Mutations affecting iron transport in Escherichia coli

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Physiology

Background:

• Iron is essential for bacterial growth and survival.
• Enterochelin is a siderophore used by many bacteria, including Escherichia coli, for iron acquisition.
• Iron transport systems are crucial for bacterial adaptation to iron-limited environments.

Purpose of the Study:

• To isolate and characterize a mutant of Escherichia coli K-12 with defects in the enterochelin-dependent iron transport system.
• To investigate the genetic basis of the observed iron transport defect.
• To explore the functional implications of the mutation on bacterial iron uptake and growth.

Main Methods:

• Isolation and genetic analysis of a mutant strain (AN102) with impaired enterochelin-dependent iron transport.
• Gene mapping to identify the mutated gene (fep) and its location relative to enterochelin synthesis genes (entA, entD).
• Biochemical assays including measurement of enterochelin accumulation, cytochrome b(1) content, total iron content, and (55)Fe(3+) uptake to assess iron transport efficiency.

Main Results:

• A mutant strain, AN102, carrying the fep(-) allele was isolated, exhibiting an inability to form a component of the enterochelin-dependent iron transport system.
• The fep gene was mapped near entA and entD, genes involved in enterochelin synthesis.
• Strain AN102 accumulated high levels of enterochelin and demonstrated impaired (55)Fe(3+) uptake, confirming a defective enterochelin-dependent iron transport system.
• The mutant strain showed a growth response to sodium citrate, indicating the presence of an inducible citrate-dependent iron transport system.

Conclusions:

• The fep mutation disrupts the enterochelin-dependent iron transport pathway in Escherichia coli K-12.
• Escherichia coli possesses an inducible citrate-dependent iron transport system that can compensate for defects in enterochelin-mediated iron uptake.
• This study elucidates the genetic and functional aspects of bacterial iron acquisition, highlighting the complexity and adaptability of microbial iron metabolism.