In bacteriophage biology, what is the correct definition of lysogeny?

Introduction / Context:
Lysogeny is an important concept in the study of bacteriophages, the viruses that infect bacteria. It describes an alternative life cycle to the lytic cycle and has major implications for bacterial genetics and evolution. Many exam questions in microbiology require you to differentiate between lytic and lysogenic cycles. This question focuses on the correct definition of lysogeny in bacteriophage biology.

Given Data / Assumptions:
The stem asks for the definition of lysogeny. The options include immediate lysis, a dormant integrated state, active transport, random mutation, and ingestion of solid particles. We assume that the learner has basic knowledge that some bacteriophages can either lyse the host quickly or integrate their DNA into the host genome. The question aims to check whether you can correctly associate lysogeny with integration and dormancy rather than immediate cell death.

Concept / Approach:
Lysogeny refers to a state where the bacteriophage genome, called a prophage, integrates into the bacterial chromosome or remains in a stable plasmid like form and replicates along with the host DNA. In this state, the host cell is not lysed immediately and can continue dividing, passing the prophage to daughter cells. Under certain conditions, the prophage can be induced to enter the lytic cycle, leading to production of new phages and lysis. Therefore, the correct definition must mention integration of phage DNA and replication with the host without immediate lysis.

Step-by-Step Solution:
Step 1: Recall that bacteriophages can follow either a lytic cycle or a lysogenic cycle.Step 2: In the lytic cycle, phage infection leads quickly to replication of viral particles and lysis of the host cell.Step 3: In the lysogenic cycle, the phage DNA integrates into the host genome and remains dormant as a prophage.Step 4: Recognize that the integrated phage DNA replicates passively with the bacterial chromosome during cell division.Step 5: Choose the option that describes a dormant state with integrated phage DNA and no immediate lysis.

Verification / Alternative check:
You can verify by thinking of the classic example of lambda phage in Escherichia coli. Lambda phage can integrate its DNA into the E. coli chromosome and remain lysogenic for many generations. Under stress, the prophage may become induced and enter the lytic cycle, producing phage particles and lysing the cell. This behaviour clearly demonstrates that lysogeny involves integration and dormancy rather than immediate cell destruction. None of the other options match this description.

Why Other Options Are Wrong:
A process in which a bacteriophage immediately lyses and kills its host cell after infection describes the lytic cycle, not lysogeny. Active transport of solutes across a bacterial cell membrane using energy is a general cellular process and is unrelated to phage life cycles. Random mutation of bacterial DNA due to ultraviolet radiation refers to mutagenesis, not to lysogeny specifically, although ultraviolet light can induce prophages. The process by which bacteria ingest solid particles from their environment describes phagocytosis, which is more characteristic of eukaryotic cells and is not the definition of lysogeny. These alternatives do not include integration of phage DNA and its stable replication with the host.

Common Pitfalls:
Students often confuse lysogeny with lysis because the words are similar and both involve bacteriophages. Another mistake is to focus on the eventual cell death that can occur when a lysogenic phage becomes lytic, forgetting that lysogeny itself is the dormant integrated phase. To avoid confusion, remember that lysogeny equals latent integration and lytic equals active destruction. Keeping these short keywords in mind will help you select the correct definition during exams.

Final Answer:
Lysogeny is best defined as a dormant state in which bacteriophage DNA integrates into the bacterial chromosome and replicates with it without immediate lysis.