Fig. 1

Growth and survival kinetics of the alanine racemase mutants in vitro. a Growth curve of SEN ∆alr, SEN ∆dadX, SEN ∆3897, WT Salmonella Enteritidis in LB. b Growth curve of wild-type Salmonella and alr dadX double mutant in liquid culture with d-alanine supplementation (5, 10, and 50 µg/ml). Growth was measured by monitoring the OD at 600 nm. c Fluorescence microscopy images of d-alanine starvation on cell wall integrity of alr dadX double mutant and WT at 1 and 10 h time-points through DAPI/PI dual staining. d Scanning electron microscopy images of WT and alr dadX double mutant under limited and optimum d-alanine concentration (5, 10 and 50 µg/ml) for observing the morphological changes at 1 h and 10 h time-points. Arrows indicate morphological alterations on cell surface due to d-alanine starvation. Data represent the average of three independent determinations. Scale: 1 µm (1 h time-points), scale: 200 nm (10 h time-points)