Microbiology, part 45: Acellular Infectious Agents - Generalized & Specialized Transduction

Hi, I'm Cathy with Level Up RN. In this video, I will be continuing my coverage of viral replication. Specifically, I'll be talking about transduction, including generalized and specialized transduction. At the end of the video, I'm going to give you guys a little quiz to test your understanding of some of the key facts I'll be covering. So be sure to stay for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcard on transduction so you can follow along with me. And pay close attention to the bold red text on the back of the card because those are the things that you are likely to get tested on.

Transduction is the transfer of bacterial DNA from one bacterium to another by a bacteriophage, which is a virus that only infects bacterial cells. There are two main types of transduction, including generalized transduction and specialized transduction. Let's first talk about generalized transduction. So as a review, during the lytic cycle of viral replication, the bacteriophage attaches to the bacterial cell, injects its genome into the cell, hijacks the cell's machinery to make new viral particles, and then those viral particles are released when the cell lyses or bursts open. Now, sometimes when the phage is assembling those new viral particles, it accidentally inserts a random piece of the host cell's DNA into the capsid, which means that when the host cell lyses and that new virus is released, it will go on to infect a new host cell and inject that bacterial DNA into another bacterium. The transfer of genes from one bacterium to another is a form of horizontal gene transfer, which introduces genetic diversity into a bacterial population.

The other main type of transduction is specialized transduction, which occurs during the lysogenic cycle of viral replication. So as a review, during the lysogenic cycle, the bacteriophage attaches to the bacterial cell, injects its genome into the cell, and that genome is incorporated into the host cell's chromosome, forming a prophage. With specialized transduction, when induction occurs and the prophage is excised or cut out of the cell's chromosome, sometimes bacterial genes next to the phage DNA are also accidentally cut out. And then when the phage replicates its DNA and assembles new viral particles, the genome containing viral genes and bacterial genes gets packaged into the capsids. And then those new viruses containing the combined genomes are released and go on to infect new bacterial cells. And when they do, the bacterial genes from the original bacterium are incorporated into the new bacterium. And just like with generalized transduction, that transfer of genes from one bacterium to another is a form of horizontal gene transfer. So one key difference between generalized and specialized transduction is that with generalized transduction, a random bacterial gene ends up getting incorporated into the new viral particle. Whereas with specialized transduction, specific bacterial genes that were next to or adjacent to the phage DNA end up getting incorporated into the new viral particle.

All right. It's quiz time. And I have three quick questions to test your knowledge of some of the things we just talked about.

Question number one, is transduction a form of vertical or horizontal gene transfer?

The answer is...horizontal.

Number two, with blank transduction, a random piece of host DNA is inserted into the viral capsid.

The answer is...generalized.

And number three, with blank transduction, specific genes from one bacterial cell are transferred to another bacterial cell.

The answer is...specialized.

All right, that's it for this video. I hope it was helpful.

[BLOOPERS]

Which occurs during the lysogenic cycle of viral [inaudible]-- I don't know; I have the worst time saying viral replication.