Catalyzes both the ATP-dependent activation of exogenously supplied lipoate to lipoyl-AMP and the transfer of the activated lipoyl onto the lipoyl domains of lipoate-dependent enzymes. Is also able to use octanoate as substrate. (R)-lipoate + ATP + L-lysyl-[lipoyl-carrier protein] = (R)-N(6)-lipoyl-L-lysyl-[lipoyl-carrier protein] + AMP + diphosphate + H(+) Protein modification; protein lipoylation via exogenous pathway; protein N(6)-(lipoyl)lysine from lipoate: step 1/2. Protein modification; protein lipoylation via exogenous pathway; protein N(6)-(lipoyl)lysine from lipoate: step 2/2. Cells lacking this gene grow normally in minimal medium in the absence of supplements and have a wild-type pattern of lipoylated proteins. However, a double mutant strain lacking both lplJ and lipM is unable to grow in minimal medium either in the presence or in the absence of lipoic acid, indicating that LplJ is the sole B.subtilis lipoic acid salvage enzyme. In the transfer reaction, the free carboxyl group of lipoic acid is attached via an amide linkage to the epsilon-amino group of a specific lysine residue of lipoyl domains of lipoate-dependent enzymes. Belongs to the LplA family.