Genetic diversity and growth promoting characteristics of diazotrophic bacteria isolated from 20 genotypes of Brachiaria spp.

Abstract

Diazotrophic bacteria, including those of the genus Azospirillum and Nitrospirillum, colonize Brachiaria genotypes and contribute to plant development through nitrogen fixation, production of phytohormones and bioavailability of nutrients. This study aimed to determine the phylogenetic positioning and evaluate the functional abilities of diazotrophic bacteria isolated from Brachiaria genotypes. Diazotrophic bacterial counting and isolation were carried out with rhizosphere soil and root samples from 20 Brachiaria genotypes after inoculation in nitrogen-free semi-solid NFb and LGI media. The isolates were analyzed using 16S rRNA and nifH sequences, and tested for their functional abilities to produce auxin and siderophores, to solubilize phosphate and zinc, and to degrade cellulose. The diazotrophic population ranged from 102 to 108 g−1 rhizosphere soil or roots. Sequencing of 16S rRNA from 213 isolates confirmed the presence of genera Azospirillum and Nitrospirillum, and revealed the presence of 14 other diazotrophic genera. The genus Nitrospirillum was detected colonizing all niches of most Brachiaria species. A PCA analysis showed a positive correlation between the ability to produce siderophores with the ability to produce IAA; and between phosphate and zinc solubilisation. The results showed a high diversity of diazotrophic bacterial species colonizing 20 Brachiaria genotypes and revealed the presence of bacteria with variable growth-promoting characteristics, highlighting their potential as good candidates for the development of biofertilizers.