The AsbB enzyme, which is involved in the biosynthesis of the virulence-conferring siderophorepetrobactin in Bacillus anthracis, is shown to catalyze efficient ATP-dependent condensation of spermidine, but not N¹-(3,4-dihydroxbenzoyl)-spermidine, with N⁸-citryl-spermidine or N¹-(3,4-dihydroxbenzoyl)-N⁸-citryl-spermidine, suggesting that N¹-(3,4-dihydroxbenzoyl)-spermidine is very unlikely to be a significant intermediate in petrobactinbiosynthesis, contrary to previous suggestions.