Question

Define plaque, lysogeny, and prophage.

Short answer

Answer: A plaque is a clear area on a bacterial lawn formed due to the lysis of bacterial cells by bacteriophages. Lysogeny is a type of life cycle of a bacteriophage, in which the phage's genetic material integrates into the bacterial host's genome and replicates without causing immediate harm. A prophage is the genetic material of a bacteriophage that has integrated into the genome of a bacterial host during the lysogenic cycle.

Step-by-step solution

Definition of Plaque

A plaque is a clear area on a bacterial lawn, formed due to the lysis (destruction) of bacterial cells by bacteriophages (viruses that infect bacteria). A plaque results from the multiplication and spread of a single bacteriophage, as the phage reproduces within the bacteria, causing cell lysis and releasing more phages that go on to infect nearby bacterial cells.

Definition of Lysogeny

Lysogeny is a type of life cycle of a bacteriophage, in which the phage's genetic material integrates into the bacterial host's genome and replicates along with the host's genetic material without causing lysis or immediate destruction of the host cell. This is called the lysogenic pathway, and the bacterium containing the prophage is called a lysogen.

Definition of Prophage

A prophage is the genetic material (DNA) of a bacteriophage that has integrated into the genome of a bacterial host during the lysogenic cycle. The prophage replicates passively along with the host's DNA, without causing immediate harm to the bacterial cell. Under certain conditions, the prophage can switch to the lytic pathway, excise itself from the host genome, and enter into the active multiplication phase, leading to the production of new phage particles and lysis of the bacterial cell.

Key concepts

Plaque in Bacteriology

In the study of bacteriology, the term plaque refers to a distinct zone of cell death or clearing that is notably visible on a bacterial lawn— usually a layer of bacterial cells grown on a nutrient agar surface. This phenomenon occurs when a single bacteriophage infects a bacterial cell and begins its reproductive cycle. As the phage multiplies, it causes the host cell to lyse, or break apart, releasing new phages that proceed to infect adjacent cells. This cascading effect creates a circular area where the bacterial cells have been destroyed, which is visible to the naked eye as a clear spot against the opaque lawn of bacteria.

Plaques are important in microbiology for several reasons. They allow researchers to quantify the number of bacteriophages in a sample, a method known as plaque assay. Each plaque originates from a single virus particle; thus, counting plaques can determine the viral concentration. Furthermore, plaques can be used to isolate pure strains of bacteriophages for study. Enhancing student comprehension of the role plaques play in bacteriology can be achieved through visual aids like diagrams and actual images of plaque formation, in combination with hands-on laboratory exercises where students perform plaque assays themselves.

Lysogeny

Lysogeny describes a non-destructive relationship between a bacteriophage and its bacterial host. In this alternate life path, instead of commandeering the host's cellular machinery to produce more virus particles immediately, the bacteriophage becomes dormant. It incorporates its genetic material into the host's chromosome, where it is referred to as a prophage. While in this latent phase, the prophage is replicated alongside the bacterial DNA every time the cell divides, passing the phage's genetic information to each new generation of bacteria without causing any harm.

The lysogenic cycle offers a stark contrast to the lytic cycle, where the phage actively replicates and causes cell lysis. The transition from lysogeny to lytic cycle can be triggered by various environmental factors, such as UV radiation or chemical agents that cause DNA damage. An understanding of lysogeny is critical, as it has implications for bacterial genetics and the evolution of both bacteria and bacteriophages. Furthermore, it is pertinent to concepts like horizontal gene transfer, which can confer novel traits to bacteria, including antibiotic resistance. For educational purposes, it is vital to emphasize the conditions under which lysogeny occurs and the implications for bacterial host and phage.

Prophage

A prophage is the genome of a lysogenic bacteriophage that is integrated into the bacterial chromosome. This state is possible due to the nature of the bacteriophage lifecycle, which allows for the virus's genetic material to become a part of the host's genome without disrupting the bacterial cell's normal functions. The prophage remains inert within the host, evading detection by the immune system of an infected organism and being passively replicated along with the host's DNA during cell division.

While silent, the prophage can potentially affect the phenotype of the bacterial host. For instance, certain prophages carry genes that can enhance the virulence of a bacterium, leading to an increased pathogenicity of the bacterial strain. Additionally, the presence of a prophage within the bacterial genome provides a level of immunity against infection by other phages of the same type. Explaining the potential outcomes and importance of prophages in bacterial behavior is crucial for students to understand the broader implications of bacteriophage infection and the dynamic between bacterial-phae interactions. Clear explanations and examples of prophage behavior can help to underscore their relevance in the field of microbiology.