Cross-feeding assay
Single colonies of S. epidermidis 1457 were inoculated into sterile, 16x125 mm borosilicate glass tubes containing 2 ml of CDM. Cells were grown to stationary phase overnight. The liquid culture was centrifuged at 5450 x g for 15 minutes and the supernatant was filter-sterilized using 0.45 µm membranes (Avantor Sciences) to prepare conditioned medium. A single colony each of S. aureus WT,lpdA single mutant, and lpdA mbcS double mutant cells was inoculated to OD600 0.05 in CDM, CDM supplemented with either 0.5 mM short branched-chain carboxylic acids ora 17:0 branched-chain fatty acid (Sigma-Aldrich), or decreasing concentrations of conditioned medium as indicated in Fig 7. Cells were grown to stationary phase overnight and OD600 was measured using Amersham Ultraspec 2100 Pro UV-visible spectrophotometer.