Produção de auxinas por bactérias endofíticas isoladas de bananeira "Prata Anã"

Abstract

The characterization of the biochemical profile of endophytic bacteria that promote plant growth can provide valuable information that allow extend the use of these microorganisms and apply the knowledge generated in the development of bioinoculants. The present work aimed to study the capacity of indole compounds production in vitro by the endophytic bacteria and compare the quantification methods: Salkowski method determined via spectroscopy and high-performance liquid chromatography (HPLC) and evaluate the biological fixation capacity nitrogen. The initial screenings were conducted by using triptic soy agar (TSA 10%) supplemented with L-tryptophan and in the absence of L-tryptophan through the use of Salkowski method, in a completely randomized design with 40 treatments (endophytic bacteria isolates) and three replications. In the second experiment, the five isolates that produced more auxin by Salkowski method were selected and used for detection and quantification of indole compounds by HPLC in a completely randomized design with five treatments and three replications. To determine the biological nitrogen fixation, the 40 isolates were inoculated in NFB in a randomized design, with 40 treatments and three replications. Of 40 isolates evaluated in the initial screening (Salkowski method), 16 presented the ability to synthesize indole-3 acid acetic acid in the presence of L-tryptophan and only three in the absence of the amino acid. The concentration of indole acetic acid (IAA) determined by absorption spectrophotometer indicated that the isolated EB-07 Agrobacteruim tumefaciens specie showed higher concentration of AIA in the presence of L-tryptophan, averaging 16.61 μg.ml-1. HPLC method detected four indole compounds produced by the bacteria: indole acetic acid, indole pyruvic acid, lactic acid and indole acetaldehyde acid. When comparing the two quantification methods, significant differences were observed for all tested isolates. The isolated Bacillus sp. (EB.78) presented an average of 9.76 μg.mL-1 of AIA detected by HPLC. None of the 40 isolates evaluated in N-free medium presented the capacity of growing in NFB medium, indicating a low potential for biological nitrogen fixation. According to the results Salkowski method can be used as a qualitative method and the HPLC quantitative method and, since this is more sensitive and has greater efficiency.