Quorum Sensing And Its Importance To Biotechnology Biology Essay


Quorum sensing offers potential to create engineered bacteria capable of invading cancer cells. It is possible to envision the creation of novel anti-cancer therapeutics by the addition of cancer-destructing modules to these microbial biosensors. Another application of QS and quorum quenching lies in the creation of transgenic plants that are able to defend themselves against common bacterial pathogens. It plays a main role in controlling a diversity of microbial cell activities, such as biofilm formation and virulence that considerably impact human health, agriculture, and commercial production and transport systems. Quorum sensing is cell-to-cell communication in bacteria have ability to control development, sporulation, and antibiotic synthesis also virulence factor induction, cell differentiation, moreover nutrient flux along with extra physiological events in pathogenic bacterial infections. Scientists now a days creating more possible benefits from quorum sensing and off course there is lots of potential development for advancement in 2011ranging from marine to human disorders.



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Several unicellular microorganisms use smallsignaling molecules to find out their local concentration. The processes involved in the production and recognitionof these signals are generally known as quorum sensing (QS). Unicellular microorganisms to manage their activities use this kind of cell-to-cell communication, which allows them to work as multi-cellular systems. Newly, several groups have confirmed artificial intraspeciesand inter-species communication through synthetic circuits, which incorporate components of bacterial QSsystems. Engineered QS-based circuits have a broad range of applications such as production of biochemical's, tissueengineering, also mixed-species fermentations. They are also extremely useful in designing microbial biosensors toidentify bacterial species present in the environment andinside living organisms. In this articlethe different ways inwhich researchers have designed QS-based circuits andtheir applications in biotechnology are explained.

A decade ago, the secretion and perception of minorsignalling molecules that in turn are transduced tocoordinate behavior of a 'smallest unit' of microorganisms was named quorum sensing by EP Greenberg with colleagues. Ever since then, an exponential growth in understanding and occurrence of quorum-sensing systemshas developed, with sightings ranging from virulence inhuman along with plant pathogens to degradative capacity ofactivated sludge. Not amazingly, regulatory mechanisms span traditional inducer/repressor motifs homologous to thelac operon to the newly discovered interfering RNAs.Advance characterization of signalling circuits, coupled with creative position applications, propose a wealth of prospects for advancing commercial biotechnology(reviewed by John C March and William E Bentley 2004).

Researchers in biotechnology continuously seek new platforms from which to address problems: manifesto that, in a broad sense, improve efficacy, while maintaining or intensifying specificity. Most freshly, microbial quorum sensing has emerged as such a technology. Because microbial communities absorb a small space, concentrations of extracellular signalling molecules build up, providing motivation for unique and various cellular responses along with protection from rival microbial communities. Referred to as 'quorum sensing' for its regularly reported and concurrent dependence on high population density (Joyce EA et al 2004), extracellular signalinggives a novel basis for control over molecular also cellular processes along with population behaviour, possibly in a manner more reliable with that of native physiology. Quorum sensing might be the base upon which the more complicated intracellular communication found in advanced level organisms has evolved.

Defining quorum sensing

Quorum Sensing considered a signalling molecule, a compound has to result a reaction in a population of cells that is different from the approach in which the cells would perform independently. There are two types of quorum sensing: species- specific and interspecies.

Species-specific quorum sensing in Gram-negative bacteria is intercede by acyl-homoserine lactones (AHLs) with numerous moieties distinguishing signals between species (Fuqua C, Parsek MR, Greenberg EP 2001). In Gram- positive bacteria, species-specific quorum sensing is generallyassist through small peptides

Figure1.Structure of bacterial Quurom sensing signals. Gram-negative bacteria like V.Fischeri and Pseudomonas aeruginosa use acyl homoserine lactones (AHLs) as signals. The structure of mature AIP-I (from Staphylococcus aureus) is shown as a representative of the translationally derived auto-inducing peptides (AIPs) used by Gram-positive bacteria as signals for QS.Source-

Functions of quorum sensing

Quorum sensing is supposed to control ability development, sporulation, and antibiotic synthesis also virulence factor induction, cell differentiation, and nutrient flux along with extra physiological events in pathogenic bacterial infections (Cvitkovitch DGGreenberg EP,Yarwood JM,2003).More lately, quorum sensing was connected through proteomic analysis to increased pathogenic ability in tubercular strains of Pseudomonas aeruginosa (Arevalo-Ferro C, et all 2004)

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Webb and co-workers (Webb JS, et al 2003), reviewed work on programmed cell death plusmicro colony differentiation in biofilms. As biofilms age, cellular differentiation and death improve nutrient sequestration and allow for bio- film sustenance when nutrients become limited. Though the functions of cell differentiation and programmed cell death are actually at odds, they can be described as an evolutionary progressionthat allows biofilms of prokaryotes to perform and adapt as multiceewllular organisms, a behavior that emerges to be matched through quorum sensing (Webb JS, et al 2003).


Applications of Quorum sensing in biotechnology

Components of bacterial QS systems form an important part of many artificial genetic circuits that control phenomena such as bistable behavior, pulse response, spatio-temporal control of gene expression, and population control (Purnick and Weiss 2009). In this section, the applications of engineered QS systems for the production of biochemical's, tissue engineering, and mixed- species fermentations are highlighted (Fig. 2). Detailed explanation ofcurrent progress in building QS-based microbial biosensors and QS-based biocontrol are given. Lastly, discussion of QS inhibition as a viable strategy for the decline of biofouling is given. Also different applications of QS in biotechnology are given.

Engineered Quorum Sensing systems

The promisingfield of synthetic biology seeks to generatenovel biological systems by applying the fundamental engineering principles of standardization and hierarchical abstraction to GE engineering (Purnick and Weiss 2009). This method allows designers to build and optimize compound genetic circuits that perform new functions, such as DNA-damage-induced biofilm formation and preservation of synthetic ecosystems (Balagadde et al. 2008; Kobayashi et al. 2004). Various genetic modules can be included into complex gene networks also called "genetic systems" or "devices"using a "plug-and-play" strategy (Kobayashi et al. 2004). These gene networks are then commenced into a well-characterized, steady host cell known as a "chassis", which supplies the essential raw materials and support machinery. Operation of the artificial genetic device imparts new functionalities to the host and makes a microbial cell factory that is capable of performing preferred tasks.

Figure-2.Various applications of Quarum Sensing in Biotechnology.Source-

Figure 2. Various applications of quorum sensing (Source-

Autoinducers are very useful as input signals as they are little, diffuse freely in aqueous media, and are simply taken up through cells. As the engineered cells synthesize QS signals by themselves, they are able to watch their own cell density with modulate their activities appropriately, thereby falling the need for outerprotection(Brenner et al. 2007).

Scientists have devised QS-inducible mammalian genetic circuits by mixing bacterial QS receptors with either a eukaryotic transactivation domain or with a eukaryotic transcription repressor domain (reviwed from Neddermann et al. 2003; Weber and Fussenegger 2009; Weber et al. 2005; Weber et al. 2003; Williams et al. 2004).These synthetic gene regulation systems will have functions in drug discovery, tissue engineering, and also industrial production of biochemical'sduring mammalian cell culture.

Consumption of a bistable switch module gives a pointed(ON or OFF) or binary profile of aim gene expression depending on the store concentration. Engineered QS systems including bistable switches are probable to be extremely useful in industrial production of toxic gene products and in designing environmental biosensors. Scientistshave used components of the V. fischeri Quorum Sensing system to engineer spatio-temporally keeping up cell to cell communication in E. coli (Basu et al. 2004). Depending on the comparative distribution of Sender and Receiver cells in a 2-D matrix, different reporter formats such as bulls'eye, ellipse, oval, heart, and clover were formed. Moreexpansion of this research into programming spatial patterning in 3-D will have applications in biosensing, tissue engineering, plus fabrication of biomaterials.

Quorum Sensing like cell-to-cell communication systems have also been developed by using metabolites, antibiotics, hormonesor volatile compounds to give signals to extract a cell-density dependent population-wide reactions (Bulter et al. 2004; Chen and Weiss 2005; Weber et al. 2007). The capacity to develop QS type communication systems using non-Quorum Sensing signals considerablygrows the design possibilities for genetic engineering systems. Through inserting the producing signal components in one species, and the receptor in another, scientists have engineered inter and intra-kingdom communications among bacteria, yeast, plants, and mammalian cells (Balagadde et al. 2008; Brenner et al. 2007; Weber et al. 2007). Depending on the planned synthetic communication device, relationships like predator-prey, commensalism, mutualism, amensalismand parasitism were producedamong the communicating species.

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Different from engineering inter-species communication, Quorum Sensing based genetic devices can control diverse features of mixed-species fermentations. Forcase, basedon QS population control circuits can be used to manage the cell densities of the contributing species (You et al. 2004). Based on QS gene-expression circuits can also be used to initiate expression of mark genes when the cell densities of contributing species reach a definite threshold (Brenner et al. 2007).

At present, the majority of the engineered QS devices are built on Gram-negative AHL systems, which, as stated previously, are absolutely unreliable.

Various applications of Quorum Sensing:


An interesting application of Quorum Sensing is in the engineering of whole cell microbial biosensors to distinguish pathogenic microbes present in the environment with diseased host organisms. Quorum Sensing have also been used to produce engineered bacteria capable of attacking cancer cells. It is probable to visualize the creation of new anti-cancer therapeutics by the addition of cancer-destructing elements to these microbial biosensors. Another function of QS and quorum quenching lies in the designing of transgenic plants that are able to protect themselves against general bacterial pathogens.

Pathogen diagnostics and therapeutics

The majority of the whole cell QS biosensors that have been explained so far recognize Gram-negative AHLs (Kumari et al. 2008; Steindler and Venturi 2007). A standard AHL biosensor contains an AHL responsive transcriptional regulator also a cognate promoter, which directs the transcription of a reporter gene. It has been recommended that QS signals only can be used as markers for the occurrence of pathogenic bacteria in clinical and environmentalsamples. Thus, QS signals should not be engaged as the only inputs for microbial biosensors. However, Quorum sensing based amplification circuits can still be used to engineer biosensing circuits to find the occurrence of pathogenic microbes in contaminated groundwater products, dairy, and meat products. Upcoming design directions willinclude the formation of ingestible whole cell biosensors by launching QS-based bio- sensing devices into GRAS organisms such as lactic acid bacteria(Konings et al. 2000). Such diagnostic biosensors would be much useful in identifying the existence of pathogens in the gut micro flora. So collecting these resultsbring up the exciting possibility that future QS-based microbial biosensors may possibly not only detect pathogens, but also increase a concerted reaction against them.

Cancer detection

The P. aeruginosa Quorum Sensing signal 3-oxo-C12- HSL reduces proliferation alsoinduceapoptosis breast cancer cell lines in human(Li et al. 2004).


The rhizosphere is a limited region of soil that surroundings a plant's roots and is affected by secretions from the root also soil microbes in the vicinity. Quorum sensing bacteria form amain component of the rhizosphere community. Scientists have also engaged quorum-quenching enzymes to decrease bacterial virulence against plants. This researchproposes that engineering the production also secretion of quorum- quenching enzymes into plants and plant-associated microbes can also serve as a crop protection plan. Though, QS systems also controlnecessary functions in useful rhizosphere bacteria, as well as biofilm formation, antibiotic production, and nitrogen fixation (Muller et al. 2009; Sanchez-Contreras et al. 2007). More research is therefore essential to understand the promising effects of quorum quenching on plant biochemical pathways. In brief, while quorum quenching is an attractive approach for biocontrol, more research isessential to demonstrate its safety and efficacy.

Prevention of biofouling

Biofouling is the increase of bacteria, algae;also animals like protozoans and crustaceans on surfaces that prolonged contact with water. Biofouling can happen on surfaces as assorted as pipes, tanks, ship hull, membrane bioreactors, medical or dental implants, and catheters. This unwantedgrowth of living organisms and their secretions lead to contamination, colonization, also corrosion of machine parts expose to water and reduce machine efficiency. Incorporation of Quorum Sensing inhibitors on the device surface is a possible strategy for declining P. aeruginosa biofouling of surgical implants. QS inhibition may be used to givedefense against many pathogens that rely on QS to start biofilm development.

Recombinant gene expression

Possibly one of the exciting areas for research in quorum sensing is the synthesis of recombinant gene products withmetabolic engineering. Quorum sensing has been used to control gene expression and cellular growth. Brief reviews by Toniatti et al. (Toniatti C, et al 2004) discusssome of the progress in control of gene expression through the perceptions of possible gene therapy applications.

Pathogen/pest management

Pathogen and pest (i.e. some organism whose existence in a specific environment is undesirable) management include most of the present applications of quorum-sensing technology. Inhibition of quorum signalling is theevident and, in practice, most appreciated application of quorum-sensing knowledge.


New technologies in Quorum Sensing

The discovery of antibiotics early in the past century marked the beginning of active control and prevention of infectious microbial diseases. However, extensive use of antibiotics has also unavoidably resulted in the emergence of 'superbugs' that resist conventional antibiotics. The finding that many pathogens rely on cell-to-cell communication mechanisms, known as quorum sensing, to synchronize microbial activities essential for infection and survival in the host suggests a promising disease control strategy, i.e. quenching microbial quorum sensing or in short, quorum quenching. Work over the past few years has demonstrated that quorum-quenching mechanisms are widely conserved in many prokaryotic and eukaryotic organisms. These naturally occurring quorum-quenching mechanisms appear to play important roles in microbe-microbe and pathogen-host interactions and have been used, or served as lead compounds, in developing and formulating a new generation of antimicrobials.

An advance study of bacterial quorum sensing process can facilitate development of novel technologies intended at interfering with bacterial communication and virulence.

The term "quorum sensing" explains the capability of a microorganism to recognize and response to diffusible signal molecules. Bacterial cells sense their inhabitant's density by a complicated cell-to-cell communication system also triggers expression of exact genes.

Quorum sensing in Seaweeds

Explaining this title, the quorum sensing is wider spread among bacterial population then was previously thought, in Gram positive, Gram-negative bacterial communication. Followed by this numerous researchers have concluded that in Gram negative bacteria acyl-homoserine lactone is dependable for the cell to cell communication system.

In gram-positive bacteria peptide and derivative peptide based signaling molecules appear to be the main mode of communication. Throughout high cell density the marine bacteria can produce enzymes, surfactants, toxins, antibiotics by the chemical signal communication. Marine epibiotic bacteria are also identified to produce compounds active beside drug resistant hospital pathogen by the cross species induction process. Austin described in building on assays (Billaud and Austin 1990) a screening method has been developed in which marine bacteria are confront by exposing them to terrestrial bacteria prior to assay of antimicrobial compounds. Therefore, in currentstudies it is proposed to search the abilities of seaweed epibiotic bacterial organisms to createantibacterial compounds by quorum sensing. Theseconclusions have important consequences for the discovery of new antimicrobial compounds from marine bacteria and might allow the growth of novelprocess for screening new compounds effective against multidrug resistant bacteria.



Quorum Sensing plays a main role in controlling a diversity of microbial cell activities, like biofilm formation and virulence, that considerably impact human health, agriculture, marine, commercial manufacture and transport systems. As mentioned in above applications of QS there are many areas that are fully touched by QS method. Therefore, significant research efforts are needed to understanding Quorum Sensing and the growth of strategies to disrupt and influence Quorum Sensing. Our understanding of quorum-sensing mechanisms currently restricts applications for quorum sensing. Though there has been progress made in the use of quorum sensing, more understanding of quorum functionality is necessary before the control of this tool can be completely raised. However, the full-scale management of the bacterial quorum circuit in a biotechnological application yet to be an unconvinced goal.

More studyand deep research is needed to uncover andthe details of QS in a diversity of microbial species, with Gram- positive bacteria's and fungi's. The task of QS in microbial populations, with Quorum Sensing crosstalk and signal specificity, is another significant area of research and study that will influence strategies to prevent biofilm formation and for biocontrol.

Quorum sensing seems to be a distinctive example of how the exploitation of bacteria cell-to-cell communication in biotechnology can be used to significantly drive the growth and development of medicine, diagnosis tics, therapies and gene control. For sure, it will influence every part of biology, with novel research and technologies in science world.