It all comes down to the first electron
by Staff Writers
Zurich, Switzerland (SPX) Jan 13, 2022
Every living thing requires energy. This is also true of microorganisms. This energy is frequently generated in the cells by respiration, that is by the combustion of organic compounds, in other words: food. During this process, electrons are released which the microorganisms then need to get rid of. In the absence of oxygen, microorganisms can use other methods to do so, including transporting the electrons to minerals outside the cells.
Reduction rates vary considerably.
These extracellular electron shuttles (EES) have been known about for a long time. Until now, however, it has never been clear why their efficiency is so dependent on their structure and the environmental conditions - and why the speed of the iron oxide reduction varies by several orders of magnitude. All attempts to explain the massive efficiency differences on the basis of known parameters such as pH or temperature have failed until now.
The electrons have to be considered individually
The researchers have shown that the energy difference between the first electron transferred from the EES to the iron oxide determines the iron reduction rate. Using this concept, it is possible to explain the efficiency differences between various EES, even across a sizeable pH range, as well as between two different iron oxides. Michael Sander from the ETH Zurich explains the process with an analogy: "Under many conditions, the first electron is actually very reluctant to leave the EES taxi, but it is pushed out from the back seat, so to speak, by the second electron."
Electron transfer made visible using UV light
The rate of electron transfer from the EES to the iron oxide, and thus the efficiency of the electron transport, can be made visible with UV light. This light is absorbed differently by the EES depending on whether they are underway with or without the two electrons.
Tiny but crucial
This paper is therefore a must-read for anyone working with anaerobically-respiring microorganisms and their carbon exchange. While this step may appear to be a small one, it is nevertheless highly relevant for the understanding of global biogeochemical processes - for example the anaerobic breakdown of organic substances in thawing arctic soilsside, a process in which enormous quantities of climate-critical CO2 are released.
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