Biological Sciences
Quorum Sensing
Quorum sensing is a communication process used by bacteria to coordinate behavior based on population density. Bacteria release signaling molecules, and when the concentration of these molecules reaches a threshold, specific genes are activated. This allows bacteria to synchronize activities such as biofilm formation, virulence factor production, and other behaviors that are more effective when carried out collectively.
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12 Key excerpts on "Quorum Sensing"
eBook - PDF- Victor R. Preedy, Vinood Patel(Authors)
- 2012(Publication Date)
- CRC Press(Publisher)
11 Quorum Sensing in Microbial Biosensors Swati Choudhary 1,a and Claudia Schmidt-Dannert 1,b, * ABSTRACT Small signaling molecules are utilized by several unicellular organisms to assess the cell density of other organisms of the same species in their vicinity. Together, the biochemical pathways involved in the production, secretion and recognition of these diffusible signals are known as Quorum Sensing (QS). Upon establishing that their local concentration has reached a threshold, the unicellular organisms collectively undertake a change in their transcriptional profiles, initiating complex activities which benefit the group as a whole but would have had limited relevance at a lower population count. In bacteria, QS regulates diverse functions such as formation of biofilms, onset of virulence, competence and bioluminescence. Researchers have developed whole-cell microbial biosensors that detect the presence of QS signals in clinical and environmental isolates. These biosensors enhance our understanding of microbial ecosystems present in diverse locations including the mammalian gut and lake sediments. Components of bacterial QS machinery have found widespread application in the emerging field of synthetic biology for the engineering of complex genetic circuits with novel functionalities—for example, production of biochemicals, spatio-temporal control of gene expression and 1 Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, 140 Gortner Laboratory, St. Paul, MN 55108, USA. a E-mail: [email protected] b E-mail: [email protected] *Corresponding author List of abbreviations after the text. 192 Biosensors and Environmental Health creation of synthetic ecosystems. Engineered QS-based devices have been used to create microbial biosensors that localize to cancer cells or serve as improved live attenuated vaccines.
eBook - ePub- Iqbal Ahmad, Fohad Mabood Husain, Iqbal Ahmad, Fohad Mabood Husain(Authors)
- 2017(Publication Date)
- Wiley-Blackwell(Publisher)
Chapter 6 Quorum Sensing Mechanisms in Rhizosphere BiofilmsJorge BarriusoCentro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain6.1 Background
Since the 1960s, it has been known that unicellular microorganisms do not live as independent cells isolated in the environment. There is a communication between single cells that allows the population to coordinate their behavior [1]. This cell-to-cell signaling system is known as Quorum Sensing (QS) and is mediated by small, diffusible, chemical signal molecules. The QS molecules (QSM) are secreted by the microbial cells and accumulate in the environment as the population density grows. Each individual cell it is able to sense the amount of QSM present in the medium, and when the concentration reaches a threshold, the gene expression in the population is altered (induced or repressed) in a coordinated manner [2]. Hence, the QS phenomena depend on cell population density. These molecules are autoinducible, which means that the sensing of the QSM stimulates the biosynthesis of more QSM [3].The QS mechanisms allow the coordination of diverse processes in microbial populations and communities, and suppose a great evolutionary advantage for the adaptation to the rapid changing conditions of the environment. Microorganisms utilize QS mechanisms to adapt to unfavorable conditions. Furthermore, some authors propose the role of these processes as neo-Darwinian mechanisms of evolution, with an important participation in the apparition of the first multicellular organisms [4, 5].QS has extensively been studied in bacteria during the past 50 years [4, 6] and it is known to be involved in the regulation of processes such as pathogenesis, symbiosis, competence, conjugation, nutrients uptake, morphological differentiation, secondary metabolites biosynthesis, or biofilms production [7]. In one study using Gram-negative bacteria, it was discovered that QSM was produced by a two-component system: the enzyme synthase LuxI that produces N-acyl-homoserine-lactone (AHLs) and a sensor receptor (LuxR) responsible of the detection of the molecule in the environment [8, 9]. Later on, quinolones were found as QSM in other Gram-negative bacteria such as Pseudomonas aeuroginosa [10]. In Gram-positive bacteria, QS mechanisms were discovered mediated by peptides, and the autoinducer 2 (AI-2) was also later described in Gram-negative bacteria [4]. In the following years, ɣ-butirolactone was found as the QSM used by species of the genus Streptomyces
- Maulin P. Shah, Susana Rodriguez-Couto, S. Sevinc Sengor, Maulin P. Shah, Susana Rodriguez-Couto, S. Sevinc Sengor(Authors)
- 2020(Publication Date)
- Elsevier(Publisher)
Chapter 6Bacterial Quorum Sensing in environmental biotechnology: a new approach for the detection and remediation of emerging pollutants
Debapriya Sarkar, Kasturi Poddar, Nishchay Verma, Sayantani Biswas and Angana Sarkar, Department of Biotechnology and Medical Engineering, National Institute of Technology Rourkela, Odisha, IndiaAbstract
The cell to cell communication among microorganisms using signaling molecules is known as Quorum Sensing (QS). This is a mechanism in which the bacteria communicate and coordinate the group behavior by releasing autoinducers and regulate gene expression in accordance with the population density. QS plays a key role in stress tolerance, biofilm formation, as well as in the regulation of virulence properties. It provides electrochemical sensitivity to several microorganisms, thus enabling their potential for the biosensing of different metallic contaminants like arsenic, lead, zinc, copper, etc. The most popular examples of this type organism are Shewanella oneidensis , Vibrio harveyi for biosensing activity. QS has also been found to have an influence on bacterial metabolism, especially in biodegradation. This effect was confirmed in hydrocarbon degradation by Pseudomonas aeruginosa , and Acinetobacter sp. The mechanism makes a great contribution in the biofilm formation ability of different bacteria, as biofilm is one of the virulence properties of any pathogen. Regulating QS-mediated biofilm formation can provide a means to biocontrol the virulence properties of pathogens. This book chapter will focus on the mechanism of microbial QS and its application in environmental contaminant detection and bioremediation.Keywords
Quorum Sensing; bacteria; biosensor; bioremediation; biofilm; virulence; biodegradation6.1 Introduction
Quorum Sensing (QS) of bacteria or microbes can be defined as a stimuli or response which can be visible as a phenotypic change, correlated to microbial population. It is the cell to cell communication phenomenon of prokaryotes. This prokaryotic cell to cell signaling is mediated by autoinducers (AI) which are formed and secreted by the microbes (Williams, 2007 ). QS is the mechanism of communication between the microorganisms depending upon their cell density which can have an influence on behaviors like virulence factor secretion, biofilm formation, bioluminescence competence, and others in bacteria (Miller & Bassler, 2001 ). The first QS in bacteria was observed in Streptococcus pneumoniae on genetic competence and in marine Vibrio sp. on bioluminescence. This communication depends on specialized AI (signaling) molecules (Albuquerque & Casadevall, 2012
- Frans J. de Bruijn(Author)
- 2016(Publication Date)
- Wiley-Blackwell(Publisher)
Bacteria in nature live predominantly in biofilms, which allows the resident members to establish complex social interactions and networks in the biofilm community. Bacterial interactions can occur among or within species and can be either competitive or cooperative (see Section 22). It is now well recognized that cooperation within the same species against competitors is a widespread phenomenon and can occur more frequently in nature than was previously thought. Indeed, cooperation is needed for evolution to construct new levels of organization. However, natural selection implies that competition opposes cooperation unless a specific mechanism is at work. In recent years, the mechanisms behind this conflict have been elucidated by evolutionary theories and experiments. Great progress has been made in our understanding of bacterial cooperation, competition, and effects on microbial ecology and evolution. In particular, the discovery of widespread quorum-sensing mechanisms in bacteria is crucial for guiding researchers to study bacterial multicellular behaviors, rather than the previous emphasis on individual cell biology. Quorum-sensing-mediated activities are emerging as an integral component of bacterial social cooperation, profoundly affecting bacterial physiology, ecology, and evolution. Analyses of bacterial interactions have shown that bacteria often cooperate to resist competition of other species. It is therefore reasonable to speculate that similar cooperative traits may be required for a given pathogen to initiate an infectious disease. However, research on how bacterial Quorum Sensing works mechanistically in biofilms and the extent to which bacterial cooperation can be maintained in nature remains to be studied. Answering these questions will undoubtedly provide new insights into bacterial cooperative behaviors, ecology, and roles in infectious diseases.Acknowledgements
This work was supported by the Canadian Institutes for Health Research (CIHR) Operating Grant MOP-115007 and by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant RGPIN 311682-07. The authors would like to apologize to those researchers whose work was not included in this chapter due to space limitation.References
- Amarasekare P. 2002. Interference competition and species coexistence. Proceedings of Biology Sciences of the Royal Society 268: 2541–2550.
- Antunes LC, Ferreira RB, Buckner MM, Finlay BB. 2010. Quorum Sensing in bacterial virulence. Microbiology 156(8): 2271–2282.
- Aoki SK, Pamma R, Hernday AD, Bickham JE, Braaten BA, Low DA. 2005. Contact-dependent inhibition of growth in Escherichia coli. Science 309(5738): 1245–1248.
- Aoki SK, Poole SJ, Hayes CS, Low DA. 2011. Toxin on a stick: modular CDI toxin delivery systems play roles in bacterial competition. Virulence 2(4): 356–359.
- Basler M, Mekalanos JJ. 2012. Type 6 secretion dynamics within and between bacterial cells. Science
- V Ravishankar Rai, Jamuna A. Bai(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
399 21 Quorum Sensing in Food-Borne Bacteria and Use of Quorum Sensing Inhibitors as Food Intervention Techniques Jamuna A. Bai and V. Ravishankar Rai 21.1 Introduction In the last few years, significant progress has been made in understanding the virulence, transmission, survival, stress response, and interactions of food-borne bacteria with other microbiota. However, the knowledge we have about the ecology of food spoilage bacteria and the biochemical mechanisms behind spoilage at the molecular level is considerably less. A number of studies imply that virulence- and spoilage-regulated phenotypes in food-borne bacteria are cell density–dependent phenomenon regulated at the genetic level by the mechanism of Quorum Sensing. In Quorum Sensing (QS) or cell-to-cell com-munication, bacteria produce, detect, and respond to the signaling molecules, also known as autoinduc-ers. Bacteria sense their population density by monitoring the signal molecules in their environment and respond to it by activating or repressing target genes and the expression of certain phenotypes. In this CONTENTS 21.1 Introduction .................................................................................................................................. 399 21.2 Quorum Sensing Systems in Bacteria .......................................................................................... 400 21.2.1 Acylated Homoserine Lactones ....................................................................................... 400 21.2.2 Autoinducer 2 .................................................................................................................. 400 21.2.3 Autoinducer-3/QseC System ............................................................................................ 401 21.2.4 AIP/Agr System ...............................................................................................................
- Alexandru Mihai Grumezescu(Author)
- 2018(Publication Date)
- William Andrew(Publisher)
However, in the natural environment or inside an eukaryotic host, these microbes live in mixed communities. Within these complex communities, they practice a very active communication with members of their own and other microbial communities, as well as with the host cells. All these communicative events involve a variety of chemical signaling molecules that can be described under the broad umbrella of Quorum Sensing (QS). The ability to sense and respond to these signaling molecules enables microbes to exert collective behavior on a population-wide scale, as if they are a multicellular entity. Accordingly, QS can be considered as a tool for synchronization of the behavior of microbial members of a given population or community. There are considerable overlaps among the QS circuits of bacteria belonging to different taxonomic groups, so signals produced by one species can be also compatible with receptors of other species (Miller and Bassler, 2001). QS allows bacteria to modulate their behavior in relation to their cell density, and the QS-regulated traits will not be expressed until the minimum requisite cell density (i.e., quorum) has not been reached. A considerable part of bacterial genome is regulated through this QS mechanism, and genes therein code for traits such as biofilm formation, virulence, swarming motility, horizontal gene transfer, pigment production, etc. (Castillo-Juárez et al., 2015). Among the traits which are regulated by QS, some are important to us from a clinical perspective, and some from an industrial perspective. Some metabolites can be important from both angles. For example, lactic acid production among Lactobacilli is a desired trait, as lactic acid is an organic acid with high market potential; production of it by some probiotic strains has also been shown to be beneficial for human health. At the same time, lactic acid production by Streptococcus mutans in the oral cavity is the cause for teeth demineralization
eBook - ePub- Shivendra Tenguria, Ashutosh Kumar(Authors)
- 2022(Publication Date)
- Academic Press(Publisher)
Allen et al., 2014 ). These strategies are believed to posit lesser selection pressure on pathogenic bacteria to develop resistance since these do not inhibit the normal growth or function. This antivirulence strategy can potentially provide better alternatives to traditional antibiotics with better control of pathogens and aimed at better return-on-investment for pharmaceutical companies. This can also spur drug development efforts to counter the infectious disease and resistance burden.Quorum-sensing and quorum quenching
Quorum-sensing phenomenon was discovered in Vibrio fischeri , where their symbiotic relationship with Hawaiian bobtail squids was studied based on bioluminescence. The bioluminescence was controlled by Quorum Sensing and it has been a subject of interest for biologists to understand the mechanism underlying the process. Bacteria have devoted around 4%–10% of their genomes and >20% of proteomes for QS, which regulates a large number of genes and regulons. This suggests the role of QS in regulating critical signaling networks in manifesting virulence. A coordinated communication network is critical for pathogenic bacteria to mount an attack or colonize a niche effectively. The outcome of tussle between infectious bacteria and the human host hinges on effective exploitation of these communication systems. Virulence in many bacteria is under QS regulation. Several competing organisms eavesdrop on interspecies communication and produce QS inhibitors as signal mimics to confuse the competitor by interrupting the communication channel. The consequence of this signal war decides the species composition and dominance stratification of the microbial community. While bacteria jam the interspecies signals, they inform their kin of their presence by enhancing their own QS signals. This helps the bacteria decide on the behavioral switch between living a solitary life at low cellular densities (LCD) versus a multicellular social life at higher cell densities (HCD) (Mukherjee and Bassler, 2019 ).The bacterial communication varies from one species to another. In gram-negative bacteria, the QS signals are autoinducer molecules (AHLs) synthesized from S-adenosyl-methionine (SAM), which can freely diffuse through the membrane. These can bind to membrane-bound receptors and regulate hundreds of genes covering numerous biological processes (Papenfort and Bassler, 2016 ). The acyl-chain lengths may differ for different variants/homologs of the common LuxI/R QS systems in different species that impart specificity to the intraspecies bacterial dialog. Sometimes bacteria may harbor multiple QS systems interconnected to provide functional redundancy to these circuits like—LasI/R, RhlI/R, PQS, IQS—systems in P. aeruginosa (Mukherjee and Bassler, 2019 ; Papenfort and Bassler, 2016 ). In gram-positive bacteria, the signals are oligopeptides that are synthesized and modified in the cell and secreted out of the cell using ABC transporters. These peptides are detected by specific two-component sensory apparatus (histidine-kinase two-component system) that receives and transduces the signal to the response regulator. The response regulator controls the expression of genes under QS control. ComX peptide autoinducer in Bacillus subtilis is sensed by ComP/ComA system to activate ComK that controls the competence state of the bacterium. Some bacteria have evolved multiple ways of communication, for example, Vibrio harveyi , which communicates between different species via AI-2, and within the same species via AI-1. Some of these systems have been represented in Fig. 12.1
eBook - ePubTrends in Quorum Sensing and Quorum Quenching
New Perspectives and Applications
- V. Ravishankar Rai, Jamuna A Bai, V. Ravishankar Rai, Jamuna A Bai(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
Quorum Sensing regulates the production of an ample repertoire of extracellular chemical compounds such as exopolysaccharides, enzymes, and bioactive metabolites that can act as signals, cues, and virulence determinants, which are known to greatly influence the interaction of microbes with their environment. These biomolecules are believed to mediate intra- and interspecies, as well as interkingdom interactions (Rumbaugh and Kaufmann 2012), which play important roles in the ecology of the microorganisms (O’Brien and Wright 2011, Davies 2013), and influence human health and disease (Rutherford and Bassler 2012). This entails an even greater significance as the vast majority of microbial life exists in complex communities, often associated with higher organisms, in ways that are still poorly understood. Although it is assumed that microbial populations use Quorum Sensing processes for coordinating social behaviors driving colonization and survival, very little is known with respect to the impact of chemical exchange processes on the competitive fitness of microbes in the host and the natural environment (Liu, Qin, and Defoirdt 2018). Furthermore, a better understanding of how Quorum Sensing is used by microbes to interact with their hosts could assist novel strategies to improve human health and combat infectious diseases (Defoirdt 2018). Traditionally, the characterization of Quorum Sensing systems has been carried out by analytical techniques that rely on the isolation or purification of the effectors and signals involved, as well as by the use of Quorum Sensing mutant strains and genetically modified biosensors (Fletcher et al. 2014). These approaches have greatly expanded our understanding of how microbial cells communicate. However, the capability to noninvasively monitor the dynamics of Quorum Sensing in natural microbial populations could provide new fundamental insights into their function and impact in the ecology and social behavior of microbes. To achieve this challenging task, techniques such as imaging mass spectrometry (Stasulli and Shank 2016, Dunham et al. 2017), electrochemical sensing (Connell et al. 2014, Bellin et al. 2014), and surface-enhanced Raman scattering (SERS) spectroscopy (Bodelón et al. 2018) have been recently applied for noninvasive detection and visualization of the molecules involved in microbial communication processes.We commence this chapter with a brief introduction of SERS, describing the enhancement mechanisms and the strategies for SERS detection. Next, we highlight recent advances in the application of SERS for the study of Quorum Sensing and, with the aim to facilitate new opportunities and synergies for the study of microbial communication, we conclude the chapter with a summary of perspectives focusing the integration of SERS with microfabricated devices, which have recently revolutionized our understanding of the social behavior of bacteria at the microscale.
- V. Rajesh Kannan, Kubilay Kurtulus Bastas(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
Chapter 11Quorum Sensing in Plant Pathogenic and Plant-Associated Bacteria
Mani Jayaprakashvel and Vellasamy ShanmugaiahABSTRACT Scientists used to think that microorganisms, especially unicellular bacteria, are simple entities that function individually. However, research in the 1970s found that unicellular microorganisms use small signaling molecules, which function analogously to language, to determine their local population densities and to exhibit certain phenotypes. Collectively, the processes involved in the production and recognition of these signals (called autoinducers) are known as Quorum Sensing (QS). Using this form of cell–cell communication allows unicellular organisms to function as multicellular systems. Studies of QS systems in bacteria have also revealed that these bacterial languages can be intercepted, modulated, or destroyed by other organisms (quorum quenching [QQ]). The basic chemistry, biosynthesis, and mechanisms of autoinducers and types of QS systems contain an ocean of scientific information about how plants combat microbial infections. The influence of QS systems in plant pathology, plant microbial interaction, and rhizosphere ecology has been well documented. QQ, also known as anti-QS, is a promising concept for plant disease-management programs. Several beneficial microorganisms, such as Rhizobium , have been found to operate QS systems that govern plant–microbe interactions and symbiotic associations. This chapter, which contains a comprehensive overview of QS systems in bacteria, considers their mechanisms, autoinducers, QQ, and mechanisms of QQ, as well as applications of QS in biological control from the perspective of plant pathology.KEYWORDS: Quorum Sensing, quorum quenching, plant pathogens, plant-associated bacteria, biocontrol of plant diseases11.1 Introduction
Spoken language is considered to be one of the most important developments in the history of mankind. In an anthropological context, the histories of both spoken and written languages are very important indexes of human development. Microorganisms, especially bacteria, also have a way of communicating: through chemical language, in a process known as Quorum Sensing. Through QS, a cell–cell communication system, bacteria monitor the presence of other bacteria by producing and responding to signaling molecules known as autoinducers (AIs) (Taga and Bassler, 2003). Generally, QS is a population-density-dependent expression of certain phenotypes of bacteria (Bassler, 2002).
eBook - PDF- Dana M. Santos(Author)
- 2011(Publication Date)
- Apple Academic Press(Publisher)
Chapter 2 Quorum Sensing Drives the Evolution of Cooperation in Bacteria Tam á s Cz á r á n and Rolf F. Hoekstra INTRODUCTION An increasing body of empirical evidence suggests that cooperation among clone-mates is common in bacteria. Bacterial cooperation may take the form of the excretion of “public goods”: exoproducts such as virulence factors, exoenzymes, or components of the matrix in biofilms, to yield significant benefit for individuals joining in the common effort of producing them. Supposedly in order to spare unnecessary costs when the population is too sparse to supply the sufficient exoproduct level, many bac-teria have evolved a simple chemical communication system called Quorum Sensing (QS), to “measure” the population density of clone-mates in their close neighborhood. Cooperation genes are expressed only above a threshold rate of QS signal molecule re-capture, that is, above the local quorum of cooperators. The cooperative popula-tion is exposed to exploitation by cheaters, that is mutants who contribute less or nil to the effort but fully enjoy the benefits of cooperation. The communication system is also vulnerable to a different type of cheaters (“Liars”) who may produce the QS signal but not the exoproduct, thus ruining the reliability of the signal. Since there is no reason to assume that such cheaters cannot evolve and invade the populations of honestly signaling cooperators, the empirical fact of the existence of both bacterial cooperation and the associated QS communication system seems puzzling. Using a stochastic cellular automaton (CA) approach and allowing mutations in an initially non-cooperating, non-communicating strain we show that both cooperation and the associated communication system can evolve, spread and remain persistent. The QS genes help cooperative behavior to invade the population, and vice versa ; coopera-tion and communication might have evolved synergistically in bacteria.
eBook - PDFBiosensing Technologies for the Detection of Pathogens
A Prospective Way for Rapid Analysis
- Toonika Rinken, Kairi Kivirand, Toonika Rinken, Kairi Kivirand(Authors)
- 2018(Publication Date)
- IntechOpen(Publisher)
3. Biosensors for detections of Quorum Sensing signals molecules Due to Quorum Sensing (QS), communication system allows bacteria to act in a coordinate manner, to coordinate gene expression and to have a greater impact on their host, and this system has become a new target for the development of antimicrobial therapies as well as for bacterial diagnosis and therapeutic purposes [23, 24]. In this context, a diverse number of biosensors have been designed and developed to identify QS communication signals called autoinducers (AIs). Airborne pathogen Pathology Main autoinducer(s) type Refs. Pseudomonas aeruginosa Opportunistic infections AHL * 3-oxo-AHL * [14, 15] Klebsiella pneumoniae Pneumonia, bronchitis AI-2 ** [19] Acinetobacter baumannii Opportunistic infections 3-hydroxy-AHL * [18] Streptococcus pyogenes Pharyngitis, cellulitis AI-2 ** [22] Legionella pneumophila Legionnaire’s disease LAI-1 *** (3-hydroxypentadecane-4-one) [20] * AHL: acyl homoserine lactone. ** AI-2: autoinducer-2. *** LAI-1: Legionella autoinducer. Table 1. Selected airborne pathogens with Quorum Sensing communication system. Detection and Control of Indoor Airborne Pathogenic Bacteria by Biosensors Based on Quorum… http://dx.doi.org/10.5772/intechopen.72390 77 3.1. Diversity of Quorum Sensing biosensors: accuracy, precision and sensibility for autoinducers detection Biosensors are analytical bio-physicochemical-electronic devices that are able to detect and quantify analytes from a sample (for review, see Ref. [25]). The physical-chemical-electronic component of a biosensor is a detector and transducer able to capture a specific signal gener -ated by the biological component when it is associated with its cognate analyte. The biological component of a biosensor can be whole cells (genetically modified microorganisms contain -ing a genic construct based on a sensing-reporter system); proteins (enzymes, antibodies and antigens) or nucleic acids.
eBook - ePub- Alexandru Mihai Grumezescu, Alina Maria Holban(Authors)
- 2017(Publication Date)
- Academic Press(Publisher)
Microbial communication systems can ultimately influence food quality by affecting both sensory quality (development of beneficial bacteria) and safety (limiting the growth of pathogens and spoilers) (Rul and Monnet, 2015). QS signaling molecules serve to inter- or intrabacteria species communication but also modulate the host immune response. Prior exposure of the host organism to QS molecular agents facilitated the survival of the infected host organism that is able to increase the propagation of infecting bacteria (Bjarnsholt et al., 2005). Figure 4.3 Schematic of the Quorum Sensing “Switch” and Types of Signal Molecules. (A) Signal molecules are produced by the bacteria and accumulate in the extracellular environment. Once the concentration of AI-2 reaches a particular “threshold” concentration, the QS genes and phenotypes are switched “on.” Phenotypes include biofilm formation, bioluminescence, and toxin production. (B) Three main families of QS signal molecules that occur in various bacteria (Roy et al., 2011). 4. QS and Biofilms in Food Safety The QS can play a very important role in the control of bacterial infections by interfering with their signaling systems, so that pathogenic gene expression can be locked. Numerous chitinolytic, lipolytic, proteolytic, and pectinolytic activities related to foods deterioration can be regulated by QS. It is well known that many pathogenic microorganisms make biofilms on food and food-contact surfaces under appropriate environments. Adhesion of Salmonella to food surfaces was the first published report on food-borne bacterial biofilm (Lianou and Koutsoumanis, 2012). Since that time, some authors have described the ability of food-borne pathogens to bind to food and food-contact surfaces, including L. monocytogenes, Yersinia enterocolitica, Campylobacter jejuni, and E. coli O157:H7 (Shi and Zhu, 2009)
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