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Applied and Environmental Microbiology, October 2007, p. 6224-6232, Vol. 73, No. 19
0099-2240/07/$08.00+0     doi:10.1128/AEM.01254-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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

Daniel Aguirre de Cárcer,1 Marta Martín,1 Ulrich Karlson,2 and Rafael Rivilla1*

Departamento de Biología, Universidad Autónoma de Madrid, 28049 Madrid, Spain,1 National Environmental Research Institute, University of Aarhus, Roskilde, Denmark2

Received 6 June 2007/ Accepted 2 August 2007

The aim of this study was to analyze the structural and functional changes occurring in a polychlorinated-biphenyl (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 (Alpha- and Betaproteobacteria, Acidobacteria, and Actinobacteria) and the genes encoding iron-sulfur protein {alpha} (ISP{alpha}) subunits of the toluene/biphenyl dioxygenases in soil and rhizosphere by screening gene libraries using temperature gradient gel electrophoresis. The results, based on the analysis of 415 clones grouped into 133 operational taxonomic units that were sequence analyzed (>128 kbp), show that the rhizospheric bacterial community 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 enriched in the rhizosphere and dominated both in rhizosphere and soil. There was a higher than expected abundance of Betaproteobacteria in the native and in the planted PCB-polluted soil. The ISP{alpha} sequences retrieved indicate a high degree of catabolic and phylogenetic diversity. Many sequences clustered with biphenyl dioxygenase sequences from gram-negative bacteria. A distinct cluster that was composed of sequences from this study, some previously described environmental sequences, and a putative ISP{alpha} from Sphingomonas wittichii RW1 seems to contain greater diversity than the presently recognized toluene/biphenyl dioxygenase subfamily. Moreover, the rhizosphere selected for two ISP{alpha} sequences that accounted for almost 60% of the gene library and were very similar to sequences harbored by Pseudomonas species.

* Corresponding author. Mailing address: Departamento de Biología, c/Darwin 2, Universidad Autónoma de Madrid, 28049 Madrid, Spain. Phone: 34 914978188. Fax: 34 914978344. E-mail: rafael.rivilla{at}uam.es

{triangledown} Published ahead of print on 10 August 2007.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, October 2007, p. 6224-6232, Vol. 73, No. 19
0099-2240/07/$08.00+0     doi:10.1128/AEM.01254-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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