luxS Mutant Strain Research Articles

The Quorum Sensing Mechanism of Aggregatibacter actinomycetemcomitans in Pathogenesis of Periodontitis: Systematic Literature Review

Background: Periodontitis is one of the most prevalent oral diseases worldwide and a significant public health concern. Periodontitis characterized by inflammation of the tissues supporting the teeth. It is primarily caused by bacteria in the subgingival biofilm, with A. actinomycetemcomitans and P. gingivalis as a key pathogens. These bacteria contribute to oral dysbiosis, leading to periodontal tissue damage. A. actinomycetemcomitans is particularly virulent, utilizing quorum sensing (QS) to regulate biofilm formation and enhance its pathogenicity, playing a significant role in the development and progression of periodontitis. Objective: This study aims to explain the quorum sensing mechanism in the pathogenesis of periodontitis caused by A. actinomycetemcomitans. Methods: This study employed a systematic literature review design by searching for articles based on predetermined inclusion and exclusion criteria. The search strategy used keywords and boolean operators across three databases (PubMed, Ebsco, ScienceDirect). Results: The variation between wild-type (Aa-WT) and LuxS mutant (Aa-LuxS) strains of A. actinomycetemcomitans impacts its pathogenicity. Quorum sensing (QS) interactions between A. actinomycetemcomitans and other periodontopathogens (P. gingivalis, T. denticola, P. intermedia) amplify virulence, promoting biofilm formation and disease progression. AI-2 regulates key processes, underscoring A. actinomycetemcomitans significant role in periodontitis. Conclusion: The quorum sensing mechanism in A. actinomycetemcomitans, through AI-2 production, is essential for microbial communication and biofilm formation, influencing the bacterium's virulence and role in periodontitis.

Effects of AI-2 quorum sensing related luxS gene on Streptococcus suis formatting monosaccharide metabolism-dependent biofilm.

Biofilm is the primary cause of persistent infections caused by Streptococcus suis (S. suis). Metabolism and AI-2 quorum sensing are intricately linked to S. suis biofilm formation. Although the role of the AI-2 quorum sensing luxS gene in S. suis biofilm has been reported, its specific regulatory mechanism remains unclear. This study explored the differences in biofilm formation and monosaccharide metabolism among the wild type (WT), luxS mutant (ΔluxS) and complement strain (CΔluxS), and Galleria mellonella larvae were used to access the effect of luxS gene deletion on the virulence of S. suis in different monosaccharide medias. The results indicated that deletion of the luxS gene further compromised the monosaccharide metabolism of S. suis, impacting its growth in media with fructose, galactose, rhamnose, and mannose as the sole carbon sources. However, no significant impact was observed in media with glucose and N-acetylglucosamine. This deletion also weakened EPS synthesis, thereby diminishing the biofilm formation capacity of S. suis. Additionally, the downregulation of adhesion gene expression due to luxS gene deletion was found to be independent of the monosaccharide medias of S. suis.

The absence of luxS reduces the invasion of Avibacterium paragallinarum but is not essential for virulence.

The contagious respiratory pathogen, Avibacterium paragallinarum, contributes to infectious coryza in poultry. However, commercial vaccines have not shown perfect protection against infectious coryza. To search for an alternative approach, this research aimed to investigate whether the quorum-sensing system of pathogens plays a crucial role in their survival and pathogenicity. The LuxS/AI-2 quorum-sensing system in many Gram-negative and Gram-positive bacteria senses environmental changes to regulate physiological traits and virulent properties, and the role of the luxS gene in Av. paragallinarum remains unclear. To investigate the effect of the luxS gene in the quorum-sensing system of Av. paragallinarum, we constructed a luxS mutant. Bioluminescence analysis indicated that the luxS gene plays a vital role in the LuxS/AI-2 quorum-sensing system. The analysis of the LuxS/AI-2 system-related genes showed the level of pfs mRNA to be significantly increased in the mutant strain; however, lsrR, lsrK, and lsrB mRNA levels were not significantly different compared with the wild type. The ability of the luxS mutant strain to invade HD11 and DF-1 cells was significantly decreased compared with the wild-type strain. In addition, all chickens challenged with various doses of the luxS mutant strain developed infections and symptoms, and those challenged with the lowest dose exhibited only minor differences compared to chickens challenged with the wild-type strain. Thus, the deletion of the luxS gene reduces the invasion, but the luxS gene does not play an essential role in the pathogenesis of A. paragallinarum.

Effect of Quorum Sensing Systems on Biofilm Formation and Virulence in Salmonella

In recent years, as the paradigm of communication between cells has been clarified, the ability of bacteria to change their gene expression patterns in response to various extracellular signals has attracted great interest. In particular, intracellular and intercellular communication between bacterial populations, called quorum sensing (QS), is essential for coordinating physiological and genetic activities. QS studies are critical, particularly in elucidating the regulatory mechanisms of infectious processes in food-borne pathogens. Elucidating the QS mechanisms in Salmonella is effective in silencing the virulence factors in the fight against this bacterium. The aims of this study were; to create luxS gene mutants that play a vital role in the QS activity of Salmonella and to determine the effect of this mutation on the expression of virulence genes in the bacteria and to determine the impact of synthetic N-hexanoyl-homoserine lactone (C6HSL) on biofilm formation and AI-2 signaling pathway of Salmonella wild strain and luxS gene mutants. luxS gene mutants were constructed by recombining the gene region with the chloramphenicol gene cassette based on homologous region recombination. In the luxS mutants obtained in this way, the expression of eight different virulence genes (hilA, invA, inv, glgC, fimF, fliF, lpfA, gyrA), which have essential roles in Salmonella pathogenicity, was determined by quantitative real-time reverse transcriptase polymerase chain reaction (rRT-qPCR) method and compared with natural strains. As a result of these studies, it was determined that the expression of each gene examined was significantly reduced in luxS mutant strains. The relative AI-2 activities of Salmonella strains were analyzed depending on time. It was determined that the highest activity occurred at the fourth hour and the AI-2 activities of luxS mutants were reduced compared to the wild strain. Finally, it was determined that C6HSL increased the biofilm activity of Salmonella Typhimurium DMC4, SL1344 wild strains, and mutants, mainly at the 72nd hour. In conclusion, our results proved that C6HSL stimulated QS communication in all strains and increased biofilm of Salmonella formation and autoinducer activity. This situation determines that Salmonella responds to external signals by using QS systems. In addition, this research contributed to provide additional information on interspecies communication mechanisms to develop strategies to prevent biofilm formation of this pathogen.

The luxS deletion reduces the spoilage ability of Shewanella putrefaciens: An analysis focusing on quorum sensing and activated methyl cycle

The luxS mutant strains of Shewanella putrefaciens (SHP) were constructed to investigate the regulations of gene luxS in spoilage ability. The potential regulations of AI-2 quorum sensing (QS) system and activated methyl cycle (AMC) were studied by analyzing the supplementation roles of key circulating substances mediated via luxS, including S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), methionine (Met), homocysteine (Hcy) and 4,5-dihydroxy-2,3-pentanedione (DPD). Growth experiments revealed that the luxS deletion led to certain growth limitations of SHP, which were associated with culture medium and exogenous additives. Meanwhile, the decreased biofilm formation and diminished hydrogen sulfide (H2S) production capacity of SHP were observed after luxS deletion. The relatively lower total volatile base nitrogen (TVB-N) contents and higher sensory scores of fish homogenate with luxS mutant strain inoculation also indicated the weaker spoilage-inducing effects after luxS deletion. However, these deficiencies could be offset with the exogenous supply of circulating substances mentioned above. Our findings suggested that the luxS deletion would reduce the spoilage ability of SHP, which was potentially attributed to the disorder of AMC and AI-2 QS system.

LuxS-deficiency reduces persistence of Cronobacter to low-moisture but contributes to virulence after rehydration

Low‐moisture foods (LMF) have arisen an increasing concern as vehicles of foodborne pathogens. Cronobacter genus, a class A pathogen in powdered infant formula (PIF), is crucial to the safety of LMF. Researchers have concentrated more on the bacterial survival caused by key hazardous factors, yet they often ignore the alteration of virulence properties in the surviving strains following rehydration of LMF mediated by the key factors. Our previous transcriptional profiling showed that luxS might participate in desiccation response. Herein, we further investigated the role of Cronobacter LuxS under desiccation stress by combining with the phenotypic and gene analysis between the Cronobacter parent and luxS mutant strains. Desiccation stress destructing assays confirmed that luxS can significantly enhance the resistance of Cronobacter towards desiccation. Our results also showed that cell hydrophobicity, aggregation, motility, the content of polysaccharide, and AI-2 synthesis pathway involved in luxS-mediated desiccation response. The luxS mutant strain exhibited higher swimming and swarming motility, more content of capsular polysaccharide, and more rapid of aggregation, but lower hydrophobicity than that of the wild-type strain, whereas desiccation stress would result in a opposite effect on these cell surface properties in ΔluxS during rehydration. Additionally, the comparation of gene expression profiles indicated that low moisture would trigger Cronobacter luxS to promote transport osmoprotectants by regulating the expression of proX, proW, and treC, and suppress the expression of cpsG associated with polysaccharide colanic acid. Notably, this study also discovered for the first time that the luxS-deficiency dramatically attenuated adhesion and invasion to intestinal and brain cells, but ΔluxS subjected to desiccation could aggravate the cell virulence instead. Therefore, thinking the alteration of toxicity caused by low‐moisture, approach based on blocking the expression of the luxS gene to prevent Cronobacter in LMF needs to be adopted with caution.

The Antibacterial Effect of Cannabigerol toward Streptococcus mutans Is Influenced by the Autoinducers 21-CSP and AI-2

Bacteria can communicate through an intercellular signaling system referred to as quorum sensing (QS). The QS system involves the production of autoinducers that interact with their respective receptors, leading to the induction of specific signal transduction pathways. The QS systems of the oral cariogenic Streptococcus mutans regulate the maturation of biofilms and affect its virulent properties. We have previously shown that the non-psychoactive compound cannabigerol (CBG) of the Cannabis sativa L. plant has anti-bacterial and anti-biofilm activities towards S. mutans. Here we were interested in investigating the effect of the two QS systems ComCDE and LuxS on the susceptibility of S. mutans to CBG and the anti-QS activities of CBG. This was assessed by using various comCDE and luxS mutant strains and complementation with the respective autoinducers, competence stimulating peptide (CSP) and (S)-4,5-dihydroxy-2,3-pentandione (DPD, pre-AI-2). We found that S. mutans comCDE knockout strains were more sensitive to the anti-bacterial actions of CBG compared to the WT strain. Exogenously added 21-CSP prevented the anti-bacterial actions caused by CBG on the ΔcomC, ΔcomE and ΔluxS mutants, while having no effect on the susceptibility of the WT and ΔcomCDE strains to CBG. Exogenously added DPD increased the susceptibility of WT and ΔluxS to CBG. Vice versa, CBG significantly reduced the 21-CSP-induced expression of comCDE genes and ComE-regulated genes and suppressed the expression of luxS with concomitant reduction in AI-2 production. DPD induced the expression of comCDE genes and ComE-regulated genes, and this induction was repressed by CBG. 21-CSP alone had no significant effect on luxS gene expression, while ΔcomCDE strains showed reduced AI-2 production. In conclusion, our study shows that the susceptibility of S. mutans to CBG is affected by the ComCDE and LuxS QS pathways, and CBG is a potential anti-QS compound for S. mutans. Additionally, we provide evidence for crosstalk between the ComCDE and LuxS QS systems.

The role of AI-2/LuxS system in biopreservation of fresh refrigerated shrimp: Enhancement in competitiveness of Lactiplantibacillus plantarum for nutrients

Quorum sensing of lactic acid bacteria, mediated by the Autoinducer-2 (AI-2)/LuxS system, positively regulates antibacterial activity, which is an effective strategy for aquatic product preservation. This study revealed that AI-2/LuxS system regulates the nutritional competitiveness of LAB by facilitating membrane transport systems in preservation of vacuum-packaged refrigerated shrimp (VPRS), using Lactiplantibacillus plantarum SS-128 wild-type and the luxS mutant strain. In VPRS preservation, organisms that cause spoilage and total volatile basic nitrogen were significantly lower in the VPRS inoculated with L. plantarum SS-128 than those inoculated with the luxS mutant strain (L. plantarum ΔluxS/SS-128) (p < 0.05). Simulations in vitro using diluted shrimp juice showed the growth inhibitory effects of wild-type strain SS-128 on the main VPRS spoilage microorganism Shewanella baltica. This could potentially be attributed to more efficient nutrient utilization, presumably mediated by AI-2/LuxS system, as revealed by interaction analysis. In support of this, in vitro nutritional competition test showed that L. plantarum SS-128 was more competitive for nutrients when cocultured with S. baltica under conditions of limited nutrient availability. Subsequently, an integrated analysis of transcriptomic and metabolomic revealed that AI-2/LuxS enables a continuous expansion of L. plantarum SS-128 by balancing energy expenditure followed by enhancing membrane transport systems, which is the main driven forces for it to occupy a favourable niche quickly. Our results showed that the AI-2/LuxS system may regulate the nutritional competitiveness of lactic acid bacteria and may be a regulatory strategy for biological preservation of aquatic products.

Exogenous autoinducer-2 inhibits biofilm development of Desulfovibrio sp. Huiquan2017.

Sulfate-reducing bacteria (SRB) are culprits for microbiologically influenced corrosion, and biofilms are believed to play essential roles in the corrosion induced by SRB. However, little is known about the regulation of SRB biofilms. Quorum sensing signal molecules acyl-homoserine lactones (AHLs) and autoinducer-2 (AI-2) regulate biofilm formation of many bacteria. In this study, the production of AHLs and AI-2 by one SRB strain, Desulfovibrio sp. Huiquan2017, was detected, and the effect of exogenous AI-2 on bacterial biofilm formation was discussed. It was found that the cell-free supernatants of Desulfovibrio sp. Huiquan2017 induced luminescence in a ∆luxS mutant strain Vibrio harveyi BB170, indicating the production of functional AI-2 by the bacterium. In the presence of exogenous AI-2, the growth of Desulfovibrio sp. Huiquan2017 and early biofilm formation were not affected, but the later stage of biofilm development was inhibited significantly. The biofilms became looser, smaller, and thinner, and contained less bacteria and extracellular polymeric substances (EPS). The inhibition effect of AI-2 on the biofilm development of Desulfovibrio sp. Huiquan2017 was mainly achieved through reducing the amount of EPS in biofilms. These findings shed light on the biofilm regulation of SRB.

MRNA-Seq reveals the quorum sensing system luxS gene contributes to the environmental fitness of Streptococcus suis type 2

BackgroundStreptococcus suis type 2 (SS2) is an important zoonotic pathogen. We have previously reported the structure of LuxS protein and found that the luxS gene is closely related to biofilm, virulence gene expression and drug resistance of SS2. However, the mechanism of luxS mediated SS2 stress response is unclear. Therefore, this experiment performed stress response to luxS mutant (ΔluxS) and complement strain (CΔluxS), overexpression strain (luxS+) and wild-type SS2 strain HA9801, and analyzed the differential phenotypes in combination with transcriptome data.ResultsThe results indicate that the luxS gene deletion causes a wide range of phenotypic changes, including chain length. RNA sequencing identified 278 lx-regulated genes, of which 179 were up-regulated and 99 were down-regulated. Differential genes focus on bacterial growth, stress response, metabolic mechanisms and drug tolerance. Multiple mitotic genes were down-regulated; while the ABC transporter system genes, cobalamin /Fe3+-iron carrier ABC transporter ATPase and oxidative stress regulators were up-regulated. The inactivation of the luxS gene caused a significant reduction in the growth and survival in the acid (pH = 3.0, 4.0, 5.0) and iron (100 mM iron chelator 2,2′-dipyridyl) stress environments. However, the mutant strain ΔluxS showed increased antioxidant activity to H2O2 (58.8 mmol/L).ConclusionsThe luxS gene in SS2 appears to play roles in iron metabolism and protective responses to acidic and oxidative environmental conditions.

Clostridioides difficile LuxS mediates inter-bacterial interactions within biofilms

The anaerobic gut pathogen, Clostridioides difficile, forms adherent biofilms that may play an important role in recurrent C. difficile infections. The mechanisms underlying C. difficile community formation and inter-bacterial interactions are nevertheless poorly understood. C. difficile produces AI-2, a quorum sensing molecule that modulates biofilm formation across many bacterial species. We found that a strain defective in LuxS, the enzyme that mediates AI-2 production, is defective in biofilm development in vitro. Transcriptomic analyses of biofilms formed by wild type (WT) and luxS mutant (luxS) strains revealed a downregulation of prophage loci in the luxS mutant biofilms compared to the WT. Detection of phages and eDNA within biofilms may suggest that DNA release by phage-mediated cell lysis contributes to C. difficile biofilm formation. In order to understand if LuxS mediates C. difficile crosstalk with other gut species, C. difficile interactions with a common gut bacterium, Bacteroides fragilis, were studied. We demonstrate that C. difficile growth is significantly reduced when co-cultured with B. fragilis in mixed biofilms. Interestingly, the absence of C. difficile LuxS alleviates the B. fragilis-mediated growth inhibition. Dual species RNA-sequencing analyses from single and mixed biofilms revealed differential modulation of distinct metabolic pathways for C. difficile WT, luxS and B. fragilis upon co-culture, indicating that AI-2 may be involved in induction of selective metabolic responses in B. fragilis. Overall, our data suggest that C. difficile LuxS/AI-2 utilises different mechanisms to mediate formation of single and mixed species communities.

Effect of the luxS gene on biofilm formation and antibiotic resistance by Salmonella serovar Dublin

Biofilms are communities of bacterial cells that serve to protect them from external adverse influences and enhance bacterial resistance to antibiotics and sanitizers. Here, we studied the regulatory effects of glucose and sodium chloride on biofilm formation in Salmonella serovar Dublin (S. Dublin). To analyze expression levels of the quorum sensing gene luxS, we created a luxS knockout mutant. Also, antimicrobial resistance, hydrophobicity and autoinducer-2 (AI-2) activity of both the wild-type (WT) and the mutant strain were investigated. Our results revealed that glucose was not essential for S. Dublin biofilm formation but had an inhibitory effect on biofilm formation when the concentration was over 0.1%. NaCl was found to be indispensable in forming biofilm, and it also exerted an inhibitory effect at high concentrations (>1.0%). Both the WT and the mutant strains displayed significant MIC growth after biofilm formation. An increase of up to 32,768 times in the resistance of S. Dublin in biofilm phonotype against antibiotic (ampicillin) compared to its planktonic phonotype was observed. However, S. Dublin luxS knockout mutant only showed slight differences compared to the WT strain in the antimicrobial tests although it displayed better biofilm-forming capacity than the WT strain. The mutant strain also exhibited higher hydrophobicity than the WT strain, which was a feature related to biofilm formation. The production of the quorum sensing autoinducer-2 (AI-2) was significantly lower in the mutant strain than in the WT strain since the LuxS enzyme, encoded by the luxS gene, plays an essential role in AI-2 synthesis. However, the limited biofilm-forming ability in the WT strain indicated AI-2 was not directly related to S. Dublin biofilm formation. Furthermore, gene expression analysis of the WT and mutant strains revealed upregulation of genes related to biofilm stress response and enhanced resistance in the luxS mutant strain, which may provide evidence for the regulatory role of the luxS gene in biofilm formation.

Role of luxS in Stress Tolerance and Adhesion Ability in Lactobacillus plantarum KLDS1.0391.

Lactobacillus plantarum, a probiotic, has a high survival rate and high colonization ability in the gastrointestinal tract. Tolerance to the gastrointestinal environment and adhesion to intestinal epithelial cells by some Lactobacillus species (excluding L. plantarum) are related to luxS/AI-2. Here, the role of luxS in tolerance to simulated digestive juice (SDJ) and adhesion to Caco-2 cells by L. plantarum KLDS1.0391 (hereafter, KLDS1.0391) was investigated. The KLDS1.0391 luxS mutant strain was constructed by homologous recombination. When luxS was deleted, acid and bile salt tolerance and survival rates in SDJ significantly decreased (p < 0.05 for all). The ability of the luxS deletion strain to adhere to Caco-2 cells was markedly lower than that of the wild-type strain (p < 0.05). The ability of the luxS mutant strain to adhere (competition, exclusion, and displacement) to Escherichia coli ATCC 25922 was significantly lower than that of the wild-type strain (p < 0.05 for all). A significant decrease was noted only in the exclusion adhesion inhibition of the luxS mutant strain to Salmonella typhimurium ATCC 14028 (p < 0.05). These results indicate that the luxS gene plays an important role in the gastrointestinal environment tolerance and adhesion ability of KLDS1.0391.

LuxS/AI-2 in Streptococcus agalactiae reveals a key role in acid tolerance and virulence

LuxS-mediated autoinducer-2 (AI-2) directly or indirectly regulates important physiologic function in a variety of bacteria. We found a luxS homologue in the genome of Streptococcus agalactiae, an important pathogen of tilapia. To investigate the relationship between luxS/AI-2 and pathogenicity for tilapia, its bioluminescent activity, acid resistance, cell adherence, virulence, and regulation of virulence gene were evaluated. Compared with the wild-type strain, the bioluminescent activity lost in the luxS mutant, its resistance to acid (pH2.8) was significantly decreased 33.8 times, and furthermore, its adherence to the NGF-2 cell line was dramatically reduced 3 times in the mutant strain. The virulence of the mutant strain was decreased in the tilapia infection model, exogenous AI-2 molecule (7.4nM) and luxS gene complementation with plasmid could complement the deficiencies of function in the luxS mutant strain. These results showed that inactivation of luxS gene caused a significant decrease of bioluminance, acid resistance, cell adhesion, virulence to tilapia and transcription levels of many virulence genes in S. agalactiae. Expression of the known stress resistance factors DnaK and GroEL, relative regulator factors CovR/CovS and virulence factor cpsE verified above results. These findings suggest that luxS may be involved in the interruption of bacterial virulence and resistance to environmental factors.

Effect of the quorum-sensing luxS gene on biofilm formation by Enterococcus faecalis.

Enterococcus faecalis is the species of bacterium most frequently isolated from the root canals of teeth that exhibit chronic apical periodontitis refractory to endodontic treatment. In this study, we evaluated the effect of the S-ribosylhomocysteine lyase (luxS) quorum-sensing gene on E. faecalis biofilm formation by constructing a knockout mutant. The biofilms formed by both E. faecalis and its luxS mutant strain were evaluated using the MTT method. Important parameters that influence biofilm formation, including cell-surface hydrophobicity and the nutrient content of the growth medium, were also studied. Biofilm structures were observed using confocal laser scanning microscopy (CLSM), and expression of biofilm-related genes was investigated using RT-PCR. The results showed that the luxS gene can affect biofilm formation, whereas it does not affect the bacterial growth rate. Deletion of the luxS gene also increased cell-surface hydrophobicity. Biofilm formation was accelerated by the addition of increasing concentrations of glucose. The CLSM images revealed that the luxS mutant strain tends to aggregate into distinct clusters and relatively dense structures, whereas the wild-type strain appears confluent and more evenly distributed. All genes examined were up-regulated in the biofilms formed by the luxS mutant strain. The quorum-sensing luxS gene can affect E. faecalis biofilm formation.

Culture of low density E. coli cells in alginate–chitosan microcapsules facilitates stress resistance by up-regulating luxS/AI-2 system

Entrapped low density cells with culture (ELDCwc) have been proved as a more effective way than direct entrapped high density cells (dEHDC) and free cells to protect probiotics from harsh environment, that is, to improve their stress resistance. The aim of this study was to investigate whether bacterial quorum sensing (QS) facilitated the stress resistance of Escherichia coli in microcapsules by detecting the expression of luxS/AI-2 system. As a result, both the expression of luxS gene and the concentration of autoinducer-2 (AI-2, QS signal molecule) have been discovered higher in ELDCwc than in dEHDC and free cells. Besides that, the luxS mutant E. coli strain was used as a negative control of QS to verify the influence of QS on bacterial stress resistance in microcapsules. The significantly decreased viability of luxS mutant strain in simulated gastric fluid also indicated that the QS played a critical role in protecting microorganisms from severe environment.

Role of the luxS Gene in Initial Biofilm Formation by Streptococcus mutans

Quorum sensing (QS) is a process by which bacteria communicate with each other by secreting chemical signals called autoinducers (AIs). Among Gram-negative and Gram-positive bacteria, AI-2 synthesized by the LuxS enzyme is widespread. The aim of this study was to evaluate the effect of QS luxS gene on initial biofilm formation by Streptococcus mutans. The bacterial cell surface properties, including cell hydrophobicity (bacterial adherence to hydrocarbons) and aggregation, which are important for initial adherence during biofilm development, were investigated. The biofilm adhesion assay was evaluated by the MTT method. The structures of the 5-hour biofilms were observed by using confocal laser scanning microscopy, and QS-related gene expressions were investigated by real-time PCR. The luxS mutant strain exhibited higher biofilm adherence and aggregation, but lower hydrophobicity than the wild-type strain. The confocal laser scanning microscopy images revealed that the wild-type strain tended to form smaller aggregates with uniform distribution, whereas the luxS mutant strain aggregated into distinct clusters easily discernible in the generated biofilm. Most of the genes examined were downregulated in the biofilms formed by the luxS mutant strain, except the gtfB gene. QS luxS gene can affect the initial biofilm formation by S. mutans.

Use of the quorum sensing inhibitor furanone C-30 to interfere with biofilm formation by Streptococcus mutans and its luxS mutant strain

Streptococcus mutans is recognised as a major aetiological agent of dental caries. One of its important virulence factors is its ability to form biofilms on tooth surfaces. The aim of this study was to evaluate the effects of the quorum sensing inhibitor furanone C-30 on biofilm formation by S. mutans and its luxS mutant strain. The effects of furanone C-30 on biofilms of both strains formed on 96-well microtitre plates at 37°C were determined by a colorimetric technique (MTT assay). Different concentrations of furanone C-30 (0.0, 2.0 and 4.0μg/mL) and different time points of biofilm formation (4, 14 and 24h) were investigated. The structures and thickness of the biofilms were observed by confocal laser scanning microscopy (CLSM). Quorum sensing-related gene expression (ftf, smu630, brpA, gbpB, gtfB, vicR, comDE and relA) was investigated by real-time polymerase chain reaction (RT-PCR). The results showed that synthetic furanone C-30 can inhibit biofilm formation by S. mutans and its luxS mutant strain, although it does not affect the bacterial growth rate itself. The quantities of biofilm formed by both strains significantly decreased (P<0.05) and the biofilms became thinner and looser as revealed by CLSM with increasing concentrations of furanone C-30. Expression of the genes tested was downregulated in the biofilms by the addition of furanone C-30. These results revealed that synthetic furanone C-30 can effectively inhibit biofilm formation by S. mutans and its luxS mutant strain.

AI-2 does not function as a quorum sensing molecule in Campylobacter jejuni during exponential growth in vitro.

BackgroundCampylobacter jejuni contains a homologue of the luxS gene shown to be responsible for the production of the signalling molecule autoinducer-2 (AI-2) in Vibrio harveyi and Vibrio cholerae. The aim of this study was to determine whether AI-2 acted as a diffusible quorum sensing signal controlling C. jejuni gene expression when it is produced at high levels during mid exponential growth phase.ResultsAI-2 activity was produced by the parental strain NCTC 11168 when grown in rich Mueller-Hinton broth (MHB) as expected, but interestingly was not present in defined Modified Eagles Medium (MEM-α). Consistent with previous studies, the luxS mutant showed comparable growth rates to the parental strain and exhibited decreased motility halos in both MEM-α and MHB. Microarray analysis of genes differentially expressed in wild type and luxS mutant strains showed that many effects on mRNA transcript abundance were dependent on the growth medium and linked to metabolic functions including methionine metabolism. Addition of exogenously produced AI-2 to the wild type and the luxS mutant, growing exponentially in either MHB or MEM-α did not induce any transcriptional changes as analysed by microarray.ConclusionTaken together these results led us to conclude that there is no evidence for the role of AI-2 in cell-to-cell communication in C. jejuni strain NCTC 11168 under the growth conditions used, and that the effects of the luxS mutation on the transcriptome are related to the consequential loss of function in the activated methyl cycle.

Study on the biofilm early formation of Streptococcus mutans luxS gene mutation

To investigate the effect of Streptococcus mutans luxS mutarotation on the early biofilm formation. Based on the immobilization of magnetic beads by adherent cells, an assay of biofilm quantitative analysis was developed for the kinetic quantification of biofilm formation in this study. Streptococcus mutans luxS mutant strain was constructed and subject to this biofilm luxS mutant strain were compared. The delta luxS mutant started to form a biofilm from the 6th hour (delta BFI = 2.015), and the delta BFI of luxS mutant increased more quickly than that of the wild type strain, until reaching a complete immobilization of the beads after 10 hours (delta BFI = 7.025). The wild-type strain start to form a biofilm from the 10 th hour (delta BFI = 1.875) and the beads were completely immobilized between 12 and 14 hours. The luxS mutation can accelerate biofilm on a polystyrene surface during the mid-exponential growth phase. And a luxS-dependent signal may play an important role in the early biofilm formation of Streptococcus mutans.