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19.04.2021 08:48
News from geological history: How oxygen-producing cyanobacteria made our lives possible
The “Great Oxygen Catastrophe” (GOE or “Great Oxygenation Event”) began 2.43 billion years ago: The earth’s atmosphere was continuously enriched with oxygen, a waste product of photosynthesis. According to science, photosynthetic cyanobacteria were the trigger. But why did this important turnaround come so late? Rock samples show that there was cyanobacterial life at least 300 million years before the GOE. Achim Herrmann, who is researching the spread of early cyanobacteria in his doctoral thesis at the Technical University of Kaiserslautern, is on the trail of answers. His latest research paper has now been published in the journal Nature Communications.
“There are many scientific theories that intertwine and explain why the spread of cyanobacteria necessary for the GOE or the oxygen catastrophe was delayed,” explains Herrmann, who is doing his doctorate in geomicrobiology with Michelle Gehringer. “For example, that they could have originated in fresh water, which then, as now, only made up a fraction of the earth’s surface. It was only when they adapted to salty waters and finally made their home in the open ocean that they were able to produce sufficient amounts of biomass to bring about a global change in the earth’s atmosphere could have. In the anoxic geological age “Archean” at that time, iron accumulated mainly in the form of easily soluble, reduced iron (II) ions in the ocean.
In his research, Herrmann tied in with the iron poison hypothesis. “We wanted to check whether iron (II) is not only modern, but also more primitive strains of marine origin, specifically Pseudanabaena sp. PCC7367 and Synechococcus sp. PCC7336, inhibits their growth and photosynthesis, ”according to biology.
It quickly became apparent how crucial the experimental setup is. In the already established system – the bacteria are cultivated in closed glass bottles – they developed poorly: “The biological activity was very low in both strains, and in Synechococcus it was almost completely suppressed,” says the biologist. The solution: “An anaerobic workstation specially made by the TUK metal workshop, in whose chambers the composition of the atmosphere can be regulated fully automatically,” says the biologist. “We cultivated the cyanobacteria in large laboratory bottles with gas-permeable lids to enable gas exchange. The oxygen they produced was regularly removed from the system, and carbon dioxide was kept constant in low concentrations. Thus we were able to create a shallow marine oxygen oasis, as it is implied in rock samples from the Archean. “
As expected, it turned out that the cyanobacteria “felt more comfortable” in the more lifelike environment. But what happened when iron was added once in increasing concentrations? The bacteria from the Pseudanabaena strain grew consistently well – but more slowly than in the parallel control system. In the case of the bacteria from the Synechococcus strain, on the other hand, it was clearly shown that the rate of cell division decreased as the amount of iron increased. Another finding: the oxygen produced primarily oxidized the dissolved Fe (II) ions instead of escaping into the atmosphere. And the oxygen production capacity of the strains reached a significantly higher value in the anoxic test environment than in a control structure with an oxic atmosphere as it surrounds us today.
In addition, only in this system was the formation of so-called “green rust”, a mixed form of Fe (II) and iron that had already been oxidized to Fe (III). The formation of green rust was accompanied by a strong decrease in biological activity, presumably due to the “encrustation” of the cells with iron oxides. During the Archean Era, the formation of such green rust may have contributed significantly to the formation of ribbon iron ores, the most important source of pig iron ore today.
Finally, Herrmann changed the experimental scenario again and adapted the iron gift to a simulated sequence of tides. The addition was initially carried out regularly at the beginning of the night when the oxygen concentration in the medium sank to zero without photosynthetic activity. As a result, growth slowed significantly in both strains, but never came to a complete standstill. This indicated that an Archean oxygen oasis could also have tolerated the influx of iron-rich water during the night. Here, too, green rust was formed, which, however, could be further oxidized quickly and thus did not result in a complete stoppage of growth.
All in all, Herrmann’s research has filled further gaps in the earth’s history puzzle. He was able to show for both cyanobacteria strains how the iron cycle could have run in an archaic oxygen oasis and also that, due to the higher oxygen production, less overgrown area would probably have been necessary for the start of the GOE. In addition, he has developed a concept for the cultivation of cyanobacteria, which better reflects the living conditions in the Archean.
“I hope that with my research paper I can help us to better understand how our oxygen-containing atmosphere could develop in the first place,” concludes Biologie.
Information on the published research paper:
Herrmann A.J., Sorwat J., Byrne J.M., Frankenberg-Dinkel, N. and Gehringer M.M.
„Diurnal Fe(II)/Fe(III) cycling and enhanced O2 production in a simulated Archean marine oxygen oasis“
https://www.nature.com/articles/s41467-021-22258-1
DOI: 10.1038/s41467-021-22258-1
Questions answered:
Achim Herrmann
Email [email protected]
Tel.: (0)631 205-2199
Scientific contact:
Achim Herrmann
Email [email protected]
Tel.: (0)631 205-2199
Originalpublikation:
Herrmann A.J., Sorwat J., Byrne J.M., Frankenberg-Dinkel, N. and Gehringer M.M.
„Diurnal Fe(II)/Fe(III) cycling and enhanced O2 production in a simulated Archean marine oxygen oasis“
https://www.nature.com/articles/s41467-021-22258-1
DOI: 10.1038/s41467-021-22258-1
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