In recent decades we have come to realize that the microbial world is hugely diverse, and can be found in the most extreme environments. Fungi, single-celled protists, bacteria, archaea, and the vast array of viruses and sub-viral particles far outnumber plants and animals. Microbes, we now know, play a critical role in ecosystems, in the chemistry of atmosphere and oceans, and within our bodies. The field of microbiology, armed with new techniques...