(A) Model of the lipoic acid biosynthesis and salvage pathways in S. aureus. S. aureus synthesizes lipoic acid via de novo biosynthesis using the enzymes LipM- octanoyl transferase; LipA – lipoyl synthethase; and LipL – amidotransferase. During lipoic acid salvage, S. aureus is thought to use two lipoic acid ligases, LplA1 and LplA2. Current evidence suggests LplA1 lipoylates GcvH, while LplA2 lipoylates the GcvH-Like protein, GcvH-L. (B–D) Growth (OD550) of the indicated lipoic acid auxotrophs in (B) RPMI, (C) RPMI + 25 μM octanoic acid (OA), and (D) RPMI + 5 μM lipoic acid (LA). Strain designations are as follows: Wildtype (WT), ΔlipA ΔlplA1 (ΔA ΔA1), ΔlipA ΔlplA2 (ΔA ΔA2), ΔlipA ΔlplA1 ΔlplA2 (ΔA ΔA1 ΔA2), ΔlipA ΔlplA1 ΔlplA2 + lplA1 (ΔA ΔA1 ΔA2 + A1), and ΔlipA ΔlplA1 ΔlplA2 + lplA2 (ΔA ΔA1 ΔA2 + A2).