Riley, D.R. et al. PLoS Comput. Biol. 9, e1003107 (2013).

Although the estimated 1014 bacterial cells living in the human body serve important functions, Riley et al. show that this cohabitation can also lead to genetic transfer between the species, which can negatively affect the genome of somatic human cells. By mining data from the Human Genome Project, the 1000 Genomes Project and The Cancer Genome Atlas for the presence of any of 2,241 bacterial genomes, the researchers found evidence of lateral gene transfer (LGT), which occurred more frequently in tumor samples than in healthy cells. They documented an example in which the integration of a particular species of bacteria into the 5′ and 3′ regulatory regions of proto-oncogenes led to the upregulation of transcription of those genes, supporting the hypothesis that LGT may play a role in carcinogenesis.