IntroductionAliphatic cellular polyamines, linear diamines, triamines, tetra-amines, penta-amines and hexa-amines, and quaternary branched penta-amines, were found in eubacteria (domain Bacteria) and archaebacteria (doPolyamine analysis for chemotaxonomy of thermophilic eubacteria:Polyamine distribution profiles within the orders Aquificales, Thermotogales, Thermodesulfobacteriales, Thermales, Thermoanaerobacteriales, Clostridiales and Bacillales Cellular polyamines of 45 thermophilic and 8 related mesophilic eubacteria were investigated by HPLC and GC analyses for the thermophilic and chemotaxonomic significance of polyamine distribution profiles. Spermidine and a quaternary branched penta-amine, N 4 -bis(aminopropyl)norspermidine, were the major polyamine in Thermocrinis, Hydrogenobacter, Hydrogenobaculum, Aquifex, Persephonella, Sulfurihydrogenibium, Hydrogenothermus, Balnearium and Thermovibrio, located in the order Aquificales. Thermodesulfobacterium and Thermodesulfatator belonging to the order Thermodesulfobacteriales contained another quaternary penta-amine, N 4 -bis(aminopropyl)spermidine. In the order Thermotogales, Thermotoga contained spermidine, norspermidine, caldopentamine and homocaldopentamine. The latter two linear penta-amines were not found in Marinitoga and Petrotoga. In the order Thermales, Thermus and Marinithermus contained homospermidine, norspermine and the linear penta-amines. Meiothermus lacked penta-amines. Vulcanithermus contained linear penta-amines and hexa-amines but not homospermidine. Oceanithermus contained spermine alone. Within the order Thermoanaerobacteriales, the two quaternary branched penta-amines were found in Thermanaeromonas and Thermoanaerobacter. Caldanaerobacter contained N 4 -bis(aminopropyl)spermidine. Thermoanaerobacterium lacked penta-amines. Thermaerobacter of the order Clostridiales contained N 4 -bis(aminopropyl)spermidine and agmatine. Thermosyntropha, Thermanaerovibrio, Thermobrachium (the order Clostridiales), Sulfobacillus, Alicyclobacillus, Anoxybacillus, Ureibacillus, Thermicanus (the order Bacillales), Desulfotomaculum, Desulfitobacterium and Pelotomaculum (the family Peptococcaceae) ubiquitously contained spermine. Some thermophiles of Bacillales added linear and branched penta-amines.