Growth response and tolerance of heavy metals and Echinochloa polystachya Cyperus elegans inoculated with rhizobacteria isolated from a soil contaminated with petroleum hydrocarbons

The benefic interactions between cultures of plants and bacteria have been demonstrated to be useful for the decrease of toxicity produced by heavy metals and nutritional deficiency. With this, the microbial communities have been applied as tools for bioremediation, particularly the plant growth promoting rhizobacteria (PGPR's). This study evaluated the growth response and tolerance to heavy metals of two swamp plant species: Cyperus elegans and Echinochloa polystachya, both inoculated with phosphate solubilizing rhizobacteria Bacillus sp. exposed to cadmium (Cd) and zinc (Zn). The growth response of both species was favored by the presence of the rhizobacteria without metals; although, the grown with both metals and inoculated with the rhizobactera metal tolerant did not show a significant promotion of their growth; this suggests that their response to the metals are related with the doses and the exposition time and to the intrinsic tolerance of the plant species to these metals. Even these results, the presence of the rhizobacteria maintained the growth of C. elegans seedlings exposed to the heavy metals assessment; this could be associated with a plant protecting effect that diminishes the metal toxicity. It is relevant to emphasize the research importance about the colonization by rhizobacteria not only at the spermosphere but also at the roots of the inoculated seedlings with the increase of the radical surface for the metals absorption and the protecting role of the rhizobacteria against the toxicity of metals, that allows the establishment of a better growth and development of plant species to the stabilization, vegetation recover and the remediation of contaminated soils with heavy metals.