 When Karl Woz decided to revolutionize the classification system, he divided all Monerans into two domains, Archaea and Bacteria. Now Archaea are the special ones. They have some genes and enzymes which are closely related to that of the eukaryotes. All the other prokaryotes that didn't have such a thing were placed in the domain Bacteria. In this video, we're gonna be taking a closer look at this domain and talk about its characteristics and diversity. One of the most characteristic features in a Bacteria is the cell wall and most of them have pretty rigid cell walls. It's made up of something called peptidoglycan which is a compound that is not found anywhere else and the cell walls most crucial purpose is to provide overall strength, protection and maintain the shape of the bacteria. Now I don't know if you notice this but I never said that all bacteria have cell walls because they don't. One such exception is the Bacterial Genus Mycoplasma which completely lacks a cell wall and peptidoglycan. Other than cell walls, bacteria like every other living being on this planet also has DNA which is the genetic material of the Bacteria. Now besides these two things that is the DNA and the cell wall, some bacteria also come with some extra stuff like a flagella and chlorophyll. So you see this wavy tail like thing over here, this is the flagella. So a flagella or the singular form is called flagellum. So it is a hair like organ that provides the bacteria with motility. So it's basically like a tail like I said that helps the bacteria move or swim from one place to another. Now some bacteria will have only one flagellum like Vibrio Cholery which is the cholera causing bacteria and then there are some other bacteria like E. Coli or Esturacea Coli which is the bacteria that is found inside your gut. They have not one but they have multiple flagella on them. Now bacteria that have chlorophyll or chlorophyll like pigments can carry out photosynthesis which makes them photosynthetic autotrophs. That means that they can make their own food like glucose from simple inorganic compounds like carbon dioxide and water using light as a source of energy. Now some bacteria which is actually this bacteria that we have right over here, this is cyanobacteria. Now cyanobacteria has the pigment chlorophyll A which is the same pigment that you will find in plants. So they can use this pigment to harvest light energy and then absorb carbon dioxide from the atmosphere to produce food and release oxygen via photosynthesis. Exactly like plants do. So does that mean that in order to be an autotroph you need to perform photosynthesis? Well not really. There are some bacteria which are chemosynthetic rather than photosynthetic. Now these bacteria are also autotrophs but they cannot use light as a source of energy. Instead they get their energy from the oxidation of inorganic compounds like hydrogen sulfide, nitrites, ferrous ions and compounds like that and they use that energy to make their own food. And while they are doing this while they're making their own food from using this oxidation energy they actually end up recycling different compounds in the environment like iron or sulphur or nitrogen. And an example of such a chemosynthetic bacteria is actually the bacteria that I've shown over here. So this is nitrosomonas. So nitrosomonas is a chemosynthetic bacteria which plays a major role in the nitrogen cycle of the atmosphere. And other than that, nitrosomonas is also a nitrifying bacteria which is found in the soil. Now the thing about nitrifying bacteria is that they can convert ammonia into nitrates and these nitrates are very easily absorbed by plants. So in a way these bacteria can increase the fertility of the soil. So soil bacteria like nitrosomonas are extremely extremely useful to us. Now that we've gotten the autotrophs out of the way, let's take a look at the heterotrophs. Majority of bacterial species are heterotrophic in nature. That means that they cannot make their own food and they get their energy from other organisms. And a lot of these bacteria, these heterotrophic bacteria, are also very very useful to us. For example, there are some bacteria which feed on the dead and decaying organic matter, breaking them down or decomposing them in the process. These type of bacteria are called saprophytes. So these decomposers, they are basically a part of the cleanup crew of the earth. So they're basically cleaning up all the garbage that is lying around. And an example of such a saprophytic bacteria is this bacteria, the picture that I have right over here, this is basillus subtilis. So this is a saprophytic bacteria. Other than cleaning up, bacteria have also become superstars in the field of biotechnology. They help us in the production of many many things, including food. For example, there are some heterotrophic bacteria called lactic acid bacteria which help us in making curd from milk. And an example of that is this bacterial genus called lactobacillus, lactic acid bacteria. And other than this, there are some bacteria which also help us in the production of antibiotics. So these are antibiotics. And as you can see that bacteria also help us in the production of antibiotics. And an example of that is streptomyces. Some bacteria are also genetically modified for various purposes. Speaking of useful bacteria, there are bacteria even inside our guts. Yes, there are like trillions of bacteria in our gut and they are super super friendly. They help us in many ways like making vitamins and keeping us safe from harmful microbes. But as you might have guessed already by now that these are the good guys and not all bacteria are the good guys. Some of these bacteria are such villains that they will give the joker a run for his money. Now most villainous bacteria are actually pathogens. That means they can cause diseases. They affect plants, animals and definitely us too. Now we've already mentioned one disease which is cholera. It is caused by this bacterium called vibrio cholerae and during this disease you will suffer from very bad diarrhea and dehydration. A few other diseases include typhoid and sore throat. Let's bring those into focus a little bit over here. Now typhoid is caused by this bacterium called salmonella typhi, which is spread through contaminated food. Sore throat on the other hand is caused by a bacteria called streptococcus and when somebody suffers from sore throat caused by streptococcus their throat turns white kind of like this. Now there are many many bacterial diseases seen in animals but what about plants? A very common bacterial disease that is seen in plants is the citrus canker disease. Have you ever seen a lemon with spots like this? So this is an actual disease which is the citrus canker disease and it is caused by a bacterium called xanthomonas. Now again there are many bacterial diseases seen in plants as well and this is just a tiny example of that. Now bacteria can cause a disease only when it multiplies like crazy or it reproduces like crazy. So let's take a look at exactly how a bacterium can reproduce. Mainly and most commonly bacteria reproduce by binary fission. In this process a bacterial cell splits into two daughter cells and each of these daughter cells are identical to the parent cell. So this is the parent cell and these daughter cells over here will be identical to this parent cell. In some bacteria like actinomycetes spore formation is seen as a mode of reproduction. So a spore which is this green colored round thing over here. So this is a tiny structure which is extremely resistant to harsh unfavorable environmental conditions. When the environment around the bacteria becomes favorable once again these spores will give rise to new bacteria and this is seen in actinomycetes. So let's write that down as well. Actinomycetes. So you'll see spore formation as a mode of reproduction in these bacteria. Another mode of reproduction is conjugation. Now some bacteria can transfer genetic material aka DNA to other bacteria and conjugation is one way of doing that. The main thing about conjugation is that the DNA is transferred through direct contact and this direct contact is established with the help of this long tube like bridge that you can see in the picture right over here. This bridge gets formed between the two bacterial cells and this is what facilitates the transfer of the DNA. Bacterial reproduction is quite fascinating right? Do you know that there are actually bacteria that reproduce so rapidly like within 10 to 15 minutes? Like in a span of 10 to 15 minutes some bacteria can double their entire population and a bacteria that comes really close to this is E. coli. They can reproduce in literally 20 minutes. The world of bacteria is huge and a lot of it still remains unknown to this very day. Some scientists estimate that there are millions even billions of bacterial species on our planet. I can only imagine the kind of stuff that is still waiting for us to discover about them.