CHARACTERIZATION OF PLANT GROWTH-PROMOTING BACTERIA AND THEIR TOLERANCE TO POTENTIALLY TOXIC ELEMENTS

Abstract

Thirteen bacteria strains were isolated and characterized biochemically, their tolerance to potentially toxic elements (PTE) was studied. Seven were isolated from acacia nodules (Acacia farnesiana), one from clover (Trifolium repens) and five from rhizosphere soil from contaminated sites with mine residues from Zimapan, Hidalgo, México. All the strains showed tolerance to NaCl at 2%; however, only eight were highly tolerant to NaCl at 5%. All the bacteria strains were tolerant to As, Pb, Cd, Zn, Cu and Cd. Based on the production of indole-acetic acid (IAA), the activity of the ACCdeaminase enzyme, solubilization of phosphorus and production of siderophores. Five strains (Mesorhizobium loti Af1, Agrobacterium tumefaciens (Rhizobium radiobacter) Af6, Enterobacter cancerogenus K131, Escherichia vulneris. K123 and Enterobacter sp. K162) have potential as plant growth-promoting bacteria (PGPB). The strain Alcaligenes faecalis T2, tolerant to 168 mg Cd L^-1, formed a plaque that coated the bacterial colony surface and represented 54% of the Cd associated to P. Meanwhile, 41% of accumulated Cd was observed within the bacterial colony, this could represent detoxification, biosorption, enzymatic precipitation or transformation of this element. The results showed that bacteria have relevant characteristics for phytoremediation purpose. However, with the exception of Mesorhizobium loti Af1 and Agrobacterium tumefaciens (Rhizobium radiobacter) Af6, it should be ruled out whether other bacterial strains are pathogenic for humans and plants, and in this case avoid their use in phytoremediation