Itamar De Melo | EMBRAPA - Empresa Brasileira de Pesquisa Agropecuária (original) (raw)

Papers by Itamar De Melo

Pesquisa Agropecuaria Brasileira, 2007

Resumo -O objetivo deste trabalho foi realizar um levantamento da diversidade de microrganismos e... more Resumo -O objetivo deste trabalho foi realizar um levantamento da diversidade de microrganismos endofíticos, em plantas de mandioca (Manihot esculenta Crantz) coletadas de áreas comerciais, no Estado de São Paulo, e de etnovariedades dos estados do Amazonas e Bahia e, também, avaliar seu potencial para fixar N atmosférico e para produzir ácido indolacético. Nos três estados, foram identificadas 47 espécies de microrganismos pertencentes a 27 gêneros. Bacillus spp. foi o mais freqüente em todas as regiões. O maior número de gêneros foi encontrado em plantas provenientes do Estado do Amazonas, que apresenta a maior diversidade de microrganismos endofíticos. Amplificações por PCR do gene nifH foram avaliadas em espécies bacterianas pertencentes às γ-Proteobacteria. Isolados AIA positivos foram obtidos de material coletado em todos os estados, e foram representados por microrganismos pertencentes aos subgrupos γ-Proteobacteria, β-Proteobacteria, Bacilli e Actinobacteria. A ocorrência de bactérias endofíticas em plantas de mandioca, com capacidade para fixar N atmosférico e produzir AIA in vitro, indica potencial para promover o crescimento da planta.

Planta, 2007

Certain plant growth-promoting rhizobacteria (PGPR), in the absence of physical contact with a pl... more Certain plant growth-promoting rhizobacteria (PGPR), in the absence of physical contact with a plant stimulate growth via volatile organic compound (VOC) emissions, through largely unknown mechanisms. To probe how PGPR VOCs trigger growth in plants, RNA transcript levels of Arabidopsis seedlings exposed to Bacillus subtilus (strain GB03) were examined using oligonucleotide microarrays. In screening over 26,000 protein-coded transcripts, a group of approximately 600 diVerentially expressed genes related to cell wall modiWcations, primary and secondary metabolism, stress responses, hormone regulation and other expressed proteins were identiWed. Transcriptional and histochemical data indicate that VOCs from the PGPR strain GB03 trigger growth promotion in Arabidopsis by regulating auxin homeostasis. SpeciWcally, gene expression for auxin synthesis was up regulated in aerial regions of GB03exposed plants; auxin accumulation decreased in leaves and increased in roots with GB03 exposure as revealed in a transgenic DR5::GUS Arabidopsis line, suggesting activation of basipetal auxin transport. Application of the auxin transport inhibitor 1-naphthylphthalamic acid (NPA) restricted auxin accumulation to sites of synthesis thereby preventing GB03-mediated decreases in shoot auxin levels as well as thwarting GB03-mediated growth promotion. In addition, microarray data revealed coordinated regulation of cell wall loosening enzymes that implicated cell expansion with GB03 exposure, which was conWrmed by comparative cytological measurements. The discovery that bacterial VOCs, devoid of auxin or other known plant hormones regulate auxin homeostasis and cell expansion provides a new paradigm as to how rhizobacteria promote plant growth.

World Journal of Microbiology & Biotechnology, 2009

Mangrove ecosystems are environments subject to substantial degradation by anthropogenic activiti... more Mangrove ecosystems are environments subject to substantial degradation by anthropogenic activities. Its location, in coastal area, interfacing the continents and the oceans makes it substantially important in the prospection for biotechnological applications. In this study, we assessed the diversity of culturable bacteria present over the seasons at two depths (0–10 and 30–40 cm) in a mangrove sediment and in a transect area from the land to the sea. In total, 238 bacteria were isolated, characterized by Amplified Ribosomal DNA Restriction Analysis (ARDRA) and further identified, by Fatty Acid Methyl Esther (FAME-MIDI), into the orders of Vibrionales, Actinomycetales and Bacillales. Also the ability of the isolates in producing economically important enzymes (amylases, proteases, esterases and lipases) was evaluated and the order Vibrionales was the main enzymatic source.

Archives of Microbiology, 2008

Lipopeptides produced by Bacillus subtilis are known for their high antifungal activity. The aim ... more Lipopeptides produced by Bacillus subtilis are known for their high antifungal activity. The aim of this paper is to show that at high concentration they can damage the surface ultra-structure of bacterial cells. A lipopeptide extract containing iturin and surfactin (5 mg mL−1) was prepared after isolation from B. subtilis (strain OG) by solid phase extraction. Analysis by atomic force microscope (AFM) showed that upon evaporation, lipopeptides form large aggregates (0.1–0.2 μm2) on the substrates silicon and mica. When the same solution is incubated with fungi and bacteria and the system is allowed to evaporate, dramatic changes are observed on the cells. AFM micrographs show disintegration of the hyphae of Phomopsis phaseoli and the cell walls of Xanthomonas campestris and X. axonopodis. Collapses to fungal and bacterial cells may be a result of formation of pores triggered by micelles and lamellar structures, which are formed above the critical micelar concentration of lipopeptides. As observed for P. phaseoli, the process involves binding, solubilization, and formation of novel structures in which cell wall components are solubilized within lipopeptide vesicles. This is the first report presenting evidences that vesicles of uncharged and negatively charged lipopeptides can alter the morphology of gram-negative bacteria.

Pesquisa Agropecuaria Brasileira, 2007

Resumo -O objetivo deste trabalho foi realizar um levantamento da diversidade de microrganismos e... more Resumo -O objetivo deste trabalho foi realizar um levantamento da diversidade de microrganismos endofíticos, em plantas de mandioca (Manihot esculenta Crantz) coletadas de áreas comerciais, no Estado de São Paulo, e de etnovariedades dos estados do Amazonas e Bahia e, também, avaliar seu potencial para fixar N atmosférico e para produzir ácido indolacético. Nos três estados, foram identificadas 47 espécies de microrganismos pertencentes a 27 gêneros. Bacillus spp. foi o mais freqüente em todas as regiões. O maior número de gêneros foi encontrado em plantas provenientes do Estado do Amazonas, que apresenta a maior diversidade de microrganismos endofíticos. Amplificações por PCR do gene nifH foram avaliadas em espécies bacterianas pertencentes às γ-Proteobacteria. Isolados AIA positivos foram obtidos de material coletado em todos os estados, e foram representados por microrganismos pertencentes aos subgrupos γ-Proteobacteria, β-Proteobacteria, Bacilli e Actinobacteria. A ocorrência de bactérias endofíticas em plantas de mandioca, com capacidade para fixar N atmosférico e produzir AIA in vitro, indica potencial para promover o crescimento da planta.

Planta, 2007

Certain plant growth-promoting rhizobacteria (PGPR), in the absence of physical contact with a pl... more Certain plant growth-promoting rhizobacteria (PGPR), in the absence of physical contact with a plant stimulate growth via volatile organic compound (VOC) emissions, through largely unknown mechanisms. To probe how PGPR VOCs trigger growth in plants, RNA transcript levels of Arabidopsis seedlings exposed to Bacillus subtilus (strain GB03) were examined using oligonucleotide microarrays. In screening over 26,000 protein-coded transcripts, a group of approximately 600 diVerentially expressed genes related to cell wall modiWcations, primary and secondary metabolism, stress responses, hormone regulation and other expressed proteins were identiWed. Transcriptional and histochemical data indicate that VOCs from the PGPR strain GB03 trigger growth promotion in Arabidopsis by regulating auxin homeostasis. SpeciWcally, gene expression for auxin synthesis was up regulated in aerial regions of GB03exposed plants; auxin accumulation decreased in leaves and increased in roots with GB03 exposure as revealed in a transgenic DR5::GUS Arabidopsis line, suggesting activation of basipetal auxin transport. Application of the auxin transport inhibitor 1-naphthylphthalamic acid (NPA) restricted auxin accumulation to sites of synthesis thereby preventing GB03-mediated decreases in shoot auxin levels as well as thwarting GB03-mediated growth promotion. In addition, microarray data revealed coordinated regulation of cell wall loosening enzymes that implicated cell expansion with GB03 exposure, which was conWrmed by comparative cytological measurements. The discovery that bacterial VOCs, devoid of auxin or other known plant hormones regulate auxin homeostasis and cell expansion provides a new paradigm as to how rhizobacteria promote plant growth.

World Journal of Microbiology & Biotechnology, 2009

Mangrove ecosystems are environments subject to substantial degradation by anthropogenic activiti... more Mangrove ecosystems are environments subject to substantial degradation by anthropogenic activities. Its location, in coastal area, interfacing the continents and the oceans makes it substantially important in the prospection for biotechnological applications. In this study, we assessed the diversity of culturable bacteria present over the seasons at two depths (0–10 and 30–40 cm) in a mangrove sediment and in a transect area from the land to the sea. In total, 238 bacteria were isolated, characterized by Amplified Ribosomal DNA Restriction Analysis (ARDRA) and further identified, by Fatty Acid Methyl Esther (FAME-MIDI), into the orders of Vibrionales, Actinomycetales and Bacillales. Also the ability of the isolates in producing economically important enzymes (amylases, proteases, esterases and lipases) was evaluated and the order Vibrionales was the main enzymatic source.

Archives of Microbiology, 2008

Lipopeptides produced by Bacillus subtilis are known for their high antifungal activity. The aim ... more Lipopeptides produced by Bacillus subtilis are known for their high antifungal activity. The aim of this paper is to show that at high concentration they can damage the surface ultra-structure of bacterial cells. A lipopeptide extract containing iturin and surfactin (5 mg mL−1) was prepared after isolation from B. subtilis (strain OG) by solid phase extraction. Analysis by atomic force microscope (AFM) showed that upon evaporation, lipopeptides form large aggregates (0.1–0.2 μm2) on the substrates silicon and mica. When the same solution is incubated with fungi and bacteria and the system is allowed to evaporate, dramatic changes are observed on the cells. AFM micrographs show disintegration of the hyphae of Phomopsis phaseoli and the cell walls of Xanthomonas campestris and X. axonopodis. Collapses to fungal and bacterial cells may be a result of formation of pores triggered by micelles and lamellar structures, which are formed above the critical micelar concentration of lipopeptides. As observed for P. phaseoli, the process involves binding, solubilization, and formation of novel structures in which cell wall components are solubilized within lipopeptide vesicles. This is the first report presenting evidences that vesicles of uncharged and negatively charged lipopeptides can alter the morphology of gram-negative bacteria.