Conjugation has classically been considered a bacterium-to-bacterium DNA transfer driven by the donor cell and is typically plasmid-encoded. Theoretically it is possible that any type of cell can serve as the recipient. In December Nature Genetics, Virginia Waters from the University of California, San Diego shows the first evidence for bacterial conjugation to mammalian cells.

Waters used the RK2 'shuttle vector' plasmid system to determine if Escherichia coli can transfer a fluorescent DNA signal to a culture of Chinese hamster ovary (CHO K1) cells. She found that DNA transfer can occur, but was dependent on an intact RK2 system in an all-or-none manner. Southern-blot analysis of post-conjugation CHO K1 DNA confirmed the genetic transfer (Nat Genet 2001, DOI: 10.1038/ng779).

These results may explain the presence in the human genome of 41 genes that are shared by humans and bacteria.

In practical terms, bacteria could become important vectors in...