Prokaryote Lineages - Online Tutor, Practice Problems & Exam Prep

Prokaryote Lineages 1

Hi. In this video, we're going to take a quick tour of some of the major lineages of prokaryotes. We're going to begin with proteobacteria, a diverse clade of gram-negative bacteria that's actually organized into 5 subgroups that are named with Greek letters alpha, beta, gamma, delta, and epsilon. And you can see a phylogenetic tree of proteobacteria right here. Now you might notice that this also includes zeta proteobacteria. This is a newer grouping, and your books likely won't include it. Now, many species of proteobacteria are involved in nitrogen fixation. Don't forget that it was proteobacteria that was engulfed by a cell and eventually would become mitochondria. So, and of course, they led to a super important structure in eukaryotes. Now, moving on, we have Chlamydia which is a group of gram-negative bacteria that lack peptidoglycan in their cell walls. Hopefully, remember that gram-negative bacteria usually have a thin layer of peptidoglycan, below the outer lipopolysaccharide layer. Well, these bacteria don't have that peptidoglycan at all. They're also all parasites. All of the species in this group are parasites that live inside host cells and you can see a picture of that happening right here. These translucent blobs are those host cells and you can see these 3 have these brown spots inside them. Those brown spots are the Chlamydia cells that have been stained with a particular stain, turning them brown so that we can visualize them. Those cells have been infected with Chlamydia. The Chlamydia is living inside of them. Again, if this name sounds familiar, it's because the famous STD, Chlamydia, is caused by bacteria in this group. We often just refer to it as Chlamydia though, the sort of group name. Now, spirochetes are gram-negative heterotrophs and what's distinct about them is their corkscrew shape that you can see in these two pictures. This sort of zoomed-out one, those little dark squiggles, these cells that are stained in yellow in this image. And for a more zoomed-in look, an image of a spirochete, much more zoomed in. You can really see that corkscrew shape of the bacteria. Spirochetes have 2 famous diseases caused by spirochetes that you've probably heard of. Those are Lyme disease and the STD syphilis. Lovely things, spirochetes, right? Lovely diseases. All right. With that, let's and I'm sorry. I'm just making a joke. I'm being sarcastic. Don't mean to make light of diseases caused by these bacteria. But yeah. Basically, the endpoint is nasty little guys, these spirochetes. Alright. With that, let's turn the page to talk about some other bacteria.

Prokaryote Lineages 2

Cyanobacteria are gram-negative photoautotrophs, and many species actually perform nitrogen fixation. Now they are sometimes termed blue-green algae, but this is a bit of a misnomer, as they are in fact prokaryotes, not eukaryotes at all. They're actually the only bacteria that perform oxygenic photosynthesis, and it's pretty incredible because they're responsible for the origin of oxygen in the atmosphere. And you can see a nice up-close image of some cyanobacteria here. These are cyanobacteria that grow in filaments. Some grow as free-floating little cells and others form colonies. And you can see that this is a satellite photo here. And this green mass here, that is just cyanobacteria. That is a huge bloom of cyanobacteria, obviously generating a bunch of oxygen because it's performing a bunch of photosynthesis. I mean, pretty amazing. This is a satellite photo and there are so many of these tiny microorganisms that we can see it from space. And actually, the oldest fossils we have of life on Earth come from cyanobacteria. These are stromatolites. These blobs of what look like rock, it's actually calcium carbonate, and this is exuded by certain types of cyanobacteria. And, basically, the oldest fossils we have of life on Earth are stromatolites from cyanobacteria. These are modern, you know, living cyanobacteria, but we have stromatolites that look like these from, you know, over a billion years ago. It's amazing. Now, and also, don't forget, lastly, that cyanobacteria are the organisms that were engulfed and eventually became chloroplasts.

Now, actinobacteria are high GC gram-positive bacteria. And what that means is they have a large, or a high percentage of guanine-cytosine, right, GC from DNA in their chromosome. So they have a high GC content, so to speak. They're gram-positive bacteria and they include the genus Streptomyces, which is responsible for many antibiotics. Many antibiotics have come from this genus of actinobacteria. Now, these were initially misclassified as fungi because they have a fungus-like morphology. And as you'll see in the name, it ends with myces. What you'll see once we or when we discuss fungi is that the names, the Latin names for fungi end in 'myces'. So these were initially thought to be fungi, actually, bacteria. Now, the misclassification comes from the fact that chains of cells form these branching mycelia. And it's these structures that caused biologists to think that these were actually fungi.

Lastly, we have the Firmicutes, which are low GC gram-positive bacteria. So, the high GC is basically in comparison to these low GC bacteria. And this group includes the genus Lactobacillus, which is super important to humans. Not only are they responsible for yogurt production, obviously very important, and also they're involved in cheese production, very important. And most important to me, they're involved in sour beer production. If you've never heard of sour beer, you should try it. It's delicious. And it involves fermentation with Lactobacillus inside humans that are super important, for our health. I mean, many species live in our gut and help us with digestion. There are species that live in the vagina that help maintain that environment, and that's actually what this image is depicting. This is a human cell and you can see all these little dark rods. Those are Lactobacillus, and they are a species of Lactobacillus that live in the vagina.

Here’s what students ask on this topic:

What are the major lineages of prokaryotes and their characteristics?

Prokaryotes include diverse groups such as proteobacteria, chlamydia, spirochetes, cyanobacteria, actinobacteria, and firmicutes. Proteobacteria are known for nitrogen fixation and gave rise to mitochondria. Chlamydia are gram-negative parasites lacking peptidoglycan. Spirochetes, with their corkscrew shape, cause diseases like Lyme disease and syphilis. Cyanobacteria are responsible for oxygenic photosynthesis, crucial for atmospheric oxygen, and form ancient stromatolites. Actinobacteria, including Streptomyces, produce antibiotics. Firmicutes, like Lactobacillus, are vital for yogurt production and gut health.

How do cyanobacteria contribute to the Earth's atmosphere?

Cyanobacteria are gram-negative photoautotrophs that perform oxygenic photosynthesis, producing oxygen as a byproduct. They are the only bacteria capable of this process and are responsible for the origin of oxygen in the Earth's atmosphere. Cyanobacteria's photosynthetic activity led to the Great Oxygenation Event, which dramatically increased atmospheric oxygen levels, enabling the evolution of aerobic life forms. Additionally, cyanobacteria form ancient stromatolites, which are some of the oldest fossils on Earth.

What diseases are caused by spirochetes?

Spirochetes are gram-negative heterotrophs with a distinct corkscrew shape. They are responsible for causing several diseases, most notably Lyme disease and syphilis. Lyme disease is transmitted through tick bites and can lead to symptoms such as fever, headache, fatigue, and a characteristic skin rash. Syphilis is a sexually transmitted infection that progresses through multiple stages, potentially causing severe health issues if left untreated.

What is the significance of proteobacteria in the evolution of eukaryotes?

Proteobacteria are a diverse clade of gram-negative bacteria, some of which are involved in nitrogen fixation. A significant evolutionary event involving proteobacteria is their endosymbiotic relationship with early eukaryotic cells. A proteobacterium was engulfed by a primitive eukaryotic cell, eventually evolving into mitochondria, the powerhouse of eukaryotic cells. This endosymbiotic event was crucial for the development of complex eukaryotic life, providing cells with efficient energy production capabilities.

How do actinobacteria contribute to antibiotic production?

Actinobacteria are high GC gram-positive bacteria, meaning they have a high percentage of guanine and cytosine in their DNA. This group includes the genus Streptomyces, which is renowned for its role in antibiotic production. Streptomyces species produce a variety of antibiotics, such as streptomycin, which are used to treat bacterial infections. These antibiotics are derived from the secondary metabolites produced by Streptomyces, making actinobacteria crucial in medical and pharmaceutical fields.