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Soils of the Ross Sea region of Antarctica are among the least diverse ecosystems on earth. Few plants and animals have colonised these soils, but bacteria are distributed throughout. We compared the bacterial communities of soil samples from 5 locations in the Ross Sea region, representing different soil taxonomic groups, using culture-in dependent methods. Four mineral soils and one ornithogenic soil were analysed. Organic C, Total N, and moisture of the mineral soils were low, total P and EC were variable. In contrast, the water content, organic C, and Total N and P, and EC of the ornithogenic soil were 10-100 fold higher than the mineral soils. Soil pH was alkaline. One thousand and fourteen clones were screened by restriction fragment length polymorphisms. While the majority of the ribotypes were rare, some were dominant and occurred >= 3 times in the respective clone libraries. The dominant ribotypes were sequenced and shown to be phylogenetically affiliated with the phyla Acidobacteria, Actinobacteria, Bacteroidetes, Proteobacteria, Demococcus-Thermus, Firmicutes, Cyanobacteria and Candidate TM7. The closest relatives of the clones retrieved from the mineral soils were uncultured environmental clones or bacterial isolates not assigned to recognised genera. In contrast, the clones from the ornithogenic soil were most closely related to the endospore-formers; Oceanobacillus profundus, Clostridium acidiurici and Sporosarcina aquimarina. We found no convincing evidence that the Haplorthels from Scott Base, Marble Point, and Cape Hallett, have bacterial communities structured fundamentally different from those of Anhyorthels from Bull Pass and Vanda. Nonetheless the composition of the communities did vary substantially and were readily discriminated by multivariate statistics on the basis of soil properties. (c) 2007 Elsevier B.V All rights reserved.