Pervasive horizontal gene transfer in Chlamydia
The genome era has really taught us something impressive about the plasticity of bacterial genomes.
Gene exchange between strains of the same species and gene exchange between different species is not limited to special categories of genes and is not limited to ‘oddball’ species. It is pervasive, frequent and it is also a public health problem.
Last week, a paper that is beautiful in its execution really highlighted the importance of gene transfer from a public health perspective.
Simon Harris and co-workers from various UK institutions, South Africa, Sweden, The Netherlands and France have published an analysis of whole genome sequences from a diverse collection of Chlamydia strains.
The work shows that using the ompA gene – which is often used for diagnosis of what kind of Chlamydia is present – is not sensible. The history of this gene is filled with instances of gene splicing and exchange. Other diagnostic markers have the same kind of history.
Phylogenetic trees from different markers conflict with one another, revealing that these genomes are chimaeric in many different kinds of ways.
To me this news is not surprising, merely that it is impressive.
Gene exchange defines the evolution of most ‘evolving entities’ on the planet (let’s operationally define an evolving entity as anything that is uses DNA or RNA as its genetic material and not restrict our discussion to just cellular life forms).
Gene exchange is restricted by protein-protein interactions and perhaps in sexually reproducing organisms it is restricted because only gene exchange into the single cells that are involved in reproduction are the only gene exchanges that will ever count.
Otherwise, horizontal gene transfer seems to be unstoppable and it seems to be frequent and it presents us with a significant public health problem both from the perspective of managing antibiotic resistance, but also from the perspective that this is the likely source of entirely new infectious agents.
Feel free to leave a comment below.
Harris SR, Clarke IN, Seth-Smith HM, Solomon AW, Cutcliffe LT, Marsh P, Skilton RJ, Holland MJ, Mabey D, Peeling RW, Lewis DA, Spratt BG, Unemo M, Persson K, Bjartling C, Brunham R, de Vries HJ, Morré SA, Speksnijder A, Bébéar CM, Clerc M, de Barbeyrac B, Parkhill J, Thomson NR. Whole-genome analysis of diverse Chlamydia trachomatis strains identifies phylogenetic relationships masked by current clinical typing. Nat Genet. 2012 Mar 11. doi: 10.1038/ng.2214.
Also, perhaps take a look at:
McInerney, J.O., Pisani, D., Bapteste, E., and O’Connell, M.J. (2011). The Public Goods Hypothesis for the Evolution of Life on Earth. Biology Direct doi:10.1186/1745-6150-6-41. [link]