Diazotrophic bacteria associated to coconut palms in a coastal lowland region in Sergipe State, Brazil

Abstract

The aim of this work was to isolate, identify and quantify diazotrophic bacteria existing in roots and leaves of coconut palms (hybrid PB121) grown in a coastal lowland of Sergipe, in Brazil. Diazotrophic populations in these organs were quantified by the most probable number (MNP) technique on NFb and JNFb semi-solid media and identified by the evaluation of microscopic, cultural and biochemical characteristics of the isolates. Biochemical characteristics were evaluated using the API 20-E and API 20-NE galleries. Nitrogen content in NFb and JNFb semi-solid media inoculated with each of the isolates and incubated for eight days at 32°C was colorimetrically evaluated to estimate the biological nitrogen fixation capacity of the isolates. Bacteria of the Enterobacter genus and pseudomonads formed the predominant types of N2-fixers. Enterobacteria and pseudomonads isolated from leaves were predominantly endophytic. Regarding to the diazotroph bacteria isolated from roots, it was observed that enterobacteria were predominant in the root-surface, while pseudomonads were found in nearly equivalent proportions in the surface and in the interior of this organ. After eight days of incubation, pseudomonads isolates presented higher N fixation capacity than enterobacteria.