Protozoa – Introduction to Microbiology

by Vincent Racaniello, PhD

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    00:00 So that brings us to the other kinds of eukaryotic microbes I'd like to tell you about, there are several that we won't touch upon, there are slime molds for example which are considered microbes, there are microscopic algae and then there are protozoa. Collectively we call these last three protists. And I just want to focus on the protozoa because we'll be talking about those in some detail.

    00:24 The protozoas are a diverse group of unicellular eukaryotes. That means they consist of just one cell. And a very famous one is the Paramecium, which is a protozoan with cilia on it, it has tiny hair-like extrusions around the surface. You may know Paramecium because when you were in school, you may have looked at a drop of pond water and seeing these very tiny protozoans swimming around. It's often studied in schools because it's safe. Many human pathogens happen to be protozoans, for example as shown in this photograph, there are flagellated protozoans that cause human disease, the Trypanosoma, the agents of sleeping sickness. Amoeba are also protozoa and some of these are known to cause human diseases, for example the Entamoeba shown in this photograph which are agents of diarrheal disease. There are ciliated protozoan parasites also; this one is called Balantidium, which in humans can cause gastrointestinal disease. And finally some of the protozoas called Apicomplexa can cause human disease and these include the very well-known Plasmodium, the agents of malaria, and Toxoplasma, the agents of toxoplasmosis.

    01:42 Let's take a look at the timeline of evolution on earth, because it turns out that microbes are incredibly ancient. We think that the Earth formed about four and a half billion years ago.

    01:57 And about 4 billion years ago, life began. We're not really sure what that life looked like, we don't have any experimental evidence for it, but many scientists think that it composed of small nucleic acids replicating in the waters of earth. About three and a half billion years ago, the first bacteria evolved, these were photosynthetic bacteria that could take sunlight and make energy from it, but these were not oxygenic bacteria, in other words they didn't make oxygen, so up to that point there was no oxygen on the earth. About two and a half billion years ago, two and a half to 3 billion years ago, the photosynthetic cyanobacteria emerged on earth. These were oxygenic, these bacteria actually produced the first oxygen on earth. And because of that, then about two and a quarter billion years ago, the aerobic bacteria arose. Those are the bacteria that can use oxygen to grow. Unicellular eukaryotes arose about 2 billion years ago, a little less than a billion years ago, the multicellular eukaryotes arose, like jellyfish and then plants and animals about 1 and a half billion years ago.

    03:18 The hominids, which include humans, chimpanzees and the apes and so forth, are arosed about 14 million years ago and humans only a 150,000 years ago. So microbes are truly ancient.

    03:36 We classify living things by using what we call phylogenetic trees and sometimes we call them the tree of life. And the purpose of these trees is to show how organisms are related.

    03:47 So let's take a look at these microbes that we've talked about and put them on the tree of life. First we will start with the bacteria, they're all shown here and the way this tree is organized, it shows you the relationships with the different bacteria, so the further apart they are, the more distant. All the bacteria are related as you can see, but different kinds of bacteria obviously have differences among each other. Now let's put onto this the eukaryotic microbes and other eukaryotes that we've talked about. Here we include the protozoa, the algae, plants, animals and fungi, you can see they form a separate branch on the tree of life. They are more related to each other, than they are to the bacteria.

    04:31 And finally let's add the archaea, they are in green here and you can see that they too form a separate branch on this tree of life. So the three groups of eukaryotic and bacterial and archaea microbes that we've talked about, all arose from a common ancestor billions of years ago and over time they have diverged and become very different.

    About the Lecture

    The lecture Protozoa – Introduction to Microbiology by Vincent Racaniello, PhD is from the course Microbiology: Introduction.

    Included Quiz Questions

    1. Plasmodium
    2. Entamoeba
    3. Paramecium
    4. Trypanosome
    5. Balantidium

    Author of lecture Protozoa – Introduction to Microbiology

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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    interest devolp
    By mishal m. on 07. December 2020 for Protozoa – Introduction to Microbiology

    better way of making it very interesting,short lectures. easily understable

    Very easy to understand!
    By Berenice G. on 14. March 2018 for Protozoa – Introduction to Microbiology

    very well explain and illustrate! The information match perfectly the pictures and the speed of the expositor is flawless.