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Sorin Sonea
Léo G. Mathieu


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1This volume stresses the major differences between prokaryotes and eukaryotes, differences which are both profound and astonishing. They show that the general strategy of life in prokaryotes differs strikingly from that in eukaryotes despite the fact that many of the fundamental biochemical reactions are very similar in the two groups. However, too few scientists have as yet come to realize this. Our understanding of prokaryotic biology has progressed considerably with the in-depth studies of more than a thousand different types. We have learned to cultivate many of them, assess some of their properties and, for a small number, their role in nature. This vast and reliable new knowledge tells us that prokaryotes are ancient but not primitive, highly specialized and standardized cells which show an amazing capacity and tendency to collaborate among themselves. Most of them live in close association with each other in mutualistic, mixed groups (the metaphor of community is apt) practicing an effective division of labor. When advantageous or necessary, these communities can easily modify the mixture of their cells, replacing some strains with others, drawn from the prokaryotes’giant reserve of differently specialized cells. This allows them to react and adjust quickly and opportunistically to the changes around them. Moreover, in contrast with eukaryotes, individual prokaryotic cells are able to function as two-way communication stations, exchanging bits of hereditary information (DNA) which can be easily and frequently transmitted horizontally between different strains. The exchange of prokaryotic cells between mixed communities, added to the constant and opportune horizontal transfer of genes, constitutes an original and efficient adaptation System which endows the prokaryotic world with the ability to perform very complex functions and solve problems. There are no species among prokaryotes. Rather, together they form one global, extremely diversified, yet functionally unified peculiar being.

2It is from prokaryotic stock that the eukaryotes most probably originated, i.e. from the permanent association of a few complementary strains of the already rich and varied prokaryotic entity. This association gave birth to a completely new type of cell. Much later, other prokaryotes also joined some more evolved eukaryotes in successful symbioses. Thus, in parallel with their own evolution, the prokaryotes have been extensively involved in eukaryotes’ evolution, contributing genetic information on a much larger scale than previously thought.

3We postulate that the prokaryotic world behaves as a global System or superorganism of elements capable of solidarity. It has continually improved the life-supporting capacity of our biosphere and constitutes the main positive ecological factor on our planet. Its general way of functioning may be compared to the one practiced in a technically advanced economy. It is based on the ability to use, for its own needs, available nutrients and produce a large variety of products (metabolites) which can be exchanged for the temporary benefit of the different members of its population. In addition, the prokaryotic world practices among its constituents a permanent competition which selects locally favorable changes and eventually eliminates the less productive elements or associations with resulting increased efficiency and economy. This new vision of the prokaryotic world comes as a coherent counterproposition to the generally accepted idea that many thousand bacterial “species” live as independent infighting cells in a global chaotic mixture. In order to make our thesis more convincing, we have presented all these aspects from several different angles, each, hopefully, adding some new light to the subject. This procedure did, however, give rise to some unavoidable repetitition.

4In the 1970’s, a new category of prokaryotes, the Archaebacteria (Archaea) was recognized and described. Many of these types have been studied since then, and it is evident that some of their bio-energetic and macromolecular characteristics are more closely related to those of eukaryotes than to those of Eubacteria. In fact, some biologists consider Archaebacteria sufficiently different from Eubacteria to support the suggestion that all living beings be divided into three kingdoms or domains: Eukarya, Bacteria and Archaea. Metabolic and macromolecular differences notwithstanding, we wish to stress the fact that Eubacteria and Archaebacteria share fundamental ways of life based on interdependence and solidarity. They include life in communities with efficient and adaptable division of labor and also active horizontal exchanges of genes among their strains involving the same general mechanisms that were originally observed and described in Eubacteria. To this may be added the fact that after a long evolution, likely from a common progenote ancestor, the size, shape and general organization of Archaeabacteria cells have retained essential similarities. For all these reasons we insist here mostly on important and general differences between eukaryote and prokaryote (Eubacteria and Archaeabacteria) patterns and strategies of life, differences we consider are not sufficiently emphasized and studied in Biology and Microbiology. Our purpose therefore is not to question the well established fact that diversity does exist among the members of the prokaryotic world. Rather, we wish to recall and discuss some essential biological differences between the prokaryotic and the eukaryotic worlds and their respective evolution. We consider these differences as essential elements on which a coherent study of prokaryotology can be founded and built. Understanding of the entire field of biology would benefit from this.

© Presses de l’Université de Montréal, 2000

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