Mechanisms of lead tolerance and oxidative stress response in Bacillus pumilus , a rhizobacterium isolated from Enydra anagallis

Lead contamination represents a significant risk to the environment and public health. Although plant-associated bacteria can be used in heavy metal phytoremediation, the microbial mechanisms involved remain poorly explored. This study investigated the Pb tolerance and oxidative stress response of Bacillus pumilus, a rhizobacterium isolated from Enydra anagallis. The bacterium was exposed to increasing concentrations of Pb(NO3)2 (0–200 mg L−1) to evaluate growth, Pb tolerance and removal, antioxidant enzyme activity, and lipid peroxidation. B. pumilus exhibited high resistance to Pb and effectively removed 71.1% after 72 h the metal from the nutrient broth, with no inhibition of enzymatic activity, even at the highest tested concentration. Pb accumulation reached 46.12 mg kg−1 in roots, 45.5 mg kg−1 in leaves, and 40.87 mg kg−1 in stems of E. anagallis, highlighting its potential as a bioaccumulator. In the Santa Bárbara Stream, Pb concentrations ranged from 0.0134 to 0.0250 mg L−1 in water, exceeding the Brazilian limit for freshwater, and from 8.77 to 14.32 mg kg−1 in soil. Lipid peroxidation in E. anagallis averaged 381.79 nmol MDA g−1 across sampling points, with no significant differences among them. Despite this, neither B. pumilus nor E. anagallis showed signs of metabolic stress, suggesting the presence of resistance mechanisms. These findings contribute to a better understanding of microbial tolerance to heavy metals and support the potential application of this bacterium-plant association in bioremediation strategies.