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Open Access Research article

Comparative metagenomics of three Dehalococcoides-containing enrichment cultures: the role of the non-dechlorinating community

Laura A Hug1, Robert G Beiko2, Annette R Rowe3, Ruth E Richardson3 and Elizabeth A Edwards14*

Author affiliations

1 Department of Cell and Systems Biology, University of Toronto, Toronto, Canada

2 Faculty of Computer Science, Dalhousie University, Halifax, NS, Canada

3 Civil & Environmental Engineering, Cornell University, Ithaca, NY, USA

4 Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON, Canada

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Citation and License

BMC Genomics 2012, 13:327  doi:10.1186/1471-2164-13-327

Published: 23 July 2012

Abstract

Background

The Dehalococcoides are strictly anaerobic bacteria that gain metabolic energy via the oxidation of H2 coupled to the reduction of halogenated organic compounds. Dehalococcoides spp. grow best in mixed microbial consortia, relying on non-dechlorinating members to provide essential nutrients and maintain anaerobic conditions.

A metagenome sequence was generated for the dechlorinating mixed microbial consortium KB-1. A comparative metagenomic study utilizing two additional metagenome sequences for Dehalococcoides-containing dechlorinating microbial consortia was undertaken to identify common features that are provided by the non-dechlorinating community and are potentially essential to Dehalococcoides growth.

Results

The KB-1 metagenome contained eighteen novel homologs to reductive dehalogenase genes. The metagenomes obtained from the three consortia were automatically annotated using the MG-RAST server, from which statistically significant differences in community composition and metabolic profiles were determined. Examination of specific metabolic pathways, including corrinoid synthesis, methionine synthesis, oxygen scavenging, and electron-donor metabolism identified the Firmicutes, methanogenic Archaea, and the ∂-Proteobacteria as key organisms encoding these pathways, and thus potentially producing metabolites required for Dehalococcoides growth.

Conclusions

Comparative metagenomics of the three Dehalococcoides-containing consortia identified that similarities across the three consortia are more apparent at the functional level than at the taxonomic level, indicating the non-dechlorinating organisms’ identities can vary provided they fill the same niche within a consortium. Functional redundancy was identified in each metabolic pathway of interest, with key processes encoded by multiple taxonomic groups. This redundancy likely contributes to the robust growth and dechlorination rates in dechlorinating enrichment cultures.