The purpose of this book is to show the essential and indispensable role of prokaryotes in the evolution of aliving world. The evolutionary success of prokaryotes is explained together with their role in the evolution of the geosphere, the biosphere and its functioning, as well as their ability to colonize all biotopes, including the most extreme ones. We consider that all past and present living beings emerged from prokaryotes and have interacted with them. Forces and mechanisms presented in the various theories of evolution apply to prokaryotes. The major stages of their evolution and biodiversity are also described. Finally, it is emphasized that prokaryotes are living organisms that provide indisputable evidence of evolutionary processes. Many examples of ongoing evolution in prokaryotes, observable at the human scale, are provided.

This work was designed to study the specific and functional diversity of small aquatic heterotrophic flagellates (HF). Two environmental 18S rDNA surveys were conducted on the 0.6 - 5 um planktonic fraction of the oligotrophic Lake Pavin, at the begining and at the end of the thermal stratification period, when unidentified small HF develop. Phyogenetic analysis of the retrieved sequences highlighted original results. (i) Recovered sequences differed from microscopic diversity studies. (ii) The revealed diversity within HF was higher than the diversity previously detected using traditional methods. (iii) Most of the detected HF species were not bacterivorous, but saprotrophs and (or) parasites. Finally, a quantitative PCR assay was developped in order to quantify chytrids zoospores (Fungi), i.e. phytoplanktonic parasites which actually are totaly ignored in the dynamic of lacustrin systems. Overall, the main findings indicate that we need to revise the functional role of HF, by including saprotrophs and parasites in our conception of matter and energy flows in aquatic microbial food webs, and the related biogeochemical cycles as well.