Quorum Sensing and Bioremediation
Authors: Jyotsana Prakasha,b, Shikha Koula,b, Subhasree Raya,b, Ravi Kumara, Vipin Chandra Kaliaa,b
aMicrobial Biotechnology and Genomics, CSIR - Institute of Genomics and Integrative Biology (IGIB), Delhi University Campus, Mall Road, Delhi-110007.
bAcademy of Scientific & Innovative Research (AcSIR), 2, Rafi Marg, Anusandhan Bhawan, New Delhi- 110001.

Environmental pollution is increasing rapidly as most of the organic matter is not easily accessible to microbial activity. Biosurfactants are among those biochemicals which facilitate the availability and uptake of organic matter by microbes. Bacteria have the unique ability to express genes responsible for biosurfactants production at high cell densities only. This expression of genes at cell densities above a threshold level is termed as quorum sensing (QS). QS operates through signal molecules such as acyl homoserine lactones (AHLs) and peptides. This QS system can be exploited to treat waste waters from domestic and industrial sources.

Biosurfactants
Biosurfactant molecules increase the hydrophobicity of the contaminants, thereby enhancing their solubility and biodegradation. Pseudomonas and Burkholderia sp. are known to produce biosurfactants - rhamnolipids through QS mediated activities. These have been reported to be used industrially for the treatment of lipid containing waste water. Rhamnolipids also find use in removal of oil and toxic metals from contaminated sites and soils. Burkholderia cenocepacia produces biosurfactants which increase the solubility of pesticides thereby speeding up their removal from contaminated soil. Putisolvin produced by Pseudomonas putida and surfactin by Bacillus are surfactants having an ability to remove metal contaminants from the soil. Surfactin by Bacillus is also known to act as an antibiotic, enabling it to survive in large microbial communities, which makes it a potent organism for waste treatment.

Biodegradation
QS mediated processes like denitrification, ammonium oxidation and exoenzyme production enables Aeromonas hydrophila, Pseudomonas spp., and Acinetobacter spp., to enhance biodegradation of organic matter from waste water. Similarly, Sinorhizobium meliloti and Agrobacterium, through QS dependent entry into the roots in the rhizophere, enhances the process of the degradation of chlorinated ethenes in soil.

Biofilms
Bioremediation of toxic pollutants on industrial scale is carried out by biological means using whole cell microbes or enzymes. However, to make the process economical, immobilization of cells become mandatory. Biofilms provide a natural means of immobilization of cells. It overcomes the disadvantages including lower mass transfer, higher costs, and reduced activity of biological catalysts, encountered in other chemical immobilization techniques. QS can be used for forming robust biofilms, which allow a large population of cells to be retained in the bioreactor. Here, these bacterial cells with enhanced tolerance to contaminants such as polycyclic aromatic hydrocarbons (PAH), the lethal contaminants, and thus help in efficient cleanup.

Conclusion
Bacterial QS is paving new ways for efficient and rapid bioremediation.

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About Author / Additional Info:
Researchers in Microbial Biotechnology and Genomics at CSIR-IGIB, Delhi.