Caracterização funcional de isolados bacterianos de solo rizosférico e não rizosférico na cultura do girassol

Abstract

Soil is a heterogeneous environment, composed of different habitats, where different types and groups of microorganisms are stablished. The rhizosphere and non-rhizosphere compartments are examples of soils heterogeneity, commonly resulting in differences on microbial diversity and activity. Irrespective of these factors, microbiota acts, directly or indirectly, on aspects of soil quality and fertility, as well as on plant development and health. In this context, this study aimed to isolate soil microorganisms from the rhizosphere and non-rhizospheric environments from sunflower (Helianthus annuus) cropping, in order to evaluate, in vitro, their ability of producing extracellular enzymes, solubilizing inorganic phosphate, and of displaying antagonistic activity against a phytopathogenic fungus. The results of the microorganisms count in rhizospheric soil was 1.5 ± 0.23 × 10 6 CFU g -1 dry soil, being higher than the counts in non- rhizospheric soil (8.9 ± 0.28 × 10 5 CFU g -1 dry soil). A total of 24 bacterial isolates were obtained, 12 isolates from rhizospheric and 12 from non-rhizospheric soil. The Gram stain test indicated that 75% of the rhizosphere isolates where Gram-positive rods; for non-rhizosphere soil, 50% of the isolates were characterized as Gram-positive rods. Among the enzymatic activities evaluated for the 24 bacterial isolates, 37.5%, 54.17%, 66.67%, and 66.67% presented the capacity to produce cellulase, amylase, lipase and protease, respectively. Only one isolate of rhizospheric soil demonstrated the ability to solubilize inorganic phosphate. Also, from the 24 bacterial isolates, 29.17% inhibited, in vitro, the growth of the phytopathogenic fungus Rhizoctonia solani. One of the rhizospheric isolates, named R19, presented all the activities investigated, in the experimental conditions employed in this study. Even considering the limited number of evaluated bacteria, results indicate the potential participation of bacterial isolates in the cycling of organic matter, elements transformation, and control of phytopathogens, which are processes associated with fertility and productivity of agricultural soils.