Cyanobacteria and Its Legacy of Life

For lack of a better term, we call the tiny particles of stuff floating around in the universe dust. We see it when we look at the Milky Way on a clear night or in the Orion nebula in the sword below the hunter’s belt. The Hubble and Webb telescopes have shown us thick billowing clouds of it. Although it is called dust, it is actually made of innumerable atoms such as carbon, oxygen, iron, hydrogen, helium and other elements that have been blown out from old stars, some of which have exploded as supernovas. It is cosmic dust, not like the fuzzy stuff that gets on our furniture.

As these atoms move around in space, they run into each other and form clumps, or the cosmic equivalent of dust bunnies that we find under our bed. Over millions of years, these cosmic clumps can grow to the point that their gravity increases greatly. In time the force of gravity in the center of the clump raises the heat and pressure to the point that it begins fusing hydrogen atoms into helium. What had been a clump of dust particles is now a star. Quite often, the dust particles and debris that did not become part of the star begin orbiting around it and in time coalesce into its planets. Four and a half billion years ago leftover dust and debris from the formation of our sun clumped together into the planets of our solar system, including Earth.

Then, only 800 million years later, a short time evolutionarily speaking, the electrical-chemical journey of life on Earth began. Atoms such as carbon, hydrogen, oxygen, and nitrogen that had been forged in the cores of far distant stars and were part of the dust that formed us, were able to take advantage of their auspicious location on a planet not too close and not too far from a young and energetic star in a brand-new solar system. Fortunately, Earth turned out to be a planet where most of the water did not stay frozen or boil away into space.

Time was no problem; there was no one around to be in a hurry. Earth’s atoms had time to bounce around and configure themselves into one arrangement after another. Like the universe that takes its own good time coalescing stars and solar systems from gigantic masses of cosmic dust and gases, these atoms took their time, learned from their mistakes, and when conditions were right, they gave to Earth a most profound gift.

When life’s atomic components began to come together, the young Earth spun faster than it does today and a rotation took only 20 hours; the gravities of Earth and her moon had not had time to slow each other down to today’s 24 hours of solar day. But then as now, Earth’s sideral orbit around the sun of 584 million miles was established. The primal elements of life had all the years they needed to do their evolving.

Nature provided Earth with everything it needed to allow the elements to spawn life and instigate the march of evolution. The universe gave millions of years of time; the stars provided a rich array of atoms they had been forging for billions of years; photons of light that our sun created in its hydrogen to helium fusion inside its 28-million-degree Fahrenheit core streamed toward Earth at 186,282 miles per second. The Earth provided water that had accumulated in its spreading oceans and rivers. And acting as an ignition spark, were millions of volts of electric power from lightning generated as electrons and protons flowed through Earth’s carbon dioxide, methane, and ammonia atmosphere. All of the elements were in place.

This auspicious blend of ingredients — time, atoms, sunlight, and water — allowed inorganic atoms to proceed through countless random chemical combinations, until the right protobiological configuration of life-building amino acids evolved into peptides and proteins. The protein molecules were then the bridge to a rare and profound phenomenon: the great leap from inorganic chemicals to living entities. Thus, from the dust of exploding stars, the procession of life was spawned.

Once life was established, creatures on Earth were now subject to the conditions inherent in all living things: birth, growth, maturity, and death. These primitive molecules that through the genesis of organic evolution made a dead planet a living one, would in time drastically change the Earth.

In the next few million years, single-cell bacteria formed and thrived. Some learned to cooperate, building symbiotic relationships that led to the formation of prokaryotic cells, small cells that contain DNA and ribosomes, but no nucleus. Then the cells themselves began to come together to form multicellular organisms. One of the earliest and most important living organisms has been named cyanobacteria after its blue-green color, the beautiful blue-green that today we humans associate with Earth’s water and forested land.

Although weak at first…merely a few molecules of watery cytoplasm and primitive organelles, the power of the stars that had spawned cyanobacteria’s fundamental components was deep inside its prokaryotic cells. It persisted when other organisms failed. Its strength was in its perseverance and how it organized itself to make use of the elements around it: water, carbon dioxide, and sunlight. Through one configuration after another, its molecules began fitting together into a functioning system of cells in a collaboration where each cell became specialized and learned to do its part in the processes needed for the organism to survive and reproduce.

In a hostile world of volcanos spewing magma from below and fiery meteorites falling from above with very little atmosphere to slow them down, the primitive organism continued to organize itself. For millions of years the cells experimented haphazardly with the photons, water, and carbon dioxide available to them. It took time but the organism’s cells, through selecting what worked and passing on from what did not work, created a complex functioning network.

Would humans today call it a type of plant intelligence or just fortuitous biological engineering that through trial and error these primitive cells arranged themselves in such a way that they were able to figure out how use the power of sunlight to split water molecules into their oxygen and hydrogen component parts, then combine the hydrogen with carbon from the carbon dioxide they got from the atmosphere to make a carbohydrate sugar called glucose, the food it uses for energy and growth? And in the process they exhaled the unneeded oxygen back into the atmosphere.

Cyanobacteria figured out this process, and by making use of a pigment called bacteriochlorophyll, it was able to become photoautotrophic, that is, it became able to make its own food from the elements in its environment, light, carbon dioxide, and water. That was profound in itself. But it was cyanobacteria’s waste product, oxygen atoms, that also made the bacteria truly revolutionary to future life on Earth.

Today we honor cyanobacteria, as the creator of photosynthesis, which has been called one of the most important biological processes on Earth. For millions of years, the blue-green bacteria thrived in Earth’s carbon-rich atmosphere taking in carbon dioxide and exhaling oxygen. In a few million years it had spread over much of the Earth and exhaled so much oxygen that by around 2.2 billion years ago the amount of oxygen it was exhaling began to accumulate and in time replace other elements such as the methane and ammonia gases surrounding the planet.

The exhaled oxygen was the key to future life on Earth yet fatal for many anaerobic organisms that had evolved to breathe in the primal blend of atmospheric elements. Oxygen was toxic to many of these organisms, and the ones that were not able to adapt to respire oxygen perished. However, a few types of anaerobic bacteria survived, such as fermentation enzymes which are important in many chemical processes. Today we use anaerobic fermentation in the preparation of foods such as pickles, sauerkraut, beer, and wine. Also, surviving were a few types of parasitic anaerobic protozoa which can cause several diseases in humans.

Solar powered photosynthesis provided the strength that cyanobacteria needed to grow and reproduce. Countless trillions of these blue-green cells populated nearly every square meter of the Earth and exhaled a whole Earth atmosphere of oxygen. In time, this powerful gas helped move evolution beyond primitive bacterial prokaryotic cells to the development of more complex eukaryotic cells – cells with a nucleus and a variety of organelles in its cytoplasm. It is the complex eukaryotic cells that now make up nearly every plant and animal.

With cyanobacteria leading the way, photosynthesis caught on in the plant world. Today nearly all of the 375,000 species of vascular plants on Earth, such as grass and vegetables, use photosynthesis to make their food. And that is good for humans who eat plants or eat animals that eat plants. In this way, cyanobacteria became the first link in the vital food chain that keeps our bodies metabolizing and our brains thinking.

Thus, cyanobacteria were critical in starting the food chain that feeds us as well as putting the first oxygen in our atmosphere that enables us to breathe. Had cyanobacteria not developed the ability to turn sunlight into food and separate oxygen from carbon dioxide molecules, the Earth would probably still be inhabited only by bacteria and archaea and have an atmosphere consisting mostly of methane and carbon dioxide. No reptiles, no mammals, and no humans.

Could a science fiction writer come up with a scenario in which our descendants find an exoplanet inhabited by single celled organisms and introduce cyanobacteria that would put enough oxygen in the atmosphere to make it habitable. It might take a few years, but it could work in principle.

What does cyanobacteria have in common with tree leaves and sunflowers? Although, cyanobacteria are not plants, it is interesting that studies have shown that like photosynthetic plants, cyanobacteria will follow sunlight across the sky. This sun follower lets us know that we Earthlings are on a planet that sets the standard for the term “habitable planet” where nature, cyanobacteria, delicious edible plants, and generally tolerable weather conditions have enabled us to evolve, flourish, and have hope for the future, if we take care of the things Nature has provided.

II

By the time cyanobacteria started exhaling oxygen into Earth’s atmosphere, those oxygen atoms had already been on a long journey through the universe. We now know that all of the oxygen we breathe is produced in the high-pressure fusion process inside stars. It is created when a carbon atom with 6 protons, 6 neutrons, and 6 electrons, with an atomic weight of 12, fuses with a helium atom which contains 2 protons, 2 neutrons, and 2 electrons thus giving the oxygen atom 8 protons, 8 neutrons, and 8 electrons and an atomic weight of 16. (only protons and electrons are counted in atomic weight)

Our sun is not hot enough to fuse oxygen yet, but it will be in about 5 billion years. At this time, it is only hot enough to fuse hydrogen atoms into helium. In the distant future, as it begins to run out of hydrogen, it will expand in size and get hot enough to start fusing its helium atoms into carbon, and fusing carbon and helium atoms into oxygen. Once the expansion phase is finished–a phase in which the sun becomes a red giant – it will collapse into a dense white dwarf star made mostly of carbon and oxygen atoms and not much bigger than Earth. It will cease providing Earth with heat and light.

The effects of oxygen or lack of it have been known for years. It was around 240BC that Greek engineer Philo Mechanicus first reported that putting a candle in an air-tight contain will make the flame go out.

Years later, the importance of oxygen was recognized early in humanity’s scientific revolution. Experiments were done as early as the 1500s, but it was not until 1772 that Swedish chemist Carl Wilhelm Scheel actually discovered a few of oxygen’s chemical properties. However, he did not publish his results, and when Joseph Priestly made the same discoveries in 1774, he published the results of his work and today is given credit as the discoverer. Priestly, who did not fully understand what he had found, gave the gas the cumbersome name of ‘dephlogisticated air’. He noticed that when he added the gas to a candle flame it increased the intensity of the flame.

In 1777 Antoine Lavoisier did further experiments and thinking that the substance was an acid because it caused rust, or oxidation, came up with the name oxygen after the Greek words oxys for acid and genes for producer. Thus, to Lavoisier, oxygen was an acid producer. A few years later in 1812, chemist Humphrey Davy determined that oxygen is not an acid, but the name stuck.

In Earth’s long history, numerous plants and animals have come and gone, but cyanobacteria have hung on and are still with us today. Cyanobacteria have survived through environmental changes from droughts to ice ages, earthquakes, and asteroid impacts, and many other natural disasters. But after more than 3 billion years, several varieties of it are still found living in just about every ecosystem on Earth.

Geologists, biologists, and paleontologists have learned a lot about our history by studying stromatolites, those sedimentary structures of billions of cyanobacteria layered in vertical columns up to about 3 feet tall found at various places around the world. A lot of them that scientists have found are fossilized, the oldest being around 3.4 billion years old, making them some of the oldest fossils ever found on Earth. Yet, stromatolites are still being built today in some parts of the world, such as along ocean shores that have high salinity, but also in lakes, and in several countries such as Australia, Brazil, and the Bahamas.

The resilience of cyanobacteria is heartening to us humans whose wanton irresponsibility sometimes hints of self- destruction. With awe and wonder we revere and study it as an essential constituent of our living history. Without it, life might never have evolved beyond mere anaerobic, fermenting bacteria that did not generate enough energy to continue the progression toward plants, animals and us. The billions of oxygen breathers on earth today appreciate cyanobacteria’s long history and on-going efforts.

Through ice ages, droughts, fires, and floods, both cyanobacteria and people have adapted well to our Earthly environment, at least so far. Let us hope that we humans can be as resilient as our ancient oxygen provider. Now both of us have another challenge. If the climate continues to get hotter, will we be able to adapt to that situation as well?

Ted McCormack