Ferri-bacillibactin uptake and hydrolysis in Bacillus subtilis

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Bacillus subtilis requires iron for growth and utilizes siderophores for iron acquisition.
• Bacillibactin (BB) is a secreted siderophore that chelates ferric iron.
• Iron uptake mechanisms are crucial for bacterial survival under iron-limiting conditions.

Purpose of the Study:

• To elucidate the transport mechanism of iron-loaded bacillibactin (ferri-BB) in Bacillus subtilis.
• To identify and characterize the enzyme responsible for ferri-BB hydrolysis and iron release.
• To understand the role of these components in bacterial iron homeostasis.

Main Methods:

• Construction and analysis of Bacillus subtilis mutants (e.g., DeltafeuABC, DeltayuiI).
• Quantification of intra- and extracellular siderophore concentrations.
• Biochemical assays to determine enzyme kinetics and substrate specificity (in vitro hydrolysis).
• Characterization of protein-ligand interactions (FeuA binding affinity).

Main Results:

• The FeuABC transporter is essential for ferri-BB uptake, as evidenced by impaired growth and siderophore accumulation in DeltafeuABC mutants.
• Ferri-BB binds with high affinity to the periplasmic binding protein FeuA.
• The novel hydrolase YuiI (BesA) catalyzes ferri-BB hydrolysis, releasing iron and showing higher efficiency with ferri-BB than with BB.
• DeltayuiI mutants exhibit impaired growth and significant accumulation of ferri-BB.

Conclusions:

• FeuABC mediates high-affinity uptake of ferri-BB in Bacillus subtilis.
• YuiI (BesA) is a crucial esterase for releasing iron from ferri-BB intracellularly.
• The identified pathway highlights a novel mechanism for bacterial iron acquisition and utilization.