Promising strains of phosphate-mobilizing rhizobacteria resistant to glyphosate and nickel

A search was carried out for phosphate-soluble rhizobacteria capable of growing in the presence of different concentrations of the herbicide glyphosate and nickel heavy metal ions (Ni2+). Using the Muromtsev medium, the phosphate-mobilizing activity was determined only in 3 out of 20 strains of Rhizobium spp. – with a low solubilization index (IS). On the contrary, all strains of Pseudomonas sp. showed a positive result, and the highest IS was in Pseudomonas sp. OBA 2.4.1 and GOR 4.17. The highest growth activity under stressful conditions was shown by 4 strains of Pseudomonas spp.: OBA 2.4.1, OBA 2.9, 4.17 and STA 3, their growth was noticeably inhibited with an increase in the concentration of glyphosate in the medium to 10.0 mg/ml. The growth activity of Rhizobium spp. strains was characterized as average. When growing on a medium with NiCl2, Pseudomonas strains sp. 65 HM and 67 HM grew to a concentration of 9 mM NiCl2 in the medium, at a concentration of 11 mM, strain 67 HM gave growth in the form of single colonies. These strains were isolated from soil samples taken from sites contaminated with chemical effluents. It is possible that nickel chlorides were already present in such soil in high concentrations exceeding the norm, that is why these strains had such high resistance to nickel ions. Thus, Rhizobium sp. strains did not have the most active PGPR properties, but different strains of Pseudomonas sp. showed high resistance to glyphosate and nickel chloride. Thus, Pseudomonas sp. they demostrated their high ability to adapt to stressful conditions. It is such PGPR bacteria (Plant Growth Promoting Rhizo bacteria) that can be considered as biological agents to increase the efficiency of bioremediation of agricultural soils.