Temporal characterization of bacterial communities in a phytoremediation pilot plant aimed at decontaminating polluted sediments dredged from Leghorn harbor, Italy

The AGRIPORT project (Agricultural Reuse of Polluted Dredged Sediments, Eco-innovation EU Project n. ECO/08/239065) aims at developing a new technology for the treatment of polluted sediments dredged from the seabed of commercial ports through phytoremediation processes. Through plant activities and microorganism metabolisms, it is possible to recover dredged saline sediments by decontaminating them until an artificially prepared soil that is reusable in the terrestrial environment is obtained. This is an important advantage from the environmental point of view, and allows to partially solve one of the main problems of most commercial ports, that is the accumulation, storage and disposal of polluted dredged sediments. Considering that bacteria provide a significant contribution to phytoremediation process. Aim of the present study is the monitoring of temporal variation of microbial communities developing in an experimental phytoremediation plant during the decontamination process. The treatment plant consists of a sealed 80 m3 basin that is filled with a mixture of dredged sediments (75%) and natural soil (25%). It was planted with three plant species, and has been properly cultivated and fertilized for two years. Terminal Restriction Fragment Length Polymorphism (T-RFLP) on 16S rRNA gene was used to study the composition of bacterial communities at different times and points in the basin. Cluster Analysis (CA) and Non Metric Multidimensional Scaling (NMDS) multivariate statistics were applied for data interpretation. At the onset, the bacterial communities were heterogeneous and discrete, reflecting those inherited from the sediment–soil mixture, from compost and from plant's rhizospheres. The communities’ composition rapidly changed to become stabilized after one year.