TOWARDS A UNIFIED EVOLUTIONARY GENETICS OF MICROORGANISMS

I propose here that evolutionary genetics, apart from improving our ba sic knowledge of the taxonomy and evolution of microbes (either eukary otes or prokaryotes), can also greatly contribute to applied research in microbiology. Evolutionary genetics provides convenient guidelines for better interpreting genetic and molecular data dealing with microo rganisms. The three main potential applications of evolutionary geneti cs in microbiology are (a) epidemiological follow-up (with the necessi ty of evaluating the stability of microbial genotypes over space and t ime); (b) taxonomy in the broad sense (better definition and sharper d elimitation of presently described taxa, research of hidden genetic su bdivisions); and (c) evaluation of the impact of the genetic diversity of microbes on their relevant properties (pathogenicity, resistance t o drugs, etc). At present, two main kinds of population structure can be distinguished in natural microbial populations: (a) species that ar e not subdivided into discrete phylogenetic lineages (panmictic specie s or basically sexual species with occasional bouts of short-term clon ality fall into this category); (b) species that are strongly subdivid ed by either cryptic speciation or clonal evolution. Improvements in a vailable statistical methods are required to refine these distinctions and to better quantify the actual impact of gene exchange in natural microbial populations. Moreover, a codified selection of markers with appropriate molecular clocks (in other words: adapted levels of resolu tion) is sorely needed to answer distinct questions that address diffe rent scales of time and space: experimental, epidemic, and evolutionar y. The problems raised by natural genetic diversity are very similar f or all microbial species, in terms of both basic and applied science. Despite this fact, a regrettable compartmentalization among specialist s has hampered progress in this field. I propose a synthetic approach, relying on the statistical improvements and technical standardization s called for above, to settle a unified evolutionary genetics of micro organisms, valid whatever the species studied, whether eukaryotic (par asitic protozoa and fungi) or prokaryotic (bacteria), Apart from benef its for basic evolutionary research, the anticipated payoff from this synthetic approach is to render routine and commonplace the use of mic robial evolutionary genetics in the fields of epidemiology, medicine, and agronomy.