2004 Volume 19 Issue 4 Pages 249-264
One of the most astonishing findings of whole-genome sequencing is the massive degree of horizontal gene transfer, which implies that gene exchange among organisms is not a laboratory peculiarity but a constitutive factor in microbial consortia. Although the rRNA operon is highly conserved, Escherichia coli has an extremely variable genome size ranging from 4.5 to 5.5 Mb, of which ca 10% consists of acquired genes as the result of horizontal gene transfer over 100 million years. Direct evidence of such horizontal gene transfer is provided by a huge amount of prophage or prophage remnant sequences. It is often assumed that viruses do not intrude on the genus barrier, but this concept has been questioned since host range can vary greatly between marine phages even with insufficient knowledge of transduction in natural microbial communities. Novel "broad-host-range vector particles", with a variety of recipients and an extremely high transduction frequency of up to 2.6×10-3 per particle, have been discovered among virus-like particles (VLPs) in marine and thermal environments. The discovery might provide a clue as to the role of environmental gene mediators contributing to evolutionary diversification and speciation.