The invisible world of microorganisms has fascinated researchers for more than 200 years. How can organisms too small to be seen with the naked eye exist and function, and how can their actions have so important and sometimes dramatic consequences? One would think that 200 years would be enough to know everything about microorganisms. Yet, more than ever we find ourselves in a revolution of new possibilities to study the smallest living beings and try to understand things we have not appreciated so far. Let me give two examples.
First, the development of DNA sequencing technologies over the past ten years has dramatically accelerated our knowledge of individual microbial species. It has also offered us insights in the capacities and the diversity of microorganisms living on our planet, the majority of which have never been cultured in the laboratory. The activities of some of those microbes have global importance, but we can only study them in their own environment.
As a second example, new molecular techniques coupled with advances in microscopy now enable the study of microorganisms as individuals, revealing the organization of the protein and DNA machineries inside cells. Microbial cells are not mixed enzyme bags, but instead highly structured and organized entities. At the same time, we find that individual cells in clonal populations can behave very differently. Such different behaviour can have very important consequences, from the action of certain mobile DNA elements to the virulence character of specific individual cells.
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