Question

The flashlight fish has an organ under its eyethat emits light, which servers to startle predators and attract prey, and allows the fish to communicate with other fish. Some species can rotate the organ inside and then out, so the light appears to flash on and off. The light is actually emitted by bacteria (of the genus Vibrio) that live in the organ in a mutualistic relationship with the fish. (The bacteria receive nutrients from the fish). The bacteria must multiply until they reach a certain density in the organ (a "quorum"; see Chapter 11.1), at which point they all begin emitting light at the same time. There is a group of six or so genes, called lux genes, whose gene products are necessary for light formation. Given that these bacterial genes are regulated together, propose a hypothesis for how the genes are organized and regulated.

Short answer

The flashlight fish has an organ under its eye that illuminates light during prey attraction. There are a set of genes such as lux genes for light formation. These genes are activated together due to the structural component present in the gene, especially the operator.

Step-by-step solution

Description of the operon

The operon is the cluster of genes present in the prokaryotic organism that is involved in gene expression. The structural components of operons are the promoter, operator, and repressor. The examples of the operon are the lac operon and trp operon.

Structural organization of lux operon

The structural component of the lux operon consists of set genes such as lux AB, lux CDE, lux I, and lux R. The luciferase is the enzyme coded by the lux AB. The lux CDE codes for the protein to produce the aldehyde substrate.

The lux R gene acts as a quorum-sensing regulator. Lux I is the gene coding for the auto-inducer molecule such as homoserine lactone.

Step 3: Gene regulation of the emission of light in the flashlight fish

The genes responsible for the flashlight emission are lux genes. The lux operon regulates the lux genes. The operon has to be activated by the binding of the luciferase enzyme to the promoter region. This results in the transcription of genes.

The on and off condition of the operator region and promoter regulates the flashlight glow and off. Hence, the lux operon is responsible for regulating bacterial genes present in the organ of the flashlight fish.