ABSTRACT
The prokaryotes consist of many thousands of known species, to which some order has been applied with the advent of 16S rRNA sequencing. The resulting phylogenetic tree (Figure 1) has been used as an indication of how life started. To view the two kingdoms in the prokaryotes as primitive is an oversimplification, as both the Bacteria and the Archaea are extremely well adapted to their environments. A brief survey of the Bacteria and Archaea cannot hope to encompass their diversity, and may even give a misguided view that the Bacteria are predominantly pathogenic or that Archaea are predominantly thermophilic. However, the best studied Bacteria are pathogenic (despite the numerous examples of beneficial species) and the best studied Archaea are thermophiles.
