Bettina Schmidt et al. “Establishment of Normal Gut Microbiota Is Compromised Under Excessive Hygiene Conditions”. PLoS ONE 6, № 12 (2011).
445
Luis P. Villarreal, Guenther Witzany. “Viruses Are Essential Agents within the Roots and Stem of the Tree of Life”. Journal of Theoretical Biology 262, № 4 (2010).