Catalyzes the attachment of the second N-acetyl-N-hydroxylysine to the carboxylic group of N-citryl-N-acetyl-N-hydroxylysine to yield aerobactin. Involved in the biosynthesis of the siderophore aerobactin which is a chelator that mediates the high-affinity iron transport systems induced under iron-stressed conditions. ATP + N(2)-citryl-N(6)-acetyl-N(6)-hydroxy-L-lysine + N(6)-acetyl-N(6)-hydroxy-L-lysine = aerobactin + AMP + diphosphate + H(+) Siderophore biosynthesis; aerobactin biosynthesis. Cells lacking this gene are not able to produce aerobactin and accumulate N-citryl-N-acetyl-N-hydroxylysine. Belongs to the IucA/IucC family.