A Bacterial Endosymbiote inCrithidia (Strigomonas) oncopelti:Biochemical and Morphological Aspects*

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Abstract
SYNOPSIS.It is concluded that the trypanosomatid flagellate,Crithidia (Strigomonas, Herpetomonas, Lepiomonas) oncopelti, contains a bacterial endosymbiote, which provides the protozoon with biosynthetic capabilities and, hence, with a measure of nutritional independence; the protozoon in turn gives the endosymbiote the protection of an intracellular environment. Tracer experiments show thatC. oncopeltihas the “bacterial” kind of lysine pathway (via α,ε‐diaminopimelic acid). Diaminopimelic decarboxylase, the last enzyme in this pathway, is associated with the endosymbiote. Electron micrographs of the endosymbiote reveal structures consistent with a cytoplasmic membrane and a cell wall. Endosymbiotes that are dividing, as judged by the presence of a constriction, exhibit membrane septa. Additionally, there are zones that are interpreted as representing nuclear material. The protozoon is “cured” of the endosymbiote by treatment with penicillin in a complex medium. The absence of the endosymbiote from “cured” protozoa can be checked with a staining method that permits the reliable detection of the endosymbiote in untreated protozoa.