Quorum sensing
Bacterial individual cells can use quorum detection to coordinate with others in their colony in order to perform constitutive tasks, especially those involving substances can assist in a variety of ways, including survival, competence, bioluminescence, biofilm formation and even sporulation. Signal molecules are released by bacteria in quorum sensing systems in a cell density-dependent manner, and signal transduction is induced via cascading quorum sensing regulatory proteins. Small molecule QSIs are one type, which can be extracted from natural resources or synthesised chemically, and quorum quenching enzymes, which include acylases, lactonases that target acyl-homoserine lactones (AHLs) as signalling molecules, AI-2 kinases that target furanosyl borate ester (auto inducer 2, AI-2) as signalling molecules, and so on (J. Zhao et al., 2019). Signal molecules bind to response regulators, which then start transcription of Quorum Sensing regulated genes, allowing for population-wide transcription. The Lux A-E, LuxG, Lux I, and Lux R genes were found to be involved in these phenomena and were classified as bi-directionally transcribed operons. Lux A and Lux B are two proteins that make up the luciferase enzyme, which creates light. The Lux C-D-E proteins make the luciferase substrates, while Lux G is a flavin reductase. The Lux I and Lux R proteins, on the other hand, generate the most interest in quorum sensing research. Lux R is the bacteria’s diffusible signal receptor, and the AI synthase Lux I is responsible for AI creation. The AIs bind to the Lux R receptors, which operate as transcription factors and stimulate the production of all lux genes when they reach a threshold concentration in the immediate environment of bacterial cells (indicating an increase in cell abundance). The AI designation is given to the five diffusible signals because they promote their own production through the automatic induction of Lux I (Lami, 2019) (Fig 2. Mechanism of Quorum Sensing).