# Quorum Sensing --- **Quorum sensing** is a method of [[unicellular cell signaling|cell signaling]] that bacteria can use in order to sense if their population has reached a certain critical mass. It can then [[gene regulation|regulate it's genes]] based on if it's colongy population has reached a certain threashold. ![[quorum sensing.png]] ## Method When there are few cells in a wide open space, and a bacteria sends out a [[signaling molecule]], it is not very likely for that molecule to end up actually reaching a fellow bacteria. However, when the population density gets to a certain point, the chances that the signal will reach a bacteria is much more likely. This signaling molecule often kickstarts a [[two-component regulatory system]] response. ## What Are the Benefits of Quorum Sensing? Quarum sensing is useful because there are just certain genes that would be a waste of energy and resources to transcribe if there aren't enough bacteria around to make the effect worth while. ## Examples ### *Vibrio fishcheri* The bioluminescent bacteria ***Vibrio fischeri*** have a symbiotic relationship with the Hawaiin bobtail squid. Even though every single bacteria *can* bioluminese, if there isn't a quorum then the light produced would not be enough to help the Hawaiin bobtail squid hunt. Since if the squid can't hunt the bacteria don't get fed, it makes sense that the bacteria would want to shine bright (like a diamond). ### *Psudomonas aeruginosa* ***Psudomonas aeruginosa*** are associated with cystic firbosis in humans. Each individual cell has the ability to produce a [[capsule]], but they don't unless they have critical mass. The reason they want to produce the capsule is to create [[capsule|biofilm]], and since they can't do that on their own, they bide their time. ___