Lactate conversion to acetate,CO2 and H2 in cell suspensions of Desulfovibrio vulgaris (Marburg): indications for the involvement of an energy driven reaction

Cell suspensions of Desulfovibrio vulgaris were found to catalyze, in the absence of sulfate, the complete conversion of 1 lactate to 1 acetate, 1 CO₂, and 2 H₂ (G₀=-8.8 kJ/mol) and of 1 pyruvate to 1 acetate, 1 CO₂, and 1 H₂ (G₀=-52 kJ/mol). Protonophores, the proton translocating ATPase inhibitor N,N-dicyclohexylcarbodiimide, and arsenate specifically inhibited H₂ formation from lactate but not from pyruvate. The results suggest that lactate oxidation to pyruvate and H₂ (G ₀=+43.2 kJ/mol) is energy driven.     

Mechanisms of sugar transport byThiobacillus A2

Comparison of the effects of uncoupling agents, arsenate, fluoride and cyanide on sugar transport byThiobacillus A2 indicated that (a) glucose uptake by fast-growing strain GFI involved a high energy phosphate dependent system; (b) transport of glucose by the wild type and of fructose and sucrose by both strains, was by respiration dependent systems requiring a membrane proton gradient. Glucose and sucrose were competitive inhibitors of the transport of each other. Bacteria grown on glucose +sucrose (20+2 mM) transported glucose much faster than those grown on glucose alone. This could explain the great stimulation of growth rate on glucose, in the presence of sucrose.Abbreviations Butyl PBD 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole - DBP 2,4-dibromophenol - DNP 2,4-dinitrophenol - FCCP carboxylcyanide p-trifluoromethoxyphenylhydrazone - 3-OMG 3-O-methylglucose - PCP pentachlorophenol - Tris tris(Hydroxymethyl)-aminomethane - TTFB 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole - PEP phosphoenolpyruvate     

Uptake kinetics of different arsenic species by Brassica carinata

The time- and concentration-dependent uptake kinetics for arsenate and arsenite were determined in 15-day-old excised roots. In both cases, arsenite showed a mono-phasic influx with the isotherm data fitting a linear model better than a non-linear one. The time- and the concentration-dependent uptake of arsenate displayed a hyperbolic kinetic. Greater uptake of arsenate, compared with arsenite, was found especially at lower external substrate concentrations. Competitive inhibition of uptake with phosphate showed that arsenite and arsenate were taken up by different uptake systems because arsenate uptake was strongly inhibited in the presence of phosphate, whereas arsenite uptake was not affected.     

Proteome analysis of maize roots reveals that oxidative stress is a main contributing factor to plant arsenic toxicity

To gain insight into plant responses to arsenic, the effect of arsenic exposure on maize (Zea mays L.) root proteome has been examined. Maize seedlings were fed hydroponically with 300 microM sodium arsenate or 250 microM sodium arsenite for 24 h, and changes in differentially displayed proteins were studied by two-dimensional electrophoresis and digital image analysis. About 10% of total detected maize root proteins (67 out of 700) were up- or down-regulated by arsenic, among which 20 were selected as being quite reproducibly affected by the metalloid. These were analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and 11 of them could be identified by comparing their peptide mass fingerprints against protein- and expressed sequence tag-databases. The set of identified maize root proteins highly responsive to arsenic exposure included a major and functionally homogeneous group of seven enzymes involved in cellular homeostasis for redox perturbation (e.g., three superoxide dismutases, two glutathione peroxidases, one peroxiredoxin, and one p-benzoquinone reductase) besides four additional, functionally heterogeneous, proteins (e.g., ATP synthase, succinyl-CoA synthetase, cytochrome P450 and guanine nucleotide-binding protein beta subunit). These findings strongly suggest that the induction of oxidative stress is a main process underlying arsenic toxicity in plants.     

Localization and speciation of arsenic in Glomus intraradices by synchrotron radiation spectroscopic analysis

The protective mechanisms employed by arbuscular mycorrhizal fungi (AMF) to reduce the toxic effects of arsenic on host plants remain partially unknown. The goal of this research was identifying the in situ localization and speciation of arsenic (As) in the AM fungus Rhizophagus intraradices [formerly named Glomus intraradices] exposed to arsenate [As(V)]. By using a two-compartment in vitro fungal cultures of R. intraradices-transformed carrot roots, microspectroscopic X-ray fluorescence (μ-XRF), and microspectroscopic X-ray absorption near edge structure (μ-XANES), we observed that As(V) is absorbed after 1 h in the hyphae of AMF. Three hours after exposure a decrease in the concentration of As was noticed and after 24 and 72 h no detectable As concentrations were perceived suggesting that As taken up was pumped out from the hyphae. No As was detected within the roots or hyphae in the root compartment zone three or 45 h after exposure. This suggests a dual protective mechanism to the plant by rapidly excluding As from the fungus and preventing As translocation to the plant root. μ-XANES data showed that gradual As(V) reduction occurred in the AM hyphae between 1 and 3 h after arsenic exposure and was completed after 6 h. Principal component analysis (PCA) and linear combination fitting (LCF) of μ-XANES data showed that the dominant species after reduction of As(V) by R. intraradices extra-radical hyphal was As(III) complexed with a reduced iron(II) carbonate compound. The second most abundant As species present was As(V)–iron hydroxides. The remaining As(III) compounds identified by the LCF analyses suggested these molecules were made of reduced As and S. These results increase our knowledge on the mechanism of As transport in AMF and validate our hypotheses that R. intraradices directly participates in arsenic detoxification. These fungal mechanisms may help AMF colonized plants to increase their tolerance to As at contaminated sites.     

抗砷性微生物及其抗砷分子机制研究进展

砷(Arsenic, As)是一种剧毒类金属(Metalloid), 在自然环境中主要以三价亚砷酸盐[Arsenite, AsO2-, As(III)]和五价砷酸盐[Arsenate, AsO43-, As(V)]的无机形式广泛存在。许多微生物在含砷环境的长期适应过程中, 进化了多种不同的砷解毒抗性机制。目前研究发现主要存在4种类型的砷抗性机理, 包括: As(III)氧化, 细胞质As(V)还原, 呼吸性As(V)还原, As(III)甲基化, 这些机制赋予微生物砷抗性并在砷的转化和地球化学循环中起着极     

Oxidation and reduction of arsenic by Sulfolobus acidocaldarius strain BC

Abstract The mineral leaching archaebacterium Sulfolobus acidocaldarius strain BC is shown to have the ability to oxidise arsenite to arsenate. Arsenite oxidation activity was 8-fold higher for cells grown in the presence of arsenite when compared with cells grown without arsenite. In cell-free extracts, the arsenite oxidation activity was found in the membrane fraction. The arsenite oxidation activity was sensitive to proteinase K and showed the highest activity at acidic pH. A tetrathionate-dependent arsenate reduction activity was also observed.     

Dissimilatory arsenate and sulfate reduction in Desulfotomaculum auripigmentum sp. nov.

A newly discovered arsenate-reducing bacterium, strain OREX-4, differed significantly from strains MIT-13 and SES-3, the previously described arsenate-reducing isolates, which grew on nitrate but not on sulfate. In contrast, strain OREX-4 did not respire nitrate but grew on lactate, with either arsenate or sulfate serving as the electron acceptor, and even preferred arsenate. Both arsenate and sulfate reduction were inhibited by molybdate. Strain OREX-4, a gram-positive bacterium with a hexagonal S-layer on its cell wall, metabolized compounds commonly used by sulfate reducers. Scorodite (FeAsO₄2· H₂O) an arsenate-containing mineral, provided micromolar concentrations of arsenate that supported cell growth. Physiologically and phylogenetically, strain OREX-4 was far-removed from strains MIT-13 and SES-3: strain OREX-4 grew on different electron donors and electron acceptors, and fell within the gram-positive group of the Bacteria, whereas MIT-13 and SES-3 fell together in the ɛ-subdivision of the Proteobacteria. Together, these results suggest that organisms spread among diverse bacterial phyla can use arsenate as a terminal electron acceptor, and that dissimilatory arsenate reduction might occur in the sulfidogenic zone at arsenate concentrations of environmental interest. 16S rRNA sequence analysis indicated that strain OREX-4 is a new species of the genus Desulfotomaculum, and accordingly, the name Desulfotomaculum auripigmentum is proposed. Received: 22 October 1997 / Accepted: 16 June 1997