As well as reproducing and passing on their genes to their offspring (vertical gene transfer - VGT) bacteria can also pass their genes to each other by a mechanism known as horizontal gene transfer (HGT). This allows the rapid spread of advantageous genes, such as genes for antibiotic resistance, so HGT has played a large role in bacterial evolution. However, its role in animals is controversial.
Previous studies have largely focussed on single species and invertebrates, so for our recent paper in Genome Biology, we chose to look at 40 species from around the animal kingdom and in every species we looked at, including humans and primates, we found evidence of HGT. We found some HGT that had previously been detected, but we also identified many new 'foreign' genes and the number was markedly greater than seen before. For example, the HAS1 gene (yellow) was acquired early in vertebrate evolution (red) from fungi (pink), as shown in this phylogenetic tree from our paper where they group together. If the gene were acquired by VGT it, and the other vertebrate genes, would group with the other animals (black). These foreign genes come from bacteria, fungi and other single-celled organisms, and mostly control biochemical functions.
Our findings suggest that rather than being confined to simpler, single-celled organisms (e.g. bacteria) or to specific relationships (e.g. host-parasite pairings) HGT may occur in all species, even in humans. This means we need to re-evaluate our evolutionary models to take into account the contribution of HGT. A better understanding of HGT and the mechanisms underlying it may provide new insights into how genomes evolve, including our own.
Expression of multiple horizontally acquired genes is a hallmark of both vertebrate and invertebrate genomes. Alastair Crisp, Chiara Boschetti, Malcolm Perry, Alan Tunnacliffe and Gos Micklem. Genome Biology 2015, 16:50 doi:10.1186/s13059-015-0607-3