Functioning of local strains of bacteria under heavy metal stress (Uzbekistan)

Abstract Cadmium (Cd) and nickel (Ni) are among the most toxic metals and high levels of Cd and Ni in soil have been observed in several studies to slow down plant growth, mainly biomass, chlorophyll content and photosynthetic properties. Beneficial soil bacteria are promising targets for reducing Cd and Ni toxicity and increasing plant tolerance to heavy metal stress. Different strains of bacteria were isolated from soil contaminated with heavy metals. These isolates were identified at the species level and investigated for their involvement in mitigating the deleterious effects of heavy metal stress. In this study, the minimum inhibitory concentration, biosorption of bacteria with high resistance to heavy metals to Ni(II) and Cd(II), and stimulating properties of plant productivity under conditions of heavy metal stress were studied. Isolates 5, 11, 18 and 10, 16, 11, 8 was determined against high viability to concentrations of Ni (II) and Cd (II) cations. These isolates were identified as Enterobacter cloacae (5), Enterobacter ludwigii (11), Pseudomonas aeruginosa (18), Bacillus licheniformis (10), Bacillus megaterium (16) and Bacillus simplex (8) by morphological-cultural and biochemical identification. Growth and multiplication of Bacillus megaterium (16), B. licheniformis (10) and B.subtilis (13) strains at 1–3 mM concentration of CdEnterobacter ludwigii (11) was the most effective in reducing Cd and Ni, reaching values of 36% and 41%, respectively. Pseudomonas aeruginosa (18) synthesized auxin 4, 4.8, 5.3 times higher amount compared to control and Enterobacter ludwigii (11), Bacillus licheniformis (10), Bacillus simplex (8) synthesized auxin in equal amount compared to the control at different concentrations of Cd cation (2.4, 4.1, 8.2 mg/l). Pseudomonas aeruginosa (18) strain produced 78 mg/l EPS at the concentration of 24.6 mg/l Cd cation on the 7th day of cultivation. Using microorganisms tolerant of high concentrations of heavy metals and their activity, bioremediation of ambience contaminated with heavy metals is possible. Their reduction of Ni and Cd cations, increased synthesis of phytohormones and exopolysaccharides under heavy metal stress conditions indicate that these microorganisms are promising objects in the future.