Genome-Wide Search for Genes Required for Bifidobacterial Growth under Iron-Limitation

Area of Science:

• Microbiology
• Bacterial Physiology
• Molecular Biology

Background:

• Iron is a vital micronutrient essential for bacterial survival and cellular processes.
• Bacteria have evolved diverse mechanisms to acquire iron from their environment.
• Understanding iron acquisition is critical for bacterial health and pathogenesis.

Purpose of the Study:

• To identify genes and mechanisms essential for Bifidobacterium breve UCC2003 survival under iron-restrictive conditions.
• To characterize novel iron uptake systems in B. breve.
• To investigate the regulation and function of identified iron transport systems.

Main Methods:

• Random mutagenesis and global gene expression profiling were employed.
• Identification and characterization of essential genes under iron limitation.
• Analysis of gene clusters encoding putative iron uptake systems (bfeUO and sifABCDE).
• Transcriptional studies to determine gene regulation.

Main Results:

• Several genes essential for iron-restrictive survival were identified, including those for Fe-S clusters, ferric reductase, cell wall proteins, and DNA repair.
• Two novel iron uptake systems, bfeUO and sifABCDE, were characterized.
• sifABCDE is involved in ferrous iron transport, while bfeUO transports both ferrous and ferric iron.
• Both bfeUO and sifABCDE are separate transcriptional units induced by iron limitation.

Conclusions:

• Bifidobacterium breve UCC2003 possesses distinct iron uptake systems (bfeUO and sifABCDE) to scavenge both ferrous and ferric iron.
• These systems are regulated by iron availability and are crucial for bacterial survival in iron-poor environments.
• While sifABCDE is important for iron acquisition, its mutation did not impact gut colonization in a murine model, suggesting alternative colonization strategies or redundant mechanisms.