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  • Hi. It's Mr. Andersen and in this podcast I'm going to talk about these

  • guys, bacteria. Here's a couple of e. coli that are undergoing binary fission. Bacteria

  • is an ancient domain. They're quite a bit different than us. We're in the domain eukarya.

  • But they're just as fascinating. They've been around billions of years. Some of them are

  • evil to us. And some of them are beneficial to us. And so if you look at their phylogeny,

  • basically if this is that last universal common ancestor, or LUCA, basically they diverge

  • from us a long time ago. And we have all these different types of bacteria. Know this though.

  • That there was horizontal gene transfer as well. So mitochondria, chloroplasts inside

  • our cells used to be bacteria of their own. And so they went like this. And became part

  • of our cells. And so there's a ton of this horizontal transfer. But basically bacteria

  • is going to be this other group. And they're going to be diverse. And they fill all of

  • these different niches on our planet. We're more related archaea bacteria and I'll talk

  • more about that is the next podcast. Let's talk about the structure of them. First thing

  • would be the size. Imagine this right here. This bacteria under a computer screen is about

  • this big. Then eukaryotic cells are going to be about the size of you. So we're like

  • 10 times bigger than a prokaryotic cell. Or a bacterial cell. A few other things that

  • are different. Well, our DNA is going to be organized in chromosomes which are linear

  • stretches. And they're going to be inside a nucleus. And so inside a bacteria they have

  • what's called a nucleoid region. So all of their genetic information is going to be in

  • here in this wadded up center location inside the bacteria. But they'll also have extra

  • bits of DNA. And those are going to be found in these structures called plasmids. They're

  • genetic material instead of being in a line is actually going to be in a loop. And so

  • they're going to have a loop of DNA. Another thing they don't have are going to be introns.

  • In other words every little bit of this DNA is going to code for genes or is going to

  • have a function. And then they're going to have these plasmids which are little extra

  • bits of DNA. But the whole thing is wound up so it fits inside the bacteria. Another

  • thing that they're going to have is let me kind of jump ahead, as we move out is going

  • to be the cell wall. And so if we go here all cells of course are going to have cytoplasm

  • or cytosol. And they're going to have ribosomes. However, bacteria ribosomes look a little

  • different than ours. But if we move our way out, they're going to have a plasma membrane.

  • So they're going to have a lipid bilayer. But outside of that they're going to have

  • a cell wall. And so bacteria are going to have a cell wall. And that cell wall is going

  • to be made up of a chemical called peptidoglycan. And peptidoglycan is polysaccharide. But it's

  • going to have all of these cross links between it. So it's a really stable structure. It's

  • going to be different than the cell wall that we'd find in plants. And different from the

  • cell wall that we'd find in fungi. And remember, we don't have a cell wall. Now luckily we

  • can target this. So a lot of antibiotics like penicillin for example is going to punch holes

  • in that peptidoglycan in the cell wall. It's going to lyse the cell. And we can take a

  • whole bunch of penicillin, as long as we're not allergic to it, and it's not going to

  • impact us because we don't have that cell wall. Okay. So they got a cell wall. And then

  • as we move our way out, the next thing is going to be a capsule. A capsule is going

  • to be like polysaccharide. So it's going to be this jelly like material. And then lots

  • of times you'll have pilli that will move outside of that. So these little appendages

  • on it. Now we can get some movement in a bacteria from these pilli, but most of that movement

  • in a bacteria is just going to come from a flagella. Which is just going to move around

  • and allow that bacteria to move. Again it's really really small. These are really really

  • microscopic. But the pilli are going to allow them to grab on to material. And then this

  • capsule is going to allow them to, for example, to start forming a biofilm. Another thing

  • about the pilli is that that's going to be where those antibodies grab one. And so as

  • the pilli change then we're not going to be immune to that. We're not going to make those,

  • the antibodies to that specific type of bacteria. So these are the structures of a bacteria

  • that's shared by all bacteria. But they have a ton of different shapes or a ton of different

  • morphologies. And so a lot of them are going to be this spherical shape. We call that cocci.

  • A lot of them are going to be this bacilli shape. So e. coli being an example of this.

  • Or like strep throat is going to be a bacteria. Strepto means strings of cocci or this spherical

  • shape. Staphylococci, maybe you've heard of like staph, food poisoning. So that's going

  • to be their morphology that they have. But some are going to be spiral. Some are going

  • to be vibrio shape. Some are going to be these spirochete. So there's a whole bunch of different

  • shapes. And we'll classify according to that shape. And then the other way that we can

  • classify them is using what's called a gram stain. So gram stain is going to use chemicals

  • to stain the bacteria. Because they don't really show up under a microscope unless we

  • stain them. But there are basically two types of bacteria. What are called gram negative,

  • and what they'll have is a plasma membrane. So they're going to have a membrane. Then

  • they're going to have that layer of peptidoglycan, that cell wall. And then they're going to

  • have another membrane on the outside. And so when they stain it, they're not going to

  • stain as brightly. And so we're going to call those gram negative. These are some of the

  • nastier types of bacteria because it's hard for us to get to that peptidoglycan layer.

  • And then we're going to have gram positive. So they're basically going to have this lipid

  • bilayer and then they're going to have the peptidoglycan on the outside. And so you can

  • see they're going to be much darker in color. And so you can classify bacteria by calling

  • it like a gram positive staphylococci. But there's going to be hundreds of different

  • varieties of that. And each of those are going to have different metabolism. And so what

  • do they eat? How do they make a living? Well they pretty much do it in every way possible.

  • And so there are three different types of nutritional types. What are called phototrophs.

  • You can think of that. It's light eaters. Lithotrophs. So that's going to be like earth

  • eaters. And then organotrophs. So like living eaters or the eaters of life. And so basically

  • there are two ways that we can classify them. First one is going to be where do they get

  • their energy. So they could get it from sunlight, inorganic compounds, so that is going to be

  • just chemicals, or organic compounds. And then where do they get their carbon from?

  • So it would be important to kind of mention where we are. So we are going to be what's

  • called a chemoheterotroph. And so we're going to get our energy from the food that we eat

  • or organic compounds. And then we're going to get our carbon from organic compounds as

  • well. So we're what's called a chemoheterotroph. But there are going to be a whole different

  • variety of lives that bacteria can live. In other words some of them will get their source

  • of energy from inorganic compounds. And then they'll fix carbon out of the atmosphere.

  • We call those lithoautotrophs. And so what are the two major groups? Because you're going

  • to have bacteria in all six of these groups. Well we would have the photoautotrophs. An

  • example of that in eukaryotic cells would be like plants. But in bacteria it's going

  • to be algae like these blue green algae. So they're getting energy from the sun and then

  • they're getting their carbon from the atmosphere. Or chemoheterotrophs are going to be like

  • us. And so most bacteria are going to be of that type. So like e. coli. They're eating

  • their food and then they're doing cellul respiration. Getting the carbon from that food. So how

  • do they reproduce? Well they don't do mitosis or meiosis. What they do is they reproduce

  • through a process called binary fission. So basically what they'll do is they'll copy

  • that nucleoid region and then it's simply splits in half. And so we'll get two. And

  • those two split in half and it just keeps splitting in half. And so basically what you

  • get are a bunch of bacteria. And all of those bacteria are going to be identical to that

  • first bacteria. And so that's going to be really quick. Sometimes it's as fast as like

  • 20 minutes for them to just make a reproduction. So you can make them really quick. Really,

  • really fast. However, they're all genetically identical to that first bacteria. As long

  • as we don't have mutations. And so you might think that makes them easy targets are far

  • as natural selection goes. But then they have these elements that they can swap between

  • each other. So they can let go of DNA. And that can be either released into the atmosphere

  • and picked up by another bacteria. They have these plasmids that they can release and can

  • transform other bacteria. Bacteria can come together and transfer plasmids between them.

  • There can be viruses that release the, take the DNA from one bacteria and bring it to

  • another. And so these are all forms of I would call biological sex. In other words ways that

  • we can create new bacteria without doing the steps of mito, excuse me, of meiosis and all

  • of that crossing over. So an example. Let's say that you take a, let's say you have tuberculosis.

  • And you start taking antibiotics but you don't take all of the antibiotics. Well you're going

  • to kill all of the bacteria that are susceptible to antibiotics. But you're going to leave

  • those behind that have some resistance. And a lot of that resistance will be found in

  • these plasmids. Well now the bacteria that are left can actually transfer those plasmids

  • to another bacteria giving them resistance. And so then they can grow. And so it's a really

  • quick way for them to get a huge amount of variability. There's actually three ways they

  • transfer that. Transformation is picking up something loose in the environment. We have

  • conjugation. It's the closest to actual sex, where pilus will attach between two and they

  • can share genetic information. And then the last one is going to be transduction. When

  • a virus infects one and then infects another. So we used to think they were fairly simple.

  • That bacteria just lived this kind of lonely life. Or we call that a planktonic life. And

  • so a great study was done in the 1980s on vibrio fischeri which is a type of bacteria

  • that when it's alone in the ocean by itself it doesn't make any kind of a color. But if

  • you get it living together in a colony. If there's a bunch of them close to each other,

  • then they can start to glow. So it's like they were talking to each other. And in fact

  • the bobtail squid uses these vibrio fischeri inside it to illuminate. And so especially

  • these eye pouches right here. And so scientists finally figured out how they communicate.

  • And they communicate through a process called quorum sensing. So basically a bacteria is

  • going to give off chemicals. And we call those autoinducers. Some of them will be picked

  • up by bacteria of the same species. But some of them are going to be given off and they're

  • going to be picked up by all bacteria in an area. And so if you're just by yourself, nobody

  • is going to hear that message. But if there's more bacteria, and more bacteria, eventually

  • they're are going to be so many autoinducers that those are going to trigger genes to be

  • released. And so is this case it would trigger a luciferase gene which would make all of

  • them glow. And so basically bacteria are working together, communicating with each other to

  • say how crowded it is. Or maybe to start increasing virulence so they can actually start promoting

  • a disease. And so this is a great area of research that is going on as far as stopping

  • bacterial growth. Because we've figured out if you just treat them with antibiotics they

  • quickly evolve around that. And so if we could somehow target the communication that would

  • be another great way that we could kind of stop bacteria. At least the evil ones. And

  • so that's domain bacteria. Incredibly important. Incredibly complex. And we seem to learn something

  • new everyday. And I hope that's helpful.

Hi. It's Mr. Andersen and in this podcast I'm going to talk about these

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細菌 (Bacteria)

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    Cheng-Hong Liu 發佈於 2021 年 01 月 14 日
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