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Summary
Ever since Woese's seminal work nearly 40 years ago (1), life has been divided into three domains: Archaea, Bacteria, and Eukaryota. But could there be life that does not fit into any of these domains? Novel techniques for exploring microbes that cannot readily be grown in the laboratory offer hope that scientists can discover such life, if it exists (see the first figure). These methods include metagenomics, which involves the sequencing of DNA extracted from environmental samples, and single-cell genomics, where individual microbial cells are isolated from the environment and their genomes amplified and sequenced.
