Despite 300 years of peering through microscopes, growing bacteria in culture, and screening soil, air, and water for new microbial species, scientists have clearly overlooked much of life on earth. Thanks to powerful new research tools, bacteriologists are discovering that the living world is suddenly far bigger and more complex than they imagined even a decade ago. The finding is similar in magnitude, perhaps, to Dutch microscopist Antonie van Leeuwenhoek's first glimpse of microbes-he called them "animalcules"-cavorting beneath his crude glass lenses.

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