Question

Iron, despite its abundance in the environment as Fe(OH)₃, is often a limiting growth factor. Very briefly, how can organisms overcome this problem?

Answer 1

Iron exists in both ferrous (Fe2+) and ferric (Fe3+) oxidation states and this property confers on it the ability to act as a catalyst in biological systems.
The bacteria and indeed all living cells must use special mechanisms in order to solubilize and assimilate this iron. These methods must be efficient enough to compete against other microorganisms in the same environment. In the case of pathogenic bacteria the situation is further complicated because these bacteria must acquire iron from the host in which it is usually tightly bound in such complexes as transferrin, lactoferrin or haemoglobin. In many cases the efficiency of iron acquisition by the bacteria under these circumstances can be important in determining their pathogenicity. Organisms secreting high affinity iron-binding compounds which can sequester iron from their host transferrin and other iron proteins are obviously at an advantage.