Which type of signaling molecules do bacteria use in quorum sensing?

In quorum sensing, bacteria utilize signaling molecules known as autoinducers to communicate with one another. Autoinducers are small, diffusible molecules that are produced and released by individual bacterial cells into their environment. As the population of bacteria increases, the concentration of these autoinducers also rises. Once a certain threshold concentration is achieved, bacteria can detect the autoinducers through specific receptors. This detection leads to coordinated behavior and gene expression changes among the bacterial population, enabling them to act in unison, such as in biofilm formation or virulence factor production.

In contrast, hormones are typically associated with multicellular organisms and their endocrine systems, while enzymes serve catalytic roles in biochemical reactions rather than signaling. Neurotransmitters, on the other hand, play a critical role in signaling within nervous systems of multicellular animals but are not involved in bacterial communication. Thus, autoinducers are the specific signaling molecules used by bacteria in quorum sensing to facilitate intra- and inter-species communication based on population density.