Endophytic bacteria has been reported as plant growth promoters in various cultivated and uncultivated plants. Thus, the objective onf this study was to evaluate the potential of 21 endophytic bacterial isolated from leaves of passionfruit plants (Passiflora edulis Sims f. flavicarpa). In vitro antagonism, indole-3-acetic acid (IAA) production, gibberellins, cytokines and phosphate solubilization were also tested. In vitro antagonism was investigated using volatile metabolites detection by means of the overlapping dishes technique and direct confrontation. The production of IAA was evaluated by means of the colorimetric method with the absorbance reading of the optical density at O.D. (550nm). The phosphate solubilization was measured in a qualitative method by reading the solubilization halo diameter and the quantitative evaluation in liquid medium and reading of O.D. (450 nm). All bacterial isolates were able to inhibit the growth of Phytophthora sp. in both methods with values ranging from 50% to >90% inhibition (Skott-Knott, p ≤0 0.05). All the tested endophytic bacteria were also able to produce plant hormones. The phosphate solubilization was more than mean of the liquid medium. Thus, the studied endophytic bacterial isolates are suggested as potential plant growth promoters.

The aim of this study was to isolate and select bacteria from the cacti rhizosphere naturally occurring in an adverse environment in culture medium under water stress. Samples of rhizospheric cacti soil were collected in two distinct locations with natural occurrence of the Caatinga vegetation of the Alagoas State, Northeast Brazil. With the use of culture-dependent methodologies, the isolation and purification of the bacteria was performed for exopolysaccharide production analyzes by quantification of halos and biofilm formation in a spectrophotometer under optical density (OD) of 560 nm. In total, 42 strains were isolated, with the isolates BCM02, BCM06, BCM10 and BCM13 being the major producers of EPS, followed by bacteria BCM01, BCM05, BCM28 and BCM35 with medium production, and bacteria BCM22 and BCM33 with low production. On the other hand, for the biofilm formation, all the isolates were efficient in the synthesis of the same, being 38% of the bacteria with high formation performance. Thus, strains BCM02 and BCM28 presented the best results in evaluations of water stress tolerance mechanisms, and could later be used for future tests to promote plant growth.

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INTRODUÇÃOA água é imprescindível para a manutenção da vida e essencial para a produção de alimentos, contudo devido as constantes adversidades climáticas e o mau uso desse recurso, o setor agropecuário brasileiro vem sofrendo graves consequências, limitando a atividade no país. Durante o processo evolutivo, as xerófitas (plantas que se adequaram e desenvolveram mecanismos ao longo do tempo, que permitiram viver em ambientes secos e quentes), adquiririam mecanismos de tolerância a escassez de água no ambiente em que estão dispostos, dentre eles, o fechamento dos seus estômatos para reduzir a perda de água para o meio, poré m, ao mesmo tempo que as cactáceas evoluíram, os microorganismos associados a essas plantas também sofreram mudanças que proporcionaram que as mesmas tolerassem a ambientes com atividade hídrica restrita (KAVAMURA et al, 2013). Dentre estes mecanismos podemos citar: a produção de EPS (exopolissacarídeos), produção de biofilme. Estes mecanismos auxiliam na colonização do sistema radicular por micro-organismos que conferem tolerância a estresses ambientais, como o salino, as variações de temperatura, produção de ácido hialurônico, fazendo com que a planta resistam a ambientes com atividade hídrica