Changes in Bacterial Populations and in Biphenyl Dioxygenase Gene Diversity in a Polychlorinated Biphenyl-Polluted Soil after Introduction of Willow Trees for Rhizoremediation

摘要

The aim of this study was to analyze the structural and functional changes occurring in a polychlorinatedbiphenyl (PCB)-contaminated soil ecosystem after the introduction of a suitable host plant for rhizoremediation (Salix viminalis). We have studied the populations and phylogenetic distribution of key bacterial groups\ud(Alpha- and Betaproteobacteria, Acidobacteria, and Actinobacteria) and the genes encoding iron-sulfur protein \ud(ISP ) subunits of the toluene/biphenyl dioxygenases in soil and rhizosphere by screening gene libraries using\udtemperature gradient gel electrophoresis. The results, based on the analysis of 415 clones grouped into 133\udoperational taxonomic units that were sequence analyzed (>128 kbp), show that the rhizospheric bacterial\udcommunity which evolved from the native soil community during the development of the root system was distinct from the soil community for all groups studied except for the Actinobacteria. Proteobacteria were\udenriched in the rhizosphere and dominated both in rhizosphere and soil. There was a higher than expected\udabundance of Betaproteobacteria in the native and in the planted PCB-polluted soil. The ISP sequences\udretrieved indicate a high degree of catabolic and phylogenetic diversity. Many sequences clustered with\udbiphenyl dioxygenase sequences from gram-negative bacteria. A distinct cluster that was composed of sequences\udfrom this study, some previously described environmental sequences, and a putative ISP from\udSphingomonas wittichii RW1 seems to contain greater diversity than the presently recognized toluene/biphenyl\uddioxygenase subfamily. Moreover, the rhizosphere selected for two ISP sequences that accounted for almost 60% of the gene library and were very similar to sequences harbored by Pseudomonas species.