Question

How do bacteria communicate with each other

Answer 1

Bacterial cell-cell communication is referred to as quorum sensing. Quorum sensing-controlled behaviors are those that only occur when bacteria are at high cell population densities. These behaviors are ones that are unproductive when undertaken by an individual bacterium but become effective by the simultaneous action of a group of cells. For example, quorum sensing regulates bioluminescence, virulence factor expression, biofilm formation, sporulation, and mating. Quorum sensing is achieved through the production, release, and subsequent detection of and response to threshold concentrations of signal molecules called autoinducers. The accumulation of a stimulatory concentration of an extracellular autoinducer can only occur when a sufficient number of cells, a “quorum,” is present.
MECHANISM:-
Quorum sensing is based on the production and detection of autoinducers, signaling molecules continually secreted by bacteria to announce their presence to their neighbors (typically, neighbors of the same species). Autoinducers let bacteria sense population density and change their behavior in a synchronized fashion when the density reaches a certain threshold.
In some types of bacteria, the secreted autoinducers are small, hydrophobic molecules such as acyl-homoserine lactone (AHL). AHL is the autoinducer made by A. fischeri, the bacteria that occupy a squid’s light organ. In other types of bacteria, the autoinducers may instead be peptides (short proteins) or other types of small molecules,
Because AHL is small and hydrophobic, it can diffuse freely across the membranes of the bacterial cells.

When there are few cells in the area, the little AHL that's made will diffuse into the environment, and the levels of AHL inside the cells will remain low.
When more bacteria are present, a larger amount of AHL will be produced ,
If AHL levels get high enough, indicating a critical density of bacteria, the AHL will bind to and activate a receptor protein inside the cells.
The active receptor acts as a transcription factor, attaching to specific sites on the bacterium’s DNA and changing the activity of nearby target genes.

In A. fischeri, the transcription factor turns on genes that encode enzymes and substrates required for bioluminescence, as well as the gene for the enzyme that makes AHL itself (amplifying the response in a positive feedback loop