Sodium Required by some but not all microorganisms. Usually seawater organisms have a requirement but freshwater or terrestrial organisms do not. Iron Required in small amounts but still considered a macro-nutrient. Required for cytochromes and iron-sulfur proteins that are important for electron transport. Found as insoluble inorganic form in nature.
Bacteria produce siderophores to chelate insoluble iron and transport it to the cell.
Siderophores produced by Escherichia coli or S. typhimurium are called enterobactins . Micronutrients are found in your text. These are inorganic elements that are required in trace amounts by some or all bacteria for growth. Used primarily as enzyme cofactors. Includes vitamins, amino acids, purines or pyrimidines.