The plasmids were transformed into the wildtype and strain ALSM3 to generate strains ALSM20, ALSM13, ALSM33, and ALSM34. Luciferase assay Luciferase assays were performed by withdrawing 1 ml culture. The OD600 was

measured and samples were held on ice until the start of the assay. 100 μl of each sample were mixed find more with 3× assay buffer (75 mM tricine, 15 mM MgSO4, 1.5 mM EDTA, 1.5 mM DTT, 900 μM ATP, 3 mg/ml (w/v) BSA, and 3% (w/v) D-Glucose, pH = 7.8) and incubated 10 min prior to injection of 100 μl D-luciferin (120 μM final concentration) solved in 20 mM tricine (pH 7.8). D-Luciferin (Carl-Roth, Karlsruhe, Germany) was resuspended in 20 mM tricine (pH = 7.8, 1 mg/ml), aliquoted and stored at -70°C until use. Luminescence was recorded for 35 s (POLARstar OPTIMA luminometer, BMG LABTECH) and normalized against the OD600 to calculate the relative light units (RLU). For calculation of the fold change, the RLU were normalized against the RLU of time zero. All measurements were done in triplicate. RNA extraction and quantitative real-time RT PCR S. mutans wildtype was incubated anaerobically in BM medium containing 0.5% (w/v) sucrose until early-log phase. A sample was withdrawn for time zero, transferred into the double volume of RNA-protect (Qiagen, Hilden, Germany)

Apoptosis inhibitor and centrifuged according to the manufacturer’s instructions. The cultures were split in two halves and free malic acid was added to one of them (final concentration 25 mM). After two hours samples for RNA extraction were withdrawn and treated as described above. For lysis, cells were incubated with lysozyme (2.5 mg/ml culture pellet) and mutanolysin (50 U/ml culture pellet) at room temperature for 45 min. The mixture was transferred into RLT buffer containing sterile, acid washed glass beads (diameter 106 μm) and vortexed for 3 min. Subsequent RNA extraction was carried out using the

RNeasy mini kit (Qiagen). Genomic DNA was removed using the DNAse I (Qiagen) in-solution digestion protocol. The quality of the total RNA was controlled on a denaturating formaldehyde agarose Fossariinae gel. Synthesis of cDNA was carried out using random hexamers and SuperScript II reverse transcriptase (Invitrogen, Karlsruhe, Germany), followed by purification using the PCR Purification kit (Qiagen). All reactions included a control without SuperScript II to assess genomic DNA contamination. Real-time PCR was performed using the LightCycler 480 system (Roche, Mannheim, Germany) and the reaction mixtures were prepared using the Quantitect SYBR Green PCR Kit (Qiagen). Changes in the level of gene expression were calculated automatically by the LightCylcer 480 software using the ΔΔC T method. The gyrase A gene (Smu.1114) was used as the housekeeping reference gene. All steps were performed according to the manufacturer’s protocols. All measurements were done in duplicate. Acid killing and hydrogen peroxide killing The ability of S.