Question

Once a prophage is present in a bacterial genome, viral genes are reproduced every time the bacterium multiplies; expression of viral genes is repressed. Bacterial cell stress can lead to prophage induction. What will result? Select one:

a. The bacterium will reject the viral genes.

b. The virus will enter the lytic cycle.

c. The virus will enter the lysogenic cycle.

d. The bacterial genome will be denatured.

Answer 1

Prophage induction leads the virus to enter into the lytic cycle.

A bacteriophage genome inserted and integrated into the circular bacterial DNA chromosome or exists as an extrachromosomal plasmid is called as a prophage. This is a latent form of a phage, in which the viral genes are present in the bacterium without causing disruption of the bacterial cell. Pro means ''before'', therefore the prophage means the stage of a virus in the form of genome inserted into host DNA before being activated inside the host.

Prophages can increase the virulence potential of bacterial strains in both humans and plant pathogens as well as increase the ability of the bacteria to survive in extream environments. Pathogens have been able to adapt and thrive in a wide range of environments. Some anaerobic pathogens such as Clostridium perfringens and Clostridium difficile exist in the intestines and are unable to survive in places with large amounts of oxygen for extended periods of time. Still others can reside in the soil such as B. anthracis, while pathogens such as C. difficile can even survive in very sterile hospital settings. Prophages can provide these bacteria with both resistance mechanisms as well as metabolic advantages which give the host cell the best chance of survival, sometimes even completely altering the bacterial genome.

The host cell damage made by UV light or certain chemicals, the prophage is excised from the bacterial chromosome in a process called prophage induction. After induction, viral replication begins via the lytic cycle. In the lytic cycle, the virus commandeers the cell's reproductive machinery. The cell may fill with new viruses until it lyses or bursts, or it may release the new viruses one at a time in a reverse endocytotic process. The period from infection to lysis is termed the latent period. A virus following a lytic cycle is called a virulent virus. Prophages are important agents of horizontal gene transfer, and are considered part of the mobilome. All families of bacterial viruses with circular (single-stranded or double-stranded) DNA genomes or replicating their genomes through a circular intermediate (e.g., Caudovirales) have temperate members.