ABSTRACT

Although they are mostly small single-celled organisms, members of domains Bacteria and Archaea represent extremely diverse groups of organisms. Some live miles underground, whereas others have been found miles into the atmosphere, and the majority live somewhere between those extremes. Some grow in hot pools of water, inside glaciers, under high pressures deep in the ocean, in saline soils, or on and inside plants and animals. In fact, just about anywhere on the Earth, one or more species of these microbes will be found. A few can survive on their own, but most require other species to supply some of their food and energy requirements. This diversity is reflected in the genomes of these organisms. As of 2014, approximately 4000 bacterial genomes had been completely sequenced, and nearly 200 archaeal genomes had been sequenced. Although this is a small proportion of the estimated hundreds of thousands of species included in both domains, the genomes do provide some insight into the evolution of these organisms. In this chapter, a few of these genomes will be discussed to highlight the similarities as well as the differences.