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An Introduction to Microorganisms | Ultra Fresh

An Introduction to Microorganisms

An Introduction to Microorganisms

Microorganisms, as implied in their name, are microscopic organisms, otherwise known as microbes. Microbes are living organisms that are so small they require a microscope to be seen by the human eye. Since the discovery of microscopic life by Dutch scientist Antonie van Leeuwenhoek in the 1600s, microbes have been identified as existing in almost every environment found on Earth, including some that were previously thought to be uninhabitable, such as the Earth’s crust, acidic pools, and hot springs.

Microscopic organisms, despite their insignificant size, play a vital role in maintaining the Earths’ – and all its inhabitants’ – well-being. Microbes are fundamental to sustaining human, animal, and plant life as they take part in nutrient recycling, filter out harmful gases and break down dead plant and animal matter into simpler substances. While most microorganisms found on Earth are necessary for maintaining life, some can negatively impact life, causing illness, allergies and disease, bad odours or damage to products such as staining and decomposition.

The term “microorganism” represents an incredibly diverse group of organisms, including well-known organism groups such as micro-animals, bacteria, fungi, and algae. While viruses are not considered to be living organisms, they are often considered to be microorganisms due to their extremely small size.

Microorganisms definition

Let’s explore five of the most commonly talked about microorganisms!

Are Bacteria Considered Microorganisms?


Perhaps the most well-known microbe, bacteria are a member of the prokaryotes, which means they are single-celled organisms that have neither a distinct nucleus within the membrane nor specialized organelles (cellular ‘organs’).

Bacteria are extremely diverse and are by far the most prominent microorganism on the planet. They are the only microorganisms that can live within the human body harmlessly; often bacteria aid in digestion and other regular bodily functions. In fact, there are more bacterial cells living inside your body than there are human cells, albeit, the bacterial cells are much smaller.

While some bacteria living inside the human body can have positive effects, bacteria are also the microorganisms that cause the most problems for humans and animals in terms of health. Bacteria are also responsible for putting the tang in your yogurt and take part in the fermentation process of other foods and drinks.

Bacteria are considered microorganisms

Examples of Common Bacteria:

  • Streptococcus mutans, the primary culprit of tooth decay
  • Helicobacter pylori, a microorganisms that causes ulcers
  • Lactobaccilus acidophilus, a probiotic that is good for the gut
  • Escherichia coli, a common food poisoning organism while certain strains are also beneficial and essential gut bacteria
  • Salmonella, often associated with food poisoning
  • Campylobacter jejuni, often associated with the onset of intestinal issues
  • Bacillus botulinum, produces the botulinum toxin that is the cause of the neuro-condition, botulism and is also used in Botox

Fun Fact: Of the estimated 3 million species of bacteria that are believed to exist, only 4,000 are currently known.

Are Fungi Considered Microorganisms?


Fungi are eukaryotes, meaning each organism possesses a clearly defined nucleus. Eukaryotes are larger than prokaryotes (such as a bacteria), and fungal colonies can grow big enough to be visible to the human eye, such as when you notice mold growing on bread. Fungi can be categorized into three main groups: mushrooms (which possess a fruiting body to produce spores), molds (which display thread-like filamentous growth and multi-cellular structures), and yeasts (which are typically non-filamentous and can be single-celled).

Fungi are beneficial in that they act as decomposers and are happy partners, partaking in a symbiotic relationship with animals, plants, and algae. Fungal microorganisms are also commonly known for their widespread uses in the food industry, including the production of beers and cheeses. Fungi can be problematic for the immunocompromised and can carry parasites or pathogens of other organisms, making them harmful to human, animal, and even plant life.

Many fungi are considered to be microorganisms

Examples of Common Fungi:

  • Aspergillus, common soil organism that will grow on almost anything under the right conditions, causes allergic reactions
  • Candida, a yeast that can infect the mucosal lining, causing illnesses such as thrush and yeast infections
  • Penicillium, a common organism that grows on bread, fruit and cheese which also known for causing allergic reaction
  • Saccharomyces, brewers yeast
  • Trichoderma, can be found growing in damp basements.  Is also able to grow on polymers and plastics such as vinyl, polyethylene and polypropylene

Fun Fact: The fungal kingdom is more like the animal kingdom than it is to the plant kingdom.

Are Viruses Considered Microorganisms?

No…and Yes!

While many experts would argue that viruses are not living things, we have included viruses in this list as they are still considered by many to be microorganisms – and one of the most commonly known, at that. Viruses depend on host cells – cells of other living organisms – to reproduce. When found outside of a host cell, viruses exist as a capsid (a ‘protein coat’) which is sometimes enclosed within a membrane. The capsid contains either DNA or RNA, which essentially codes the viruses’ elements.

Within human anatomy, a virus enters a human cell, hijacks it, and uses the contents of the cell to reproduce. In most cases, the humans’ immune system will detect the presence of the virus soon enough to act against it, leaving the host with symptoms of a common cold or influenza. However, more serious strains of virus can cause permanent and even irreversible damage to cells, for example HIV.

Viruses are considered to be microorganisms

Examples of Well-known Viruses:

  • Rhinovirus, one of the 200 viruses that are known to cause “the common cold”
  • Herpes Simplex viruses, cause a wide spectrum of infections including cold sores and genital herpes
  • Influenza virus, this vial microorganism causes the dreaded flu
  • Varicella-zoster virus, a type of herpes virus that causes the chicken pox in younger people while also causing shingles later in life
  • Human immunodeficiency virus, most commonly referred to as HIV

Fun Fact: Viruses are not technically classified in any of the five kingdoms of living things; meaning, they are not considered bacteria, fungi, protists, plants, or animals.

Are Algae Considered Microorganisms?


Algae are a wide range of diverse microorganisms that are typically photosynthesis and aquatic.  These include eukaryotic protists and prokaryotic cyanobacteria, also known as blue-green algae. There are two main categories of algae: microscopic single-celled microalgae, and larger, multi-celled macroalgae.

Microscopic algal species were at one time considered to be plants but more recent  research has shown that algae don’t belong to the plant family. Like plants, algae species use photosynthesis to capture light energy to “feed” themselves. Despite being like plants in this way, algal microorganisms lack the structures that characterize land plants, such as distinct cell and tissue types, including stomata, xylem, and phloem.  Algae species exhibit a wide range of reproductive activities, from simple asexual cell division to complex forms of sexual reproduction.

Today algae are both necessary and harmful to the planet – some species generate oxygen and help to keep our waters clean, while others produce hazardous poisons that can end up in the water we drink and in the seafood we eat.

Many algae are considered to be microorganisms

Major Types of Algae:

  • Euglenophyta, Euglenoids
  • Chrysophyta, Golden-brown algae
  • Pyrrophyta, Fire algae
  • Chlorophyta, Green algae
  • Rhodophyta, Red algae
  • Paeophyta, Brown algae
  • Xanthophyta, Yellow-green algae

Fun Fact: It’s estimated that algae produce between 50 and 85 percent of the earth’s oxygen.

What are Micro-animals?

There are some animals that require magnification to be seen.  These multi-celled eukaryotic microorganisms, also referred to as “micro-animals” are essential to the global ecosystem, making up a large segment of biomass and representing the bottom of some food chains.  There are others, such as the pesky house dust-mite, that produce highly allergenic agents that cause symptoms that include sneezing, wheezing and coughing.

Micro-animals are organisms that cannot be seen with the naked eye

Common Micro-animals:

  • Arthropods, such as dust mites, spider mites, microscopic crustaceans
  • Tardigrades, also known as water bears or moss piglets
  • Rotifers, a type of zooplankton
  • Loricifera, microscopic animals that live in ocean sediments
  • Nematodes, also known as roundworms

Fun Fact: Tardigrades can withstand 1,000 times more radiation than other animals

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