Bacteria may be tiny little micro-organisms but like any other living creature there are certain molecules that they need for survival. No matter what niche a bacterial colony occupies, it eventually requires a source of iron. For bacteria that live within the human body, there is one incredibly iron-rich molecule that circulates throughout the human body and can be found permeating the tissues.
Haemoglobin – the molecule that gives blood its red colour and is used to transport oxgyen through the body.
The image above shows the structure of the haemoglobin molecule. It consists of four sub-chains (shown in red and blue) each of which carries an iron containing “haem co-factor” which you can just about see in the diagram as the spikey green things. These haemoglobin molecules are packed tight into red blood cells, so tightly that the red blood cells don’t even have a nucleus but are just haemoglobin carrying machines. The lack of nucleus means that they can’t grown or divide (or do anything much), so after being put together in the bone marrow and circulating the blood for around three months red blood cells are discreetly removed and replaced.