Ferri-bacillibactin uptake and hydrolysis in Bacillus subtilis

Mol Microbiol. 2006 Sep;61(6):1413-27. doi: 10.1111/j.1365-2958.2006.05321.x. Epub 2006 Aug 3.


Upon iron limitation, Bacillus subtilis secretes the catecholic trilactone (2,3-dihydroxybenzoate-glycine-threonine)3 siderophore bacillibactin (BB) for ferric iron scavenging. Here, we show that ferri-BB uptake is mediated by the FeuABC transporter and that YuiI, a novel trilactone hydrolase, catalyses ferri-BB hydrolysis leading to cytosolic iron release. Among several Fur-regulated ABC transport mutants, only DeltafeuABC exhibited impaired growth during iron starvation. Quantification of intra- and extracellular (ferri)-BB in iron-depleted DeltafeuABC cultures revealed a fourfold increase of the extracellular siderophore concentration, confirming a blocked ferri-BB uptake in the absence of FeuABC. Ferri-BB was found to bind selectively to the periplasmic binding protein FeuA (Kd = 57 +/- 1 nM), proving high-affinity transport of the iron-charged siderophore. During iron starvation, a DeltayuiI mutant displayed impaired growth and strong intracellular (30-fold) and extracellular (6.5-fold) (ferri)-BB accumulation. Kinetic studies in vitro revealed that YuiI hydrolyses both BB and ferri-BB. While BB hydrolysis led to strong accumulation of the tri- and dimeric reaction intermediates, ferri-BB hydrolysis yielded exclusively the monomeric reaction product and occurred with a 25-fold higher catalytic efficiency than BB single hydrolysis. Thus, ferri-BB was the preferred substrate of the YuiI esterase whose gene locus was designated besA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / genetics
  • ATP-Binding Cassette Transporters / metabolism*
  • Bacillus subtilis / enzymology
  • Bacillus subtilis / metabolism*
  • Esterases / genetics
  • Esterases / metabolism
  • Esters / metabolism*
  • Gene Deletion
  • Hydrolysis
  • Iron / metabolism*
  • Iron Chelating Agents / metabolism*
  • Oligopeptides / metabolism*


  • ATP-Binding Cassette Transporters
  • Esters
  • Iron Chelating Agents
  • Oligopeptides
  • bacillibactin
  • Iron
  • Esterases