Bacteria respond to changing environments by modulating their gene expression programs. One of the mechanisms by which this may be accomplished is by substituting the primary σ factor with an alternative σ factor belonging to the family of extracytoplasmic function (ECF) σ factors. ECF σ factors are activated only in presence of specific signals, and they direct the
RNA polymerase (RNAP) to transcribe a defined subset of genes. One condition, which may trigger the activation of an ECF σ factor, is
iron limitation. To overcome
iron starvation, bacteria produce and secrete
siderophores, which chelate
iron and facilitate its cellular uptake. In the genus Burkholderia, which includes several serious human pathogens, uptake of
iron is critical for virulence, and expression of biosynthetic gene clusters encoding
proteins involved in synthesis and transport of the primary
siderophores are under control of an ECF σ factor. This review summarizes mechanisms involved in regulation of these gene clusters, including the role of global transcriptional regulators. Since
siderophore-mediated
iron acquisition is important for virulence, interference with this process constitutes a viable approach to the treatment of
bacterial infections.