Microbial quorum sensing systems: new and emerging trends of biotechnology in bioremediation

Every pathogen uses some mechanisms to make sense of their environment and tries to acclimatize them by regulating various gene expression and making changes in their virulence, cell concentration, adaptability, etc. Quorum sensing (QS) is also a signaling process, by which bacterial pathogens can contact cell to cell and bacteria can manipulate their density. The literal meaning of quorum is number. So, QS is a number-dependent phenomenon. The QS mechanism is not confined only within the bacterial kingdom, but also in viruses, Archaea, plants, and social insects like honey bees and ants. In 1970 J. Woodland Hastings, Terry Platt, and Kenneth Nealson discovered the mechanism of QS in an experiment with photoluminescent marine bacterium Aliivibrio fischeri and Vibrio harveyi. In this mechanism some autoinducers are released at a threshold level of microbial population and then the receptors detect the autoinducers. Autoinducers remain in the bacterial membrane or in the cytoplasm and after that some transcription factors are activated by gene regulation and finally the QS phenomenon takes place. QS is very helpful in modulating various microbial properties like biosurfactant production, biofilm formation, horizontal gene transfer (HGT), chemotaxis, bacterial motility, exopolysaccharide synthesis, etc. These novel features of bacteria are imperative for detoxification or degradation of environmental contaminants or pollutants, which may be biological, physical, or chemical like hydrocarbon, toxic heavy metals, pesticides residue, and various industrial by-products. The increased pollution in the environment has made it necessary to implement a method of bioremediation to neutralize the pollutants. Various methods like chemical, physical, and mechanical approaches are capable of mitigating a wide range of contaminants. Bioremediation using the bacterial features that are regulated by QS is a new and emerging trend and an eco-friendly approach for resisting the bad impacts of contaminants and pollution in the environment. In bacterial extracellular membranes different ampiphilic compounds like bioemulsifiers and biosurfactants are produced. Oil pollution can be mitigated using these compounds. Plasmid-mediated bioaugmentation or HGT may spread the ability of bacteria to degrade the complex organic compounds. QS signals are also effective for enhanced degradation kinetics of biofilms. Bioremediation of lead can be done using bacterial exopolysaccharides. Hydrophilic exopolysaccharides contain different anions like phosphate, hydroxyl group, cyanide, amino, and carbonyl groups that bind to cations like lead. This process reveals the presence of a ligands assay. Bacterial gliding or swarming motility or chemotaxis movements under the influence of chemical gradients help in identifying the presence and concentration of xenobiotic toxic materials and exaggerate the degradation process of that compound. This ever-increasing environmental pollution has given birth to dramatic research for an alternative sustainable management practices and in this regard QS-based bioremediation is a good and wise alternative to conventional management systems.