Whereas Gram-negative bacteria primarily use acylated homoserine lactones, Gram-positive bacteria generally use oligopeptides as autoinducers for quorum sensing.  These molecules are often synthesized as larger polypeptides that are cleaved post-translationally to produce “processed” peptides.  Unlike AHLs that can freely diffuse across cell membranes, peptide autoinducers usually require specialized transport mechanisms (often ABC transporters).  Additionally, they do not freely diffuse back into cells, so bacteria that use them must have mechanisms to detect them in their extracellular environments.  Most Gram-positive bacteria use a two-component signaling mechanism in quorum sensing.  Secreted peptide autoinducers accumulate as a function of cell density.  Once a quorum level of autoinducer is achieved, its interaction with a sensor kinase at the cell membrane initiates a series of phosphorylation events that culminate in the phosphorylation of a regulator protein intracellularly.  This regulator protein subsequently functions as a transcription factor and alters gene expression.  Similar to Gram-negative bacteria, the autoinduction and quorum sensing system in Gram-positive bacteria is conserved, but again, individual species have tailored specific aspects for surviving and communicating in unique niche environments.