1. Arumugam M, Raes J, Pelletier E et al (2011) Enterotypes of the human gut microbiome. Nature 473:174–180
2. Baird D (1987) Exploratory factor analysis, instruments, and the logic of scientific discovery. Br J Philos Sci 38:319–337
3. Brenner DJ, Staley JT, Krieg MR (2006) Classification of procaryotic organisms and the concept of bacterial speciation. In: Garrity G (ed) Bergey’s manual of systematic bacteriology. Vol. II: The proteobacteria. Part A: Introductory essays. Springer, New York, pp 27–32
4. Collins FS, Green ED, Guttmacher AE et al (2003) A vision for the future of genomics research. Nature 422:835–847
5. Committee on Metagenomics (2007) The new science of metagenomics: revealing the secrets of our microbial planet. National Academies Press, Washington, DC