What Are Microorganisms?
We have all seen microorganisms in our lives and we also use them in our daily life as well. from making yogurt to producing one of our favorite beers. You can see them on the spoiled bread peace to the deadliest Pandemic that humankind faced.
If I speak in more technical terms that microorganism is a microscopic organism that we can’t see through our eyes. Microscopic organisms mean you can measure those organisms in a few micrometers and some of them are nanometers in size. The study of this tiny litter organism is called microbiology and the person who studies this microorganism is called the microbiologist.
Term microorganism includes a variety of organisms such as Bacteria, Algae, Fungi, Archaea, and Protists. Some of them are not considered true microorganisms because they are generally regarded as nonliving organisms, they only get active when they come in contact with their host such as viruses and prions but they aren’t also different from the microorganisms.
As you know microorganism is a diverse group of living organisms and because of that, there are part of many discussion currently going on about the organization and classification of living organisms.
Currently, all living organisms are divided into two groups based on their cellular characteristics unicellular and multicellular which are also known as Prokaryotes and Eukaryotes.
No matter how you classify all living organisms’ microorganisms are found in all the domains of life. If you see the five Kingdome classification, bacteria and some algae are placed in the Monera Kingdom (Sometimes it is divided into two separate kingdoms Eubacteria and Archaebacteria). If you look at the Kingdom Protista you will find Algae Protozoa and fungi have their own kingdom. Even the Kingdom Animalia has several animals that are microscopic.
However, any of these five kingdoms did not include Viruses or prions as their member. This is because Viruses are considered to be on the line between living and non-living organisms.
It has been a question of great debate whether viruses are living organisms or non-living organisms. Most virologists considered them a non-living organisms as they are do not meet all the criteria of generally accepted definitions of living organisms.
Most viruses do not respond to changes in the surrounding environment, which is the most important trait of the living organism. In addition to this viruses can only replicate by infecting a host cell otherwise they cannot reproduce on their own and stay in an inactive state.
Apart from the Viruses, Prions are the recently discovered infectious agent. Prions are nothing but abnormally folded proteins that can convert normally folded proteins into abnormally folded ones and prevent them from functioning it properly. Because folding is the main property of proteins it enables them to take a proper shape that is critical for their function. Â
Now you know that microorganisms are present everywhere and we cannot live without microorganisms and they can be beneficial and harmful. They help us to fight disease and they can cause disease as well they are just like humans as we say not all humans are good or vice versa not all humans are bad same thing applies to microorganisms as well.
Let’s discuss all these 7 types of Microorganisms in detail and know where each of these microorganisms is found and how can they benefit Humans in every possible way.
7 Types Of Microorganisms
The major groups of microorganisms namely bacteria, archaea, fungi (yeasts and molds), algae, protozoa, viruses, and Multicellular Animal Parasites are summarized below. Links to more detailed articles on each of the major groups are provided.
1. Bacteria
Bacteria are unicellular organisms. The cells are described as prokaryotic because they lack a nucleus. They exist in four major shapes:
- Bacillus (rod shape)
- Coccus (spherical shape)
- Spirilla (spiral shape)
- Vibrio (curved shape)
Most bacteria have a peptidoglycan cell wall; they divide by binary fission, and they may possess flagella for motility. The difference in their cell wall structure is a major feature used in classifying these organisms.
According to the way their cell wall structure stains, bacteria can be classified as either Gram-positive or Gram-negative when using the Gram staining.
Bacteria can be further divided based on their response to gaseous oxygen into the following groups:
- Aerobic (living in the presence of oxygen)
- Anaerobic (living without oxygen)
- Facultative anaerobes (can live in both environments)
According to the way they obtain energy, bacteria are classified as heterotrophs or autotrophs. Autotrophs make their own food by using the energy of sunlight or chemical reactions, in which case they are called chemoautotrophs. Heterotrophs obtain their energy by consuming other organisms. Bacteria that use decaying life forms as a source of energy are called saprophytes.
2. Archaea
Archaea or Archaebacteria differ from true bacteria in their cell wall structure and lack peptidoglycans. They are prokaryotic cells with avidity to extreme environmental conditions.
Based on their habitat, all Archaeans can be divided into the following groups:
- Methanogens (methane-producing organisms)
- Halophiles (archaeans that live in salty environments)
- Thermophiles (archaeans that live at extremely hot temperatures)
- Psychrophiles (cold-temperature Archaeans)
Archaeans use different energy sources like hydrogen gas, carbon dioxide, and sulfur. Some of them use sunlight to make energy, but not the same way plants do.
They absorb sunlight using their membrane pigment, bacteriorhodopsin. This reacts with light, leading to the formation of the energy molecule adenosine triphosphate (ATP).
3. Fungi
Fungi (mushrooms, molds, and yeasts) are eukaryotic cells (with a true nucleus). Most fungi are multicellular and their cell wall is composed of chitin.
They obtain nutrients by absorbing organic material from their environment (decomposers), through symbiotic relationships with plants (symbionts), or harmful relationships with a host (parasites).
They form characteristic filamentous tubes called hyphae that help absorb the material. The collection of hyphae is called mycelium. Fungi reproduce by releasing spores.
4. Protozoa
Protozoa are unicellular aerobic eukaryotes. They have a nucleus, complex organelles, and obtain nourishment by absorption or ingestion through specialized structures. They make up the largest group of organisms in the world in terms of numbers, biomass, and diversity.
Their cell walls are made up of cellulose. Protozoa have been traditionally divided based on their mode of locomotion: flagellates produce their own food and use their whip-like structure to propel forward, ciliates have tiny hair that beat to produce movement, amoeboids have false feet or pseudopodia used for feeding and locomotion, and sporozoans are non-motile. They also have different means of nutrition, which groups them as autotrophs or heterotrophs.
5. Algae
Algae also called cyanobacteria or blue-green algae, are unicellular or multicellular eukaryotes that obtain nourishment by photosynthesis. They live in water, damp soil, and rocks and produce oxygen and carbohydrates used by other organisms. It is believed that cyanobacteria are the origins of green land plants.
6. Viruses
Viruses are noncellular entities that consist of a nucleic acid core (DNA or RNA) surrounded by a protein coat. Although viruses are classified as microorganisms, they are not considered living organisms.
Viruses cannot reproduce outside a host cell and cannot metabolize on their own. Viruses often infest prokaryotic and eukaryotic cells causing diseases.
7. Multicellular Animal Parasites
A group of eukaryotic organisms consists of flatworms and roundworms, which are collectively referred to as helminths.
Although they are not microorganisms by definition, since they are large enough to be easily seen with the naked eye, they live a part of their life cycle in microscopic form.
Since the parasitic helminths are of clinical importance, they are often discussed along with the other groups of microbes.