Bacteria that attach to surfaces aggregate in a hydrated polymeric matrix of their own synthesis to form biofilms. Formation of these sessile communities and their inherent resistance to antimicrobial agents are at the root of many persistent and chronic bacterial infections. Studies of biofilms have revealed differentiated, structured groups of cells with community properties. Recent advances in our understanding of the genetic and molecular basis of bacterial community behavior point to therapeutic targets that may provide a means for the control of biofilm infections.

Bacteria in nature often exist as sessile communities called biofilms. These communities develop structures that are morphologically and physiologically differentiated from free-living bacteria. A cell-to-cell signal is involved in the development of Pseudomonas aeruginosa biofilms. A specific signaling mutant, a lasI mutant, forms flat, undifferentiated biofilms that unlike wild-type biofilms are sensitive to the biocide sodium dodecyl sulfate. Mutant biofilms appeared normal when grown in the presence of a synthetic signal molecule. The involvement of an intercellular signal molecule in the development of P. aeruginosa biofilms suggests possible targets to control biofilm growth on catheters, in cystic fibrosis, and in other environments where P. aeruginosa biofilms are a persistent problem.

▪ Abstract Quorum sensing is an example of community behavior prevalent among diverse bacterial species. The term “quorum sensing” describes the ability of a microorganism to perceive and respond to microbial population density, usually relying on the production and subsequent response to diffusible signal molecules. A significant number of gram-negative bacteria produce acylated homoserine lactones (acyl-HSLs) as signal molecules that function in quorum sensing. Bacteria that produce acyl-HSLs can respond to the local concentration of the signaling molecules, and high population densities foster the accumulation of inducing levels of acyl-HSLs. Depending upon the bacterial species, the physiological processes regulated by quorum sensing are extremely diverse, ranging from bioluminescence to swarming motility. Acyl-HSL quorum sensing has become a paradigm for intercellular signaling mechanisms. A flurry of research over the past decade has led to significant understanding of many aspects of quorum sensing including the synthesis of acyl-HSLs, the receptors that recognize the acyl-HSL signal and transduce this information to the level of gene expression, and the interaction of these receptors with the transcriptional machinery. Recent studies have begun to integrate acyl-HSL quorum sensing into global regulatory networks and establish its role in developing and maintaining the structure of bacterial communities.