Prokaryotes in the Environment - Online Tutor, Practice Problems & Exam Prep

Bacteria and archaea are crucial for biogeochemical cycles, particularly the nitrogen cycle, where they perform nitrogen fixation, converting atmospheric nitrogen (N₂) into usable forms like ammonium. They also play significant roles in the carbon cycle as decomposers and in producing oxygen through photosynthesis. The human microbiome consists of resident and transient microbiota, with resident microbes living long-term in the body, while transient microbes are temporary. Pathogens can produce toxins, classified as exotoxins and endotoxins, which damage host tissues and can overstimulate the immune system, causing further harm.

Prokaryote Ecology

There are many cycles of energy flow and nutrient flow or, you know, the flow of matter through the biosphere. Bacteria and archaea play very important roles in all of these processes. The most notable one, the one that really could not happen without them, is the nitrogen cycle. Specifically, prokaryotes are responsible for what's called nitrogen fixation, where they take atmospheric nitrogen. Right? N2, that gas that most of the air we breathe is made up of. Right? Like over 70% is N2. And they convert it to a usable form of nitrogen, as in a form that other organisms can actually utilize and must utilize. And this is ammonium or nitrogen dioxide. So, essentially, the entire nitrogen cycle depends on prokaryotes to perform nitrogen fixation. This makes bacteria and archaea the drivers of the nitrogen cycle on this planet. Now, here we have a little image of the nitrogen cycle. You don't need to worry about all the specifics of the nitrogen cycle. That's something we'll cover in ecology. The main thing that I want you to appreciate and understand is this bottleneck that essentially occurs here. These processes all rely on bacteria. We need that bacteria to generate usable nitrogen that will feed back into plants, animals, and other organisms, and is essential for much of life as we know it. So, it's a super important process that is completely and eloquently performed by these prokaryotes.

Now that's not the only way that prokaryotes influence the biosphere on a cycle level. For example, there's also what's termed the carbon cycle, how carbon flows through the biosphere. And remember that bacteria, or prokaryotes in general, are very important decomposers. They break down organic matter, so they help cycle carbon through the biosphere as well. Additionally, photosynthetic bacteria like cyanobacteria produce oxygen and they actually are responsible for having generated a lot of the atmospheric oxygen on Earth. We're talking ancient history, billions of years ago. These organisms were responsible for all of this oxygen in the atmosphere. Huge impact on the biosphere. Unbelievable impact on the biosphere. As I mentioned previously, bacteria and archaea also play an important role in the internal environments of humans and ruminants, like cows. Actually, a lot of other organisms too. I'm specifically mentioning ruminants because of the methanogens previously mentioned that help them digest their food. Also, it's become a very hot topic in medicine as of late, exploring the relationship between humans and the bacteria that help us function. Not only the bacteria that live inside us but also the bacteria that live on us. Specifically, the hottest topic is how the bacteria in our gut help us live, and the implications are way beyond what you'd expect. There are even studies that have shown some connection between the animal brain and these bacteria. Like literally, these bacteria can influence the brains of animals and their thinking. Really cool stuff. And also, you wouldn't be able to live without these bacteria. That should also be said. The bacteria that live inside you allow you to stay alive. And the last fact about how important bacteria are because I can just go on and on. I love prokaryotes. I think they're amazing. There are more cells living inside of you, more of these bacteria inside of you, than there are cells that make up your entire body. Okay. Drop the mic. I'm done. That's all I've got for this video. Go bacteria.

The Human Microbiome

In this video, we're going to refocus our attention on the human microbiome. And so first, we need to recall from some of our previous lesson videos that the microbiome is also sometimes referred to as the normal flora. The microbiome or the normal flora refers to the communities of microbes that grow on and in the bodies of all humans at all times. These microbes that are part of the microbiome or normal flora live in symbiotic relationships with humans, and they can be further classified into 2 groups. They can be classified as resident microbiota, or they could be classified as transient microbiota.

Resident microbiota, as its name implies, include microbes that are going to be residing in our bodies for long periods of time. The resident microbiota are microbes that are almost always on or in the host for extended periods of time. The transient microbiota, on the other hand, includes microbes that are only temporarily found on the body for relatively short periods of time. Of course, pathogens, disease-causing agents, are going to be considered transient microbiota. They're only on us for relatively short periods of time in most cases, but not in all cases.

Now, if we take a look at our image down below, we can get a better understanding of the difference between resident and transient microbiota. On the left hand side, notice it's an image focused on the resident microbiota, which are going to be microbes that are almost always on the host for extended periods of time. Notice here we have a cartoon showing you these microbes that are residing in the lungs, calling the lungs "home sweet home." And notice it's saying, "I love our home in the lungs. I never want to leave." They seem pretty comfortable and relaxed and they don't look like they're going anywhere anytime soon. These resident microbiota are on or in our bodies for long periods of time.

On the right hand side, we're focused in on the transient microbiota. The transient microbiota, of course, are only found in our bodies for temporary periods of time, or short periods of time. Notice that these microbes right here don't look like they're sticking around much longer. They've got their bags packed and they're ready to hop on the microbe transit to make their way to their next destination because they're not going to remain in or on the host for extended periods of time. So notice their next stop is going to be outside of the host, and again, they are going to be temporarily found on the body.

This here concludes our brief intro to the microbiome and normal flora and our intro to resident and transient microbiota, and we're going to continue to talk more about the microbiota as we move forward in our course. So I'll see you all in our next video.

Scientists commonly call humans 'superorganisms'. What is this description referring to?

• A. Humans are the most intelligent and influential organisms on the planet.
• B. Each human is an ecosystem for trillions of microorganisms.
• C. Humans are the only organisms that determine the success of other organism species.
• D. Each human is host to a unique species of microorganism.

Which of the following answers does not include an example of transient microbiota?

• A. Microorganisms that inhabit certain body sites for extended periods of time.
• B. Microorganisms that are able to inhabit different body sites during their lifetime.
• C. Microorganisms that only occupy the body for a short period of time.
• D. Microorganisms that are pathogenic and eventually removed by the body's immune system.

Introduction to Pathogenic Toxins

In this video, we're going to begin our introduction to pathogenic toxins. Certain pathogens are capable of producing biological poisons called toxins, which allow the pathogens to invade and damage host tissues. The term toxicogenicity refers to the ability of the pathogen to produce toxins that damage the host cells. Toxins can be classified into two groups: the first group being the exotoxins and the second group being the endotoxins.

Exotoxins are soluble proteins released by a pathogen during an infection or following the lysis of the pathogen. As we move forward in our course, we will discuss exotoxins in more detail. We will also learn that there are three different categories of exotoxins, grouped by their structures and functions, which we will see in our image shortly. Endotoxins, on the other hand, specifically refer to lipopolysaccharide or LPS, found in the outer membrane of gram-negative bacteria.

We will talk more about endotoxins as we continue. For now, this is just the introduction. In our image below, you'll notice a map of our lesson on pathogenic toxins. These toxins can be categorized either as exotoxins or as an endotoxin. The exotoxins can be further categorized into three groups: the AB toxins, the membrane damaging toxins, which include pore-forming toxins and phospholipases, and the superantigens.

As we progress, we will discuss each of these groups of exotoxins in more detail. Endotoxin specifically refers to the lipopolysaccharide or the LPS found in the outer membrane of gram-negative bacteria. It is also important to note that the host immune system is capable of causing unintended damage to host cells when it is overstimulated during an infection. Sometimes pathogens can harm simply by inducing our own host immune system to overstimulate and cause damage.

This concludes our brief introduction to pathogenic toxins, and we will learn more about them as we move forward in our course. I'll see you all in our next video.

Phospholipases are characterized by all of the following except which of these answers?

• A. Possess the ability to damage host cells.
• B. Are released by pathogens into host cells during infection.
• C. Are able to form pores in the cell membranes of host cells.
• D. Are able to hydrolyze cell membranes of host cells.

The term endotoxin is synonymous with:

• A. A-B toxins.
• B. Lipopolysaccharide (LPS).
• C. Phospholipase.
• D. None of the above.

Characteristics of a pathogen that promote pathogenicity are called:

• A. Pathogen factors.
• B. Colonization factors.
• C. Infectious agents.
• D. Virulence factors.

Virulent pathogens are:

• A. Less likely to cause disease.
• B. More likely to cause disease.
• C. Only able to cause disease in weakened hosts.
• D. Always cause disease whenever inside a host.

Which of the following pathogen characteristics may be considered virulence factor(s)?

• A. Adhesins (molecules that allow a pathogen to adhere to a host cell).
• B. Capsules (protective coatings on the outside of certain bacteria).
• C. Endotoxins (damaging molecules created by certain bacteria).
• D. Proteases (damaging molecules created by certain bacteria).
• E. All of the choices are correct.

An encapsulated bacterium can be a virulent pathogen because the capsule:

• A. Resists phagocytosis.
• B. Destroys host tissues.
• C. Is composed of endotoxins.
• D. The capsule has no effect on the virulence of a bacterium.

Which of the following is a true statement?

• A. A successful pathogen never kills the host.
• B. Throughout disease evolution, the most virulent diseases have spread the fastest.
• C. A successful pathogen does not kill the host before it is transmitted.
• D. The primary goal of a pathogen is to kill the host.