<P> Quorum sensing functions based on the local density of the bacterial population in the immediate environment . It can occur within a single bacterial species, as well as between diverse species . Both Gram - positive and gram - negative bacteria use quorum sensing, but there are some major differences in their mechanisms . </P> <P> In order for the bacteria to use quorum sensing constitutively, they must possess three characteristics: to secrete a signaling molecule, an autoinducer, to detect the change in concentration of signaling molecules, and to regulate gene transcription as a response . This process is highly dependent on the diffusion mechanism of the signaling molecules . Signaling molecules are usually constitutively secreted at a low level by individual bacteria . At low cell density, the molecules may just diffuse away . At high cell density, the local concentration of signaling molecules may exceed its threshold level, and trigger changes in gene expressions . </P> <P> Gram - positive bacteria use autoinducing peptide (AIP) as their autoinducers . </P> <P> When gram - positive bacteria detect high concentration of AIP in the environment, AIP bind to a receptor to activate kinase . The kinase phosphorylates a transcription factor, which regulated gene transcription . This is called a two - component system . </P>

Quorum sensing is a bacterial phenomena related to the presence of which of the following