Iron-responsive regulators (Irr): Irr proteins are transcriptional regulators that control the expression of genes involved in iron uptake and utilization. When iron levels are low, Irr proteins bind to specific DNA sequences and activate the transcription of these genes.
Fur (ferric uptake regulator): Fur is a transcriptional repressor that controls the expression of genes involved in iron uptake and utilization. When iron levels are high, Fur binds to specific DNA sequences and represses the transcription of these genes.
Siderophores: Siderophores are small molecules that are produced by bacteria to chelate and transport iron. Siderophores are secreted into the environment, where they bind to iron and form complexes that can be taken up by the bacteria.
Fe-S clusters: Fe-S clusters are small iron-sulfur cofactors that are essential for the activity of many enzymes. When iron levels are low, the synthesis of Fe-S clusters is decreased, which can lead to the inhibition of enzymes that require these cofactors.
Heme: Heme is an iron-containing porphyrin that is essential for the activity of many enzymes, including cytochromes and peroxidases. When iron levels are low, the synthesis of heme is decreased, which can lead to the inhibition of enzymes that require this cofactor.
ROS (reactive oxygen species): Iron can also be sensed by bacteria through the production of reactive oxygen species (ROS). ROS are produced by the Fenton reaction, which occurs when iron reacts with hydrogen peroxide. ROS can damage DNA, proteins, and lipids, and can lead to cell death. Bacteria can use the production of ROS to sense iron levels and regulate the expression of genes involved in iron uptake and utilization.
These are just a few of the mechanisms that nitrogen-fixing bacteria use to sense iron. By sensing iron levels, bacteria can regulate the expression of genes involved in iron uptake and utilization, and ensure that they have sufficient iron to meet their metabolic needs.
