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Symbiotic Interactions in Disease: Definition, Theory & Examples

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  • 0:38 What Is Symbiosis?
  • 1:41 What Is Mutualism?
  • 2:55 What Is Commensalism?
  • 3:55 What Is Parasitism?
  • 5:18 Obligate and…
  • 6:26 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will describe something known as symbiosis and symbionts. We will explore the three main types and examples of symbiotic relationships as we define mutualism, parasitism, and commensalism.

Mutually Beneficial Relationships

While away at college, a lot of people choose to live with roommates. There are plenty of reasons for this. You can save a lot of money by living together, or one person may do the cooking while the other one will do the cleaning. In any case, both you and your roommate will oftentimes benefit from one another's ideas, words, and actions. Otherwise, you wouldn't live together.

In a very similar way, this lesson will explore how it is that you, your body, is able to coexist with microbes.

What Is Symbiosis?

Any close relationship between living organisms of two different species is known as symbiosis. Each member in a symbiotic relationship is known as a symbiont.

Now, just a second ago, I mentioned how you and your roommate lived quite peacefully together. In fact, you guys lived in a relationship where both of you basically seemed to benefit from each other's deeds.

This isn't always the case. Sometimes, people go away to college only to end up living with a roommate from Hell. Other times, someone might end up rooming with a person who is just there, so to speak - meaning this person doesn't do or say much, but they don't hurt you either.

These types of living arrangements with roommates - beneficial, ambivalent, and harmful - are very representative of the living arrangements you and the microbes that reside on or in you have as well.

What Is Mutualism?

One example of a symbiotic relationship is the best kind you could possibly have, and it's called mutualism. This is where two or more organisms of a different species live in a mutually beneficial relationship. Basically, it's the kind of relationship where you and your roommate both benefit from living with one another, where you enjoy each other's company and so on.

In the world of microbes, a really great example of a mutualistic relationship is the case of certain types of gut flora, which are essentially bacteria in the gut. Some of the bacteria in the gut are really important in helping you digest your food or to fight off the bad bacteria that may be trying to cause you to fall ill. The bacteria that protect you in this way also benefit from you, as they not only have a place to call home - your gut - but can also use some of the food you eat as their own food!

Therefore, both you and these mutualistic bacteria are able to coexist, not only peacefully, but to the benefit of one another, or mutually.

What Is Commensalism?

However, sometimes the roommate you encounter in your college dorm or apartment you rent isn't necessarily your best friend. She derives a benefit by living with you since you cook some great meals, but she doesn't really cook anything for you in return and basically is just kind of there, not helping or harming you.

This type of relationship - a relationship between different species of organisms where one organism benefits while the other isn't harmed nor helped - is known as commensalism.

A great example of this is that some of your skin flora or skin microbes, such as bacteria, is basically on your skin and don't really do much for you. I mean, they have a place to call home - your skin - so the skin bacteria derive a benefit, but they don't protect you from anything like other dangerous microbes, and neither do they try and hurt you intentionally either.

What Is Parasitism?

Commensalism and mutualism are the types of symbiotic relationships you would want from a roommate. Nevertheless, I wouldn't be surprised if some of you have had the roommate from Hell - the one that basically takes, takes, takes, all to your financial and emotional detriment and gives nothing back. Basically, they're like a leech. They live with you in an apartment but don't pay the rent. You buy all the groceries, and they eat all the food, and so on.

A relationship between two different species of organisms where one is benefited and the other is hurt is known as parasitism. You've almost certainly heard of the term, 'parasite.' Well, they're called parasites because they drain you of your resources and give you nothing back in return. There are plenty of examples of these parasites.

For example, there are blood-sucking worms that could infect your digestive tract. They use your gut as a home and your blood as food. They give you nothing in return but the loss of nutrients and the gain of disease. Other well-known examples of parasitism include infestation by fleas, lice, or mites.

Obligate and Facultative Symbiosis

In any case of symbiosis, parasitic or otherwise, the relationships can be considered to be two different types.

One type of symbiotic relationship can be obligate. This is a relationship between two different species of organisms where one or both species rely on this relationship for survival. In essence, you can liken this to rooming with your BFF, where both of you absolutely must room together or else you will both 'die.'

This is in contrast to a facultative symbiotic relationship, which is a relationship between two different species of organisms where one or both species are not dependent on their symbiotic relationship for survival but may enter into such a relationship to enhance their survival.

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