Abstract
<jats:p>The aim of this study was to evaluate the effect of a bacterial preparation based on Bacillus sp. and lead, both separately and in combination, on the physiological state of Eisenia fetida earthworms under controlled laboratory conditions, for a preliminary assessment of the potential risks and benefits of using this bacterial strain in the bioremediation of lead-contaminated soils. Soil isolates of Bacillus spp. were isolated from samples from the territory of PJSC Gai Mining and Processing Plant. Four experimental groups were tested for the experiment: control (distilled water), Bac+H₂O, Pb+H₂O, Pb+Bac. A decrease in the relative weight of earthworms to 68.8%, relative to the control, by day 14 was recorded in the variant with lead without bacteria (Pb + H2O). In the combined group (Pb + Bac), a consistently higher value was recorded throughout the observation period: on day 3, worm weight exceeded the control by 11.7%, on day 14 by 15.6%, and by day 21 by 19.3%. Thus, the presence of Bacillus licheniformis-resistantPb bacteria neutralizes the toxic effect of lead and promotes worm growth. The study confirms the feasibility of using biological test systems, in particular Eisenia fetida, for an objective assessment of the effectiveness and safety of bioremediation technologies. The obtained data highlight the potential of using Bacillus bacteria to reduce the phytotoxicity of heavy metals and restore soil ecosystems.</jats:p>