The role of lateral gene transfer in prokaryotic evolution

Lateral gene transfer (LGT) is the propagation of genetic material through ways other than inheritance from a progenitor. The work presented here is part of the recent effort to better understand the importance of LGT in the evolution of the physiological properties harbored by bacteria and archaea. Since LGT is a phenomenon that potentially affects all prokaryotic functions, two main processes were chosen as model systems to study it.;Isoprenoid biosynthesis is a universal and well-characterized metabolic function. The combined genomic, phylogenetic and biochemical data accumulated points toward a critical role for LGT in the evolution of the mevalonate and methylerythritol pathways for the biosynthesis of the isoprenoid precursor isopentenyl diphosphate. The genes encoding the enzymes of pathways involved in the synthesis of archaeal isoprenoid lipids from this precursor were also investigated. This isoprenoid lipid biosynthesis apparatus was found to have evolved through a combination of evolutionary processes, including LGT.;Informational cellular processes (transcription/translation related), to which the ribosome is central, are thought to be more refractory to LGT than metabolic processes. This lead to the choice of ribosomal RNA (rRNA) genes as the second model system to study the importance of LGT. We isolated and sequenced all of the rRNA genes from two species of archaea known to display multiple heterogeneous rRNA gene copies. Clear recombination patterns were indeed found in some of the genes, suggesting a role for LGT in the creation of within species rRNA genes heterogeneity.;During the study of those two model systems for LGT, about 70 different genes were cloned and sequenced (>120kb of DNA). Phylogenetic analysis of those data and data from public databases reveals that LGT has played critical role in evolution of key physiological functions. The vertical inheritance (clonal) model of prokaryotic evolution cannot be easily modified to accommodate recurrent LGT. A new theoretical model of prokaryotic evolution based on LGT as a background force is therefore proposed to replace the old model.