Plant promoting growth and soil bioremediation by Rhodobacter sphaeroides

Industrial activities, pesticides, and improper waste disposal represent the main anthropogenic activities responsible for soil pollution. The Italian government in 1998 listed fourteen nationally relevant polluted sites in urgent need an environmental remediation [1]. Among these sites, the city of Taranto - located in southern Italy - and its nearby industrial area is included as highly polluted district. The presence of a very large steel industry, an oil refinery, a power plant, and a set of dockyards contributed altogether to the release of multiple and toxic pollutants in the environment. Although several studies were and are published focused on air and water pollution, few reports evaluated soil contamination of this area. Investigation on chemical and physical parameters (pH, electrical conductivity, available P, Organic C) and contaminant analyses of soil samples collected from a multi-contaminated area located close to Taranto were performed, [2] showing the presence of hazardous toxic pollutants, such as heavy metals (HMs) and polychlorinated biphenyls (PCBs). These pollutants are persisting and tend to bioaccumulate along the food-chain. Effective and sustainable decontamination methods are hence highly needed. Based on the synergistic action established between plant root system and soil rhizosphere microorganisms, Plant Assisted BioRemediation has been proved to be efficient in restoring quality of contaminated soils [2, 3]. In this work, the purple non-sulfur bacterium Rhodobacter sphaeroides, a prokaryote able to convert sunlight into other forms of energy by photosynthesis, was used as plant growth-promoting rhizobacteria. Due to its metabolic versatility and ability to grow in presence of heavy metals [4, 5], R. sphaeroides can be exploited for environmental applications, such as bioremediation of polluted sites. Here, the effect on the growth of Arabidopsis thaliana in PCBs and HMs-contaminated soil from Taranto area, inoculated with bacterial cells of the wild type 2.4.1 of R. sphaeroides was assessed. These preliminary results obtained in growth chamber in controlled conditions pose the foundation for the development of a more sustainable management system for soil bioremediation.