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2.
Cyanobacterial cultures tolerating 200 mmol l −1 sodium chloride isolated from terrestrial and freshwater habitats of North Maharashtra region of India were evaluated for
antifungal activity. Aqueous, methanol, n-propanol, and petroleum ether extracts of 40 cyanobacterial isolates belonging to nine genera were examined for inhibitory
activity against five fungal pathogens. Eighteen isolates belonging to genus Oscillatoria dominated the population of halotolerant cyanobacterial cultures. Four antifungal bioassays viz. double layer agar method,
disc diffusion assay, silica gel method, and minimum inhibitory concentration (MIC) were used to screen the cultures for antifungal
activity. Among the solvents used, methanol extracts showed 34.9% inhibition followed by n-propanol, petroleum ether, and water exhibiting 30.2%, 18.6% and 16.2% inhibition, respectively. The double agar layer method
was found to be a suitable method in preliminary screening for handling large number of cultures without extraction of compounds.
However, in later screening experiments, silica gel method was seen to be advantageous over MIC and agar disc diffusion methods. 相似文献
3.
The decreasing availability of energy resources has brought about a renewed interest in the enzyme hydrogenase. Hydrogen gas can be produced by organisms and represents a potential renewable energy source, or it can be utilized by certain organisms as a sole energy source during processes that result in the net fixation of carbon, a biosynthetic capability that might be exploited for the production of specific compounds. Both the production and utilization of hydrogen in biological systems are dependent on hydrogenase. The manipulation of the expression of hydrogenase in attempts to optimize hydrogen production or utilization will to a certain extent be dependent on existing knowledge concerning the regulation of hydrogenase and its interactions with other aspects of cellular metabolism. Information pertaining to the genetics of hydrogenases should play an important role in the construction of organisms affected in their hydrogen metabolism. The genetics of hydrogenase in enteric bacteria, in hydrogen bacteria, and in root nodule bacteria are reviewed, and the implications concerning the manipulation of hydrogenase genes are discussed. 相似文献
5.
There is increasing evidence that fluvial systems are influenced by anthropogenic factors, and disturbance due to pollution
and other human interference gives rise to specific problems. It is now imperative that we develop and apply novel and effective
ways which allow us to monitor water quality. The present study was planned as part of a programme to develop biological monitoring
methods to assess nutrient characteristics of upland calcareous streams and rivers. Phototrophs respond to environmental changes
over a period of time, so organisms sampled at one time can potentially provide almost as much information about nutrients
in the water as a number of individual chemical measurements. Phosphatase activity is often a good indicator of phosphorus
limitation, and field materials could be used to study changes in nutrients dynamics. The calcareous River Muga, north-east
Spain, at a site 10 km downstream from its source in the Pyrenees, was therefore chosen for the present study of surface phosphatase
activities of the main cyanobacterial communities at different seasons to assess P limitation and establish the suitability
of this method for use in monitoring catchment processes. Here we report seasonal changes of phosphatase activity in field
populations of Schizothrix coriacea, Rivularia biasolettiana, Tolypothrix distorta var. penicillata and Nostoc verrucosum. All four cyanobacteria showed marked surface phosphomonoesterase and phosphodiesterase activity on each sampling period.
Michaelis-Menten kinetic studies showed similar K
m
values for the four species suggesting similar affinity for organic P substrates. Light had no effect on phosphatase activities,
indicating that there is no need to consider this factor in short-term field assays. However, there was an increase in phosphomonoesterase
activity of Rivularia with rise in temperature over the range 10–35°C, which suggests adaptation to the frequent temperature changes in nature.
Phosphorus limitation seems the main chemical factor influencing phototrophs in R. Muga. Combined observations on macroscopically
visible phototrophs with assays of surface phosphatase activity provide a valuable means of assessing long-term changes in
a catchment. 相似文献
6.
The activity of hydrogenase was assayed in the intact cells and subcellular fractions of Brevibacterium flavum. The organism was shown to have the membrane-bound form of hydrogenase. The soluble NAD+-reducing hydrogenase was not found. Oxygen inhibited the hydrogenase activity, and its action was reversible. Molecular hydrogen activated the hydrogenase of B. flavum, which was shown to be a constitutive enzyme. 相似文献
10.
Hydrogenase from fructose-grown cells of Acetobacterium woodii has been purified 70-fold to a specific activity of 3,500 mol hydrogen oxidized per min per mg of protein measured at 35°C and pH 7.6 with methyl viologen as electron acceptor. At the same conditions with reduced methyl viologen as electron donor the enzyme catalyzes the evolvement of 440 mol of H 2 per min per mg of protein. The enzyme was found in the soluble portion of the cell, indicating that it is either not membrane-bound or is loosely associated with the membrane. The purified enzyme, which does not contain nickel, exhibits spectroscopic properties similar to the iron-sulfur hydrogenase of Clostridium pasteurianum. The enzyme is strongly inhibited by carbon monoxide, with 50% inhibition occurring at approximately 7 nM CO. Ferredoxin, flavodoxin, and carbon monoxide dehydrogenase are reduced in hydrogen-dependent reaction by the A. woodi hydrogenase.Abbreviations CO dehydrogenase
carbon monoxide dehydrogenase
- MV
methyl viologen
- SDS
sodium dodecyl sulfate
This paper is dedicated to Professor Dr. Hans G. Schlegel on the occasion of his 60-years birthday. Hans' contributions to the field of microbiology are many and it is a pleasure for us to commemorate him in this way. One of us, L. G. L., had the fortune as a Humboldt-Preis recipient to spend a year at the Institut für Mikrobiologie der Universität Göttingen. Besides the best possible working conditions memories involve pleasant evenings with a glass of Rhine-wine in the Schlegels' home to strenuous back-packing in the Austrian Alps. 相似文献
11.
The assay of the hydrogenase of glucose-grown cells of Chlorella pyrenoidosa, strain 7-11-05 by means of nitrite reduction with molecular hydrogen is described. The hydrogenase of Chlorella shows maximum activity immediately after equilibration in the hydrogen atmosphere. The hydrogenase mediated reduction of nitrite to ammonia requires the presence of CO 2. However, at pH 6.4. when the reaction proceeds optimally, there is apparently sufficient retention of metabolic CO 2 to support the reaction, which goes to completion, at near maximum rates. Reduction of nitrite in the hydrogenase system when CO2 is present results in the uptake of 3 moles of H2 per mole of nitrite and ammonia is the product. When CO2 is absent or limiting, ammonia is also formed from nitrite but with the uptake of less than the stoichiometric amount of H2. It is concluded that CO2 is essential for the uptake of H2, and that in the absence of CO2 internal hydrogen donors support nitrite reduction. The possibility that CO2 exerts a catalytic effect in all reductions mediated by hydrogenase in algae is considered, and a further hypothesis, that hydrogenase arises from that portion of the photosynthetic machinery which also shows a catalytic requirement for CO2, is proposed. 相似文献
13.
Toxic cyanobacterial blooms are a rich source of metabolites having a variety of biological activities. Two main groups of cyclic peptides, depsipeptides and ureido linkage-containing peptides, reportedly inhibit serine peptidases. We characterised their inhibitory properties against selected peptidases and investigated their influence on cell viability. The depsipeptide planktopeptin BL1125 is a strong linear competitive tight-binding inhibitor of leukocyte (K(i)=2.9 nm) and pancreatic (K(i)=7.2 nm) elastase and also of chymotrypsin (K(i)=6.1 nm). Anabaenopeptins B and F show no inhibition against chymotrypsin, but inhibit both elastases. The tested cyclic peptides do not inhibit trypsin, urokinase, kallikrein 1 or cysteine peptidases. All three tested cyanopeptides show no short-term cytotoxicity in concentrations of up to 10 mum, but impair the metabolic activity of normal human astrocytes after prolonged exposure (48-96 h), whereas glioblastoma cells, tumour cells of the same type, are resistant. Strong inhibition and relative selectivity of the tested cyanopeptides suggests that they are potential candidates for application in inflammatory diseases and possibly some types of cancers. 相似文献
15.
Hydrogenase activity in cells of the nitrogen-fixing methane-oxidizing bacterium strain 41 of the Methylosinus type increased markedly when growth was dependent upon the fixation of gaseous nitrogen. A direct relationship may exist between hydrogenase and nitrogenase in this bacterium. Acetylene reduction was supported by the presence of hydrogen gas. 相似文献
16.
Summary Hydrogen uptake has been shown to occur with pea root nodule breis and this uptake has been shown to be confined to the bacteriods. The uptake of hydrogen by washed bacteriods, in the absence of any added substrates, has been shown to be accompanied by oxygen uptake and the ratio of hydrogen uptake to oxygen uptake in these preparations has been found to be 2:1. Substrates, provided to washed bacteriods, inhibit the uptake of hydrogen and it has been found that the utilisation of substrates, as measured by carbon dioxide evolution, is inhibited by hydrogen. It is suggested that hydrogen and substrates compete for electron carriers and that electrons from the hydrogen reduce components of the electron transport pathway and ATP is produced.The action of hydrogen on nitrogen fixation in nodule breis and washed bacterioid preparations was examined and the evidence shows that some non-competitive inhibition of nitrogen fixation, by hydrogen, occurs. 相似文献
17.
The Wood-Ljungdahl pathway of anaerobic CO(2) fixation with hydrogen as reductant is considered a candidate for the first life-sustaining pathway on earth because it combines carbon dioxide fixation with the synthesis of ATP via a chemiosmotic mechanism. The acetogenic bacterium Acetobacterium woodii uses an ancient version of the pathway that has only one site to generate the electrochemical ion potential used to drive ATP synthesis, the ferredoxin-fueled, sodium-motive Rnf complex. However, hydrogen-based ferredoxin reduction is endergonic, and how the steep energy barrier is overcome has been an enigma for a long time. We have purified a multimeric [FeFe]-hydrogenase from A. woodii containing four subunits (HydABCD) which is predicted to have one [H]-cluster, three [2Fe2S]-, and six [4Fe4S]-clusters consistent with the experimental determination of 32 mol of Fe and 30 mol of acid-labile sulfur. The enzyme indeed catalyzed hydrogen-based ferredoxin reduction, but required NAD(+) for this reaction. NAD(+) was also reduced but only in the presence of ferredoxin. NAD(+) and ferredoxin reduction both required flavin. Spectroscopic analyses revealed that NAD(+) and ferredoxin reduction are strictly coupled and that they are reduced in a 1:1 stoichiometry. Apparently, the multimeric hydrogenase of A. woodii is a soluble energy-converting hydrogenase that uses electron bifurcation to drive the endergonic ferredoxin reduction by coupling it to the exergonic NAD(+) reduction. 相似文献
19.
氢化酶是微生物代谢产氢过程中的关键酶,也是目前生物制氢领域的研究热点。本文综述了厌氧发酵产氢微生物中氢化酶的分类及特点,以及[Ni—Fe]、[Fe—Fe]和[Fe—Scluster—free]三种氢化酶晶体结构和活性中心结构;阐述了多种微生物来源的氢化酶结构的研究进展,对几种典型氢化酶的结构及活性中心进行了对比分析,并根据当前研究热点,对氢化酶的研究方向进行了展望。本文阐述的内容信息量丰富且具有一定的实用性,对于氢化酶相关领域研究具有重要的意义。 相似文献
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