Bacteria often get a bad reputation for being complicated, but the reality is they are rather simple. Compared to other organisms, they don’t have a nucleus or a membrane-bound organelle.
That said, there are major differences in shapes, sizes, and structures, so today we’ll explore the different sizes, shapes, and arrangements of bacterial cells.
What Are Bacteria?
Bacteria are single-celled microorganisms that lack any internal structure.
They’re prokaryotes – which means their DNA is not enclosed within a cell membrane-like eukaryotic cells (which include animals, plants, fungi, and protists).
Instead, bacteria live as individual units with no internal organization.
This makes them very easy to study because you can just look at one part of a culture and see how it interacts with its environment.
The size of bacteria varies greatly. Some are tiny, only about 0.2 micrometers across, while others are much larger.
For example, some strains of E. coli are about 1 millimeter long.
The shape of bacteria also varies widely. Most are rod-shaped, but some are spiral, spherical, or even filamentous.
Finally, the arrangement of bacteria can vary. Sometimes they form chains, clusters, mats, or colonies.
How Do We Study Bacteria?
We study bacteria by looking at what happens when you put them into an environment.
You might do this by growing them on agar plates (a solid medium) or liquid media (like broth), or by putting them into a Petri dish.
When you grow bacteria on agar plates, you add nutrients to the plate and then place your sample on top. The bacteria will begin to reproduce and eventually cover the entire surface of the plate.
When you grow bacteria in liquid media, you typically use a flask or tube and add nutrients to the liquid.
Then you place the samples inside the container and let them sit until the growth begins.
You can also take advantage of the fact that bacteria love to stick together. If you place a small number of bacteria on a glass slide, they’ll naturally clump together.
You can also use microscopes to examine bacteria. When you look through a microscope, light shines through the specimen and onto a camera.
The image from the camera is then displayed on a computer screen.
Microscopes come in many varieties, including compound microscopes, upright microscopes, inverted microscopes, scanning electron microscopes, transmission electron microscopes, and atomic force microscopes.
In addition to observing bacteria under a microscope, you can also use techniques such as staining, culturing, and genetic analysis to learn more about them.
Size Of Bacterial Cell
The size of bacteria varies widely. Some are tiny, like the smallest free-living organism called a bacterium.
Others can grow up to 100 times their original size. The largest known cell is that of Methanosarcina mazei which grows as large as 1 mm across.
Here’s a list of the common bacteria and their lengths:
- e-coli – about 1-1 to 1.5 µm wide by 2.0 to 6.0 µm lengthways.
- Mycoplasma gallicepticum – has a size of around 200 to 300 nm and is widely thought to be one of the world’s smallest bacteria.
- Epulopiscium fishelsoni can actually be seen with the naked eye and without the need for a microscope. It’s around 600 µm long by 80 µm in diameter.
Shapes Of Bacterial Cell
There are three basic shapes of bacteria that are referred to as coccus (spherical), spiral (twisted), and bacillus (rod-shaped).
However, this is somewhat reductionist, as pleomorphic bacteria will assume a wide variety of shapes.
As bacteria come in many different shapes, including spheres, rods, spirals, and even chains, it’s worth noting that most bacteria are rod-shaped, but some are spiral or coccoid (like E. coli).
Bacteria that look spherical are called cocci. These include the common pathogen Staphylococcus aureus.
These bacteria twist into a helix shape. They include the common foodborne pathogens Salmonella and Campylobacter.
These bacteria appear rod-shaped. Bacilli include the common food-borne pathogen Listeria monocytogenes.
Arrangements Of Bacterial Cells
Most bacteria live in groups called colonies. This means that there’s a single colony of cells that work together. There are two main types of colonies:
- Planktonic – These are unicellular organisms that float freely in the water. They’re not attached to anything.
- Sessiles – These are attached to something else by an extracellular matrix. For example, if you look at the surface of your skin, it’s made up of sessile cells.
In most cases, bacteria live in colonies because they need to be protected from predators.
If they were free-floating, they’d be easy prey. Colonies also help them survive harsh conditions.
For example, when you eat food with lots of preservatives, the bacteria on the outside of the food will die before the ones inside.
But if those bacteria are part of a colony, they can share nutrients and protect each other.
Colonies are usually made up of thousands of individual cells. Sometimes these cells are arranged in layers. Other times they’re randomly scattered throughout a colony.
Colonies are very important to us because they play a big role in our health.
There are over 250 species of bacteria that live in our intestines. Many are good, while others are harmful.
Arrangement Of Cocci
Cocci are often found in pairs or small clusters. When they’re close enough, they’ll stick together. They may also form chains.
The arrangement of cocci depends on how they’re growing. As bacteria divide, they sometimes end up with uneven numbers of chromosomes.
This causes them to have unequal amounts of DNA. So, they grow differently.
When bacteria are dividing, their cell walls are stretched out. That makes them rounder and more spread out.
The result is that one side of the bacterium looks like a sphere, and the other side looks like a cylinder.
This is why we call them coccidian. It comes from the Greek word kokkos meaning “doughnut.”
Streptococci are bacteria that cause strep throat. Streptococci are divided into two major groups based on their appearance.
Group A streptococci are Gram-positive bacteria that look like long, narrow cylinders. They’re responsible for causing strep throat.
Group C streptococci are similar to group A streptococci, except they’re slightly larger. They’re also Gram-positive.
Staphylococci are Gram-negative bacteria that look like small spheres. They’re commonly found on human skin.
They’re also known as staphs. Some strains of staphylococci are harmless.
Others are dangerous pathogens. Staphylococci are divided into three different groups based on their appearance:
- Coagulase Positive Staphylococcus (CoPS). These are the most common type of staphylococcal infections. They produce coagulase which helps them clot blood.
- Coagulase Negative Staphylococcus(CoNS). These don’t produce coagulase. Instead, they use enzymes called hyaluronidases to break down connective tissue.
- Staphylococcus Aureus. These are the only staphylococci that are resistant to penicillin.
Diplococci are bacteria that look like short rods. They’re named after the Latin word Diplo which means “double.” Diplococci are Gram-positive.
Bacilli are rod-shaped bacteria that look like straws. They’re Gram-positive.
Gram-positive bacilli include many important bacterial species such as listeria monocytogenes, salmonella, E. coli, and Shigella.
Tetrads are four bacteria stuck together. They’re typically found in colonies. They’re not always visible under the microscope.
Sometimes tetrads are formed by two different types of bacteria. This happens when one type of bacteria produces an enzyme that breaks down another type of bacteria.
Sometimes tetrads are formed when two bacteria join together.
For example, if a bacterium attaches itself to another bacterium, it can be pulled along until it’s attached to something else. Then, it sticks to its new partner.
Tetrad formation is an important part of sexual reproduction.
In some cases, tetrad formation results in the production of spores. Spores are very hardy cells that can survive harsh conditions.
Arrangement Of Bacilli
This rod-shaped group of bacteria also comes in a number of forms.
These are arranged in chains as cells will divide in a single plane.
These bacteria will appear as pairs after their division.
Arrangement Of Spiral Bacteria
This type of bacteria is curved, which can differ in how much they will curve. Many types of spirilla are capable of movement, and others are slender and flexible.
These are shaped like commas with less than one twist.
These have a helical type shape and can move via axial filaments.
These are rigid and often have many turns.
A Healthy Gut Microbiome – Protection & Our Bodies Defense Mechanisms
A healthy gut microbiome has several characteristics. First, it contains a diverse population of bacteria. Second, it doesn’t contain any pathogenic bacteria.
Third, it has a low pH. Fourth, it produces short-chain fatty acids. Finally, it helps maintain a healthy immune system.
The more diversity we have in our gut, the better. Diversity means having a lot of different kinds of bacteria living in our guts.
The best way to increase diversity is through diet. Eating foods like vegetables and fruits increases the number of beneficial bacteria in our gut. Foods like meat and dairy decrease the amount of diversity.
Pathogens are bacteria that cause disease. Some of the most well-known pathogens include Salmonella, Shigella, and Vibrio cholera.
When these pathogens enter our bodies, they can cause diarrhea, vomiting, fever, cramps, and sometimes death.
To prevent infections, we have natural defenses. Our immune systems attack and destroy foreign invaders. However, this process takes time. So, many pathogens sneak past our defenses.
When pathogens get into our bodies, they start multiplying rapidly. They use their own tissues as their home base.
Eventually, they overwhelm our immune systems. Then, they begin producing toxins that damage our organs and kill us.
We don’t want pathogens in our bodies. We want our immune systems to keep them out. That’s why we have so many different kinds of bacteria in our gut.
Our stomachs normally have a pH between 2-3.5. This acidic environment kills off bacteria that aren’t used to it. It also prevents pathogens from surviving long enough to multiply.
However, some people have trouble digesting milk products or certain types of protein. Their stomachs produce too much acid.
As a result, they develop an imbalance called gastric acid reflux. Gastric acid reflux causes bad breath, heartburn, indigestion, bloating, nausea, and abdominal pain.
This condition is often treated by taking antacids. Antacids neutralize the acid in your stomach. Unfortunately, they also remove all the helpful bacteria from your digestive tract.
Short Chain Fatty Acids (SCFAs)
SCFAs are organic compounds that come from food. These chemicals help regulate our appetite, metabolism, and mood.
In addition to helping with digestion, SCFAs also promote weight loss. They stimulate the growth of new fat cells.
As you can see, bacteria come in many different shapes and sizes, and not all bacteria are created equally. In fact, there are over 100 trillion bacteria in each person’s gut alone.
There are good bacteria and bad bacteria. Good bacteria help us digest food, while bad bacteria make us sick.
To stay healthy, we need both kinds of bacteria and so it’s vital that we continue to research and study bacteria to better understand their role in our wider health.
Each individual has his or her own unique collection of bacteria. One person may have one kind of bacterium, while another person has a completely different set of bacteria.
We need to understand how bacteria work together to create a healthy gut. If we do, then we’ll be able to make healthier choices when choosing what to eat.