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K. Nealson (JPL)
Few areas of science have changed more dramatically than microbiology during the past 20 years. We have gone from a medically dominated field using standard techniques of culturing and studying what we could grow (and primarily what caused diseases) to one in which molecular phylogeny and genomics have literally invented the natural history of microbes. Using modern techniques of nucleic acid amplification, cloning, sequencing and analysis, it is now possible to identify to the genus level, organisms that have not yet been cultured. These technologies allow us to determine the taxonomy of the organisms and to place them within a phylogenetic scheme that allows us to speculate about the evolution of early life and its metabolic pathways. The methods also confirm what was earlier suspected, namely that only a small proportion (1 encounter in the environment can be easily cultured, suggesting that the microbial world may be more diverse than had been imagined. Finally, the molecular approaches allow us to see that a great deal of the genetic diversity of the planet lies within two prokaryotic groups, the Bacteria and the Archaea. These groups constitute the hardy, metabolically diverse, and tenacious organisms that inhabit nearly every niche on Earth in which physical conditions are compatible with life and where energy of some sort is available. In essence the study of these organisms during the past 20 years has given us a new appreciation for the limits of life on Earth, and redefined potentially habitable zones elsewhere.