Heavy metals-resistant PGPR strains of <i>Pseudomonas </i> sp. stimulating the growth of alfalfa under cadmium stress

Three bacteria strains of Pseudomonas sp. resistant to heavy metals were isolated from the chemically contaminated soil. According to the results on the nucleotide sequences of the 16S rRNA and rpoD genes, strain Pseudomonas sp. 17 НМ was identified as Pseudomonas capeferrum, and the strains of Pseudomonas sp. 65 НМ и 67 НМ were most closely related to the type strain of Pseudomonas silesiensis и Pseudomonas umsongensis, respectively. It has been shown that strains of Pseudomonas sp. 17 НМ, 65 НМ, 67 НМ are characterized by different levels of resistance of heavy metals: maximum tolerance concentration (MTC) of zinc was 1 mМ for all strains, cadmium 1, 1.5, 1 mМ, lead 5, 5, 4 mМ, nickel 7, 9, 7 mМ, respectively. All pseudomonad strains can form biofilms and have the properties of PGPR bacteria. Treatment of alfalfa seeds (Medicago sativa L.) with strains Pseudomonas sp. 17 НМ, 65 НМ, 67 НМ under cadmium stress led to an increase in the dry weight of alfalfa seedling up to 40 % and the content of chlorophyll a and b in the leaves by 25-33% relative to the control.