l-glutamate transport in Lactobacillus helveticus

Glutamate uptake in Lactobacillus delbrueckii subsp. bulgaricus CNRZ 208 and its enhancement by a combination of Mn2+ and Mg2+

AIMS

To demonstrate the mechanism of glutamate uptake in the dairy strain Lactobacillus delbrueckii subsp. bulgaricus CNRZ 208, and to characterize key aspects of the system.

METHODS AND RESULTS

Glutamate uptake proceeded via an active transport system requiring an exogenous source of energy. The system also transported aspartate and glutamine. It was unique, with a Kt of 2.8 micro mol l-1 and a Vmax of 900 micro mol s-1 (g dry weight)-1. The activity was optimal at pH 7.3 and 50 degrees C, was independent of the glutamate charge, and was enhanced by Mn2+ + Mg2+ in combination. Inhibition of the activity by uncouplers and ionophores showed that transport was driven by an ATP-dependent mechanism involving the proton-motive force. This inhibition was partially abolished in the presence of both Mn2+ and Mg2+.

CONCLUSIONS

We demonstrated for the first time that an active transport system governs the uptake of the essential amino acid glutamate in Lact. delbrueckii subsp. bulgaricus CNRZ 208, the activity of which is enhanced by a combination of Mn2+ and Mg2+.

SIGNIFICANCE AND IMPACT OF THE STUDY

The potential of the findings is discussed with reference to the growth of Lact. delbrueckii subsp. bulgaricus in mixed-strain cultures for the dairy industry.