Comunidades endofíticas e rizosféricas são afetadas diferentemente por hospedeiro e contaminação ambiental

Abstract

Bacteria are associated with the root system of plants in the endophytic and rhizospheric micro-habitats. In this paper, we used cultivation-independent methods to examine how the soil mercury contamination (present or absent) and the host plant species (Aeschynomene fluminensis and Polygonum acuminatum) interfered with endophytic and rhizospheric bacterial communities in a humid area of the Pantanal biome. The capacity of the most abundant species to remediate the metal was assessed in cells immobilized in alginate spheres. Sequencing the 16S rRNA gene from the 24 samples resulted in 3,039,538 filtered raw sequences with 2,439,239 endophytic reads and 600,299 rhizospheric reads. The endophytic and rhizospheric communities were composed of respectively 22 and 26 phyla, 237 and 382 genera, and 644 and 3,549 bacterial operational taxonomic units. The soil mercury contamination increased the alpha diversity indicators (observed richness, estimated Chao1 richness, and Shannon's diversity index; p <0.05, test T) only in the rhizospheric micro-habitat. Comparison between the host species detected the highest indices in endophytic communities of P. acuminatum (p <0.05; test T). The presence of the metal did not affect the beta diversity (composition and abundance) of endophytic bacteria (p <0.05; ANOSIN), but differently influenced the interactions within endophytic and rhizospheric bacterial communities. The host species and the presence of the metal significantly altered the beta diversity of the rhizospheric communities (p <0.05; ANOSIN). Bacterial species that were abundant in both communities were immobilized in alginate spheres, and they promoted bioremediation of mercury in an aqueous environment. As the bioremediation mechanisms were unclear, future studies are required to examine whether the endophytic environment acts as a buffer over other contaminants and reduces the impact of the metal on endophytic bacterial communities.