The physiological and metabolic characteristics of representative isol
ates of the various subspecies of Fusobacterium nucleatum were investi
gated by growing them in continuous culture in chemically-defined medi
a. Behaving almost identically, these organisms were found to obtain e
nergy from the fermentation of simple carbohydrates such as glucose or
fructose or from the fermentation of certain amino acids, free or in
the form of small peptides. The latter can be attacked by aminopeptida
se activity which was shown to be essential for the growth of the orga
nism in an environment lacking fermentable carbohydrate and free amino
acids but replete with small peptides. This metabolic versatility may
explain the presence of F. nucleatum in both supra- and sub-gingival
dental plaque and why it is often found together with organisms such a
s Porphyromonas gingivalis which display powerful endopeptidase activi
ties. Using the technique of allozyme electrophoresis, the current sub
speciation of F. nucleatum was shown to be of doubtful validity and ev
idence, based upon physiological and metabolic properties, for differe
nces in pathogenicity between isolates was not detected. While this or
ganism is a member of various bacterial consortia associated with peri
odontal diseases, its contribution to the disease process remains uncl
ear.