Catalyzes the dehydrogenation at the alpha-beta position of ACP-bound acyl chains. This results in the introduction of a double bond in the lipidic chain, which is further transferred to the epsilon-amino group of lysine residue in the mycobactin core by MbtK. Siderophore biosynthesis; mycobactin biosynthesis. Induced by iron starvation conditions. Transcriptionally repressed by IdeR and iron. Belongs to the acyl-CoA dehydrogenase family.