Invisible Diversity: The Many Shapes of Bacteria

Bacteria are amazing.

They were the first form of life to appear on Earth almost 3.8 billion years ago.

They make up the second most abundant lifeform, only outweighed by plants.

And most interesting of all: they exist in practically every environment on our planet, including areas where no other lifeforms can survive. As a result, bacteria exhibit a wide variety of appearances, behaviors, and applications similar to the lifeforms we see in our everyday lives.

The incredible diversity of bacteria goes underappreciated simply because they are invisible to the naked eye. Here, we illustrate how researchers classify these creatures on the basis of appearance, giving you a glimpse into this microscopic world.

A Life of Culture

Though bacteria may look similar to other microorganisms like fungi or plankton, they are entirely unique on a microscopic and genetic level.

Bacteria make up one of the three main domains of life. All life shares its earliest ancestor with this group of microbes, alongside two other domains: the Archaea and the Eukarya.

Archaea are very similar to bacteria, but have different contents making up their cell walls.

Eukarya largely consists of complex, multicellular life, like fungi, plants, and animals. Bacteria are similar to its single-celled members because all bacteria are also unicellular. However, while all Eukarya have nuclear membranes that store genetic material, bacteria do not.

Bacteria have their genetic material free-floating within their cellular bodies. This impacts how their genes are encoded, how proteins are synthesized, and how they reproduce. For example, bacteria do not reproduce sexually. Instead, they reproduce on their own.

Bacteria undergo a process called binary fission, where any one cell divides into two identical cells, and so on. Fission occurs quickly. In minutes, populations can double rapidly, eventually forming a community of genetically identical microbes called a colony.

Colonies can be visible to the human eye and can take on a variety of different shapes, textures, sizes, colors, and behaviors. You might be familiar with some of these:

Superstars of a Tiny World

The following are some interesting bacterial species, some of which you may be familiar with:

Epulopiscium spp

This species is unusually large, ranging from 200-700 micrometers in length. They are also incredible picky, living only within the guts of sturgeon, a type of large fish.

Deinococcus radiodurans

D. radiodurans is a coccus-shaped species that can withstand 1,500 times the dose of radiation that a human can.

Escherichia coli

Despite being known famously for poisoning food and agriculture spaces from time to time, not all E.coli species are dangerous.

Desulforudis audaxviator

Down in the depths of a South African gold mine, this species thrives without oxygen, sunlight, or friends—it is the only living species in its ecosystem. It survives eating minerals in the surrounding rock.

Helicobacter pylori

Known for causing stomach ulcers, this spiral-shaped species has also been associated with many cancers that impact the lymphoid tissue.

Planococcus halocryophillus

Most living things cease to survive in cold temperatures, but P. halocryophillus thrives in permafrost in the High Arctic where temperatures can drop below -25°C/-12°F.

‘Bact’ to the Future

Despite their microscopic size, the contributions bacteria make to our daily lives are enormous. Researchers everyday are using them to study new environments, create new drug therapies, and even build new materials.

Scientists can profile the diversity of species living in a habitat by extracting DNA from an environmental sample. Known as metagenomics, this field of genetics commonly studies bacterial populations.

In oxygen-free habitats, bacteria continuously find alternative sources of energy. Some have even evolved to eat plastic or metal that have been discarded in the ocean.

The healthcare industry uses bacteria to help create antibiotics, vaccines, and other metabolic products. They also play a major role in a new line of self-building materials, which include “self-healing” concrete and “living bricks”.

Those are just a few of the many examples in which bacteria impact our daily lives. Although they are invisible, without them, our world would undoubtedly look like a much different place.

Roadmapping the Evolution of the Eye

Throughout history, numerous creatures have evolved increasingly complex eyes in response to different selective pressures.

Not all organisms, however, experience the same pressures. It’s why some creatures today still have eyes that are quite simple, or why some have no eyes at all. These organisms exemplify eyes that are “frozen” in time. They provide snapshots of the past, or “checkpoints” of how the eye has transformed throughout its evolutionary journey.

Scientists study the genes, anatomy, and vision of these creatures to figure out a roadmap of how the eye came to be. And so, we put together an evolutionary graphic timeline of the eye’s different stages using several candidate species.

Let’s take a look at how the eye has formed throughout time.

Where Vision Comes From

The retina is a layer of nerve tissue, often at the back of the eye, that is sensitive to light.

When light hits it, specialized cells called photoreceptors transform light energy into electrical signals and send them to the brain. Then the brain processes these electrical signals into images, creating vision.

The earliest form of vision arose in unicellular organisms. Containing simple nerve cells that can only distinguish light from dark, they are the most common eye in existence today.

The ability to detect shapes, direction, and color comes from all of the add-ons evolution introduces to these cells.

Two Major Types of Eyes

Two major eye types are dominant across species. Despite having different shapes or specialized parts, improved vision in both eye types is a product of small, gradual changes that optimize the physics of light.

Simple Eyes

Simple eyes are actually quite complex, but get their name because they consist of one individual unit.

Some mollusks and all of the higher vertebrates, like birds, reptiles, or humans, have simple eyes.

Simple eyes evolved from a pigment cup, slowly folding inwards with time into the shape we recognize today. Specialized structures like the lens, cornea, and pupil arose to help improve the focus of light on the retina. This helps create sharper, clearer images for the brain to process.

Compound Eyes

Compound eyes are formed by repeating the same basic units of photoreceptors called ommatidia. Each ommatidium is similar to a simple eye, composed of lenses and photoreceptors.

Grouped together, ommatidia form a geodesic pattern that is commonly seen in insects and crustaceans.

Our understanding of the evolution of the compound eye is a bit murky, but we know that rudimentary ommatidia evolved into larger, grouped structures that maximize light capture.

In environments like caves, the deep subsurface, or the ocean floor where little to no light exists, compound eyes are useful for producing vision that gives even the slightest advantage over other species.

How Will Vision Evolve?

Our increasing dependency on technology and digital devices may be ushering in the advent of a new eye shape.

The muscles around the eye stretch to shift the lens when staring at something close by. The eye’s round shape elongates in response to this muscle strain.

Screen time with cellphones, tablets, and computers has risen dramatically over the years, especially during the COVID-19 pandemic. Recent studies are already reporting rises in childhood myopia, the inability to see far away. Since the pandemic, cases have increased by 17%, affecting almost 37% of schoolchildren.

Other evolutionary opportunities for our eyes are currently less obvious. It remains to be seen whether advanced corrective therapies, like corneal transplants or visual prosthetics, will have any long-term evolutionary impact on the eye.

For now, colored contacts and wearable tech may be our peek into the future of vision.