Deoxyribonucleic acid base composition and taxonomy of some protozoa

THE characteristics by which organisms are recognized are the expressions of the information contained in their nucleic acids. As such, a knowledge of their DNA base composition, or if possible the base sequences of some organisms, should be a valuable asset in their classification. Lee, Wahl and Barbu¹were the first to recognize the taxonomic importance of analysing the average DNA base compositions of micro-organisms. While the overall base compositions of some unrelated organisms may be the same, this equivalence would appear to be a minimum requirement for extensive base sequence homologies²and genetic compatibility (except in certain cases of F-duction³). Thus, similar DNA base compositions in two organisms might indicate close relationships whereas dissimilar base compositions would indicate that the organisms are unrelated.