Environmental genomics of "Haloquadratum walsbyi" in a saltern crystallizer indicates a large pool of accessory genes in an otherwise coherent species
1 Evolutionary Genomics Group, División de Microbiología, Universidad Miguel Hernández, Apartado 18, San Juan 03550, Alicante, Spain
2 Canadian Institute for Advanced Research, Centre Robert Cedergren, Departement de Biochimie, Universite de Montreal, 2900 Boulevard Edouard-Montpetit, Montreal, Quebec, H3T 1J4, Canada
3 Canadian Institute for Advanced Research Program in Evolutionary Biology, Department of Biochemistry and Molecular Biology Dalhousie University, Halifax, Nova Scotia, Canada
4 Department of Microbial Ecology, Centre of Ecological and Evolutionary Studies, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
5 Genome Atlantic and Department of Biochemistry and Molecular Biology Dalhousie University, Halifax, Nova Scotia, Canada
BMC Genomics 2006, 7:171 doi:10.1186/1471-2164-7-171Published: 4 July 2006
Mature saturated brine (crystallizers) communities are largely dominated (>80% of cells) by the square halophilic archaeon "Haloquadratum walsbyi". The recent cultivation of the strain HBSQ001 and thesequencing of its genome allows comparison with the metagenome of this taxonomically simplified environment. Similar studies carried out in other extreme environments have revealed very little diversity in gene content among the cell lineages present.
The metagenome of the microbial community of a crystallizer pond has been analyzed by end sequencing a 2000 clone fosmid library and comparing the sequences obtained with the genome sequence of "Haloquadratum walsbyi". The genome of the sequenced strain was retrieved nearly complete within this environmental DNA library. However, many ORF's that could be ascribed to the "Haloquadratum" metapopulation by common genome characteristics or scaffolding to the strain genome were not present in the specific sequenced isolate. Particularly, three regions of the sequenced genome were associated with multiple rearrangements and the presence of different genes from the metapopulation. Many transposition and phage related genes were found within this pool which, together with the associated atypical GC content in these areas, supports lateral gene transfer mediated by these elements as the most probable genetic cause of this variability. Additionally, these sequences were highly enriched in putative regulatory and signal transduction functions.
These results point to a large pan-genome (total gene repertoire of the genus/species) even in this highly specialized extremophile and at a single geographic location. The extensive gene repertoire is what might be expected of a population that exploits a diverse nutrient pool, resulting from the degradation of biomass produced at lower salinities.