Program > • Session Natural Environment

Microorganisms were the first life forms to develop on Earth, approximately four billion years ago. Their study is called microbiology,  and began with Anton van Leeuwenhoek's discovery of microorganisms in 1675, using a microscope of his own design. Microorganisms are very diverse prokaryotes or eukaryotes including bacteria, archaea, fungi, yeats, microscopic algae and protozoa (planktonic flagellates and planarian). Viruse are also considered by some microbiologists, whilst others consider them as non-living particles. Most microorganisms are unicellular (i.e., single particles), and microsopic, however some unicellular protists and bacteria (Thiomargarita namibiensis, for instance) are macroscopic and thus visible to the naked eye  Microorganisms are ubiquist. They live in all parts of environments found in nature: in fresh and marine waters, from surface to sediment; in soil; in hot springs;  in the atmosphere; deep inside rocks; and in leaving organisms. They colonize every ecosystem, even the most hostile ones (for human beeing) such as deserts, poles, geysers, deep ocean. In ecosystems, microorganisms are critical to nutrient recycling, acting as the most efficient decomposers. Microscopic phytoplankton is also responsible for about half of the global primary production while its biomass is only about 2% of the whole biomass on Earth. As some microorganisms are able to fix nitrogen, they play an important role in the nitrogen cycle. Recent studies have also shown that airborne microbes may play a role in precipitation and weather. Many micro-organisms are associated with plants or animals with which they maintain relations such as symbiosis, commensalism or parasitism. Finaly, some species are pathogenic and thus harmful as they grow within other organisms after ingestion or contamination by a wound, causing diseases that can kill people, other animals, and plants. Among all the microorganisms, prokaryotes are the most abundant unknown biodiversity on Earth, and most of them are not cultivable. Because of their high abundances, and their large variety of metabolic activities which makes them ubiquitous, microorganisms represent a key component in environmental studies and applications (both aquatic and terrestrial). To enhance our understanding of the heterogeneity and complexity of the microbial consortia, both in term of composition and functioning, their direct analysis must be done at the single cell level and requires a non-invasive interrogation of the cells. Single cell analysis has added up to our understanding of microbial ecology in terms of identification, abundance and functionality. Flow cytometry with cell sorting and static cytometry, together with advances in fluorescent probes for assessment of cell composition and functions have opened the field to many applications and strongly advanced the field. This session will concentrate on new developments and applications of single cell analysis of microbes and how it allows to gain an accurate representation of populations and communities in cultured and natural samples.

Chairman : Dr. Raffaella Casotti (Laboratory of Functional and Evolutionary Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy)