FIG 10.

Role of catechol detoxification in bacillibactin metabolism. The endogenous siderophore bacillibactin (BB) is synthesized by an NRPS (nonribosomal peptide synthetase) assembly system (DhbACEBF) (28) and secreted by a major facilitator superfamily transporter YmfD, which is under regulation of the transcriptional activator Mta, a MerR family regulator of the multidrug-efflux transporter system (29). Bacillibactin chelates iron with very high affinity, and the resulting ferric-bacillibactin complex is then imported back into the cytosol through the FeuABC-YusV system and hydrolyzed by the BesA esterase to release iron (30), which yields three bacillibactin monomers (2,3-dihydroxybenzoate-Gly-Thr). It is still unknown whether or how the bacillibactin monomer is further processed. Nonetheless, it is clear that the bacillibactin monomer and perhaps bacillibactin-derived catechol compounds require CatDE for detoxification during metabolism.