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I heard this story from one of my friends:

Cyanobacteria can convert carbon dioxide into oxygen through photosynthesis, so the concentration of oxygen in the atmosphere kept going up over a long period after their appearance. Finally, those oxygen poisoned cyanobacteria through some mechanism, which effectively killed many of them. As a side effect, the oxygen produced lead to the evolution of fishes and other fantastic creatures, including human beings.

I wonder whether it is true. After some searching, I found that cyanobacteria can perform photosynthesis. However, I can't tell whether oxygen is poisonous to them.

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    $\begingroup$ By the term "suicide", one generally refers to the decision of a single individual to self-detrsuct (which you realized I suppose as you put the term in quotation marks). The kind of process you are referring to (where a population pollutes its environment to the point of threatening the persistence of the clade) is called an evolutionary suicide. $\endgroup$
    – Remi.b
    Commented Dec 31, 2016 at 8:46
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    $\begingroup$ @Remi.b Thank you! I've edited the title to make it more scientific. $\endgroup$
    – nalzok
    Commented Dec 31, 2016 at 8:55
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    $\begingroup$ Oxygen is inherently a toxic substance as it is the second most reactive non-metal. However, most organisms have evolved mechanisms to counter the toxicity caused by oxygen. $\endgroup$
    – WYSIWYG
    Commented Dec 31, 2016 at 9:09
  • $\begingroup$ @WYSIWYG Since cyanobacteria is such a primitive creature, I guess they don't know how to protect themselves from oxygen. Also, there wasn't much oxygen in the atmosphere before their existence, so I think the resistance to oxygen hasn't been vital by the time they evolved. $\endgroup$
    – nalzok
    Commented Dec 31, 2016 at 9:18
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    $\begingroup$ @WYSIWYG In fact, I meant an individual cyanobacteria could still survive that environment even if it isn't equipped with resistance to oxygen, so those born with oxygen resistance (by accident) didn't have advantage over those who haven't. As a result, oxygen resistance failed to be passed to the next generation. When the oxygen in the atmosphere became poisonous/fatal, everything was too late (There wasn't enough time for another useful mutation to occur). Anyway, I'll read the materials in the link you provided :) $\endgroup$
    – nalzok
    Commented Dec 31, 2016 at 10:11

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Oxygen is, indeed, highly toxic to cells, due to its oxidizing power, i.e., the ability to remove electrons from another substances. Since the first carbon-reducing organisms started to increase the amount of molecular oxygen in the atmosphere, more than 2 billion years ago, life on earth has been dramatically changed by this compound: you can even consider that aerobic respiration appeared originally as a mechanism of reducing the toxic molecular oxygen to the innocuous water.

Today, organisms that use water to reduce carbon dioxide, releasing oxygen as a by-product, have molecular mechanisms (as aerobic respiration, for instance) to protect them from the very oxygen they produce.

But your question is quite interesting: how did the first photosynthetic organisms protected themselves against the oxygen they started producing?

This is a catch 22. An interesting solution was proposed by a team of geobiologists from Caltech: There was a little amount of molecular oxygen in the ocean's water before the appearance of photosynthesis. This small amount of oxygen was able to promote the evolution of biochemical mechanisms protecting organisms from its toxicity. Some of those organisms, then, were capable to develop photosynthesis and protect themselves against the huge amount of oxygen that they started releasing. According to the team:

Low levels of peroxides and molecular oxygen generated during Archean and earliest Proterozoic non-Snowball glacial intervals could have driven the evolution of oxygen-mediating and -using enzymes and thereby paved the way for the eventual appearance of oxygenic photosynthesis.

Source: Liang, M., Hartman, H., Kopp, R.E., Kirschvink, J.L. and Yung, Y.L. (2006) "Production of hydrogen peroxide in the atmosphere of a snowball earth and the origin of oxygenic photosynthesis", Proceedings of the National Academy of Sciences, 103(50), pp. 18896–18899. doi: 10.1073/pnas.0608839103.

EDIT: according to your comment, all you want to know is "whether cyanobacteria is able to survive oxygen". Well, that's even easier to answer:

Cyanobacteria can perform aerobic respiration. That means that they can easily use protons and electrons obtained from organic matter to reduce molecular oxygen to H2O:

Cyanobacteria... are among the very few groups that can perform oxygenic photosynthesis and respiration simultaneously in the same compartment,and many cyanobacterial species are able to fix nitrogen. Therefore, they can survive and prosper under a wide range of environmental conditions.

Source: Photosynthesis and Respiration in Cyanobacteria

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    $\begingroup$ Firstly, please let me thank you for your complete answer, from which I learnt that cyanobacteria know how to protect themselves from the toxic oxygen, due to the small amount of oxygen in ocean from the very beginning, along with other interesting knowledge. However, what I want to know is whether cyanobacteria is able to survive oxygen, or which level of oxygen can cyanobacteria survive. I would appreciate it very much if you could answer it and/or find some reference s. $\endgroup$
    – nalzok
    Commented Dec 31, 2016 at 12:20
  • $\begingroup$ @SunQingyao check my edit. $\endgroup$
    – user24284
    Commented Dec 31, 2016 at 14:05

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