Preface

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The cell is the basic unit of life. Yet even the simplest of them, bacteria, have an extremely complex structure and are capable of sophisticated behaviors. Eukaryotic cells are even more complex. In addition, compared to prokaryotic cells, they exhibit a fantastic diversification at the morphological level and at the level of the organization they adopt: isolated, colonial or integrated and differentiated cells in a multicellular organism. A question arises: how did the first eukaryotic cells appear? One thing is certain: that they could only have appeared from simpler precursors. How these precursors came to be will not be discussed in depth in this book. We will more specifically address the problem of understanding how the modern eukaryotic cell was able to appear from simpler cells and what precursors can be considered.

The eukaryotic cell, once it appeared, was very successful in evolution and diversified into a myriad of organisms with sizes similar to bacterial cells (1-2 μm) to organisms as massive as whales, giant sequoias or Armillaria, common fungi whose mycelia can weigh up to 2,000 tons! Very often, the biodiversity presented in biology courses or textbooks boils down to that of plants and animals. However, these two biological groups represent only a small fraction of the biological diversity of eukaryotes. The majority of eukaryotic diversity is found in groups of microscopic organisms that are grouped under the generic term of “Eukaryotic Protists”, which in this book will take an acceptance in the broad sense, with the aim to gather all organisms that are clearly neither animals (eumetazoa) nor plants (embryophytes). The analysis of these protists shows that the ancient animal / plant dichotomy has no biological meaning and is gradually replaced by a classification more in line with what we know about the evolution of the eukaryotic cell. It is this phylogenetic classification that is followed in this book.

When the term microbe, which means organism invisible to the naked eye, is mentioned, this word is often restricted to bacteria and viruses (the latter of which are not, however, strictly speaking real living organisms, but that is another debate). This notion has grown to such an extent in university courses that sometimes, eukaryotic microbes are not even mentioned! There are indeed many treatises on microbiology in which it seems that only bacteria have the right to be described as microbes. This is a shame because both in terms of the functioning of the biosphere and of human health and industries, eukaryotic microbes are of crucial importance, sometimes much greater than that of bacteria and viruses. This book proposes to correct this trend, by explaining some of the characteristics of eukaryotic protists. The term microbe is indeed not completely appropriate for these organisms, some of which are clearly visible to the naked eye…

This book has its roots in the courses that I have been teaching for more than fifteen years at the master’s degree in Biochemistry at the University of Paris Diderot. I hope it will serve as a resource for the many colleagues who, like me, teach microbiology, but also for students who in the future will hopefully no longer ignore the fascinating world of protists.