Protein toxicity to aphids: Anin vitro test onAcyrthosiphon pisum

Recent progress in plant transformation for insect resistance has increased the interest in the potential toxicity of proteins towards insect pests. While studies have been targeted to a large array of insect species, phloem-feeding Homoptera have not been investigated yet. The paper describes a routine test for screening toxicity and growth inhibition of purified proteins in artificial diets onAcyrthosiphon pisum (Harris). Twenty-five commercially available proteins of different classes were tested and compared to some non-protein chemicals (an insecticide, an antibiotic …).A. pisum proved to be very sensitive to all proteases tested and to some venoms with general cytolytic properties. A plant lectin, concanavalin A, displayed significant toxicity and growth inhibition, while various proteins such as a soybean proteinase inhibitor, a chitinase, and bovine serum albumin showed measurable impairments of growth only at higher dose (≥250 μg.ml⁻¹). Some proteins were without short-term effect onA. pisum physiology. The influence of these results on aphid-plant interactions are discussed.

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Résumé L'effet de protéines alimentaires sur les insectes phloémophages, dont les pucerons, n'a jamais été étudié. Nous proposons ici un test biologique standardisé sur milieu artificiel permettant d'analyser les effets de différentes classes de protéines sur la physiologie d'A. pisum. La validité de ce test est éprouvée (protocole, reproductibilité) et les différentes données récoltées (mortalité et inhibition de croissance) permettent de définir des paramètres toxicologiques tels que concentration létale 50 ou concentration inhibitrice 50. Cette caractérisation toxicologique a été réalisée sur 25 protéines appartenant à des classes différentes, ainsi que plusieurs substances non protéiques utilisées comme témoin de toxicité (insecticide, antibiotique, inhibiteur de synthèse protéique et glucoside phénolique). Les regroupements de protéines par proximités de profils toxicologiques ont été corrélés aux activités biochimiques des différentes protéines. Les implications de ces résultats sur les interactions plante-puceron sont discutées, ainsi que le potentiel d'une stratégie de création de variétés transgéniques résistantes aux pucerons.

     

Kinetics of competitive inhibition and cometabolism in the biodegradation of benzene, toluene, and p-xylene by two Pseudomonas isolates

Two Pseudomonas species (designated strains B1 and X1) were isolated from an aerobic pilot-scale fluidized bed reactor treating groundwater containing benzene, toluene, and p-xylene (BTX). Strain B1 grew with benzene and toluene as the sole sources of carbon and energy, and it cometabolized p-xylene in the presence of toluene. Strain X1 grew on toluene and p-xylene, but not benzene. In single substrate experiments, the appearance of biomass lagged the consumption of growth substrates, suggesting that substrate uptake may not be growth-rate limiting for these substrates. Batch tests using paired substrates (BT, TX, or BX) revealed competitive inhibition and cometabolic degradation patterns. Competitive inhibition was modeled by adding a competitive inhibition term to the Monod expression. Cometabolic transformation of nongrowth substrate (p-xylene) by strain B1 was quantified by coupling xylene transformation to consumption of growth substrate (toluene) during growth and to loss of biomass during the decay phase. Coupling was achieved by defining two transformation capacity terms for the cometabolizing culture: one that relates consumption of growth substrate to the consumption of nongrowth substrate, and second that relates consumption of biomass to the consumption of nongrowth substrate. Cometabolism increased decay rates, and the observed yield for strain B1 decreased in the presence of p-xylene. (c) 1993 Wiley & Sons, Inc.     

Microbial degradation of quinoline: Kinetic studies with Comamonas acidovorans DSM 6426

The microbial degradation of quinoline by Comamonas acidovorans was studied in a laboratory scale stirred tank reactor. In continuous culture experiments using quinoline as a sole source of carbon and nitrogen, it was shown by means of mass balances that quinoline was converted completely to biomass, carbon dioxide, and ammonia. Degradation rates up to 0.7 g/L h were obtained. Measured yield coefficients Y(x/s) for quinoline were about 0.7 g/g, which is in agreement with the theoretical value for complete mineralization. Kinetic constants based on Haldane substrate inhibition were evaluated. The values were mu(max) = 0.48 h(-1), K(i) = 69 mg/L, and K(s) < 1.45 mg/L. (c) 1993 John Wiley & Sons, Inc.     

A potent specific inhibitor of 6-phosphogluconate dehydrogenase ofCryptococcus neoformans and of certain other fungal enzymes

A particular lot of the zwitterionic buffer, 2(N-morpholino) ethane sulfonic acid (MES), contained a contaminant that inhibited a number of fungal NADP-dependent dehydrogenases. Enzymes that were particularly sensitive include 6-phosphogluconate dehydrogenases fromCryptococcus neoformans andSchizophyllum commune and glucose-6-phosphate dehydrogenase fromSchizophyllum commune. A number of NADP-dependent dehydrogenases of animal origin were tested and all were completely insensitive to inhibition except for rat liver 6-phosphogluconate dehydrogenase, which was 10-fold less sensitive than theCryptococcal enzyme. The pattern of inhibition in all cases was linear competitive versus NADP. The inhibitor has been purified and identified as an ethylenesulfonic acid oligomer. This inhibitor holds promise as a model compound for the development of a specific antifungal agent.     

Clinical pharmacology of the new COMT inhibitor CGP 28 014

CGP 28 014 is a specific inhibitor of catechol-O-methyltransferase (COMT) in vivo. In humans, the inhibition was assessed by measuring urinary excretion of isoquinolines and with the levodopa test. Following administration of CGP 28 014, urinary excretion of isoquinolines was significantly increased. In rats, CGP 28 014 reduced plasma and striatal concentrations of 3-O-methyldopa (30MD) in a dose-dependent manner. Acute and subchronic administration of CGP 28 014 alone or in combination with the peripherally acting decarboxylase inhibitor benserazide decreased plasma 30MD as an index of COMT inhibition by about 50%. There seems to be a close relationship between the time-course of plasma concentrations of CGP 28 014 and the extent of COMT inhibition assessed by the 30MD/DOPA ratio in plasma.     

细菌Ⅵ型分泌系统效应蛋白的装配及功能的研究进展

蛋白分泌作为细胞之间传递信号的途径之一,在微生物生存竞争中也扮演着重要的角色。革兰氏阴性菌可以通过Ⅵ型分泌系统(type Ⅵ secretion system, T6SS)将效应蛋白传递至胞外或原核和真核微生物中,从而介导微生物间的竞争或宿主-细菌的相互作用,最终建立竞争优势。本文主要总结了T6SS的结构与组成,并重点对效应蛋白的装配以及其与免疫蛋白的作用机制的研究进展进行阐述,为以后靶向T6SS抗菌药物的研制提供新思路。     

发酵乳杆菌CSC-19胞外粗多糖提取物抑制单核细胞增生李斯特菌生物被膜形成能力的研究

【目的】筛选能有效抑制单核细胞增生李斯特菌(Listeria monocytogenes,LM)形成生物被膜的乳酸菌,分析其活性成分并进行功能表征。【方法】采用结晶紫染色法筛选抑制LM形成生物被膜的不同乳酸菌提取物;通过酸中和、蛋白酶处理及热处理,推测抑制生物被膜活性物质以胞外多糖(extracellular crude polysaccharide,ECP)为主;乙醇沉淀法提取目标乳酸菌分离株胞外粗多糖,分析其抑制生物被膜形成活性和对LM生长的影响;运用激光共聚焦扫描显微镜(laser confocal scanning microscopy,LCSM)和扫描电子显微镜(scanning electron microscopy,SEM)观察胞外粗多糖对生物被膜细胞形态和结构的影响。【结果】发酵乳杆菌CSC-19发酵上清液对1516-2LM生物被膜的抑制率为81.7%;经热和蛋白酶处理后,发酵上清抑制生物被膜形成的活性未发生显著变化(P>0.05),表明发酵上清液中抑制生物被膜形成的物质可能为胞外多糖;在不抑制LM生长的条件下所提取的胞外粗多糖抑制生物被膜形成能力具有浓度依赖性。激光共聚焦扫描显微镜和扫描电子显微镜结果显示,胞外粗多糖显著抑制了生物被膜的形成能力,生物被膜三维、有组织的蜂窝状结构被破坏,仅有少量的粘附细胞分散于细胞爬片表面。【结论】发酵乳杆菌CSC-19胞外粗多糖能有效抑制LM生物被膜的形成,有望应用于高效防控该菌污染食品。     

Monitoring growth and acetic acid secretion by a thermotolerantBacillus using conduction microcalorimetry

Summary A method is described to determine power of heat-time curves by conduction microcalorimetry in order to monitor the viability and ability of a thermotolerantBacillus strain to secrete acetic acid both during exponential growth and during stationary-phase. In this system secreted acetic acid is neutralized by an insoluble source of lime (dolime) which results in a poor correlation between optical density and culture dry weight. As an alternative, cells and residual dolime were rapidly resuspended in isothermal fresh medium with glucose in a conduction microcalorimeter. Heat evolution was rapid over a period of 200–800 s. Steady state heat evolution rate decreased as a function of culture time and did not correlate with: 1) specific growth rate: 2) viable cell number: 3) glucose consumption rate; or 4) acetic acid secretion rate. Glucose consumption and acetic acid secretion during the stationary growth phase were correlated with specific heat evolution rate. These initial results indicate that this technique may be useful for further development as an on-line flow or stopped-flow method to monitor the physiology of bacilli in response to nutrient depletion or growth inhibition.     

低温与光对黄瓜幼苗子叶光合电子传递活性的影响

25～30℃和30 μmol m~(-2)s~(-1)光下培养的黄瓜幼苗,在黑暗下经 1～7℃处理24h或5℃处理24～72h,光合电子传递活性受不同程度的抑制;其抑制部位主要在PSⅡ氧化侧;随温度的降低和时间的延长,抑制部位可发展至PSⅡ及之后的电子递体上,但尚未影响PSⅠ的活性。160μmol m~(-2)s~(-1)的光强加重低温对电子传递活性的抑制,光强越高,则加重的程度越高;抑制部位从PSⅡ氧化侧发展至PSⅡ反应中心以及PSⅠ。