[Show abstract][Hide abstract] ABSTRACT: Horizontal gene transfer (HGT) plays a significant role in microbial evolution. It can accelerate the adaptation of an organism, it can generate new metabolic pathways and it can completely remodel an organism's genome. We examine 27 closely related genomes from the YESS group of gamma proteobacteria and a variety of four-taxon datasets from a diverse range of prokaryotes in order to explore the kinds of effects HGT has had on these organisms.
Philosophical Transactions of The Royal Society B Biological Sciences 09/2009; 364(1527):2209-19. DOI:10.1098/rstb.2009.0042 · 7.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A large number of theories have been advanced to explain why genes involved in the same biochemical processes are often co-located in genomes. Most of these theories have been dismissed because empirical data do not match the expectations of the models. In this work we test the hypothesis that cluster formation is most likely due to a selective pressure to gradually co-localise protein products and that operon formation is not an inevitable conclusion of the process.
We have selected an exemplar well-characterised biochemical pathway, the phenylacetate degradation pathway, and we show that its complex history is only compatible with a model where a selective advantage accrues from moving genes closer together. This selective pressure is likely to be reasonably weak and only twice in our dataset of 102 genomes do we see independent formation of a complete cluster containing all the catabolic genes in the pathway. Additionally, de novo clustering of genes clearly occurs repeatedly, even though recombination should result in the random dispersal of such genes in their respective genomes. Interspecies gene transfer has frequently replaced in situ copies of genes resulting in clusters that have similar content but very different evolutionary histories.
Our model for cluster formation in prokaryotes, therefore, consists of a two-stage selection process. The first stage is selection to move genes closer together, either because of macromolecular crowding, chromatin relaxation or transcriptional regulation pressure. This proximity opportunity sets up a separate selection for co-transcription.