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      Bacterial diversity associated with the rhizosphere of wheat plants (Triticum aestivum): Toward a metagenomic analysis Translated title: Diversidad bacteriana asociada a la rizósfera de plantas de trigo (Triticum aestivum): Hacia un análisis metagenómico

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          Abstract

          Rhizospheric soil is one the largest reservoirs of microbial genetic diversity. Before conducting a large-scale metagenomic analysis of an environment, such as a rhizospheric soil, it is necessary to perform a pre-screening of the resident genetic diversity. In this study, we analyzed the bacterial diversity associated with the rhizosphere of wheat plants by PCR amplification, construction of a library and sequencing of 16S rDNA genes. Thirty OTUs were detected, including the Classes Alfaproteobacteria, Betaproteobacteria, Deltaproteobacteria, Gammaproteobateria, Actinobacteria, Bacilli, Clostridia and Uncultivable bacteria. Within the Gammaproteobacteria class, the genera Pseudomonas, Stenotrophomonas and Bacillus were the most abundant, since they corresponded to 40% of the whole ribosomal library. Phylogenetic analysis showed that most of the ribosomal sequences are grouped into clades that belong to common rhizospheric or bulk-soil bacteria. To determine whether the sample is significantly diverse, a Shannon-Wiener test was performed, resulting in a rate of 3.8 bits per individual. Our results suggest that the rhizosphere of wheat plants is highly diverse and results an excellent candidate for metagenomic analysis.

          Translated abstract

          El suelo rizosférico es uno de los reservorios más grandes de la diversidad genética microbiana. Antes de realizar un estudio metagenómico a gran escala de un ambiente, tal como el suelo rizosférico, es necesario realizar un análisis previo de la diversidad genética residente. Por ello, en este trabajo se detectó la diversidad bacteriana asociada a la rizósfera de plantas de trigo por medio de la amplificación de PCR, construcción de una biblioteca y secuenciación de los genes 16S ribosomales. Se detectaron 30 OTUs, incluyendo las Clases Alfaproteobacteria, Betaproteobacteria, Deltaproteobacteria, Gammaproteobateria, Actinobacteria, Bacilli, Clostridia y bacterias no cultivables. Dentro de las Gammaproteobateria, los géneros más abundantes fueron Pseudomonas, Stenotrophomonas y Bacillus, ya que correspondieron al 40% del total de la biblioteca ribosomal completa. El análisis filogenético demostró que la mayoría de las secuencias ribosomales se agrupan en los clados que pertenecen a bacterias comunes del suelo o rizosféricas. Para determinar si la muestra es bastante diversa se llevó a cabo una prueba de Shannon-Wiener, resultando en una tasa de 3,8 bits por individuo. Nuestros resultados sugieren que la rizósfera de plantas de trigo es muy diversa y resulta un candidato excelente para otro tipo de análisis metagenómicos.

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          Most cited references49

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          Metagenomics: application of genomics to uncultured microorganisms.

          Metagenomics (also referred to as environmental and community genomics) is the genomic analysis of microorganisms by direct extraction and cloning of DNA from an assemblage of microorganisms. The development of metagenomics stemmed from the ineluctable evidence that as-yet-uncultured microorganisms represent the vast majority of organisms in most environments on earth. This evidence was derived from analyses of 16S rRNA gene sequences amplified directly from the environment, an approach that avoided the bias imposed by culturing and led to the discovery of vast new lineages of microbial life. Although the portrait of the microbial world was revolutionized by analysis of 16S rRNA genes, such studies yielded only a phylogenetic description of community membership, providing little insight into the genetics, physiology, and biochemistry of the members. Metagenomics provides a second tier of technical innovation that facilitates study of the physiology and ecology of environmental microorganisms. Novel genes and gene products discovered through metagenomics include the first bacteriorhodopsin of bacterial origin; novel small molecules with antimicrobial activity; and new members of families of known proteins, such as an Na(+)(Li(+))/H(+) antiporter, RecA, DNA polymerase, and antibiotic resistance determinants. Reassembly of multiple genomes has provided insight into energy and nutrient cycling within the community, genome structure, gene function, population genetics and microheterogeneity, and lateral gene transfer among members of an uncultured community. The application of metagenomic sequence information will facilitate the design of better culturing strategies to link genomic analysis with pure culture studies.
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            Bacillus lipopeptides: versatile weapons for plant disease biocontrol.

            In the context of biocontrol of plant diseases, the three families of Bacillus lipopeptides - surfactins, iturins and fengycins were at first mostly studied for their antagonistic activity for a wide range of potential phytopathogens, including bacteria, fungi and oomycetes. Recent investigations have shed light on the fact that these lipopeptides can also influence the ecological fitness of the producing strain in terms of root colonization (and thereby persistence in the rhizosphere) and also have a key role in the beneficial interaction of Bacillus species with plants by stimulating host defence mechanisms. The different structural traits and physico-chemical properties of these effective surface- and membrane-active amphiphilic biomolecules explain their involvement in most of the mechanisms developed by bacteria for the biocontrol of different plant pathogens.
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              Screening of free-living rhizospheric bacteria for their multiple plant growth promoting activities.

              Plant growth promoting rhizobacteria (PGPR) are known to influence plant growth by various direct or indirect mechanisms. In search of efficient PGPR strains with multiple activities, a total of 72 bacterial isolates belonging to Azotobacter, fluorescent Pseudomonas, Mesorhizobium and Bacillus were isolated from different rhizospheric soil and plant root nodules in the vicinity of Aligarh. These test isolates were biochemically characterized. These isolates were screened in vitro for their plant growth promoting traits like production of indoleacetic acid (IAA), ammonia (NH(3)), hydrogen cyanide (HCN), siderophore, phosphate solubilization and antifungal activity. More than 80% of the isolates of Azotobacter, fluorescent Pseudomonas and Mesorhizobium ciceri produced IAA, whereas only 20% of Bacillus isolates was IAA producer. Solubilization of phosphate was commonly detected in the isolates of Bacillus (80%) followed by Azotobacter (74.47%), Pseudomonas (55.56%) and Mesorhizobium (16.67%). All test isolates could produce ammonia but none of the isolates hydrolyzed chitin. Siderophore production and antifungal activity of these isolates except Mesorhizobium were exhibited by 10-12.77% isolates. HCN production was more common trait of Pseudomonas (88.89%) and Bacillus (50%). On the basis of multiple plant growth promoting activities, eleven bacterial isolates (seven Azotobacter, three Pseudomonas and one Bacillus) were evaluated for their quantitative IAA production, and broad-spectrum (active against three test fungi) antifungal activity. Almost at all concentration of tryptophan (50-500 microg/ml), IAA production was highest in the Pseudomonas followed by Azotobacter and Bacillus isolates. Azotobacter isolates (AZT(3), AZT(13), AZT(23)), Pseudomonas (Ps(5)) and Bacillus (B(1)) showed broad-spectrum antifungal activity on Muller-Hinton medium against Aspergillus, one or more species of Fusarium and Rhizoctonia bataticola. Further evaluation of the isolates exhibiting multiple plant growth promoting (PGP) traits on soil-plant system is needed to uncover their efficacy as effective PGPR.
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Journal
                phyton
                Phyton (Buenos Aires)
                Phyton (B. Aires)
                Fundación Rómulo Raggio (Vicente López, Buenos Aires, Argentina )
                1851-5657
                June 2012
                : 81
                : 1
                : 81-87
                Affiliations
                [01] orgnameUniversidad Michoacana de San Nicolás de Hidalgo orgdiv1Instituto de Investigaciones Químico Biológicas México
                Article
                S1851-56572012000100012
                10.32604/phyton.2012.81.081
                e4e2f183-76c8-4649-bc04-e3b7ac3005f8

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

                History
                : 09 November 2011
                : 03 September 2011
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 35, Pages: 7
                Product

                SciELO Argentina


                Rizósfera,Bacterial diversity,Rhizosphere,Wheat,16S ribosomal genes,Diversidad bacteriana,Trigo,Genes 16S ribosomales

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