Abstract
The base compositions of deoxyribonucleic-acids extracted from aerobic pseudomonads were determined by examination of the buoyant density of each sample in caesium chloride (CsCl) gradients. A collection of 165 strains, representing many of the principal biotypes among aerobic pseudomonads, was subjected to this examination. The similarities and differences in the base compositions of the genetic material have been compared with the taxonomic arrangements suggested by the comparison of phenotypic (largely nutritional and enzymic) features. The data on base composition of the deoxyribonucleic acids of the various cultures support, for the greater part, the conclusions of Stanier, Palleroni and Doudoroff (1966) and of Redfearn, Palleroni and Stanier (1966). Data are also presented on pseudomonads not included in the latter studies.