Growth pH and transient increases in amino acid availability influence polyglucose synthesis by Fusobacterium nucleatum grown in continuous culture.

Fusobacterium nucleatum is a Gram-negative anaerobe that has been implicated in the aetiology of several diseases including periodontal diseases. Like other fusobacteria, it derives energy from the fermentation of amino acids and, in resting (non-growing) cells, this enables the organism to transport glucose and synthesise intracellular polyglucose (IP). The continued availability and fermentation of amino acids inhibits IP breakdown. We have grown F. nucleatum in continuous culture in a chemically defined medium under amino acid limitation and determined the fate of glucose during growth at steady state and during transient increases in the concentration (pulses) of serine and glutamate. When grown under steady state conditions, IP synthesis dramatically increased at culture pH values of 6.1 and 7.8 and appeared to be a result of cell stress. IP synthesis also increased when the culture was pulsed with serine or glutamate but was rapidly metabolised as the added amino acids were depleted. These results may help to explain the role of IP synthesis in response to environmental stress.