Adjusting to alien genes.

From the perspective of a bacterium, higher eukaryotes are oversexed, unadventurous and reproduce in an inconvenient way. Sex, or recombination following horizontal gene transfer (HGT) events, to be less provocative, is a rare event for a bacterium, but a potentially profound one. Through HGT a bacterium can acquire DNA from distant as well as closely related species and, thereby, instantly obtain genes that encode novel functions or replace its existing genes with better ones. While there is an abundance of retrospective evidence for HGT in bacteria, there has been little consideration of the dynamics of the process. In this issue of Molecular Microbiology Lind et al. explore these dynamics theoretically, and then experimentally by substituting Salmonella Typhimurium ribosomal genes with orthologues from various microbial origins. The authors show that the majority of these newly acquired ribosomal proteins reduce fitness in S. Typhimurium, but within short order (40-250 generations) subsequent evolution will mitigate the fitness costs of the alien alleles. The presented results suggest that that at least the initial phase of adapting to alien genes of this informational core ilk is not by changing them but rather by increasing their level of expression by gene amplification. Lind et al. argue that their results provide an explanation as to why duplicated genes are overrepresented among horizontally transferred genes.