Bactérias endofíticas de bananeira 'Prata-Anã': fixação de nitrogênio, solubilização de fosfato de cálcio e produção de ácido indol-3 acético

Abstract

The endophytic bacteria have been showing great potential for biotechnological use, with prominence in the increment of the productivity of plant species by the nitrogen fixation, phosphorus solubilization and production of growth regulators. The association of those bacteria with the plants can reduce the need the use of nitrogen fertilizers, as well as to potentiate the use of phosphate fertilizers, promoting, also, larger acting of the plants due to the growth regulators' synthesis. Thus, the objective of the present work was to evaluate the nitrogen biological fixation, the capacity of phosphate solubilization and the production of indol-3-acetic acid (IAA) by endophytic bacteria associated to roots of "Prata- Ana" banana tree. To determine the nitrogen biological fixation, 24 isolates that presented nifH gene were selected, in entirely randomized design, with three repetitions. The selected isolates' growth was used in medium free from nitrogen NFb, when the presence of pellicle formation was evaluated. The results were submitted to studies of frequency distribution. Medium supplemented with calcium phosphate tribase was used to determine the solubilization potential of 40 isolates of endophytic bacteria, being the solubilization efficiency determined by the ratio between the solubilization halo diameter and the bacterial colony diameter. The production of IAA was detected by the bacterial growth in 10% TSA medium supplemented with L-tryptophan. The bacteria that synthesized IAA in 10% TSA medium with L-tryptophan were selected for essay of production of IAA in 10% TSA medium without supplementation of L- tryptophan. The presence of IAA was determined by the reaction of 10% TSA medium with acid-ferric reagent and its concentration was determined in spectrophotometry by the absorbance to 530 nm of wave length. The essays were carried out in entirely randomized design with 40 treatments and three repetitions. The results were submitted to analysis of variance and, when they presented significant difference by the F test, they were submitted to Scott-Knotttest to 5% of probability. Among the selected isolates for essay of biological nitrogen fixation, 83% presented the pellicle formation in N free medium, from which 67% are of the Bacillus genus. Amongst 40 isolates evaluated for the potential of phosphate solubilization, 37.5% showed solubilization halo. The isolate EB-53 (Lysinibacillus sp.) presented high solubilization, while 73% of the solubilizing isolates showed low one. The IAA synthesis was detected among the isolates, when 40% of them presented the capacity to synthesize IAA in the presence of L-tryptophan and of those, 17,5% synthesized it in the absence of L-tryptophan. The isolate EB-40 (Bacillus sp.) presented the largest IAA content (47.88 µg.ml) in medium supplemented with L-tryptophan, presenting, also, capacity to synthesize IAA in the absence of L-tryptophan. The isolates EB-126 (Bacillus subtilis) and EB-47 (Bacillus sp.) presented simultaneous capacity for fixation of N, phosphate solubilization and production of IAA in vitro.