Methionine can affect but not bypass essentiality of upstream folate biosynthetic pathways in M. tuberculosis . (A) New working model of methionine-mediated PAS antagonism. (B) M. tuberculosis Δ pabB was grown to an OD 600 of ~0.5, washed three times with PABA-free 7H9 medium to remove residual PABA and resuspended in PABA-free 7H9 medium to a starting OD 600 of 0.01. Cultures were then supplemented with the indicated metabolites and incubated for 14 days with OD 600 readings taken at the given time points.
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