Bacterial strains, growth media, and culture conditions
Strains used in the present study are listed in Table S1 . To routinely cultivate S. aureus strains, tryptic soy broth (TSB) containing 0.25% (wt/vol) dextrose (BD Biosciences) or complete chemically defined medium (CDM, pH 6.5) were used (Sheldon et al., 2014). Briefly, CDM medium was formulated with alanine (672 μM), arginine (287 μM), aspartic acid (684 μM), cysteine (166 μM), glutamic acid (680 μM), glycine (670 μM), histidine (129 μM), isoleucine (228 μM), leucine (684 μM), lysine (342 μM), methionine (20 μM), phenylalanine (240 μM), proline (690 μM), serine (285 μM), threonine (260 μM), tryptophan (50 μM), tyrosine (275 μM), valine (684 μM), thiamine (56 μM), nicotinic acid (10 μM), biotin (0.04 μM), pantothenic acid (2.3 μM), MgCl2 (1,000 μM), CaCl2(100 μM), monopotassium phosphate (40,000 μM), dipotassium phosphate (14,700 μM), sodium citrate dehydrate (1,400 μM), magnesium sulfate (400 μM), ammonium sulfate (7,600 μM), and glucose (27,753 μM). Blood agar plates were used to propagate the lpdA mbcS double mutant and its derivatives to mitigate the severe growth defect on TSB.Escherichia coli strains were grown in lysogeny broth (LB) medium without glucose (10 g L-1 tryptone, 5 g L-1 yeast extract, and 10 g L-1sodium chloride) (Bertani, 1951). When necessary, media were solidified with agar at 1.5% [w/v] and supplemented  with  antibiotics  at  the  following  concentrations  to maintain selection: ampicillin (Ap) 100 μg ml-1, chloramphenicol (Cm) 10 μg ml-1, erythromycin (Em) 10 μg ml-1, kanamycin (Km) 100 μg ml-1 or tetracycline  (Tc) 1.5 μg ml-1. When required, media were supplemented with the short branched-chain carboxylic acidsi C4, i C5, anda C5 (Sigma-Aldrich), with the branched-chain fatty acids a 15:0 (Avanti Polar Lipids) and a 17:0 (Sigma-Aldrich), or with the branched-chain aldehyde 2-methylbutyraldehyde (Sigma-Aldrich) to a final concentration of 0.5 mM. For genetic complementation, TSB was supplemented with 50 ng ml-1 anhydrotetracycline (aTc). Unless otherwise noted, all strains were grown at 37oC. A double-back dilution scheme was used to grow cells for growth curves and GC-FAME analysis to ensure steady-state growth. Briefly, for growth curve experiments, overnight cultures were used to inoculate precultures in disposable 16x125 mm borosilicate glass tubes (Fisher Scientific) to an optical density at 600 nm (OD600) of 0.05 and incubated with rotation. Cell growth was monitored by measuring OD600 using an Amersham Ultraspec 2100 Pro UV-visible spectrophotometer. After streaking from frozen stocks, overnight cultures were inoculated from single colonies and were used to initiate pre-cultures that were grown to exponential phase to an OD600 of 1.0 and diluted into fresh TSB to an OD600 of 0.05 and continued to grow. Exponential-phase samples were collected at an OD600 of 0.5±0.2. Samples were inoculated into a fresh medium in a 96-well plate to an OD600 of 0.05 and cell density was monitored over time in a computer-controlled Synergy H1 plate reader (BioTek/Agilent) running Gen5 software ver3.14. Cells for GC-FAME analysis were grown following the same scheme as above but in 125-mL DeLong shake flasks with 12.5 mL TSB (10:1 flask/medium ratio) and incubated in a gyratory water bath shaking. Exponential-phase samples were collected at an OD600 of 0.5 ± 0.1. Cells were grown to stationary phase in disposable borosilicate glass tubes for reporter and chemical complementation assays.