When you think of the microbial world, what comes to mind?
Bacteria, viruses, maybe yeast? Certain microbes get all of the attention, and it’s usually the bad ones. But the microbial world is hugely diverse. Some microbes are putting on a show in the woods, others are dancing in puddles, and some are even saving lives.
So, consider this your introduction to the different types of organisms in the microbial world. During this tour, you will also learn where you can find microbes in your daily life.
What are microbes?
Microorganisms or microbes are organisms that cannot be seen with the naked eye. So, to see them as single cells, you need a microscope.
Although you cannot see most microbes as single cells, they can grow together as colonies, biofilms, or larger structures, and become visible to the naked eye — microorganisms become macroorganisms.
Types of Microbes
Prokaryotes
Microbes are divided up into prokaryotes, eukaryotes, and viruses. Prokaryotes are organisms without a membrane around their genetic material (DNA).
Bacteria
Definition: Bacteria are single-celled prokaryotes and are similar to archaea (see below), except they have a different outer layer. This outer layer, called the cell wall, protects and provides the cells with their shape. It’s the precise chemical structure of their cell walls that differs.
Examples:
- Lactobacillus sp. in yogurt
- Escherichia coli in the human gut
- Salmonella that causes food poisoning
Where you can find them: soil, the earthy smell of geosmin is made by soil-dwelling bacteria; fermented foods, including sourdough bread, sauerkraut, yogurt, that sour smell and flavor come from bacteria that produce lactic acid; in your shower, that pink stuff that pops up sometimes is the bacterium Serratia marcescens.
Want to look at bacteria with a microscope? Check out this post about my home microscope and this post about other great compound microscopes.
Archaea
Definition: Similar to bacteria, archaea are single-celled prokaryotes. But they differ from bacteria in the structure of their cell walls (if they have one). Many archaea are famous for being able to survive in extreme conditions (hot, salty, or acidic), which earns those archaeal species the name extremophiles. However, not all archaea are extremophiles. So far, no disease-causing archaea have been discovered.
Examples:
- hot spring dwelling Sulfolobus
- salt-loving Haloarchaea
- human gut-dwelling Methanobrevibacter
Where you can find them: you can find archaea anywhere you find bacteria, which is nearly everywhere; you may not be able to see archaea extremophiles on a daily basis, but if you have the chance, go see them in the hydrothermal waters of Yellowstone National Park (go see the Grand Prismatic Spring) and salty environments like the Dead Sea and the Great Salt Lake. However, we have archaea living on (skin) and in (gut, mouth) us as a part of our microbiome. So, you can also simply know that you are carrying them with you all the time.
Eukaryotes
Eukaryotes have a membrane around their genetic material, and therefore, have a nucleus.
Fungi
Definition: Fungi can be single-celled or multicellular, and their cell walls contain chitin. The main types of fungi are yeast, mold, and mushrooms. Although we think of mushrooms as macroscopic, they are the fruiting bodies of a microbe, so some have called them “honorary microbes.”
Examples:
- Yeast – baker’s yeast Saccharomyces cerevisiae
- mold – the antibiotic penicillin forming Penicillium chrysogenum
- mushroom – button mushrooms Agaricus bisporus
Where you can find them: mushrooms appear in your yard and around hiking trails, especially after rain as they love moisture; lichens, a symbiotic relationship between a fungus and algae or cyanobacteria, make their homes just about everywhere; yeasts are on and in your body, in the air, and help us make many different fermented foods, including sourdough bread, kefir, kombucha, and beer.
Algae
Definition: Algae are photosynthetic — meaning they use light to make their food — like plants but differ from them in that they lack roots, stems, and leaves. Some algae are macroscopic, and others are unicellular and microscopic, called microalgae. The photosynthetic cyanobacteria are often called algae or “blue-green algae,” but they are prokaryotes and classified as bacteria.
Examples:
- Diatom – Tabellaria
- Dinoflagellate – Ceratium
Where you can find them: microalgae live in ponds, puddles, and the ocean, and if the water looks cloudy and smells fishy, it likely contains them. Here are some diatoms I found in a puddle. Check out this Algae Identification Field Guide to learn more about how to find them.
Protozoa
Definition: Protozoa are single-celled eukaryotes that have various means of movement, including pseudopods, cilia, or flagella.
Examples:
- Amoeba – Amoeba proteus
- Ciliate – Paramecium
- Flagellate – Euglena
- Slime molds (giant amoeba) – Physarum polycephalum
Where you can find them: pretty much any moist environment, including ponds, soil, and saltwater; plasmodial slime molds are the easiest and most fun to find because they are visible with the naked eye — look for a yellow or red blob in the woods or in your yard, white fuzzy stuff on rotting logs, orange Tic Tacs on a leaf (see photo above), or light pink cushion- or ball-shaped bumps on decaying logs.
Viruses
Definition: Viruses are very different from other microbes because they do not have cells. So, they do not fall within the prokaryotic or eukaryotic classification. They consist of genetic material (DNA or RNA) surrounded by a layer of protein. Some viruses have an additional layer of lipids. It is still debated whether viruses are alive or not.
Examples:
- Flu-causing influenza A and B
- Common cold-causing Rhinovirus
- COVID-19-causing SARS-CoV-2
Where you can find them: often, we encounter viruses when we are sick with a cold or the flu. However, phages — viruses that infect and kill bacteria — can actually be used to treat bacterial infections. (Check out the incredible memoir by Steffanie Strathdee & Tom Patterson The Perfect Predator to learn more about how phages can treat bacterial infections).
Summary
- The microbial world is incredibly diverse with organisms that we cannot see with the naked eye. However, some form large structures.
- Microbes can be broadly broken up into prokaryotes, eukaryotes, and the odd-balls the viruses.
- The prokaryotes are bacteria and archaea.
- The eukaryotes are fungi, algae, and protozoa.
- Viruses do not fall neatly within the prokaryote/eukaryote categorization scheme.
- Microbes live just about everywhere, and there are even certain smells or visual cues that you can use to identify them in your daily life. But in some cases, without the aid of a microscope, you just know they are there on and in you.
Resources
This post contains affiliate links — see my disclosure policy.
- Look at different types of microbes with a home microscope
- Read more about microbes in these books
- Show your love for microbes with these gifts
- Support a microbiology science artist
Looking for a textbook for your microbiology class? Check out this one below and my full review of microbiology textbook here.
Spark curiosity about the microscopic world!
My ebook, “Joyful Microbiology Activities,” offers 10 engaging, hands-on lessons to bring microbes to life in your classroom. Get yours today!
Understanding microbes during a pandemic
