Involved in the biosynthesis of petrobactin, a catecholate siderophore that functions in both iron acquisition and virulence (PubMed:17189355, PubMed:17346033, PubMed:22408253). Transfers the activated 3,4-dihydroxybenzoate (3,4-DHBA) moiety from 3,4-DHBA-loaded AsbD to different receipient molecules, including N-citryl-spermidine, N8,N'8-citryl-bis(spermidine) and N1-(3,4-dihydroxybenzoyl)-N8,N'8-citryl-bis(spermidine) (PubMed:22408253). Also catalyzes the transfer of the activated 3,4-DHBA moiety from 3,4-DHBA-loaded AsbD to spermidine to generate DHB-spermidine (DHB-SP) (PubMed:17346033). 3,4-dihydroxybenzoyl-[aryl-carrier protein] + N(8)-citryl-spermidine = H(+) + holo-[aryl-carrier protein] + N(1)-(3,4-dihydroxybenzoyl)-N(8)-citryl-spermidine 3,4-dihydroxybenzoyl-[aryl-carrier protein] + N(8),N'(8)-citryl-bis(spermidine) = H(+) + holo-[aryl-carrier protein] + N(1)-(3,4-dihydroxybenzoyl)-N(8),N'(8)-citryl-bis(spermidine) 3,4-dihydroxybenzoyl-[aryl-carrier protein] + N(1)-(3,4-dihydroxybenzoyl)-N(8),N'(8)-citryl-bis(spermidine) = H(+) + holo-[aryl-carrier protein] + petrobactin Siderophore biosynthesis; petrobactin biosynthesis. The deletion mutant cannot produce petrobactin on iron-depleted medium. In vitro analysis show that mutants grow to a very limited extent as vegetative cells in iron-depleted medium but are not able to outgrow from spores under the same culture conditions.