there are two main types of transduction and I went back to your textbook from openstax and I looked to see how much detail they went into on transduction because this can be a fairly complicated topic and I'm going to talk about it at just the level they do so that we're consistent between the book and then these these lecture slides so hopefully between those two resources you'll be able to follow along and get the information you need transduction just means that a virus is transferring DNA from one bacterial cell to another bacterial cell and when we say it's transferring DNA we mean is transferring bacterial DNA so you know that a virus will will inject its own DNA into the bacteria but once in a while the virus makes a mistake and it ends up with some of the host DNA and it transfers that to another cell so that's what we're talking about with transduction in generalized transduction which is the easier of the two to understand basically what happens it's just random fragments of the host DNA are accidentally picked up when the phage is being assembled and then when that phage goes and infects another bacterium instead of giving in virus DNA it's giving it DNA from the prior host that it was it had infected in specialized transduction we have to understand the difference between a lysogenic and lytic cycle in a phage and so this is this because of how this works it ends up not being so random piece of host DNA but a very specific piece of host DNA so let's talk about generalized transduction first now this picture is not a generalized transduction this picture is just a basic a basic lytic cycle of a virus but it's easy enough to figure out how this works so here's our bacterial posh here and here's our bacterial cell for bacterial cells about to get infected and we know it's not going to survive right the infection is going to kill it so the virus injects its DNA and here we have our host DNA here and when this happens the host DNA as a part of the process of just killing this cell the host DNA often breaks little pieces and I'm gonna get my little notepad here because I want to be able to draw see if I can do this so it turns out that sometimes when this happens one of these little pieces ends up being a piece of this original host DNA so do you see this here let's see if I can change the color I'm not sure I can let's see it doesn't let me change the color that I can see so anyway pretend this is pink like this host DNA so we have all of these phage and we've got all this nice viral DNA that the phage is gonna be we're gonna package this inside the phage head but once in a while one of the packages gets host DNA instead of viral DNA so here we go I'm going to draw here so this particular phage instead of having bacterial viral DNA it has some of the bacterial DNA and now when this page leaves we go again alright this particular page has bacterial DNA and when it goes and infects another bacteria that DNA it's not virus DNA anymore it's not going to be able to cause a new infection but it is going to transfer some of this DNA into another cell the next host that it lands on - so that's generalized transduction in for all the times this happens it probably happens quite a bit most of the time it doesn't have any effect on the cell sometimes that DNA just gets degraded by the new host cell but once in a while that ends up being a useful gene like for example an antibiotic resistance gene and so while this is a rare event when you think about how frequently how for example just how many bacteria grow in culture and how many phage there are even rare events end up happening fairly often because of the sheer number of potential interactions that occur between these organisms all right so that's generalized transduction go back to my other pointer let's talk about specialized transduction I haven't done a very good job sponsors okay specialized transduction before we do that I want to talk about the difference between the lytic cycle and the lysogenic cycle I realize I need to clear all my drawings there there we go okay so Linux cycle let's go back for a second this is this is the lytic cycle here this is the normal cycle where the phage infects the bacteria the phage takes over the cell it causes the cell to make all sorts of new phage DNA the phage DNA gets packaged and then the cell breaks open in some ways it kind of just blows up that cell is usually so full of phage that it kind of explodes and fades you're released when they go in fact other cells that's called a little cycle okay now there's also something called a lysogenic cycle and then the lysogenic cycle is a little different so these are called temperate sages and what they do is they will put their DNA into the cell but instead of infecting the cell right away or they're infected but instead of causing the cell to break up right away causing a big major infection what they do is they sneakily incorporate themselves into the hosts DNA do you see that so well it's nothing the cells are too innocent it doesn't think anything bad has happened but now we have a little piece of the phage DNA inside the cell and this is called a pro phage okay so this is actually really important because there are a bunch of virulence factors and some common diseases that are the result of a pro phage being incorporated into previously harmless bacteria so this pro page DNA as the cell divides that's going to divide it's gonna copy the pro base DNA so that this is kind of sneaky right the virus is here it's getting copied but it hasn't done anything to this cell yet it's actually allowing the cell just a copy it's DNA every time the cell divides now under certain conditions for example under stressful conditions this piece of viral DNA can pop back out and form a virus again and when this happens it usually transitions from the lysogenic cycle to a little cycle so we're going back to a little cycle now we're going to go ahead and we're gonna process this just like we would have you know lytic cycle we're going to destroy the cell we're gonna make lots of copies of the phage DNA we're going to package them and the cell is going to burst open with phage and they're going to go and travel and if infect other cells so this is a more complicated life cycle analytic cycles all right so how does this relate to specialized transduction well in the case of specialized transduction it involves one of these temperate phage that results in a lysogenic cycle so the phage DNA gets incorporated into the cell it becomes a pro phage and what happens is is that when the phage excises itself to go ahead and make new phage it doesn't do a perfect job so it ends up with some of the host DNA as well when these Pro fades are inserted they typically insert in one specific location and because of that it's not random with this pieces it's usually the piece that's always right next to where the insertion occurred and so here you have you have this this viral DNA and it's going to get copied but it's also copying a little piece of the host DNA and when it gets packaged and it's gonna they're showing a big step here so that DNA has gotten packaged and now it's going and infecting a new cell do you see that it's got a little piece of the host DNA from the prior cell it's also coming in along with phage DNA and so now we have phage DNA old host DNA and then our new host DNA so again this allows for genetic variability in bacteria because you're actually using the virus to transfer DNA from one host cell one bacterial host to another bacterial host so here's just a picture of a pro page I thought this might be helpful it's it's just the genetic material from a virus incorporated into the host into the host genome okay and sometimes these Pro phage genes are able to make variants factors so the the toxins that the organism corynebacterium diphtheria causes diphtheria botulinum toxin cholera toxin and some of the various factors and streptococcus pyogenes these are all fairly nasty pathogens they can all be traced to probe age DNA that resulted in these particular organisms becoming virulent the way they so that's why we've gone ahead and and made the effort to understand this because it does affect many bacteria and you know streptococcus pyogenes is an interesting example we talked about the fact that it causes necrotizing fasciitis and how terrible that is but one of the things we've actually seen is a greater incidence of necrotizing fasciitis and that's because this organism is is affected by lateral gene transfer in variety of ways but in particular it can get these these pro base genes that result in it accumulating more and more virulence as it begins to gain the ability to do a better job making enzymes that break down tissues and allow it to become more invasive so this is definitely something that's been documented in the last 10 years or so okay so I hope that was useful and if you have questions on transduction and conjugation and transformation and mutation definitely email me through your canvas inbox so that I can help you with some of these challenging concepts