Figure 1. Colonies of a bacterium on agar growth medium in a Petri dish. When a minute amount of cells is streaked out (starting at 9 o'clock on the dish), cells are so separated that round colonies can develop from single cells. Such a cell community then represents a clone because it originates from one cell. Depending on its size, a colony may contain between 50 and 500 million cells. (Photograph: Anne Kemmling, Goettingen, Germany.)

Figure 2. Base sequence of the 16S rRNAs of three archaea (Methanosarcina mazei, Archaeoglobus fulgidus, and Methanosphaera stadtmanae) and two bacteria (Escherichia coli and Bacillus licheniformis). The depiction is based on a ClustalW-alignment under standard conditions (W.A. Larkin et al., Bioinformatics 23, 2947, 2007). Visualization was done with Jaliew using the standard color code for nucleotides. (C. Clamp et al., Bioinformatics 20, 416, 2004). Gaps were inserted into the sequences to achieve maximal agreement. (Adaptation: Antje Wollherr, Goettingen, Germany.)

Figure 3. Phylogenetic tree of the three domains of all living organisms, depicted clockwise from left to right: Bacteria: Aquifex, Bacteroides, cyanobacteria, proteobacteria, Spirochaeta, Bacilli, green filamentous bacteria. Archaea: Nanoarchaeum equitans (small dots) attached to Ignicoccus hospitalis, Thermoproteus, Pyrodictium, Methanococcus, Methanosarcina, halophilic archaea. Eukarya: Entamoeba, mucilaginous fungi, humans, fungi, plants, ciliates, trichomonads, diplomonads. LUCA (at the bottom) stands for the Last Universal Common Ancestor. (Diagram: Anne Kemmling, Goettingen, Germany.)