Résumé:
This work focuses on the study of the endophytic bacterial flora of H. pallidum and L. spartum roots, growing on the soil of mining region polluted by Sb and As, and the determination of the physiological, biochemical and molecular defense mechanisms adopted by this microflora to fight against metallic stress. The morphological and biochemical analyzes reveal a high biodiversity of this endophytic microflora. The study of the Sb and As toxicity allows the selection of two strains having the highest MICs, namely 450 mM of Sb and 175 mM of As. The molecular identification of resistant strains via 16S RNA gene sequencing shows that they are identical and belong to the Serratia marcescens species with 99% homology. The batch culture in presence of gradual Sb and As concentrations reveals a progressive decrease in bacterial growth of the two strains. Moreover, the measurement of oxidative stress parameters indicates a significant increase in the H2O2 amount, the MDA amount, the intracellular proline and even the activities of antioxidant enzymes, except at high thresholds in Sb and As. These enzymes permit the detoxification of the bacteria by elimination of the H2O2 and the other free radicals generated by metallic stress. In addition, the study of the resistance of S. marcescens strains to a range of heavy metals and antibiotics shows multiple resistance to nickel and cobalt, as well as to kanamycin, ampicillin and chloramphenicol. To cope with the presence of Sb and As, S. marcescens has adopted life in group mode and form biofilms to reduce their toxicity. The molecular study of the resistance mechanisms of the two strains, using cell transformation methods, reveals that the genetic determinants responsibles for the resistance of S. marcescens to metalloids are carried mainly by the chromosome.
