Metabolism of twelve herbicides by Streptomyces

Experiments were conducted to assess the ability of Streptomyces (strain PS1/5) to metabolize twelve herbicides representing several different classes including: acetanilides, triazines, ureas, uracils, and imidazoles. Incubations in aqueous culture with dextrin as carbon source and either ammonium or Casamino acids as nitrogen source resulted in transformations (>50%) of eight of the herbicides tested: alachlor, metolachlor, atrazine, prometryne, ametryne, linuron, tebuthiuron, and bromacil; the remaining four herbicides (cyanazine, diuron, metribuzin, and imazapyr) were also transformed, but to a lesser extent. In most instances, biotransformations occurred concurrently with growth and results were consistent regardless of the nitrogen source (ammonium vs. Casamino acids). However, in some instances there were differences in rates of biotransformation as a consequence of the nitrogen source (e.g. alachlor, metribuzin), suggesting the selective induction of certain metabolic enzymes; in other instances biotransformations were not associated with growth, suggesting secondary metabolism. An experiment was also conducted to assess the ability of Streptomyces (strain PS1/5) to metabolize atrazine contaminated soil. Inoculation of soil amended with 20 μg/g of atrazine and 5% chitin as carbon source resulted in ca. 78% removal of atrazine within 28 days. These data suggest that Streptomyces species may be potential candidates for soil inoculation to bioremediate herbicide contaminated soils.     

链霉菌次级代谢调控机制进展

链霉菌除具有复杂的形态分化特征外 ,还可以产生多种具有重要应用价值的次级代谢产物 ,这两个过程密切相关。因此 ,链霉菌存在着原核生物中罕见的庞大而复杂的调控网络。链霉菌在遗传水平有三个层次的调控 ,分别是 :途径特异性调控、多效调控和全局调控。阐明这些调控网络将为利用代谢工程手段提高次级代谢产物的产量并对其进行结构改造奠定理论基础 ,还将有助于发现新的有价值的天然产物。     

链霉菌基因组及次生代谢研究进展

链霉菌属革兰氏阳性放线菌,具有复杂的生活周期和次生代谢途径,并产生大量具有重要价值的天然代谢物。本文概述了链霉菌基因组染色体的独特结构与次生代谢途径的研究进展,重点论述了利用基因组信息改造和调控链霉菌次生代谢途径的研究成果。后基因组时代的功能基因组研究使人类能深入了解链霉菌家族,对链霉菌进行更加合理高效的遗传操作,为提高具有重要价值的天然代谢物的产量和获得新代谢物创造更有利的条件。     

Metabolism of Barbital by Streptomyces mediterranei

The metabolism of barbital in cultures of Streptomyces mediterranei was studied. Small quantities were transformed during the fermentation. Four compounds were isolated and identified as 5-ethyldialuric acid, 5-ethylbarbituric acid, 5-(β-hydroxyethyl)-5-ethylbarbituric acid, and diethylmalonic acid monoureid. The influence of these compounds on the production of rifamycin was of minor importance. With the aid of C¹⁴-barbital, it was established that neither barbital nor any of its metabolic products can be considered as precursors of the rifamycin B.     

Metabolism of steroid acetates by Streptomyces albus

Fermentation of 16-dehydropregnenolone acetate (1a) with Streptomyces albus yielded 16-dehydropregnenolone (1b) and 16-dehydroprogesterone (IIa). Similar incubation of pregnenolone acetate (Ic) with the strain afforded pregnenolone (Id), progesterone (IIb) and 20 alpha-hydroxy progesterone (IIc) while dehydroepiandrosterone acetate (IIIa) under the conditions was converted to dehydroepiandrosterone (IIIb), androstenedione (IVa) and testosterone (IVc). The strain was also capable of converting testosterone acetate (IVb) having the 17-acetoxy function in the 5-membered D-ring to testosterone (IVc) and androstenedione (IVa). All the products were identified by the application of various chemical and spectrometric techniques.     

Use of In Vitro Absorption,Distribution, Metabolism,and Excretion (ADME) Data in Bioaccumulation Assessments for Fish

A scientific workshop was held in 2006 to discuss the use of in vitro Absorption, Distribution, Metabolism, and Excretion (ADME) data in chemical bioaccumulation assessments for fish. Computer-based (in silico) modeling tools are widely used to estimate chemical bioaccumulation. These in silico methods have inherent limitations that result in inaccurate estimates for many compounds. Based on a review of the science, workshop participants concluded that two factors, absorption and metabolism, represent the greatest sources of uncertainty in current bioaccumulation models. Both factors can be investigated experimentally using in vitro test systems. A variety of abiotic and biotic systems have been used to predict chemical accumulation by invertebrates, and dietary absorption of drugs and xenobiotics by mammals. Research is needed to determine whether these or similar methods can be used to better predict chemical absorption across the gills and gut of fish. Scientists studying mammals have developed a stepwise approach to extrapolate in vitro hepatic metabolism data to the whole animal. A series of demonstration projects was proposed to investigate the utility of these in vitro–in vivo extrapolation procedures in bioaccumulation assessments for fish and delineate the applicability domain of different in vitro test systems. Anticipating research progress on these topics, participants developed a “decision tree” to show how in vitro information for individual compounds could be used in a tiered approach to improve bioaccumulation assessments for fish and inform the possible need for whole-animal testing.     

取代脲类除草剂的微生物降解

取代脲类除草剂主要用来防除一年生禾本科杂草和阔叶杂草,自20世纪中期推入市场以来,在世界范围内被广泛使用,已成为重要的除草剂之一。随着取代脲类除草剂的持续施用,其在环境中的残留严重超标,危害日益凸显。因此,取代脲类除草剂在环境中的吸附、迁移和降解等行为备受关注。研究表明细菌降解N,N-二甲基取代脲类除草剂主要是通过连续脱甲基作用后断脲桥降解,而降解N-甲氧基-N-甲基取代脲类除草剂是通过脲桥的直接断裂。真菌降解取代脲类除草剂的途径则较为复杂,尚需进一步阐明。本文综述了近年来分离筛选的取代脲类除草剂降解菌株及其降解途径的最新研究进展,为取代脲类除草剂污染环境的生物修复研究提供参考。     

Capillary electrophoresis of herbicides. III. Evaluation of octylmaltopyranoside chiral surfactant in the enantiomeric separation of phenoxy acid herbicides

A chiral alkylglucoside surfactant, namely n-octyl-β-D-maltopyranoside (OM), was evaluated in the enantiomeric separation of phenoxy acid herbicides. The enantiomeric resolution of the phenoxy acid herbicides could be manipulated readily by adjusting the surfactant concentration, ionic strength, pH, the percent organic modifier and separation temperature. The optimum surfactant concentration needed for maximum enantiomeric resolution varied among the different analytes, and was an inverse function of the hydrophobicity of the phenoxy acid herbicides with the most hydrophobic solute requiring less surfactant concentration for attaining a baseline enantiomeric resolution. Due to the ionic nature of the phenoxy acid herbicides, increasing the pH of the running electrolyte increased the degree of ionization of the acidic herbicides thus decreasing their association with the chiral micelles and in turn their enantiomeric resolution. Increasing the ionic strength of the running electrolyte seems to enhance both the solubilization of the solute in the micelle and the chiral interaction of the solute with the micelle with a net increase in enantiomeric resolution. The percent of added methanol had a varying effect on the resolution of the various enantiomers in the sense that it enhanced the enantiomeric resolution for the most hydrophobic solutes while it decreased the enantiomeric resolution for the weakly hydrophobic ones. Thermostating the capillary column at subambient temperature improved enantiomeric resolution. © 1996 Wiley-Liss, Inc.     

Multiple action sites for photosystem II herbicides as revealed by delayed fluorescence

DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) at concentrations higher than 10 M suppresses the second time range delayed fluorescence (DF) of pea chloroplasts, due to inhibition of the oxidizing side of photosystem II (PS II). The inhibition of the reducing side of PS II resulting in the suppression of millisecond DF takes place at much lower (0.01 M) DCMU concentrations. The variation in the herbicide-affinities of the reducing and oxidizing sides of PS II is not the same for DCMU and phenol-type herbicides. The DCMU-affinity of the oxidizing side considerably increases and approximates that of the reducing side upon mild treatment of chloroplasts with oleic acid. Probably this is a result of some changes in the environment of the binding site at the oxidizing side. At DCMU concentrations higher than 1 mM, the chaotropic action of DCMU leads to the generation of millisecond luminescence which is not related to the functioning of the reaction centres.Abbreviations D-1 The 32 kDa herbicide-binding intrinsic polypeptide of PS II, the apoprotein of Q_B - D-2 The 32–34 kDa intrinsic polypeptide of PS II, probably the apoprotein of Z - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DF Delayed fluorescence - Dinoseb 2,4-dinitro-6-sec-butylphenol - DNOC 4,6-dinitro-o-cresol - F_m Maximal fluorescence yield (when all traps are closed) - F_o Constant fluorescence yield (when all traps are open) - PS Photosystem - Q_A and Q_B The primary and secondary plastoquinone acceptors of PS II, correspondingly - Z A plastoquinol electron donor, presumably associated with the D-2 protein     

Enantiomeric separation of imidazolinone herbicides using chiral high-performance liquid chromatography

Chiral high-performance liquid chromatography (HPLC) is one of the most powerful tools to prepare enantiopure standards of chiral compounds. In this study, the enantiomeric separation of imidazolinone herbicides, i.e., imazethapyr, imazapyr, and imazaquin, was investigated using chiral HPLC. The enantioselectivity of Chiralpak AS, Chiralpak AD, Chiralcel OD, and Chiralcel OJ columns for the three analytes was compared under similar chromatographic conditions. Chiralcel OJ column showed the best chiral resolving capacity among the test columns. The resolved enantiomers were distinguished by their signs of circular dichroism detected at 275 nm and their structures confirmed with LC-mass spectrometric analysis. Factors affecting the chiral separation of imidazolinones on Chiralcel OJ column were characterized. Ethanol acted as a better polar modifier than the other alcohols including 2-propanol, 1-butanol, and 1-pentanol. Although the acidic modifier in the mobile phase did not influence chiral recognition, it was necessary for reducing the retention time of enantiomers and suppressing their peak tailing. Thermodynamic evaluation suggests that enantiomeric separation of imidazolinones on Chiralcel OJ column is an enthalpy-driven process from 10 to 40 degrees C. This study also shows that small amounts of pure enantiomers of imidazolinones may be obtained by using the analytical chiral HPLC approach.     

二硝基苯胺类除草剂微生物降解研究进展

二硝基苯胺类除草剂是一类广谱、高效且广泛使用的除草剂,微生物的降解代谢作用是其在环境中消解的最主要因素。分离筛选除草剂的高效降解菌株、分析其降解途径并阐明其微生物降解机制,可为除草剂残留污染的微生物降解修复提供理论依据和优良的降解菌株、降解基因和酶资源。本文简述了二硝基苯胺类除草剂的微生物降解菌株、降解代谢途径和降解基因/酶的研究进展,为进一步研究该类除草剂的微生物降解及其污染生物修复提供理论依据和资源。     

Metabolism of the veterinary fluoroquinolone sarafloxacin by the fungus Mucor ramannianus

To investigate the microbial biotransformation of veterinary fluoroquinolones, Mucor ramannianus was grown in sucrose/peptone broth with sarafloxacin for 18 days. Cultures were extracted with ethyl acetate and extracts were analyzed by liquid chromatography. The two metabolites (26% and 15% of the A ₂₈₀, respectively) were identified by mass and ¹H nuclear magnetic resonance spectra as N-acetylsarafloxacin and desethylene-N-acetylsarafloxacin. The biological formation of desethylene-N-acetylsarafloxacin has not been previously observed. Journal of Industrial Microbiology & Biotechnology (2001) 26, 140–144. Received 08 May 2000/ Accepted in revised form 03 November 2000     

Regulation of photosynthetic electron transport by bicarbonate formate and herbicides in isolated broken and intact chloroplasts

In this paper, we have presented a minireview on the interaction of bicarbonate, formate and herbicides with the thylakoid membranes.The regulation of photosynthetic electron transport by bicarbonate, formate and herbicides is described. Bicarbonate, formate, and many herbicides act between the primary quinone electron acceptor Q_A and the plastoquinone pool. Many herbicides like the ureas, triazines and the phenol-type herbicides act, probably, by the displacement of the secondary quinone electron acceptor Q_B from its binding site on a Q_B-binding protein located at the acceptor side of Photosystem II. Formate appears to be an inhibitor of electron transport; this inhibition can be removed by the addition of bicarbonate. There appears to be an interaction of the herbicides with bicarbonate and/or It has been suggested that both the binding of a herbicide and the absence of bicarbonate may cause a conformational alteration of the environment of the Q_B-binding site. The alteration brought about by a herbicide decreases the affinity for another herbicide or for bicarbonate; the change caused by the absence of bicarbonate decreases the affinity for herbicides. Moreover, this change in conformation causes an inhibition of electron transport. A bicarbonate-effect in isolated intact chloroplasts is demonstrated.Paper presented at the FESPP meeting (Strasbourg, 1984)     

Effect of carbamate herbicides on VA mycorrhizal infection and plant growth

Summary The effect of the carbamate herbicides Chlorpropham, Sulfallate and Phenmedipham, which are believed to inhibit photosynthesis, on VA mycorrhizal infection and on plant growth, were examined. Foliar spraying of Phenmedipham decreased the root concentration of total and reducing sugars and the fungal metabolism (using a staining reaction for succinate dehydrogenase as indicator) 48 h after application. However, all three carbamate herbicides tested, whether applied by foliar spray or directly to soil, did not affect the amount of VA mycorrhizal infection present at the end of the experiment. These herbicides decreased plant growth when they were applied to soil. But when the herbicides were sprayed only Phenmedipham, applied at high concentrations, decreased plant growth. Moreover, our results show that VA mycorrhizas may help plants recover from the deleterious effect of Phenmedipham.     

Synthesis of potential herbicides designed to uncouple photophosphorylation

In a search for novel herbicides we attempted to make uncouplers of photophosphorylation. Good herbicides were discovered, but not all were good uncouplers and we present evidence which supports the view that their primary action is through inhibition of carotenoid biosynthesis. This paper describes the synthesis and in vivo and in vitro activities of 21 compounds of the series. The best herbicide was active enough to justify extensive field testing.     

Effect of foliar application of herbicides,Benthiocarb, 2,4-D and Fluchloralin on phyllosphere microflora of potato

Three herbicides, Benthiocarb, 2,4-D and Fluchloralin were evaluated for their effect on leaf surface microflora of potato. In general, the application of herbicides resulted into a drop in the microbial population. Throughout the study herbicide treated leaves harboured less population compared to the untreated ones.