(S)-Malic acid ((S)-2-Hydroxysuccinic acid) is a dicarboxylic acid in naturally occurring form, contributes to the pleasantly sour taste of fruits and is used as a food additive.In Vitro: It is showed that ME is essential for (S)-2-Hydroxysuccinic acid (L-malic acid) utilization in L. casei. Furthermore, deletion of either the gene encoding the histidine kinase or the response regulator of the TC system resulted in the loss of the ability to grow on (S)-2-Hydroxysuccinic acid, thus indicating that the cognate TC system regulates and is essential for the expression of ME. Transcriptional analyses shows that expression of maeE is induced in the presence of (S)-2-Hydroxysuccinic acid and repressed by glucose, whereas TC system expression is induced by (S)-2-Hydroxysuccinic acid and is not repressed by glucose.