Chemists at the University of Basel have been able to show for the first time that anaerobic bacteria can produce the vitamin ergothioneine in the absence of oxygen. This suggests that bacteria were forming this compound even before there was oxygen in the Earth's atmosphere. The vitamin's function therefore remains a mystery, as it was previously ascribed a role in oxygen-dependent processes.
Ergothioneine is a sulfur-containing vitamin. Whereas bacteria and fungi can produce it themselves, higher organisms rely on absorbing it from food or from the ground.
It is suspected that ergothioneine plays an important physiological role in combating oxidative stress in cells. However, its precise role remains unclear. There are currently no known symptoms of its deficiency, which explains why the vitamin has long been overlooked.
To gain a better understanding of its function, the group led by Professor Florian Seebeck at the University of Basel's Department of Chemistry is researching the sequence of chemical reactions by which bacteria produce the vitamin.
Scientists have long been aware of an oxygen-dependent reaction pathway in which a key step is the formation of a carbon–sulfur bond using oxygen from the air. Until now, however, studies had only focused on aerobic organisms, which require oxygen in order for their metabolism to operate.
It also works without oxygen
The Basel chemists have now studied the green sulfur bacterium Chlorobium limicola, which also produces ergothioneine. C. limicola belongs to the group of strictly anaerobic bacteria and is therefore reliant on an oxygen-free environment.
In the process, the researchers discovered a new type of biosynthetic pathway in anaerobic bacteria whereby the carbon–sulfur bond is formed without oxygen, as they report in the journal Angewandte Chemie.
Is ergothioneine an ancient molecule?
A comparison of the enzyme sequences of the oxygen-dependent and -independent biosynthetic pathways suggests that, from an evolutionary perspective, the two pathways separated from one another at an early stage of Earth's history. Ergothioneine may have been formed as early as around 3 billion years ago – that is, at a time when there was no oxygen at all in Earth's atmosphere.
This casts a different light on the importance of its physiological role in combating oxidative stress (that is, in reactive oxygen compounds), and the findings suggest that ergothioneines are also important for anaerobic life.
"Our results open up new prospects for studying the physiological function of ergothioneine in humans and in human pathogens, as well as for clarifying the cellular processes that it is involved in. In the long term, this may lead to potential starting points for the development of new therapies," says Florian Seebeck.
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Reto Burn et al. Anaerobic Origin of Ergothioneine, Angewandte Chemie (2017). DOI: 10.1002/ange.201705932