The biological nitrogen fixation constitutes a strategy to accelerate soil reclamation and the symbiotic systems Rhizobium-legume is the major N2-fixing in which the enzyme carboxymethyl cellulase plays a key role. As many rhizobia species are cellulase negative, the association with cellulolytic bacteria can be a strategy for the recovery of degraded ecosystems. It has been hypothesized that the sharing of resources should mostly be prevalent among phylogenetically and metabolically different species. Accordingly, twenty-seven actinobacteria isolates from Actinobacteria phyla and twenty-six rhizobia isolates from Proteobacteria phyla were selected from the bacterial collection of the Laboratory of Environmental Microbiology of the Federal University of Ceará. The presence of cellulolytic activity was observed for the rhizobia isolates at 28 °C and for actinobacteria isolates at 28, 39, 41, 43 and 45 °C. Rhizobia isolates deficient in cellulase and actinobacteria isolates with enzymatic activity detected at higher temperature were selected and characterized. The antagonism between isolates of two groups was tested and the pairs antagonistic were eliminated. The cross-feeding test between actinobacteria and rhizobia isolates was realized in a chemically defined medium containing carboxymethyl-cellulose as the only carbon and energy source. Growth of rhizobia strains in 50% of the pairwise indicated that the cellulose hydrolyzed by actinobacteria was used as substrate for the growth of the rhizobia. The Bradyrhizobium strain R10 associated with Streptomyces strains A09 and A18 and Nocardia A11 are promissory inoculants for recovery of semi-arid regions.
Actinobactérias são bactérias Gram-positivas encontradas principalmente no solo e que se destacam pela capacidade de produção de enzimas hidrolíticas, como amilase e celulase. Essas enzimas degradam, respectivamente, o amido e a celulose, substratos abundantes no solo, mas que por sua complexidade química são indisponíveis para nutrição de outros organismos. Essas bactérias também crescem em condições extremas, como as prevalentes no Semiárido nordestino, onde ainda são raros estudos sobre esse grupo microbiano. Assim, tendo em vista o crescente interesse sobre o funcionamento biológico do solo, aliado ao aspecto biotecnológico, esse trabalho teve por objetivo avaliar a atividade enzimática de vinte e oito cepas de actinobactérias dos gêneros Streptomyces, Terrabacter, Nocardia e Micromonospora isoladas de amostras de solo do Parque Nacional de Ubajara, no Estado do Ceará. As atividades amilolíticas e celulolíticas foram determinadas pelo índice enzimático correspondente à relação entre o diâmetro em milímetros do halo de hidrólise e o diâmetro em milímetros da colônia de cada cepa. A atividade celulolítica foi detectada em 75% e a amilolítica em 82% das cepas avaliadas. Uma das cepas avaliadas destacou-se com um índice enzimático da celulase igual a 6,90 enquanto o maior índice para a amilase foi 6,23. Os resultados indicaram o potencial ecológico e biotecnológico das actinobactérias do solo da região analisada. Actinobacterias are Gram-positive bacterias found in soil and are distinguished by their production of hydrolytic enzymes, such as amylase and cellulase. These enzymes degrade starch and cellulose, respectively, which are abundant substrates in soil, but that are unavailable for use by other organisms due to their chemical complexity. These bacteria grow in extreme conditions, such as those prevalent in the Brazilian semi-arid northeast, where there are also few studies about this microbial group. Thus, due to the growing interest in the biological functioning of the soil, together with the biotechnology aspect, this work aimed to evaluate the enzymatic activity of twenty eight strains of actinobacteria of the genus Streptomyces, Terrabacter, Nocardia, and Micromonospora obtained from the soil samples of the Ubajara National Park in the state of Ceará. The amylolytic and cellulolytic activities were determined by the enzymatic index corresponding to the relation between the diameter of hydrolysis halo, in millimeters, and the diameter in millimeters of the colony of each strain. The cellulolytic and amylolytic indexes were detected in 75% and 85% of the evaluated strains, respectively. One of the strains evaluated stood out with an enzyme cellulase index equal to 6.90 while the highest rate for amylase was 6.23. The results indicated the ecological and biotechnological potential of actinobacteria from the soil of analyzed region. Keywords: enzymes, bacteria, caatinga, Northeast
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