How do bacteria get iron from humans?

Like humans, bacteria need iron to survive and they must also take iron from their environment. While humans take iron primarily through food, bacteria evolve complex and diverse mechanisms that allow them to obtain iron.

A research group at Syracuse University under Robert Doyle - assistant professor of chemistry at the University of Science and Arts - discovered that some bacteria are equipped with genes that facilitate them. 'harvesting' iron from the environment or from the host is human in an effective and unique way. Doyle's discovery could provide researchers with new pathways to diseases like tuberculosis. The study will be published in the August issue of the prestigious Journal of Bacteriology published by the American Society for Microbiology.

Doyle said: 'The most important iron and micronutrients that bacteria need to survive. Understanding how bacteria grow in our bodies is an essential element in finding ways to eliminate them. '

Doyle's team investigated Streptomyces coelicolor - a positive gram-positive bacterium that is closely related to tuberculosis-causing bacteria. Streptomyces coelicolor occurs abundantly in soil and in rotten vegetables, but they do not harm humans. TB bacteria and Streptomyces belong to the family of bacteria called Actinomycetes. They have a unique defense mechanism that facilitates them to produce chemicals to kill the enemy. Some of these substances are used to produce antibodies as well as other drugs.

Streptomyces coelicolor bacteria.(Photo: template.bio.warwick.ac.uk)

Actinomycetes need a lot of iron to be able to carry out chemical warfare with the enemy, but getting iron from the environment in which they live, such as humans or rock, is not an easy task.Iron can combine with the salt of citric acid (citrate) in rock, forming a compound called iron - citrate. Citrate salt is a compound used by cells as a source of energy. Doyle and his team question whether iron compounds - citrate can be a source of iron for bacteria. Through many experiments conducted during the 2-year period, the researchers observed that Streptomyces can eat iron - citrate, iron conversion and use of citric acid salt as a source and free energy. Other experiments have also demonstrated that bacteria ignore citrate when it does not bind to iron. Similarly, bacteria do not care about citrate when it binds to other metals such as magnesium, nickel or cobalt.

The next step of the study is to find a mechanism to promote bacteria to eat iron salts - citrate. The computer model predicts that a gene of Streptomyces allows it to identify and eat iron compounds - citrate. The researchers isolated the gene and inserted it into E. coli (not belonging to the Actinomycete family). They found that mutant E. coli could also eat iron compounds - citrate. Without this gene, E. coli cannot get iron.

Doyle said: 'It's amazing that bacteria can learn how to purify iron from the environment in this way. We did the experiment but did not think that a mechanism like this existed. But bacteria must be creative to survive in extreme environments. Perhaps they had 3.5 billion years to find that mechanism. '

The Streptomyces gene allows bacteria to passively diffuse iron compounds - citrate through cell membranes , which means bacteria do not need to consume additional energy to get iron. Once iron is in the cell, bacteria metabolize iron. Citrate salt as a marginal reward is used as an energy source. Doyle's team is the first group to discover the mechanism of the Actinomycete family. The team is expected to conduct additional tests to confirm that the Streptomyces gene also performs the same function against tuberculosis-causing bacteria. If so, the mechanism could be exploited for the fight against tuberculosis.

Doyle said: 'TB bacteria can access iron supplies - a long-lasting citrate in the blood through the lungs. Finding a way to 'steal' iron from humans without losing energy is actually very effective for bacteria. "Our findings may allow other researchers to find a way to limit exposure to iron-citrate of TB, which causes drugs to kill bacteria that are more effective."