Bioprospecção funcional de rizobactérias heterotróficas do morangueiro (Fragaria X ananassa Duch.)

Abstract

Soil presents a high biodiversity, and the rhizosphere is acknowledged as a zone of intense microbial and enzymatic activities, presenting a complex structural and functional diversity. Biochemical transformations on the soil-plant system are highly dependent or related to the presence of microorganisms and their enzymes. Also, phosphate-solubilizing microorganisms might act in the rhizosphere, providing phosphorus (P) to the soil that might be absorbed by plants. This study aimed to evaluate, in solid culture media, the hydrolytic and phosphate- solubilizing potentials of rhizobacteria isolated from strawberry crop (Fragaria X ananassa Duch.). Rhizospheric soil presented bacterial counts of 2.75 ± 0.7 × 10 7 CFU g -1 dry soil (n = 3), which was significantly different from that of non-rhizospheric soil, which reached 1.99 ± 0.9 × 10 7 CFU g -1 dry soil (n = 3). In total, 30 rhizobacteria were isolated in pure cultures, with 60.0% (18) being cocci and 40.0% (12) being bacilli. As for Gram staining, 86.7% (26) of the isolates were classified as Gram-positive, and 13.3% (4) classified as Gram-negative. From the 30 bacterial isolates evaluated for proteolytic and cellulolytic potentials, 56.7% (17) and 33.3% (10) presented the capacity of producing proteases and cellulases, respectively. Through successive plating, some isolates no longer grew, making it impossible to carry out subsequent tests. From 26 isolates evaluated for amylolytic potential, 19.2% (5) demonstrated the ability to produce amylases. Considering the 24 isolates assessed for lipolytic potential and solubilization of inorganic phosphate, 100.0% presented the capacity to produce lipases and 16.7% (4) produced solubilization haloes. As for the 24 bacterial isolates assessed for the five activities, all presented at least one of the activities, and 29.2% (7) demonstrated a single activity. In addition, 37.5% (9) presented two of the evaluated activities, with the combination protease + lipase (66.7%) being the most frequently observed; 20.8% (5) displayed three combined activities and 12.5% (3) presented four out of five activities investigated, being the combination protease + cellulase + amylase + lipase representing 100.0%. None of the bacterial isolates in the present study displayed the five evaluated activities. Obtained results indicate the potential functional versatility of the bacterial isolates, which may be important from agronomic, ecological and biotechnological perspectives.