Aloisio Freitas Chagas Junior

Rhizobia amylase production using various starchy substances as carbon substrates

Six isolates of indigenous rhizobia of Central Amazonia were screened for the production of amylases in liquid media using various starchy substances as carbon sources. All rhizobia strains could produce more extracellular protein, biomass and amylases with the different kinds of carbon substrates. Among the carbon sources tested maltose was the best substrate for protein and amylase production. In general, peach palm flour and corn starch (maizena®) were also considered to be good carbon sources for rhizobia amylases. On the other hand, the biomass production by the rhizobia isolates was higher in the presence of oat flour. INPA strain R-926 was a good amylase producer in maltose (1.94 U) and corn starch (0.53 U) media. INPA strain R-991 was also a good amylase producer in maltose (1.66 U) and corn starch (1.59 U) yielding significant extracellular amylase. Correlation analysis showed significant and positive relationships between rhizobia amylases and final pH (r = 0.49, P < 0.05), extracellular protein (r = 0.47, P < 0.47) and biomass production (r = 0.69, P < 0.01) in the maltose medium. The results obtained in this study revealed several Central Amazonian rhizobia strains as promising sources of amylase for biotechnological applications, especially in starch industry.

Atividade enzimática de isolados de rizóbia nativos da Amazônia Central crescendo em diferentes níveis de acidez

A importância das bacterias conhecidas como rizobia no estabelecimento de leguminosas tem sido amplamente reconhecida. Porem, poucas sao as informacoes referentes ao perfil enzimatico dessas bacterias beneficas. O estudo objetivou investigar a influencia do pH do meio solido sobre a atividade enzimatica de rizobios nativos da Amazonia Central. Essa triagem constitui o primeiro passo no processo de selecao de microorganismos beneficos, como produtores de enzimas de aplicacao biotecnologica. Nesse estudo, 64 isolados de rizobia foram testados para a producao extracelular de amilase, lipase, pectinase e protease, em meio YMA modificado. Excetuando a atividade pectinolitica, todas as outras enzimas (amilase, lipase e protease) foram detectadas nos isolados investigados. Dois isolados (INPA R-975 e INPA R-926) exibiram atividades amiloliticas, lipoliticas e proteoliticas. Os indices enzimaticos amiloliticos e proteoliticos variaram significativamente entre os isolados e as condicoes de pH do meio de cultura. De maneira geral, as maiores atividades amiloliticas e proteoliticas foram exibidas pelos isolados INPA R-957, INPA R-915B e INPA R-991 em pH 6,5. O isolado INPA R-957 tambem se mostrou amilolitico e proteolitico nos pHs 5,0 e 8,0. Esse estudo mostrou que alguns rizobios nativos da Amazonia representam fontes promissoras de amilase e protease de uso biotecnologico, sobretudo na tecnologia de alimentos.

Enzimas hidrolíticas extracelulares de isolados de rizóbia nativos da Amazônia Central, Amazonas, Brasil

Legumes enrich the soil by contributing nitrogen through symbiotic biological nitrogen fixation by rhizobia bacteria. However, very little is known about the extracellular enzymatic profile of these microorganisms. In this context, the production of extracellular hydrolytic enzymes by indigenous strains of rhizobia in Central Amazonia was evaluated. This screening constitutes the first step in selecting indigenous microorganisms that are potentially exploitable as enzyme producers. Indigenous strains of rhizobia were screened for extracellular amylolytic, carboxymethylcellulolytic, lactolytic, lipolytic, pectinolytic and proteolytic activities on modified YMA. Ureolytic activity was detected on a urea-agar slant. Rhizobia strains isolated from cowpea nodules produced more enzymes than those isolated from soybean nodules. Out of all the extracellular hydrolytic enzymes evaluated, only pectinase was not detected in this study. The most frequent rhizobia enzymes were amylase (32.8%), protease (28.4%), urease (20.9%) and carboxymethylcellulase (9.0%). In this study, only amylase and protease enzymes varied significantly among rhizobia strains. INPA strains R-926 and R-915 showed the highest enzymatic levels for amylase (EI = 3.1) and protease (EI = 6.6), respectively. This paper showed some indigenous strains of rhizobia from Central Amazonia as promising sources of industrially relevant enzymes for biotechnological purposes.

Enzymatic Activity in Essential Oil-Treated and Pathogen-Inoculated Corn Plants

Bipolaris maydis and Exserohilum turcicum are important fungal pathogens that cause leaf blight in corn whose control have been difficult. Essential oils are a promising and environmentally friendly alternative for disease management, but the mechanisms of action remain poorly studied. Here, we aimed to assess the effect of B. maydis and E. turcicum as well as the essential oil of Morinda citrifolia in the activity of plant defense enzymes in corn plants. Experiments were carried out in a completely randomized design with three replications and six treatments as they follow: (T1): corn plants inoculated with B. maydis; (T2): corn plants inoculated with E. turcicum; (T3): corn plants treated with essential oil of M. citrifolia (0.25%) and inoculated with B. maydis; (T4): corn plants treated with essential oil of M. citrifolia (0.25%) and inoculated with E. turcicum; (T5): corn plants treated with essential oil of M. citrifolia (0.25%); and (T6): corn plants non-inoculated and treated with distilled water. Protein content (PC) and activities of the enzymes ascorbate peroxidase, catalase, chitinase (CHI), peroxidase (POX) and superoxide dismutase (SOD) were assessed. PC was significantly decreased, whereas CHI and SOD activity was higher in T1-T5 compared to T6. T4 and T5 significantly increased POX activity relative to T6. Therefore, our findings suggest that the essential oil of M. citrifolia may play an active role in disease control by activating defense enzymes in corn plants.

Essential Oil of Cymbopogon citratus on the Control of the Curvularia Leaf Spot Disease on Maize

The Curvularia Leaf Spot is becoming more common due to the culture expansion and the low resistance of the cultivated genotypes in tropical regions. Thus, the objective was to evaluate the fungitoxicity of the essential oil of Cymbopogon citratus upon the phytopathogen Curvularia lunata, causative agent of the Curvularia Leaf Spot. There was realized pathogenicity tests of C. lunata in maize plants, phytotoxicity of the essential oil of C. citratus and gas chromatography attached, germination tests of the conidia, and of in vitro inhibition of C. lunata. Also, there were realized tests aiming at verifying the phytopathogen control in vivo. In the pathogenicity tests, there were verified symptoms of the disease in all of the suspensions tested on plants. It was observed that the essential oil concentrations of 7.5 µL mL−1 to 50 µL mL−1 were phytotoxic. The majoritarian chemical components of the essential oil of C. citratus were Geranial (41.46%) and Neral (32.43%). The concentrations of 5 and 7.5 µL mL−1 inhibited 100% of conidia germination. None of the concentrations evaluated effectively inhibited C. lunata mycelial growth in in vitro tests. In the preventive control, the concentration of 7.5 µL mL−1 was sufficient for the reduction of the progress of the disease, however the curative control was not efficient on the tested dosages.