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Bacterium without iron

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Lyme disease is caused by the spirochete bacterium Borrelia burgdorferi, which is transmitted to humans by tick bites. The disease is often difficult to diagnose due to vagueness of the symptoms. If not treated quickly with antibiotics the pathogen can damage the host’s central nervous and circulatory systems.

Studies in 2000 revealed that B burgdorferi possesses none of the genes required to synthesise iron-containing proteins, which make up many enzyme systems in other organisms. But until recently it was not clear exactly what the bacterium used instead of iron.

A recent study, published in the Journal of Biological Chemistry, has revealed that the bacterium substitutes manganese for iron in protein synthesis. It is the first known organism to have evolved without a requirement for iron, and it helps the pathogen to evade the host’s immune systems, which often use the tactic of starving invading organisms of iron in order to attenuate them.

The enzyme superoxide dismutase (SOD) is the key to the virulence of B burgdorferi. It is used by almost all organisms, combined with manganese, copper, iron, nickel or zinc in the form of a metalloprotein. SODs prevent the damaging effects of the superoxides that are released as by-products of intracellular respiration. In B burgdorferi the SOD causes virulence only when activated with manganese. It plays an important role in combating oxidative stress caused by the release of superoxides by the white blood cells of the host, in response to the pathogenic attack.

Manganese activation of SOD in B burgdorferi can only occur when the concentration of intracellular manganese exceeds that of iron, and the bacterium has the ability to accumulate manganese actively from its environment, but the mechanism for this process is unclear.

It is hoped that the future elucidation of this mechanism may lead to a new approach to the treatment of Lyme disease.

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