Comparative proteomic analysis and characterization of benzo(a)pyrene removal by Microbacterium sp. strain M.CSW3 under denitrifying conditions

Bioprocess and Biosystems Engineering - High-molecular-weight polycyclic aromatic hydrocarbons are persistent organic pollutants with great environmental and human health risks and the associated...     

An iTRAQ-based quantitative analysis to elaborate the proteomic response of Nostoc sp. PCC 7120 under N2 fixing conditions

Nostoc sp. PCC 7120 is an oxygen-evolving photoautotrophic N2 fixing filamentous cyanobacterium. Upon nitrogen starvation, a range of processes are initiated, such as differentiation of the heterocysts, specific cells where N2 fixation takes place. We have characterized and quantified the proteome of the Nostoc sp. PCC 7120 wild-type strain grown under N2 fixing and non-N2 fixing conditions. To assess global proteome changes in response to environmental changes, measurements were made using the quantitative proteomics tool, iTRAQ, on a whole cell digest. From this approach, a total of 486 different proteins was accurately identified across 2 biological replicate experiments, where 226 identifications contained 2 or more distinct peptides. Results of metabolic regulation will be discussed to demonstrate that proteomics represents an important tool for the development of heterocystous cyanobacteria for future biological H2 production.     

Biodegradation of benzo(a)pyrene by a newly isolated Fusarium sp

Benzo(a)pyrene (BaP) is a five-ring polycyclic aromatic hydrocarbon produced by the incomplete combustion of organic materials. It is one of the priority pollutants listed by the US Environmental Protection Agency. This study describes a fungal isolate that is able to biodegrade benzo(a)pyrene. The filamentous fungus, isolated from leaves of Pterocarpus macrocarpus Kurz., was identified as a Fusarium sp. (strain E033). Fusarium sp. E033 was able to survive in the presence of benzo(a)pyrene concentrations up to 1.2 mM (300 mg L(-1)). Biodegradation experiments using 0.4 mM (100 mg L(-1)) benzo(a)pyrene demonstrated that Fusarium sp. E033 was able to degrade 65-70% of the initial benzo(a)pyrene provided, and two transformation products, a dihydroxy dihydro-benzo(a)pyrene and a benzo(a)pyrene-quinone, were detected within 30 days of incubation at 32 degrees C. The factors affecting biodegradation efficiency were also investigated. While increasing aeration promoted better fungal growth and benzo(a)pyrene biodegradation, increasing the glucose concentration from 5 to 50 mM had an adverse effect on biodegradation. Ethanol and methanol, provided at 5 mM to increase benzo(a)pyrene water solubility, increased the fungal biomass yield but did not promote degradation. The Fusarium sp. E033 isolated in this study can tolerate and degrade relatively high concentrations of benzo(a)pyrene, suggesting its potential application in benzo(a)pyrene bioremediation.     

模拟淀粉条件下乳杆菌吸附苯并芘的能力

【目的】研究了模拟淀粉条件下嗜酸乳杆菌(Lactobacillus acidophilus)NCFM、植物乳杆菌(Lactobacillus plantarum)121以及戊糖乳酸菌(Lactobacillus pentosus)ML32吸附苯并芘的能力,为利用乳杆菌去除苯并芘提供一定的理论指导。【方法】基于苯并芘的HPLC检测方法,考察了淀粉含量及类型、培养时间和p H等因素对乳杆菌吸附苯并芘能力的影响,研究了淀粉水解产物及菌体活性影响乳杆菌吸附苯并芘的效果。【结果】淀粉含量在2%–10%的范围内,乳杆菌吸附苯并芘的能力与淀粉含量的增加呈正相关性,且与淀粉种类关系不大,但经糊化处理的淀粉可以促进菌体吸附苯并芘。在模拟淀粉体系中,培养前4 h时乳杆菌吸附苯并芘的效率增长快,此后其吸附率增加缓慢。淀粉经酸性(p H为3–4)和碱性(p H为8–9)处理,乳杆菌吸附苯并芘的能力提升。淀粉的水解产物麦芽糖和葡萄糖都能显著改善乳杆菌吸附苯并芘的能力。与活细胞相比,经灭活处理后乳杆菌细胞吸附苯并芘的能力降低。【结论】在淀粉体系中,乳杆菌依然表现出良好的苯并芘吸附能力,且一定范围内淀粉含量增多、糊化作用以及麦芽糖和葡萄糖的存在可促进其吸附苯并芘的能力。因此,本研究中的乳杆菌或许可以用作生物脱除剂来减少淀粉食物中的苯并芘。     

Review on proteomic analyses of benzo[a]pyrene toxicity

Benzo[a]pyrene (BaP), a five-ring polycyclic aromatic hydrocarbon, is a well-recognized environmental pollutant. Coal-processing waste products, petroleum sludge, asphalt, creosote, and tobacco smoke, all contain high levels of BaP. Exposure to BaP elicits many adverse biological effects, including tumor formation, immunosuppression, teratogenicity, and hormonal effects. In addition to the genetic damage caused by BaP exposure, several studies have indicated the disruption of protein-protein signaling pathways. However, contrary to the large number of studies on BaP-induced DNA damage, only few data have been gathered on its effects at the protein level. This review highlights all proteomic studies to date used for assessing the toxicity of BaP and its metabolites in various organ systems. It will also give an overview on the role proteomics may play to elucidate the mechanisms underlying BaP toxicity.     

Reactivity with DNA of three pyrenofuran analogues of benzo(a)pyrene and benzo(e)pyrene

Three pyrenofurans, the pyreno[1,2-b]furan (FP1), the pyreno[2,1-b] furan (FP2) and the pyreno[4,5-b]furan (FP3) have been synthesized as analogues of the mutagenic and carcinogenic benzo(a)pyrene (FP1 and FP2) and of its non-carcinogenic isomer benzo(e)pyrene (FP3). For each of the pyrenofurans, the reactivity with DNA has been tested in presence of liver microsomes of rats induced with 3-methylcholanthrene. Fluorescence spectroscopy showed that only FP2 and FP3 which possess a "bay region" react with DNA. In both cases, metabolites bound to DNA have a fluorescence emission comparable to that of the "bay region" dihydrodiols obtained after the "in vitro" metabolism of initial molecules. FP2 is shown to react similarly to benzo(a)pyrene whereas the reactivity of FP3 is different from that of benzo(e)pyrene, in spite of their structural similarities. This is probably due to reasons of three-dimensional space configuration. The peculiar reactivity of FP3 is predicted by calculations of the bond order values.     

The microsomal metabolism of benzo(a) pyrene phenols.

Analysis of repetitive scan difference spectra of incubation mixtures containing rat liver microsomes, 3- or 9-hydroxybenzo(a)pyrene, oxygen, and NADPH shows the formation of products with absorbance in the 400–450 nm region. Based on the chromatographic retention time, absorbance, and fluorescence spectra, the two major products of 9-hydroxybenzo(a)pyrene metabolism may be diphenols. The existence of spectral intermediates which resemble phenols rather than quinones during the steady-state metabolism of 3-hydroxybenzo(a)pyrene strongly indicates that either the major product is a diphenol which slowly oxidizes to yield 3,6-quinone and/or that an active quinone reductase exists in liver microsomes.     

Modification of norfloxacin by a Microbacterium sp. strain isolated from a wastewater treatment plant

Antimicrobial residues found in municipal wastewater may increase selective pressure on microorganisms for development of resistance, but studies with mixed microbial cultures derived from wastewater have suggested that some bacteria are able to inactivate fluoroquinolones. Medium containing N-phenylpiperazine and inoculated with wastewater was used to enrich fluoroquinolone-modifying bacteria. One bacterial strain isolated from an enrichment culture was identified by 16S rRNA gene sequence analysis as a Microbacterium sp. similar to a plant growth-promoting bacterium, Microbacterium azadirachtae (99.70%), and a nematode pathogen, "M. nematophilum" (99.02%). During growth in medium with norfloxacin, this strain produced four metabolites, which were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) analyses as 8-hydroxynorfloxacin, 6-defluoro-6-hydroxynorfloxacin, desethylene norfloxacin, and N-acetylnorfloxacin. The production of the first three metabolites was enhanced by ascorbic acid and nitrate, but it was inhibited by phosphate, amino acids, mannitol, formate, and thiourea. In contrast, N-acetylnorfloxacin was most abundant in cultures supplemented with amino acids. This is the first report of defluorination and hydroxylation of a fluoroquinolone by an isolated bacterial strain. The results suggest that some bacteria may degrade fluoroquinolones in wastewater to metabolites with less antibacterial activity that could be subject to further degradation by other microorganisms.     

Thermostable phenylalanine dehydrogenase from a mesophilic Microbacterium sp. strain DM 86-1

Bacteria that produced NAD⁺-dependent phenylalanine dehydrogenase (EC 1.4.1.20) were selected among l-methionine utilizers isolated from soil. A bacterial strain showing phenylalanine dehydrogenase activity was chosen and classified in the genus Microbacterium. Phenylalanine dehydrogenase was purified from the crude extract of Microbacterium sp. strain DM 86-1 (TPU 3592) to homogeneity as judged by SDS-polyacrylamide disc gel electrophoresis. The enzyme has an isoelectric point of 5.8 and a relative molecular weight (M _r) of approximately 330,000. The enzyme is composed of eight identical subunits with an M _r of approximately 41,000. The apparent K _m values for l-phenylalanine and NAD⁺ were calculated to be 0.10 mM and 0.20 mM, respectively. No loss of the enzyme activity was observed upon incubation at 55° C for 10 min. Received: 30 July 1997 / Accepted: 4 November 1997     

Characterization of the novel HCH-degrading strain, Microbacterium sp. ITRC1

A gram-positive Microbacterium sp. strain, ITRC1, that was able to degrade the persistent and toxic hexachlorocyclohexane (HCH) isomers was isolated and characterized. The ITRC1 strain has the capacity to degrade all four major isomers of HCH present in both liquid cultures and aged contaminated soil. DNA fragments corresponding to the two initial genes involved in γ-HCH degradative pathway, encoding enzymes for γ-pentachlorocyclohexene hydrolytic dehalogenase (linB) and a 2,5-dichloro-2,5-cyclohexadiene-1,4-diol dehydrogenase (linC), were amplified by PCR and sequenced. Their presence in the ITRC1 genomic DNA was also confirmed by Southern hybridization. Sequencing of the amplified DNA fragment revealed that the two genes present in the ITRC1 strain were homologous to those present in Sphingomonas paucimobilis UT26. Both 16S rRNA sequencing and phylogenetic analysis resulted in the identification of the bacteria as a Microbacterium sp. We assume that these HCH-degrading bacteria evolved independently but possessed genes similar to S. paucimobilis UT26. The reported results indicate that catabolic genes for γ-HCH degradation are highly conserved in diverse genera of bacteria, including the gram-positive groups, occurring in various environmental conditions.     

Nitrate removal by a novel autotrophic denitrifier (Microbacterium sp.) using Fe(II) as electron donor

A novel denitrifying bacterium was isolated using bicarbonate as the sole carbon source in a defined medium. Strain W3 was isolated from deep sediments of East Lake (Wuhan, China). In this study, analysis of 16S rRNA genes showed that strain W3 was affiliated with Microbacterium sp. When using Fe2+ as the only electron donor, this strain could convert 88.6 % of NO3 −-N to N2, corresponding to an Fe2+ oxidation rate of 80 %. Meanwhile, neither NO2 −-N nor NH4 +-N was accumulated after the experiment. In similar experiments with Fe(II)-EDTA, cell encrustations did not occur and supplementary substrates were consumed. The accumulated NO2 −-N was below 2.5 mg L−1. In addition, PCR revealed five kinds of key denitrifying genes: narG, napA, nirS, norB and nosZ. These results indicated that strain W3 could be used as an alternative autotrophic denitrifier for the treatment of groundwater and low C/N ratio wastewater.     

Some properties of vicinal diol-epoxides derived from benzo(a)anthracene and benzo(a)pyrene

The alkylating properties of pairs of syn- and anti-isomers of 2 diol-epoxides derived from benzo(a)pyrene (BP) and of 1 derived from benz(a)anthracene (BA) have been investigated. Of the anti-diol-epoxides, anti-BP 7,8-diol-9,10-oxide was the most reactive compound towards DNA, towards sodium p-nitrothiophenolate in a non-aqueous solvent system, and towards 4-(p-nitrobenzyl)pyridine in aqueous solution; anti-BP 9,10,-diol-7,8-oxide was of intermediate reactivity and anti-BA 8,9-diol-10,11-oxide was least reactive. The syn-diol-epoxides gave unsatisfactory results with DNA and 4-(p-nitrobenzyl)pyridine because of their rapid solvolysis in aqueous solution, but with sodium p-nitrothiophenolate showed the order of reactivity syn-BP 7,8-diol-9,10-oxide greater than syn-BA 8,9-diol-10,11-oxide greater than syn-BP 9,10-diol-7,8-oxide. The products of the reaction between diol-epoxides and nucleic acids were examined by Sephadex LH-20 chromatography followed by high-pressure liquid chromatography (HPLC) and the diol-epoxides were shown to react principally with the guanosine and adenosine moieties of RNA.     

Phosphate removal under denitrifying conditions by Brachymonas sp. strain P12 and Paracoccus denitrificans PP15

In this study, we used the denitrifying phosphorus-removing bacterium Brachymonas sp. strain P12 to investigate the enhanced biologic phosphorus-removal (EBPR) mechanism involved with polyhydroxybutyrate (PHB), glycogen, and phosphorus uptake in the presence of acetate under anoxic or aerobic conditions. The results showed that excess acetate concentration and aerobic cultivation can enhance PHB formation efficiency and that PHB formation might be stimulated by glycogenolysis of the cellular glycogen. The efficiency of the uptake of anoxic phosphorus was greater when PHB production was lower. The EBPR mechanism of Brachymonas sp. strain P12 for PHB, phosphorus, and glycogen was similar to the conventional anaerobic-aerobic (or anaerobic-anoxic) EBPR models, but these models were developed under anoxic or aerobic conditions only, without an anaerobic stage. The anoxic or aerobic log phase of growth is divided into two main phases: the early log phase, in which acetate and glycogen are consumed to supply enough energy and reducing power for PHB formation and cell growth (phosphorus assimilation), and the late log phase, which ends the simultaneous degradation of PHB and remaining acetate for polyphosphate accumulation. Glycogenolysis plays a significant role in the alternate responses between PHB formation and phosphorus uptake under anoxic or aerobic conditions. After the application of the denitrifying phosphorus-removing bacterium Brachymonas sp. strain P12, aerobic cultivation increases the level of PHB production, and anoxic cultivation further increases phosphorus uptake.     

乳杆菌吸附苯并芘的特性

[目的]探讨植物乳杆菌(Lactobacillus plantarum)121和戊糖乳杆菌(Lactobacillus pentosus)ML32的苯并芘吸附作用与机制.[方法]采用高效液相色谱检测菌体对苯并芘的吸附率.[结果]菌株121和ML32对苯并芘的吸附率分别为65.9%和64.9%,这种吸附特性与菌体活力无关,随培养时间延长、温度提高以及细胞浓度的上升而增加.菌株121和ML32的吸附率在pH 4和5时达到最大,分别为87.6%和89.0%.当培养液中Ca2+或Mg2+浓度大于0.05mol/L时,菌体吸附率与盐离子浓度呈正相关.苯洗脱会导致乳杆菌所吸附的苯并芘减少90%.经碱性蛋白酶、中性蛋白酶、溶菌酶及TCA和SDS等方法处理后,菌体吸附率上升,且不易被苯去除.在胆盐及胃酸环境下,两株菌的吸附率均提高至70%以上,而胰蛋白酶的存在仅对菌株121的吸附率有较大影响.[结论]两株乳杆菌可以通过吸附作用从环境中清除苯并芘,其吸附效果与细菌细胞壁的结构和组成有关.