The use of nitrogen fertilizers is of paramount importance for the supply of this nutrient to plants. However, the application of these fertilizers brings numerous environmental and health problems. An alternative to these chemical products would be the use of rhizobia — plant growth-promoting rhizobacteria naturally present in the rhizosphere and capable of carrying out biological nitrogen fixation. Through the present work, we propose the co-inoculation of Actinobacteria and rhizobia, aiming at the production of a new bio-inoculant that replaces, at least in part, nitrogen fertilization in legumes. It is expected that Actinobacteria, by producing exoenzymes, enable the growth of rhizobia in non-specific culture media for these microorganisms. Ten strains of Actinobacteria with statistically distinct cellulolytic and xylanolytic activity and seven strains of rhizobia without the aforementioned enzymatic activities were used. A co-inoculation of these microorganisms was performed in culture media containing carboxymethylcellulose (CMC) and xylan as sole carbon sources, and then their compatibility indexes (CI) were calculated. Actinobacteria strains A139 and A145 (both with CI = 0.857 in the medium with CMC and CI = 1 in the medium with xylan) showed remarkable facilitation of rhizobia growth, and had only one antagonistic relation each (both with rhizobia L9 in the medium with CMC). This biological interaction, called cross-feeding, occurs when microorganisms stimulate each other’s growth and is promising for prospecting a bio-inoculant, in addition to providing an overview of the ecological relationships that occur between plant growth-promoting rhizobacteria in the semi-arid region.
RESUMO As actinobactérias constituem um importante grupo microbiano e sua atividade enzimática contribui com a estruturação de comunidades do solo. Nesse contexto, avaliou-se o efeito de fatores abióticos no crescimento e atividade amilolítica de 18 cepas de actinobactérias reconhecidamente facilitadoras de rizóbios isoladas do Parque Nacional de Ubajara-Ceará, região do semiárido Nordestino Brasileiro. As cepas foram analisadas quanto as suas atividades amilolítica em diferentes faixas e concentrações de pH e salinidade. Constatou-se que as cepas apresentaram evidente atividade enzimática, exceto no pH 4; e a análise de regressão linear forneceu um gráfico que demonstrou os maiores índices enzimáticos no pH 7 e na concentração de 2% de NaCl. Portanto, a atividade enzimática dessas cepas demonstrou o potencial dessas actinobactérias em manter os processos biológicos em que estão envolvidas mesmo em condições de estresse fisiológico, características dos solos de regiões semiáridas. PALAVRAS-CHAVE: Alterações fisiológicas. Amilase. Solo EFFECT OF ABIOTIC FACTORS ON THE ENZYMATIC ACTIVITY OF ACTINOBACTERIA FROM THE BRAZILIAN SEMI-ARID REGION ABSTRACT Actinobacteria constitute an important microbial group and its enzymatic activity contributes to the structuring of soil communities. In this context, the present study tested the effect of abiotic factors on the growth and amylolytic activity of 18 strains of actinobacteria known to facilitate rhizobia isolated from the soil of the Parque Nacional de Ubajara-Ceará, a semiarid region of the Northeast of Brazil. The strains were evaluated for their amylolytic activity in different ranges and concentrations of pH and salinity. It was found that the strains showed enzymatic activity, except at pH
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