Important terminologies Archives • Microbe Online

Adaptation is the key for the survival. Organisms with successful adaption strategies are more likely to survive than others. Dinosaurs failed to adapt to the new environment and therefore became extinct. What about unicellular organisms, are they gifted with such traits? Yes Scientists have discovered that “bacteria have developed sophisticated methods for sensing their environment and regulating the expression of genes”. In this post, I am just sharing basic concepts about Bacterial Quorum Sensing. Quorum sensing (QS) is a bacterial cell-cell communication/signaling mechanism that allows bacteria to share information about cell density and adjust gene expression accordingly. It involves the production, detection, and response to extracellular signaling molecules called autoinducers (AIs). These autoinducers are N-acyl homoserine or N- butyryl homoserine lactones that are produced continually. AIs accumulate in the environment as the bacterial population density increases. When the bacterial population reaches a certain threshold enough autoinducers are present to activate transcription factors within the cells that coordinate the expression of genes. This collective alteration of gene expression is beneficial to those bacteria. Quorum sensing controls genes that direct activities that are beneficial when performed by groups of bacteria acting in synchrony. Traits controlled by quorum sensing include; Expression of virulence factors of pathogenic bacteriaBioluminescenceSporulationCompetenceAntibiotic productionBiofilm formation Both Gram-positive and Gram-negative bacteria use quorum sensing, but there are some major differences in their mechanisms. Gram-positive bacteria use autoinducing peptides (AIPs), as signaling molecules whereas Gram-negative bacteria communicate using small molecules like acyl-homoserine lactones (AHLs) as autoinducers. Quorum sensing of Gram-negative cells (Image source: Wikimedia Commons) Many species of bacteria (both saprophytic and pathogenic) use quorum sensing to coordinate gene expression according to the density of their local population. Examples include: B. fragilisM. tuberculosisVibrio species (Vibrio fischeri, Vibrio cholerae)Clostridium perfringensStaphylococcus aureusBacillus cereusPseudomonas aeruginosaSalmonella speciesRhizobium leguminosarum