1,721,037 research outputs found
MICROBIAL ARSENIC CYCLING IN ITALIAN RICE PADDIES: AN ECOLOGICAL PERSPECTIVE
Full text linkArsenic (As) contamination of rice is an issue of global concern. Italy, although representing the European leader of rice production, is one of the countries mostly affected by As contamination of rice grain. Rice is mainly cultivated under continuous flooding, with the rapid depletion of oxygen in the soil. At the consequent highly reduced redox potentials, As is released into the porewater by the dissolution of iron-arsenic (Fe-As) minerals, and by the reduction of arsenate [As(V)] to arsenite [As(III)], a soluble compound that is rapidly taken up by the plants. In the presence of sulfide, As(III) co-precipitate with the formation of AsnSn minerals. Microorganisms are known to actively oxidize and reduce As, as well as to convert inorganic to organic As via methylation. Furthermore, microorganisms that use Fe or sulfur for their metabolic activities indirectly influence As biogeochemistry in the environment.
In this study, the role of two different practices, suggested to reduce As contamination in rice fields, in shaping rice rhizospheric microbial communities were investigated. Specifically, changes in the water management and use of sulfate (SO42-) as fertilizer were tested.
To analyze the influence of the water regime in rice rhizosphere microbiota, a semi-field experiment was set up. Plants were grown in rice field soil from Pavia (containing 18 mg kg-1 of As) in box plots managed with three water regimes: continuous flooding, continuous flooding with 2 weeks of drainage before flowering, and watering after complete soil drying (“aerobic rice”). In rhizosphere soil and in rhizoplane, aioA, arsC, arsM and arrA genes, encoding for different types of As transformation, as well as 16S rRNA genes belonging to dissimilatory Fe-reducing bacteria (DFeRB) and Fe-oxidizing bacteria (FeOB), were amplified and quantified with Real Time quantitative PCR (RT-qPCR). To analyze the whole active bacterial community, RNA was reverse-transcribed and 16S rRNA was amplified and sequenced by 454-pyrosequencing. The presence of DFeRB and FeOB was also highlighted in rhizoplane samples from plants at flowering stage with Fluorescence In Situ Hybridization (FISH). Furthermore, enrichment cultures of FeOB from roots cultivated under continuous flooding and from aerobic rice were set up on Fe(II) gradient tubes and exposed to either As(V) or As(III). Bacterial growth and related Fe(III) oxides were analyzed with Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray Spectrometry (EDS), and used for 16S rRNA gene clone library preparation.
To test the effect of SO42- amendment on As dissolution into the porewater, a greenhouse experiment was set up with rice plants grown in single pots on rice field soil from Carpiano (MI) (containing 30 mg kg-1 of As). Different pots with and without plants and with and without 0.13 % (w/w) calcium sulfate (CaSO4) amendment were installed. Microbial As genes were quantified with RT-qPCR in
i
bulk and rhizosphere soil. In a similar experiment performed using rice field soil from Vercelli, the genome belonging to a new putative SO42--reducing species of the Nitrospirae phylum was isolated from a metagenomic library by differential genome binning. The phylogenetic affiliation of this species as well as its metabolic features were characterized by the analysis of specific marker genes and expressed proteins.
In continuous flooding, active DFeRB, As(V)-reducing and sulfur-oxidizing bacteria were stimulated, potentially contributing to the release of As into the porewater. The RT-qPCR quantification confirmed that DFeRB belonging to the genus Geobacter significantly increased when rice was cultivated under continuous flooding, in concomitance with a significant increase of As in the porewater over time. This supported the hypothesis that Geobacter, by dissolving Fe(III) minerals, promoted As solubilization. In aerobic rice, genera able to oxidize Fe(II) and/or As(III) were selected. Quantification with RT-PCR confirmed that aioA genes, encoding for As(III)-oxidase, were among the most abundant As genes, increasing when drainage was applied before flowering and in aerobic rice. In Fe(II) gradient tubes, As(V) promoted the enrichment of the nitrate-reducing FeOB genus Azospira from roots developed under continuous flooding, whereas As(III) addition inhibited the growth of FeOB. The SEM-EDS analysis revealed the presence of microorganisms covered by putative Fe encrustation as well as As-Fe oxides crystals. FISH analysis on rice rhizoplane confirmed the presence of FeRB belonging to the family Geobacteraceae and of both microaerophilic and nitrate-reducing FeOB, respectively belonging to the family Gallonellaceae and to the genus Thiobacillus.
The addition of SO42- to rice field soil led, on the one hand, to a lower As release into the porewater, on the other hand, to a lower translocation of the metalloid in the plants. The bulk and rhizosphere soil bacterial community was enhanced by the addition of SO42-, but the abundance of genes involved in As transformation did not change significantly. The analysis of a genome retrieved in a metagenomic library prepared on rice bulk and rhizosphere soil from a similar SO42--addition experiment, revealed the presence of a novel species belonging to the Nitrospirae phylum in Vercelli rice field soils. These microorganisms carry the whole genetic background for dissimilatory reduction of SO42- and nitrate. Through the Wood-Ljungdahl pathway, they likely use acetate as electron donor. Amendment of SO42- in the soil promoted the expression of SO42- respiration, whereas in the control treatments genes for nitrate respiration were expressed.
These outcomes confirm and elucidate the role of the microbial community living in the rhizosphere of rice plants in decreasing As solubility when changes on the water regime are applied. Future research should be focused the possible role of endophytic bacteria on the decrease of As translocation when is rice plants are fertilized with SO42-
Electroanalytical Evidences for the Instability of Hydrogen Tetrafluoroborate in Acetonitrile
No full textHBF4 is demontrated to decompose to HF and BF3 in acetonitrile solvent. Electrochemistry is used for demonstratio
Arundo donax hydrolysates shape hydrogen-producing microbial community in dark fermentation processs
No full textDark fermentation (DF) has great potential for development as a sustainable biohydrogen production system. Mixed anaerobic microbial consortia from sewage or wastewater sludge digester can be used as seeding for fermentative hydrogen (H2) production. Biomass such as energy crops are good substrates for H2 fermentation. Arundo donax (L.), a perennial non-food crop with high biomass, was chosen as a source of lignocellulosic biomass in a pilot-scale DF process. A mixed microbial consortium from a primary sludge digester, adapted to a synthetic medium amended with glucose, was used as inoculum. Before starting the hydrolysates fermentation, the inoculum was acclimated either on glucose or on A. donax hydrolysates. A glucose fermentation with glucose-acclimated inoculum was used as control. The microbial communities were characterized by Pyrotag sequencing of 16S rRNA genes. Hydrogen producing populations were quantified by Real-Time PCR of specific 16S rRNA and hydrogenase genes. Other coexisting microorganisms were also quantified. Performances of A. donax fermentation in presence of differently acclimated consortia were compared by analyzing molecular data in conjunction to H2 production. In glucose fermentation, where H2 production was fast, the bacterial consortium was characterized by the co-dominance of Enterobacteriaceae and Lactobacillaceae being 80% and 15% of the total community respectively. Microbial communities of both A. donax fermentations strongly differed from those of glucose-fermentation, being characterized by the dominance of Lactobacillaceae (40% of the total) and low percentages of H2 producing populations (<0.5% of the total). Quantification of hydrogenase genes of Clostridium spp. confirmed that these populations were present in low amount (104 gene copies). Nevertheless, remarkable H2 yields were recorded. The study evidence that the inhibitory compounds derived from the hydrolysis of A. donax had a prompt effect on the microbial community of the inoculum. However, this noticeable shift in the microbial communities did not affect H2 production. Finally, adaptation on different carbon substrates exerted a comparable selective pressure, leading to similar H2 yields
Dv-x-alpha Calculations, Uv-pe Spectra, and Redox Properties of Nitrosyl-bridged Binuclear Cobalt Complexes
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Interpretation and stress
Full text linkThis study was carried out to analyze stress factors such as anxiety and depression on interpreters and interpreting students during simultaneous and remote interpreting. The study was taylored to interpeting conditions. The project was devided in two stages. During the first, data about the interpreters were collected to assess baseline values for psychological factors important for stress evaluation. In the second, the same group of interpreters underwent specific tests during simultaneous and remote interpreting.Psychometric instruments were chosen to this end. The results of the study show lower anxiety and depression values for interpreters than in the normal sample population, with interpeters being characterized by lower values than interpreting-students
Dioxygen-decomposition of ferrocenium molecules in acetonitrile: The nature of the electrode-fouling films during ferrocene electrochemistry
No full textDecomposition of ferrocenium by dioxygen in acetonitrile +0.1 M But(4)NClO(4) is reported. The nature of the products has been investigated by CV, FTIR, GC-MS, EQCM and elemental analysis. The insoluble materials, responsible for the commonly encountered electrode fouling during ferrocene oxidation in incompletely degassed solutions, is a mixture of hydrous iron(III) oxide and the organic polymer poly(cyclopentane-1,3-dione-4,5-diyl). Soluble products are mainly constituted by Fe(III) perchlorate, 4-cyclopenten-1,3-dione, tricyclo[5.1.2.0(2,6)]deca-4,8-dien-3,10-dione and related oligomers. (C) 1998 Elsevier Science S.A. All rights reserved
Rice plant growth-promoting rhizobacteria: a focus on phosphate solubilization
Full text linkThe application of microbial inoculants is an innovative biotechnology to preserve the productivity and sustainability of rice cultivation. Plant growth-promoting rhizobacteria (PGPR) can be applied directly to the soil by seed inoculation, plant tissue treatments or soil applications, to increase the crop biomass growth and to control several plant pathogens, thus avoiding or reducing chemical control. In particular, PGPR able to release soluble phosphorous (P) ions from insoluble mineral or organic forms is drawing attention, also in consideration of severe depletion of raw materials for phosphate fertilizer manufacturing.
In the present work, 299 bacterial strains isolated from rhizosphere compartments of rice were characterized for different PGP activities. ACC deaminase activity, phytate mineralization and N2 fixation were the most represented PGP traits. Twenty-one strains possessing most of the tested PGP activities were inoculated in growth pouches experiments to determine in vivo the ability to promote seed germination. Four PGPR identified as Pseudomonas koreensis, Priestia aryabhattai and Bacillus zanthoxyli showed a major significant promotion of biomass growth. Pot experiments with Green Fluorescent Protein- transformed Pseudomonas koreensis strain are ongoing to evaluate plant colonization and rice growth promotion under different levels of bioavailable phosphate
Ossidazione biologica dell’arsenico in accoppiamento con materiali adsorbenti in azioni di decontaminazione delle acque
No full textIn diverse regioni italiane, tra cui la Lombardia, vi sono zone che, in conseguenza di particolari condizioni geopedologiche, presentano acque di falda con concentrazioni di arsenico superiori a 10 μg/L, limite per le acque ad uso potabile ai sensi della vigente normativa italiana (D.Lgs 152/2006).
L’arsenico può essere presente nelle acque di falda in forma di arsenito e arsenato, quest’ultimo più facilmente sequestrabile dalle superfici minerali adsorbenti. Per la rimozione dell’arsenito, è spesso necessaria una fase di pre-ossidazione che lo converte nella forma di arsenato. L’ossidazione biologica, promossa da microrganismi arsenito-ossidanti, rappresenta un’interessante alternativa all’utilizzo di ossidanti chimici.
Nell’ambito di un progetto finanziato da Fondazione Cariplo sono state caratterizzate le popolazioni microbiche di acque di falda lombarde a concentrazioni di arsenico comprese tra 0,7 e 171 μg/L, la cui forma dominante era l’arsenito. Sono stati inoltre ricercati ceppi microbici arsenito-ossidanti e testate le capacità adsorbenti di diversi materiali a base di ferro, tra cui goethite e nanoferro caricato su proteina ingegnerizzata (Pf-ferritina) in acqua artificialmente contaminata con arsenito (200 μg/L). I materiali sono stati poi saggiati in accoppiamento con l’ossidazione biologica, al fine di valutare l’efficienza del trattamento combinato per la rimozione dell’arsenico da un’acqua di falda contaminata (171 μg/L di arsenico).
L’analisi delle comunità microbiche mediante pirosequenziamento dell’rRNA del 16S ha rivelato la presenza di microrganismi coinvolti direttamente, quali ad esempio Beta-proteobatteri, e indirettamente nel ciclo dell’arsenico (batteri ferro-riduttori, ferro-manganese-ossidanti). Mediante l’allestimento di colture microbiche sono stati isolati batteri capaci di trasformare l’arsenico. Tra di essi, il microrganismo Aliihoeflea sp. ceppo 2WW, per la sua capacità di ossidare l’arsenito in diverse condizioni ambientali, è stato scelto per la fase di ossidazione biologica nel processo di rimozione dell’arsenico.
I diversi materiali adsorbenti hanno dimostrato un’efficienza di rimozione dell’arsenito pari al 70% (Pf-ferritina) e all’80% (goethite), quando sperimentati in sistema artificiale, mentre nelle acque di falda tale efficienza è scesa a 40% per Pf-ferritina e 75% per goethite. Sebbene in generale l’introduzione della fase di ossidazione biologica abbia incrementato di circa 20% le efficienze di rimozione, solo l’ossidazione biologica accoppiata a goethite ha portato ad un abbattimento significativo del contenuto di arsenito sotto il limite di legge (6 μg/L in soluzione).
I risultati sino ad ora ottenuti dimostrano la potenzialità dell’accoppiamento dell’ossidazione biologica con l’adsorbimento su un materiale a base ferrosa nella rimozione dell’arsenico e saranno utilizzati nello scale-up di un processo di trattamento di acque contaminate
- …
