Involvement of luxS gene in biofilm formation by Streptococcus intermedius (original) (raw)
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QUORUM SENSING AND ITS DIFFERENT SIGNALS SYSTEMS IN BACTERIA
The chemical signal molecules called autoinducers are produced and released by the quorum sensing bacteria to levels dominating the increasing cell-population density. The attainment of minimal threshold stimulatory concentration of an autoinducer leads to an alteration in gene expression. Both Gram-positive and Gram-negative bacteria are capable of using quorum sensing communication circuits for regulating a diverse array of physiological activities. These activities include symbiosis, competence, virulence, conjugation, antibiotic production, sporulation, motility and biofilm formation.
Quorum-sensing Cascades Governing Bacterial Multicellular Communities
Israel Journal of Chemistry, 2015
In Gram-negative bacteria,q uorum sensingd epends on acyl-homoserine lactone (AHL)a utoinducers(also referred to as AI-1),w hich are the products of LuxI-type autoinducer synthases.T hese small molecules are detected by cognate cytoplasmic LuxR proteins that, upon bindingtheir partner autoinducer, bind DNAand activate transcription of target quorum-sensing genes.T od ate, Abstract:Q uorums ensing (QS) is an efficient mode of intercellular communication between bacteria.T his mode is regulated by self-produced small chemical signals, activating dedicated receptorso nce accumulated.N umerous architecturally complex QS cascades are cardinalf or governingb acterial behaviors, sucha sp athogenicity, luminescence, and bacterialc ompetence. Importantly,Q Sc ascades are essential for the formation of bacterialm ulticellularc ommunities. Once informed via QS cascades, motile cells often organize themselves into conspicuous multicellular structures that carry out specializedt asks. This review focuses on the major QS systems,p laying an active role in the rise of complex bacterial communities in different bacterialm odels.
Infection and Immunity, 2011
Streptococcus pneumoniae is the leading cause of death in children worldwide and forms highly organized biofilms in the nasopharynx, lungs, and middle ear mucosa. The luxS-controlled quorum-sensing (QS) system has recently been implicated in virulence and persistence in the nasopharynx, but its role in biofilms has not been studied. Here we show that this QS system plays a major role in the control of S. pneumoniae biofilm formation. Our results demonstrate that the luxS gene is contained by invasive isolates and normal-flora strains in a region that contains genes involved in division and cell wall biosynthesis. The luxS gene was maximally transcribed, as a monocistronic message, in the early mid-log phase of growth, and this coincides with the appearance of early biofilms. Demonstrating the role of the LuxS system in regulating S. pneumoniae biofilms, at 24 h postinoculation, two different D39⌬luxS mutants produced ϳ80% less biofilm biomass than wild-type (WT) strain D39 did. Complementation of these strains with luxS, either in a plasmid or integrated as a single copy in the genome, restored their biofilm level to that of the WT. Moreover, a soluble factor secreted by WT strain D39 or purified AI-2 restored the biofilm phenotype of D39⌬luxS. Our results also demonstrate that during the early mid-log phase of growth, LuxS regulates the transcript levels of lytA, which encodes an autolysin previously implicated in biofilms, and also the transcript levels of ply, which encodes the pneumococcal pneumolysin. In conclusion, the luxS-controlled QS system is a key regulator of early biofilm formation by S. pneumoniae strain D39.
The LuxS family of bacterial autoinducers: biosynthesis of a novel quorum‐sensing signal molecule
Molecular Microbiology, 2001
Many bacteria control gene expression in response to cell population density, and this phenomenon is called quorum sensing. In Gram‐negative bacteria, quorum sensing typically involves the production, release and detection of acylated homoserine lactone signalling molecules called autoinducers. Vibrio harveyi, a Gram‐negative bioluminescent marine bacterium, regulates light production in response to two distinct autoinducers (AI‐1 and AI‐2). AI‐1 is a homoserine lactone. The structure of AI‐2 is not known. We have suggested previously that V. harveyi uses AI‐1 for intraspecies communication and AI‐2 for interspecies communication. Consistent with this idea, we have shown that many species of Gram‐negative and Gram‐positive bacteria produce AI‐2 and, in every case, production of AI‐2 is dependent on the function encoded by the luxS gene. We show here that LuxS is the AI‐2 synthase and that AI‐2 is produced from S‐adenosylmethionine in three enzymatic steps. The substrate for LuxS is ...
Journal of Bacteriology, 2005
Quorum sensing is a process by which bacteria communicate by using secreted chemical signaling molecules called autoinducers. Many bacterial species modulate the expression of a wide variety of physiological functions in response to changes in population density by this mechanism. In this study, the opportunistic pathogen Klebsiella pneumoniae was observed to secrete type 2 signaling molecules. A homologue of luxS, the gene required for AI-2 synthesis in Vibrio harveyi, was isolated from the K. pneumoniae genome. A V. harveyi bioassay showed the luxS functionality in K. pneumoniae and its ability to complement the luxS-negative phenotype of Escherichia coli DH5␣. Autoinducer activity was detected in the supernatant, and maximum expression of specific messengers detected by quantitative reverse transcription-PCR analysis occurred during the late exponential phase. The highest levels of AI-2 were observed in minimal medium supplemented with glycerol. To determine the potential role of luxS in colonization processes, a K. pneumoniae luxS isogenic mutant was constructed and tested for its capacity to form biofilms in vitro on an abiotic surface and to colonize the intestinal tract in a murine model. No difference was observed in the level of intestinal colonization between the wild-type strain and the luxS mutant. Microscopic analysis of biofilm structures revealed that the luxS mutant was able to form a mature biofilm but with reduced capacities in the development of microcolonies, mostly in the early steps of biofilm formation. These data suggest that a LuxS-dependent signal plays a role in the early stages of biofilm formation by K. pneumoniae. luxS expression is growth phase dependent. RT-PCR was carried out by using 0.5 g of K. pneumoniae LM21 DNA-free total RNA. Primers RT-luxS-5Ј and RT-luxS-3Ј, specific to the luxS ORF, were used. The maximum luxS mRNA level was normalized to 100%, and values are indicated as relative quantifications. (A) Results of RT-PCRs of total RNA isolated from cultures of K. pneumoniae LM21 in LB, AB, BHI, and DMEM at an OD 620 of ϳ1. (B) Results of RT-PCRs of total RNA isolated at different time points of K. pneumoniae LM21 growth. The bacterial growth was monitored by measurement of OD 620 . The endogenous control, which consists of amplification of 16S rRNA with primers TM1 and TM2, was not represented. The figure represents the means and standard errors of the means of the results from three independent experiments.
QUORUM SENSING: Cell-to-Cell Communication in Bacteria
Bacteria communicate with one another using chemical signal molecules. As in higher organisms, the information supplied by these molecules is critical for synchronizing the activities of large groups of cells. In bacteria, chemical communication involves producing, releasing, detecting, and responding to small hormone-like molecules termed autoinducers. This process, termed quorum sensing, allows bacteria to monitor the environment for other bacteria and to alter behavior on a population-wide scale in response to changes in the number and/or species present in a community. Most quorumsensing-controlled processes are unproductive when undertaken by an individual bacterium acting alone but become beneficial when carried out simultaneously by a large number of cells. Thus, quorum sensing confuses the distinction between prokaryotes and eukaryotes because it enables bacteria to act as multicellular organisms. This review focuses on the architectures of bacterial chemical communication networks; how chemical information is integrated, processed, and transduced to control gene expression; how intra-and interspecies cell-cell communication is accomplished; and the intriguing possibility of prokaryote-eukaryote cross-communication. 319 Annu. Rev. Cell Dev. Biol. 2005.21:319-346. Downloaded from arjournals.annualreviews.org by Uniformed Services University -HSC EBVC Account on 12/09/07. For personal use only.
Role of Quorum Sensing in Microbial Infections and Biofilm Formation
Model Organisms for Microbial Pathogenesis, Biofilm Formation and Antimicrobial Drug Discovery, 2020
The infections and pathogenesis are continuously evolving processes to avoid the effects of hazardous situations and antibiotic susceptibility. In this process, the microbes could percept and conscientiousness towards its circumstances by their cellular and physiological mechanisms. All the bacterial populations can maintain phenotypes and genotype monitors in their competitive environment. To maintain all these community behaviors, the bacterial population utilize various natural signaling pathways under specific microbial language. The bacterial population was well regulated their extracellular or intercellular cooperative communication mechanisms known as quorum sensing. The quorum-sensing (QS) 62 mechanism responds through small diffusible signal molecules; these signaling molecules were synthesized and secreted into intercellular or extracellular microenvironment at different phage of bacterial growth. However, we focus on this chapter microbial signal communications and also QS mechanisms in biofilm formation.
Infection and Immunity, 2006
Nosocomial infections caused by Staphylococcus epidermidis are characterized by biofilm formation on implanted medical devices. Quorum-sensing regulation plays a major role in the biofilm development of many bacterial pathogens. Here, we describe luxS, a quorum-sensing system in staphylococci that has a significant impact on biofilm development and virulence. We constructed an isogenic ⌬luxS mutant strain of a biofilmforming clinical isolate of S. epidermidis and demonstrated that luxS signaling is functional in S. epidermidis. The mutant strain showed increased biofilm formation in vitro and enhanced virulence in a rat model of biofilm-associated infection. Genetic complementation and addition of autoinducer 2-containing culture filtrate restored the wild-type phenotype, demonstrating that luxS repressed biofilm formation through a cell-cell signaling mechanism based on autoinducer 2 secretion. Enhanced production of the biofilm exopolysaccharide polysaccharide intercellular adhesin in the mutant strain is presumably the major cause of the observed phenotype. The agr quorum-sensing system has previously been shown to impact biofilm development and biofilm-associated infection in a way similar to that of luxS, although by regulation of different factors. Our study indicates a general scheme of quorum-sensing regulation of biofilm development in staphylococci, which contrasts with that observed in many other bacterial pathogens.
Look who's talking: communication and quorum sensing in the bacterial world
Philosophical Transactions of the Royal Society B: Biological Sciences, 2007
For many years bacteria were considered primarily as autonomous unicellular organisms with little capacity for collective behaviour. However, we now appreciate that bacterial cells are in fact, highly communicative. The generic term ‘quorum sensing’ has been adopted to describe the bacterial cell-to-cell communication mechanisms which co-ordinate gene expression usually, but not always, when the population has reached a high cell density. Quorum sensing depends on the synthesis of small molecules (often referred to as pheromones or autoinducers) that diffuse in and out of bacterial cells. As the bacterial population density increases, so does the synthesis of quorum sensing signal molecules, and consequently, their concentration in the external environment rises. Once a critical threshold concentration has been reached, a target sensor kinase or response regulator is activated (or repressed) so facilitating the expression of quorum sensing-dependent genes. Quorum sensing enables a b...