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).