Cyanobacteria: R-E-S-P-E-C-T

We owe cyanobacteria our respect. And they might deserve our fullest gratitude as well if it weren’t for one nasty trait.

For starters, if we are to believe that our elders deserve respect, cyanobacteria certainly qualify. They date back 3.5 billion years, almost to the earliest signs of life. But they are not only old. They are interesting, they seem uncomplicated, and they are powerful and successful. They are single-celled, though many live connected to each other in colonies and filaments. They are primitive; unlike the cells of younger species, they have no nucleus. And they have not only survived all this time; they have thrived. Their species number at least two thousand that have been described and at least twice that number in total. Most are blue-green—“cyan”—but their various pigments also account for the colors of pink flamingoes and the Red Sea.

cyanobacteria (https-::i.kinja-img.com:gawker-media:image)

(gawker)

Cyanobacteria gave us oxygen—and continue to do so. For the first two billion years after the earth’s formation 4.5 billion years ago, the atmosphere contained almost no oxygen. But the blue-green pigment in cyanobacteria is a mix of green chlorophyll and a blue pigment both of which turn sunlight and carbon dioxide into sugary energy for the cell. Oxygen is the waste product—and early cyanobacteria produced so much of it for so long that it accumulated in the atmosphere and eventually supported larger, more complex cells, including ours.

Just as important, atmospheric oxygen spawned an ozone layer that reduced the lethal levels of the sun’s ultraviolet radiation. It’s that filtering that allowed early plant and animal life to finally move on to land after three billion years in the water.

Cyanobacteria made plants themselves possible by becoming part of them. Some other early bacteria engulfed cyanobacteria and then, because of cyanobacteria’s efficient energy production, turned them into one of the pieces of organic machinery enclosed within a plant’s cell. We see them today as the greenery of plants—the chloroplasts—that power them and keep them reaching for the sun.

Cyanobacteria are handy with another gas in addition to oxygen. They convert nitrogen in the atmosphere into a form that plants and animals need for such building blocks as proteins and DNA. Natural nitrogen fertilizer.

pond scum wikipedia

(Wikipedia)

Cyanobacteria often go by the name of blue-green algae. But they’re not algae. Algae is an informal term for many water-borne organisms that contain  chlorophyll but lack stems, roots, or leaves. Seaweed is algae. Cyanobacteria are bacteria—simple cells, often strung together, without nuclei.

As for that one nasty trait, cyanobacteria can kill you. Especially in freshwater ponds and lakes, blooms of cyanobacteria looking like blue-green paint slicks may be toxic to nerve and liver systems, depending on the species. The poisons may work their way into the food chain, pets may eat them, water-skiers may absorb them. The result can be respiratory failure, Parkinson’s, ALS. Not often, but too often. Respect.

Reading about cyanobacteria on the Internet, you get a glimpse of a life-form from an inconceivably ancient world that is woven throughout the air, water, and soil of our own time. We are in their debt for the breath we take, the food we eat, for our living on solid ground.  We stand on their countless, tiny shoulders.

Stem Cells: How To Build and Maintain Bodies, Including Plants

Until recently, I didn’t know much about stem cells except that they produced other kinds of cells and that the medical research on them was controversial. In the context of the history of life, it turns out, their importance is as fundamental as you can get.

It took more than a billion years for the first cell with a nucleus to come together. Since then, the only reliable source for a new cell has been another cell. Every cell is an offspring. True for plants as well as animals.

An embryonic stem cell (Wikipedia)

An embryonic stem cell
(Wikipedia)

But while cells are specialized for one task or another, they are not always very good at dividing and reproducing. Muscle cells, blood cells, and nerve cells don’t reproduce at all. Other cells in the body divide only under some circumstances or only a limited number of times.

But reproduction is the stem cell’s specialty. When it divides, it produce another stem cell, ready for the next round, along with a muscle cell or blood cell or nerve cell or a cell of another organ. It looks the part for such flexibility—blob-like, unstructured, not committed until needed.

Stem cells are stationed throughout the body, small groups of them in each organ, like local hospitals on call to repair the sick and damaged. They are a profound piece of bodily engineering, a design for the long-term, like a futuristic car that carries little 3-D printers throughout the engine and chassis to create new parts and replace the old parts automatically.

In human embryos, in contrast to adults, stem cells literally build the body. When an embryo is only a few days old, its stem cells begin to form all—all—of the specialized cells needed in a body, some 200 of them.

In this root tip, the number 1 marks the relatively unstructured stem cells in the meristem. (Wikipedia)

In this root tip, the number 1 marks the relatively unstructured stem cells in the meristem.
(Wikipedia)

Plants have stem cells too. Located near the tips of the roots and stems in a layer called the meristem, plant stem cells divide into both specialized cells for the plant and additional stem cells. Stem cells are, in other words, the place where a plant grows.

One of the wonders of any living thing is the sheer variety of its parts, the inventory of its tubes, organs, fluids, surfaces, protrusions, electric circuits and rigid pieces. As we pause to appreciate this profusion, sing the praises of the smudgy cell that creates and repairs them all.

This Electric Body

We are juiced. From head to toe, we contain miles of infrastructure flush with impulses of electricity. Mild charges pour in from the receptors that translate our five senses into electric signals, through the central processor in our head, through the wiring to  every muscle cell. Evolution built the system, its smart variation on the way electricity flows in the rest of nature.

Neurons appeared in the earliest jellyfish and sponges because, unlike plants, those swimmers moved around. They avoided threats and searched for food, so they gained loose nets of nerves for input about their environment and the coordination of their swimming.

Before the animals, two billion years ago in the first fully developed cells, membranes seem to have been the place where neurons originated. A membrane is “a selective barrier; it allows some things to pass through but stops others” (Wikipedia). Such membranes probably helped cells manage the changing salt levels in the early oceans. And since the salts of sodium, potassium and calcium easily become electrically charged, membranes began to evolve with pores that opened and closed quickly to let charged atoms pass through.

As animals became larger, such membranes lengthened into neurons with conductive axons, the “wire” of the cell. In us, the longest axon runs down the length of each leg, branching as it goes. The shortest axons, fractions of a millimeter, fill our heads by the billions.

Neurons in the brain (Wikipedia)

Neurons in the brain
(Wikipedia)

The axons don’t carry an electric charge in the way that a wire carries electricity or a lightning bolt of electrons crashes to the ground. Instead, think of the wave at a sports stadium, where groups  of fans stand up, throw their hands in the air, and sit down in a spontaneous sequence that moves through the seats. An impulse moves down the axon in the same way, charged atoms crossing through opened pores from one side of the membrane to the other and then quickly back again while the “wave” of the electric charge moves along.

The impulse never varies in strength. It is either on or it is off, moving or only ready to move. There are no drops in the current, no power failures, no biological surge protectors needed. If a muscle must contract to move a load, the nerve signal, always at the same strength, simply repeats rapidly enough so that the muscle cells remain contracted.

At the ends of the axon, where the impulse begins and terminates, clever devices translate between the electrical charge and other structures, depending on the specialty of the neuron. In our eyes, light causes molecular changes that trigger the impulses to the brain to form the image we recognize as a chair. In the ear, sound waves cause small hairs to vibrate and set off the impulse that we hear as “hello.” Where a neuron terminates at a muscle cell, the final “wave” triggers chemicals that start the muscle’s contraction.

But we barely notice all this electric action. Compared to the breath that we can feel and the blood that we can see, the electronic wizardry in our bodies is invisible to us. Unless you have been badly shocked or suffer from numbness or from irregular heartbeats, you may not pay much conscious attention to your internal circuitry at all.

But there is one way you are aware of it already, at least unconsciously. Take a moment to notice the slight tingle that is always present in your limbs and head. It’s a sense of animation, a knowing that you can move a muscle or think a thought whenever you want. Those tingles are, essentially, your neurons ready to go. And they are what remind you that you’re alive.