THE BEHAVIOR OF FUSOBACTERIUM-NUCLEATUM CHEMOSTAT-GROWN IN GLUCOSE-BASED AND AMINO ACID-BASED CHEMICALLY-DEFINED MEDIA

Fusobacterium nucleatum is a Gram-negative anaerobe, found in a number of different areas of human and animal bodies as part of the resident microbiota. However, it also appears to be involved in polymicrobial infections in such sites. It occurs in the oral cavity where it is a p rominent member of various bacterial consortia associated with periodo ntal diseases. Like most fusobacteria, it derives energy via the ferme ntation of amino acids which it can obtain through the dissimilation o f small peptides. However, the role of simple carbohydrates, such as g lucose, in its growth and metabolism are not well understood. Accordin gly, the aim of the present study was to study the behaviour of F. nuc leatum grown anaerobically in continuous culture in two different chem ically-defined media (CDM); one containing only amino acids as the ene rgy source, the other containing glucose as the predominant energy pro vider. At various dilution rates the culture were assayed for dry weig ht, intracellular polyglucose (IP) content, residual amino acids and g lucose and acidic metabolic end-products. Ln the carbohydrate-free CDM the acidic end-products were a constant acetate : butyrate : formate of 1.5:1:0.4. The values of Y-amino acids(max), maximum yield of bacte ria per mel of amino acids consumed, for two strains were estimated to be 15.2 and 18.6 g dry wt/mol, respectively. The m(amino acids), main tenance energy requirement for growth on amino acids, for the two stra ins was 0.81 and 0.94mmol/g dry wt/h, respectively. Growth of one stra in in the glucose-based CDM gave an estimated Y(glucose)max of 67.2 an d an m(glucose) of 0.38; the acidic end-products were a fairly constan t acetate : butyrate : formate : lactate of 0.7:1:0.3:2.5. Only at low growth rates, and then only in small amount, was LP produced in this medium. Overall, it was concluded that the occurrence of F. nucleatum in widely-differing oral niches may be explained, at least in part, by its metabolic versatility. (C) 1998 Academic Press.