Role of plant-associated bacteria in the remediation of contaminated soils

Abstract

The global objective of this doctoral thesis consisted in the study and optimisation of the plant-soil-microorganism system within phytoremediation strategies for soils contaminated with organic and inorganic compounds. Phytoremediation can be defined as a group of techniques based on the use of plants and their associated microorganisms for the clean-up of contaminated soils. In recent years, studies aimed at optimising the efficiency of these techniques have been increasingly more focused on the importance of the role of plant-associated bacteria in these processes. It is well known that bacteria are commonly associated with plants, either surface-dwelling (epiphytic bacteria) or in the plant interior (endophytic bacteria). Exploiting these plant-bacterial associations in the field of phytoremediation has been centred in two areas. On one hand, these approaches use bacterial strains which are capable of influencing the general status of the plant, enhancing their establishment and growth in the contaminated soils. This type of bacteria are denominated as plant growth-promoting bacteria (PGPB) and influence plant growth via various mechanisms, such as through an increase in nutrient availability (e.g. nitrogen, iron or phosphorus), or through the synthesis of phytohormones (e.g. indoleacetic acid, IAA). On the other hand, bacterial strains can be employed which act directly on the contaminant in question, for example, strains capable of degrading contaminants (in the case of organic pollutants), or those which can modify the bioavailability of contaminants (e.g. through the production of biosurfactants), thus affecting contaminant fate and/or absorption by the plant.