20 Décembre – Thesis defense - Houssem Kahli

10 h Videoconferencing

Characterization of the accumulation of metallic trace elements in three species of the genus Atriplex and Pseudomonas fluorescens and the study of their impact on certain biochemical parameters of these Species.

The belated taking into account of the consequences generated by certain human activities has led to the accumulation of toxic substances, disrupting the fragile balances of many ecosystems. Since the start of the industrial revolution, pollution of the environment, including soil, by toxic metals has accelerated dramatically. Among these substances, metallic trace elements.
Studies have shown that the presence of trace metal elements in the culture medium can result, beyond a certain limit, in the appearance of symptoms of intoxication, accompanied by an inhibition of the weight growth of plants, decreased absorption of nutrients, reduced photosynthetic and respiratory activity, and inhibition of certain enzymatic activities of the antioxidant system associated with strong lipid peroxidation. However, certain plants: notably the Atriplex genus used in the first part of our study, are able to resist these metallic stresses and are endowed with properties which allow them to accumulate these xenobiotics in very large quantities in their root or aerial parts, and can be used for soil decontamination. Likewise, the use of certain sentinel models, in particular the bacteria (Pseudomonas fluorescens) used in the second part of our study, could be used in bioremediation for rehabilitating different environments (soil and water).
The objective of our work consists in determining the effects induced by these cadmium in the cell and more especially its membrane knowing that it represents the first barrier and therefore the target of these pollutants thus causing significant damage in its structure and more especially lipid peroxidation.
In the first part of the study we established for the first time a comparison between the resistance to stress in cadmium (Cd) of three halophyte species, Atriplex canescens, Atriplex halimus and Atriplex nummularia in addition to their already known tolerance to salt and to drought.
The results show that these plants are able to neutralize the excess of reactive oxygen species resulting from the treatments by activating the antioxidant defense mechanisms in order to restore the homeostasis of the cells.
The work of the second part of the study focused on the morphological study by AFM of the bacterium Pseudomonas fluorescens. We first of all optimized the culture conditions allowing good growth of the bacterial population, we then tested two immobilization approaches of Pseudomonas fluorescens in order to be able to complete the morphological characterization and to assess the impact of cadmium. on these bacteria.

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