Identification of suppressor mutantsĀ 
To screen for spontaneous mutations, the lpdA mutant was streaked from frozen stocks on TSA plate supplemented with a mixture of the branched-chain carboxylic acids a C5, i C5, and i C4. Independent colonies were then grown overnight in borosilicate glass tubes containing TSB supplemented with the mixture of the branched-chain carboxylic acids. A double-back dilution was performed in unsupplemented medium, and once cells reached an OD600 of 0.1 (growth arrest) they were serial diluted, plated on TSA without supplementation, and incubated at 37oC. Colonies (one per liquid culture) were picked, restreaked, and growth in the absence of carboxylic acids was confirmed. Following confirmation, gDNAs were purified and submitted for whole genome sequencing as a fee for service at SeqCenter. Analysis of spontaneous mutations was performed using BRESEQ software (Barrick et al., 2009).