Deoxyribonucleic Acid Type attributable to a Bacterial Endosymbiote in the Protozoon Crithidia (Strigomonas) oncopelti

Abstract

IN the course of an investigation of the occurrence of two paths of lysine biosynthesis^1,2, tracer and enzyme experiments provided evidence that the trypanosomatid flagellate, Crithidia (Strigomonas, Herpetomonas) oncopelti, contains a bacterial endosymbiote^3,4. This evidence was supported by electron microscopy : the inferred endosymbiote shows structures consistent with a cytoplasmic membrane, a cell wall, and nuclear zones, and endosymbiotes which are dividing, as judged by the presence of a constriction, exhibit membrane septa^4,5. The protozoon can be ‘cured’ of its endosymbiote with penicillin^4,5. It was suggested that the endosymbiote furnishes lysine and probably other metabolites to the protozoon, which in turn provides a protective environment for the endosymbiote^3,4. This suggestion took into account: (a) the exceptionally simple nutritional requirements of the protozoon, which were recorded by Newton⁶; (b) the presence of ‘bipolar bodies’ within the protozoon, which were described by Newton and Horne⁷ and afterwards recognized as the endosymbiote^3,4. Attempts to demonstrate deoxyribonucleic acid (DNA) in the bipolar bodies had given inconclusive results⁷.