Growth response and heavy metals tolerance of <i>Axonopus affinis</i>, inoculated with plant growthpromoting rhizobacteria

Abstract

Different microorganisms have been used for bioremediation based on their resistance and ability to sequester heavy metals. The use of plant growth-promoting rhizobacteria (PGPR) for bioremediation of these contaminants has been successful. A PGPR isolated from hydrocarbons-contaminated soil identified as Bacillus sp., by microbiological and molecular tools and characterized as heavy metal tolerant by minimal inhibitory concentration (MIC) assay was inoculated into Axonopus affinis plants. Both of them were exposed to cadmium, nickel, and zinc and the effect of their relationship was analyzed by multivariate analysis. The results did not show a significant growth promotion and development of this Poaceae with rhizobacteria alone, but the presence of heavy metals plus the PGPR assured the survival of plants. This suggests that the plant’s response is related with the metal concentration and the exposure time to the contaminants, as well as with its intrinsic tolerance. The Bacillus sp strain allowed the growth maintenance of A. affinis and enhanced its tolerance to the assayed heavy metals, suggesting a synergistic effect between this species and the rhizobacterium in response to contaminating agents.

Keywords: Bioremediation, heavy metals, microorganisms, plants