A novel two‐gene requirement for the octanoyltransfer reaction of Bacillus subtilis lipoic acid biosynthesis

Abstract

The Bacillus subtilis genome encodes three apparentlipoyl ligase homologues: yhfJ, yqhM and ywfL,which we have renamed lplJ, lipM and lipLrespectively. We show that LplJ encodes the solelipoyl ligase of this bacterium. Physiological and biochemicalcharacterization of a DlipM strain showedthat LipM is absolutely required for the endogenouslipoylation of all lipoate-dependent proteins, confirmingits role as the B. subtilis octanoyltransferase.However, we also report that in contrast to Escherichiacoli, B. subtilis requires a third protein forlipoic acid assembly, LipL. B. subtilis DlipL strains areunable to synthesize lipoic acid despite the presenceof LipM and the sulphur insertion enzyme, LipA,which should suffice for lipoic acid biosynthesisbased on the E. coli model. LipM is only required forthe endogenous lipoylation pathway, whereas LipLalso plays a role in lipoic acid scavenging. Expressionof E. coli lipB allows growth of B. subtilis DlipL orDlipM strains in the absence of supplements. In contrast,growth of an E. coli DlipB strain can be complementedwith lipM, but not lipL. These data togetherwith those of the companion article provide evidencethat LipM and LipL catalyse sequential reactions in anovel pathway for lipoic acid biosynthesis.