Conditions required for citrate utilization during growth of Lactobacillus casei ATCC334 in chemically defined medium and cheddar cheese extract.

Conditions required for citrate utilization by Lactobacillus casei ATCC334 were identified. Citrate was utilized by this microorganism in modified Chemically Defined Media (mCDM) as an energy source, solely in the presence of limiting concentrations of galactose. The presence of glucose inhibited citrate utilization by this microorganism even when added in limiting concentrations. Utilization of citrate occurred at pH 6.0 +/- 0.2 and 5.1 +/- 0.2. Together these observations suggest that citrate is an energy source for L. casei in ripening cheese only when the residual levels of carbohydrate post-fermentation are limiting (<2.5 mM), and lactose or glucose are absent. However, citrate utilization by this organism was observed in Cheddar cheese extract (CCE), which naturally contains both lactose and galactose, at the beginning of late-logarithmic phase and regardless of the galactose concentration present in the media.