Figure 3

Distribution within the phylogenetic tree of microorganisms accumulating KCl as their sole or main osmotic solute. Groups marked with purple boxes contain at least one halophilic representative (e.g. Salinibacter ruber within the Bacteroidetes). The group of the Firmicutes contains both microorganisms that use KCl for osmotic balance (the order Halanaerobiales within the low G+C branch, consisting of anaerobic fermentative organisms) and different halophilic aerobes (Halobacillus spp. and others) that accumulate inorganic solutes. High intracellular KCl concentrations are also found in the methanogenic halophiles, but these accumulate organic solutes as well.