Identification of genes regulated by L-lactate and by DL-lactate in Lactobacillus plantarum

L. plantarum is known to possess an L-lactate inducible lactate racemase activity (Goffin et al. 2005. J. Bacteriol. 187:6750). In the present study, microarrays were used in order to identify all genes that are up-regulated by L-lactate, but not by a racemic mixture of D- and L-lactate. A mutant of L. plantarum NCIMB8826 deficient for NAD-dependent L-lactate activity (TF101; Ferain et al. 1994. 176:596), and thus producing no L-lactate, was grown in MRS medium at 28°C until mid-exponential phase (OD600nm 0.75). The culture was then divided into 3 sub-cultures. Optically pure sodium L-lactate (200 mM) was added to the first sub-culture (TF101 + L-lac 200 mM). An equimolar mixture of sodium D- and L-lactate (100 mM each) was added to the second sub-culture (TF101 + L/D-lac 200 mM). The third sub-culture was not treated (TF101; reference sample). The three sub-cultures were further incubated at 28°C for 1h30 (a time known to be sufficient for induction of lactate racemase activity by L-lactate). Cells were harvested by centrifugation. Microarray data were used ot identify genes that are specifically induced by L-lactate (comparison of TF101 with TF101 + L-lac 200 mM), but not by DL-lactate (comparison of TF101 with T101 + L/D-lac 200 mM). There are no biological replicates.