Requires Mg2+. The enzyme, characterized from the bacterium Staphylococcus aureus, is involved in the biosynthesis of the siderophore staphyloferrin B. It belongs to a class of siderophore synthases known as type A nonribosomal peptide synthase-independent synthases (NIS). Type A NIS enzymes are responsible for the formation of amide or ester bonds between polyamines or amino alcohols and a prochiral carboxyl group of citrate. The enzyme forms a citrate adenylate intermediate prior to ligation.