalate in soil by a novel pathway

Biodegradation of diethyl phthalate (DEP) has been shown to occur as a series of sequential steps common to the degradation of all phthalates. Primary degradation of DEP to phthalic acid (PA) has been reported to involve the hydrolysis of each of the two diethyl chains of the phthalate to produce the monoester monoethyl phthalate (MEP) and then PA. However, in soil co-contaminated with DEP and MeOH, biodegradation of the phthalate to PA resulted in the formation of three compounds, in addition to MEP. These were characterised by gas chromatography-electron ionisation mass spectrometry and nuclear magnetic resonance as ethyl methyl phthalate, dimethyl phthalate and monomethyl phthalate, and indicated the existence of an alternative pathway for the degradation of DEP in soil co-contaminated with MeOH. Transesterification or demethylation were proposed as the mechanisms for the formation of the three compounds, although the 7:1 ratio of H(2)O to MeOH means that transesterification is unlikely.     

Degradation of benzotrifluoride via the dioxygenase pathway in Rhodococcus sp. 065240

We previously isolated Rhodococcus sp. 065240, which catalyzes the defluorination of benzotrifluoride (BTF). In order to investigate the mechanism of this degradation of BTF, we performed proteomic analysis of cells grown with or without BTF. Three proteins, which resemble dioxygenase pathway enzymes responsible for isopropylbenzene degradation from Rhodococcus erythropolis BD2, were induced by BTF. Genomic PCR and DNA sequence analysis revealed that the Rhodococcus sp. 065240 carries the gene cluster, btf, which is highly homologous to the ipb gene cluster from R. erythropolis BD2. A mutant strain, which could not catalyze BTF defluorination, was isolated from 065240 strain by UV mutagenesis. The mutant strain had one mutation in the btfT gene, which encodes a response regulator of the two component system. The defluorinating ability of the mutant strain was recovered by complementation of btfT. These results suggest that the btf gene cluster is responsible for degradation of BTF.     

节杆菌菌株LZP08X的分离鉴定及其降解苯酚特性

目的:从柳州市某钢铁公司焦化污水处理厂的活性污泥中,筛选分离出高效降解苯酚的菌株,对其进行分类鉴定和苯酚降解特性的研究。方法:采用苯酚为唯一碳源和能源的无机盐培养基,经过富集培养,平板分离,耐受性试验和苯酚降解能力测定。结果:获得一株能高效降解苯酚的菌株,命名为LZP08X,通过形态观察和生理生化特征分析,初步鉴定为节杆菌属(Ar-throbacter sp.)。该菌株降解苯酚的最适条件为:温度35℃,pH 9.0,装液量20%(v/v);其降解苯酚过程符合一级反应动力学方程,在苯酚初始浓度为400mg/L时,于12h内,降解率达99%,降解速率常数K值为0.39,半衰期为1.78h。结论:节杆菌属(Arthrobact-er sp.)菌株LZP08X苯酚降解能力较强,对该菌的继续研究,可使其在含酚工业废水处理的实际应用中起到重要作用。     

Genetic and metabolic analysis of the carbofuran catabolic pathway in Novosphingobium sp. KN65.2

The widespread agricultural application of carbofuran and concomitant contamination of surface and ground waters has raised health concerns due to the reported toxic effects of this insecticide and its degradation products. Most bacteria that degrade carbofuran only perform partial degradation involving carbamate hydrolysis without breakdown of the resulting phenolic metabolite. The capacity to mineralize carbofuran beyond the benzofuran ring has been reported for some bacterial strains, especially sphingomonads, and some common metabolites, including carbofuran phenol, were identified. In the current study, the catabolism of carbofuran by Novosphingobium sp. KN65.2 (LMG 28221), a strain isolated from a carbofuran-exposed Vietnamese soil and utilizing the compound as a sole carbon and nitrogen source, was studied. Several KN65.2 plasposon mutants with diminished or abolished capacity to degrade and mineralize carbofuran were generated and characterized. Metabolic profiling of representative mutants revealed new metabolic intermediates, in addition to the initial hydrolysis product carbofuran phenol. The promiscuous carbofuran-hydrolyzing enzyme Mcd, which is present in several bacteria lacking carbofuran ring mineralization capacity, is not encoded by the Novosphingobium sp. KN65.2 genome. An alternative hydrolase gene required for this step was not identified, but the constitutively expressed genes of the unique cfd operon, including the oxygenase genes cfdC and cfdE, could be linked to further degradation of the phenolic metabolite. A third involved oxygenase gene, cfdI, and the transporter gene cftA, encoding a TonB-dependent outer membrane receptor with potential regulatory function, are located outside the cfd cluster. This study has revealed the first dedicated carbofuran catabolic genes and provides insight in the early steps of benzofuran ring degradation.     

Comparative protein analysis of the chitin metabolic pathway in extant organisms: A complex network approach

Chitin is a structural endogenous carbohydrate, which is a major component of fungal cell walls and arthropod exoskeletons. A renewable resource and the second most abundant polysaccharide in nature after cellulose, chitin is currently used for waste water clearing, cosmetics, medical, and veterinary applications. This work comprises data mining of protein sequences related to the chitin metabolic pathway of completely sequenced genomes of extant organisms pertaining to the three life domains, followed by meta-analysis using traditional sequence similarity comparison and complex network approaches. Complex networks involving proteins of the chitin metabolic pathway in extant organisms were constructed based on protein sequence similarity. Several usual network indices were estimated in order to obtain information on the topology of these networks, including those related to higher order neighborhood properties. Due to the assumed evolutionary character of the system, we also discuss issues related to modularity properties, with the concept of edge betweenness playing a particularly important role in our analysis. Complex network approach correctly identifies clusters of organisms that belong to phylogenetic groups without any a priori knowledge about the biological features of the investigated protein sequences. We envisage the prospect of using such a complex network approach as a high-throughput phylogenetic method.