Developing next generation antimicrobials by intercepting AI-2 mediated quorum sensing

Quorum Sensing Inhibitors: An Alternative Strategy to Win the Battle against Multidrug-Resistant (MDR) Bacteria

Antibiotic resistance is a major problem and a major global health concern. In total, there are 16 million deaths yearly from infectious diseases, and at least 65% of infectious diseases are caused by microbial communities that proliferate through the formation of biofilms. Antibiotic overuse has resulted in the evolution of multidrug-resistant (MDR) microbial strains. As a result, there is now much more interest in non-antibiotic therapies for bacterial infections. Among these revolutionary, non-traditional medications is quorum sensing inhibitors (QSIs). Bacterial cell-to-cell communication is known as quorum sensing (QS), and it is mediated by tiny diffusible signaling molecules known as autoinducers (AIs). QS is dependent on the density of the bacterial population. QS is used by Gram-negative and Gram-positive bacteria to control a wide range of processes; in both scenarios, QS entails the synthesis, identification, and reaction to signaling chemicals, also known as auto-inducers. Since the usual processes regulated by QS are the expression of virulence factors and the creation of biofilms, QS is being investigated as an alternative solution to antibiotic resistance. Consequently, the use of QS-inhibiting agents, such as QSIs and quorum quenching (QQ) enzymes, to interfere with QS seems like a good strategy to prevent bacterial infections. This review sheds light on QS inhibition strategy and mechanisms and discusses how using this approach can aid in winning the battle against resistant bacteria.

A review on antimicrobial strategies in mitigating biofilm-associated infections on medical implants

Biomedical implants are crucial in providing support and functionality to patients with missing or defective body parts. However, implants carry an inherent risk of bacterial infections that are biofilm-associated and lead to significant complications. These infections often result in implant failure, requiring replacement by surgical restoration. Given these complications, it is crucial to study the biofilm formation mechanism on various biomedical implants that will help prevent implant failures. Therefore, this comprehensive review explores various types of implants (e.g., dental implant, orthopedic implant, tracheal stent, breast implant, central venous catheter, cochlear implant, urinary catheter, intraocular lens, and heart valve) and medical devices (hemodialyzer and pacemaker) in use. In addition, the mechanism of biofilm formation on those implants, and their pathogenesis were discussed. Furthermore, this article critically reviews various approaches in combating implant-associated infections, with a special emphasis on novel non-antibiotic alternatives to mitigate biofilm infections.

Molecular Aspects of the Functioning of Pathogenic Bacteria Biofilm Based on Quorum Sensing (QS) Signal-Response System and Innovative Non-Antibiotic Strategies for Their Elimination

One of the key mechanisms enabling bacterial cells to create biofilms and regulate crucial life functions in a global and highly synchronized way is a bacterial communication system called quorum sensing (QS). QS is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small signalling molecules called autoinducers (AIs). In bacteria, QS controls the biofilm formation through the global regulation of gene expression involved in the extracellular polymeric matrix (EPS) synthesis, virulence factor production, stress tolerance and metabolic adaptation. Forming biofilm is one of the crucial mechanisms of bacterial antimicrobial resistance (AMR). A common feature of human pathogens is the ability to form biofilm, which poses a serious medical issue due to their high susceptibility to traditional antibiotics. Because QS is associated with virulence and biofilm formation, there is a belief that inhibition of QS activity called quorum quenching (QQ) may provide alternative therapeutic methods for treating microbial infections. This review summarises recent progress in biofilm research, focusing on the mechanisms by which biofilms, especially those formed by pathogenic bacteria, become resistant to antibiotic treatment. Subsequently, a potential alternative approach to QS inhibition highlighting innovative non-antibiotic strategies to control AMR and biofilm formation of pathogenic bacteria has been discussed.

High-Throughput, Quantitative Screening of Quorum-Sensing Inhibitors Based on a Bacterial Biosensor

Quorum sensing (QS) is a cell-cell communication mechanism by which bacteria synchronize social behaviors such as biofilm formation and virulence factor secretion by producing and sensing small molecular signals. Quorum quenching (QQ) by degrading signals or blocking signal transmissions has become a promising strategy for disrupting QS and preventing bacterial infection and biofilm formation. However, studies of high-throughput screening and identification approaches for quorum-sensing inhibitors (QSIs) are still inadequate. In this work, we developed a sensitive, high-throughput approach for screening QSIs based on the bacterial biosensor strain Agrobacterium tumefaciens N5 (pBA7P), which contains a traG gene promoter induced by QS signals fused with a promoterless β-lactamase gene reporter. Using this approach, we identified 31 QQ bacteria from ∼2000 soil bacterial isolates, some belonging to the genera Bosea, Cupriavidus, and Flavobacterium that have not been reported previously as QQ bacteria. We also identified four QS inhibitory compounds and one QS signal analogue from ∼5000 small-molecule compounds, which profoundly affected the expression of QS-regulated genes and phenotypes of the pathogenic bacteria. This high-throughput screening system is effective and sensitive for screening of both QQ microbes and small molecules, enabling the discovery of a wide variety of biocompatible compounds.

Gut microbiota-derived autoinducer-2 regulates lung inflammation through the gut-lung axis

OBJECTIVE

This study aimed to determine whether autoinducer-2 (AI-2), a crucial bacterial metabolite and quorum sensing molecule, is involved in lung immunity through the gut-lung axis.

METHODS

The level of AI-2 and the gut microbiome composition were analysed in the stools from pneumonic patients and the mouse model of acute lung injury. The effect of AI-2 on lung inflammation was further investigated in the mouse model.

RESULTS

The diversity of the faecal microbiota was reduced in pneumonic patients treated with antibiotics compared with healthy volunteers. The AI-2 level in the stool was positively correlated with inflammatory molecules in the serum of pneumonic patients. Intraperitoneal injection of AI-2 reinforced lung inflammation in the acute lung injury mouse model, characterized by increased secretion of inflammatory molecules, including IL-6, IL-1β, C-C chemokines, and CXCL chemokines, which were alleviated by the AI-2 inhibitor D-ribose.

CONCLUSIONS

Our results suggested that gut microbiota-derived AI-2 could modulate lung inflammation through the gut-lung axis.

Antimicrobial and cytotoxic synergism of biocides and quorum-sensing inhibitors against uropathogenic Escherichiacoli

BACKGROUND

Uropathogenic Escherichia coli (UPEC) are a primary cause of catheter-associated urinary tract infections (CAUTIs), often forming mature recalcitrant biofilms on the catheter surface. Anti-infective catheter coatings containing single biocides have been developed but display limited antimicrobial activity due to the selection of biocide-resistant bacterial populations. Furthermore, biocides often display cytotoxicity at concentrations required to eradicate biofilms, limiting their antiseptic potential. Quorum-sensing inhibitors (QSIs) provide a novel anti-infective approach to disrupt biofilm formation on the catheter surface and help prevent CAUTIs.

AIM

To evaluate the combinatorial impact of biocides and QSIs at bacteriostatic, bactericidal and biofilm eradication concentrations in parallel to assessing cytotoxicity in a bladder smooth muscle (BSM) cell line.

METHODS

Checkerboard assays were performed to determine fractional inhibitory, bactericidal, and biofilm eradication concentrations of test combinations in UPEC and combined cytotoxic effects in BSM cells.

FINDINGS

Synergistic antimicrobial activity was observed between polyhexamethylene biguanide, benzalkonium chloride or silver nitrate in combination with either cinnamaldehyde or furanone-C30 against UPEC biofilms. However, furanone-C30 was cytotoxic at concentrations below those required even for bacteriostatic activity. A dose-dependent cytotoxicity profile was observed for cinnamaldehyde when in combination with BAC, PHMB or silver nitrate. Both PHMB and silver nitrate displayed combined bacteriostatic and bactericidal activity below the half-maximum inhibitory concentration (IC₅₀). Triclosan in combination with both QSIs displayed antagonistic activity in both UPEC and BSM cells.

CONCLUSION

PHMB and silver in combination with cinnamaldehyde display synergistic antimicrobial activity in UPEC at non-cytotoxic concentrations, suggesting potential as anti-infective catheter-coating agents.

Quorum Sensing and Quorum Quenching with a Focus on Cariogenic and Periodontopathic Oral Biofilms

Numerous in vitro studies highlight the role of quorum sensing in the pathogenicity and virulence of biofilms. This narrative review discusses general principles in quorum sensing, including Gram-positive and Gram-negative models and the influence of flow, before focusing on quorum sensing and quorum quenching in cariogenic and periodontopathic biofilms. In cariology, quorum sensing centres on the role of Streptococcus mutans, and to a lesser extent Candida albicans, while Fusobacterium nucleatum and the red complex pathogens form the basis of the majority of the quorum sensing research on periodontopathic biofilms. Recent research highlights developments in quorum quenching, also known as quorum sensing inhibition, as a potential antimicrobial tool to attenuate the pathogenicity of oral biofilms by the inhibition of bacterial signalling networks. Quorum quenchers may be synthetic or derived from plant or bacterial products, or human saliva. Furthermore, biofilm inhibition by coating quorum sensing inhibitors on dental implant surfaces provides another potential application of quorum quenching technologies in dentistry. While the body of predominantly in vitro research presented here is steadily growing, the clinical value of quorum sensing inhibitors against in vivo oral polymicrobial biofilms needs to be ascertained.

Effect of Autoinducer-2 Quorum Sensing Inhibitor on Interspecies Quorum Sensing

Bacterial drug resistance caused by overuse and misuse of antibiotics is common, especially in clinical multispecies infections. It is of great significance to discover novel agents to treat clinical bacterial infections. Studies have demonstrated that autoinducer-2 (AI-2), a signal molecule in quorum sensing (QS), plays an important role in communication among multiple bacterial species and bacterial drug-resistance. Previously, 14 AI-2 inhibited compounds were selected through virtual screening by using the AI-2 receptor protein LuxP as a target. Here, we used Vibrio harveyi BB170 as a reporter strain for the preliminary screening of 14 inhibitors and compound Str7410 had higher AI-2 QS inhibition activity (IC₅₀ = 0.3724 ± 0.1091 μM). Then, co-culture of Pseudomonas aeruginosa PAO1 with Staphylococcus aureus ATCC 25923 was used to evaluate the inhibitory effects of Str7410 on multispecies infection in vitro and in vivo. In vitro, Str7410 significantly inhibited the formation of mixed bacterial biofilms. Meanwhile, the combination of Str7410 with meropenem trihydrate (MEPM) significantly improved the susceptibility of mixed-species-biofilm cells to the antibiotic. In vivo, Str7410 significantly increased the survival rate of wild-type Caenorhabditis elegans N2 co-infected by P. aeruginosa PAO1 and S. aureus ATCC 25923. Real-time quantitative PCR analysis showed that Str7410 reduced virulence factor (pyocyanin and elastase) production and swarming motility of P. aeruginosa PAO1 by downregulating the expression of QS-related genes in strain PAO1 in co-culture with S. aureus ATCC 25923. Compound Str7410 is a candidate agent for treating drug-resistant multispecies infections. The work described here provides a strategy for discovering novel antibacterial drugs.

Deciphering the Role of S-adenosyl Homocysteine Nucleosidase in Quorum Sensing Mediated Biofilm Formation

Abstract:

S-adenosylhomocysteine nucleosidase (MTAN) is a protein that plays a crucial role in several pathways of bacteria that are essential for its survival and pathogenesis. In addition to the role of MTAN in methyl-transfer reactions, methionine biosynthesis, and polyamine synthesis, MTAN is also involved in bacterial quorum sensing (QS). In QS, chemical signaling autoinducer (AI) secreted by bacteria assists cell to cell communication and is regulated in a cell density-dependent manner. They play a significant role in the formation of bacterial biofilm. MTAN plays a major role in the synthesis of these autoinducers. Signaling molecules secreted by bacteria, i.e., AI-1 are recognized as acylated homoserine lactones (AHL) that function as signaling molecules within bacteria. QS enables bacteria to establish physical interactions leading to biofilm formation. The formation of biofilm is a primary reason for the development of multidrug-resistant properties in pathogenic bacteria like Enterococcus faecalis (E. faecalis). In this regard, inhibition of E. faecalis MTAN (EfMTAN) will block the QS and alter the bacterial biofilm formation. In addition to this, it will also block methionine biosynthesis and many other critical metabolic processes. It should also be noted that inhibition of EfMTAN will not have any effect on human beings as this enzyme is not present in humans. This review provides a comprehensive overview of the structural-functional relationship of MTAN. We have also highlighted the current status, enigmas that warrant further studies, and the prospects for identifying potential inhibitors of EfMTAN for the treatment of E. faecalis infections. In addition to this, we have also reported structural studies of EfMTAN using homology modeling and highlighted the putative binding sites of the protein.

Targeting Multidrug Resistance With Antimicrobial Peptide-Decorated Nanoparticles and Polymers

As a category of small peptides frequently found in nature, antimicrobial peptides (AMPs) constitute a major part of the innate immune system of various organisms. Antimicrobial peptides feature various inhibitory effects against fungi, bacteria, viruses, and parasites. Due to the increasing concerns of antibiotic resistance among microorganisms, development of antimicrobial peptides is an emerging tool as a favorable applicability prospect in food, medicine, aquaculture, animal husbandry, and agriculture. This review presents the latest research progress made in the field of antimicrobial peptides, such as their mechanism of action, classification, application status, design techniques, and a review on decoration of nanoparticles and polymers with AMPs that are used in treating multidrug resistance. Lastly, we will highlight recent progress in antiviral peptides to treat emerging viral diseases (e.g., anti-coronavirus peptides) and discuss the outlook of AMP applications.

Biosensor Technologies in Medicine: from Detection of Biochemical Markers to Research into Molecular Targets (Review)

Infections are a major cause of premature death. Fast and accurate laboratory diagnostics of infectious diseases is a key condition for the timely initiation and success of treatment. Potentially, it can reduce morbidity, as well as prevent the outbreak and spread of dangerous epidemics. The traditional methods of laboratory diagnostics of infectious diseases are quite time- and labour-consuming, require expensive equipment and trained personnel, which is crucial within limited resources. The fast biosensor-based methods that combine the diagnostic capabilities of biomedicine with modern technological advances in microelectronics, optoelectronics, and nanotechnology make an alternative.

The modern achievements in the development of label-free biosensors make them promising diagnostic tools that combine rapid detection of specific molecular markers, simplicity, ease-of-use, efficiency, accuracy, and cost-effectiveness with the tendency to the development of portable platforms. These qualities exceed the generally accepted standards of microbiological and immunological diagnostics and open up broad prospects for using these analytical systems in clinical practice directly at the site of medical care provision (point-of-care, POC concept).

A wide variety of modern biosensor designs are based on the use of diverse formats of analytical and technological strategies, identification of various regulatory and functional molecular markers associated with infectious pathogens. The solution to the existing problems in biosensing will open up great prospects for these rapidly developing diagnostic biotechnologies.

Quinic acid: a potential antibiofilm agent against clinical resistant Pseudomonas aeruginosa

Background

The biofilm state of pathogens facilitates antimicrobial resistance which makes difficult-to-treat infections. In this regard, it has been found that the compounds screened from plant extracts represent one category of the most promising antibiofilm agents. However, the antibiofilm activities and the active ingredients of plant extracts remain largely unexplored. In this background, the study is (1) to screen out the plant extracts with antibiofilm ability against Pseudomonas aeruginosa, and (2) to identify the active ingredients in the plant extracts and elucidate the underlying mechanism of the antibiofilm activities.

Methods

Micro-broth dilution method, in vitro biofilm model, LC–MS/MS analysis and P. aeruginosa-mouse infection model were adopted to assess the antibiofilm activity. GC–MS analysis was performed to detect the active ingredients in plasma. RNA-Seq, GO analysis, KEGG analysis and RT-qPCR were adopted to elucidate the underlying mechanism of antibiofilm activities against P. aeruginosa.

Results

Lonicerae Japonicae Flos (LJF) among 13 plants could exert significant inhibitory effects on bacterial biofilm formation, mobility and toxin release in vitro, and it could exert antibiofilm effect in vivo too. Moreover, quinic acid, as one metabolite of chlorogenic acid, was found as an active ingredient in LJF against the biofilm of P. aeruginosa. The active ingredient significantly inhibited EPS secretion in biofilm formation and maturity and could achieve synergistic antibiofilm effect with levofloxacin. It reduced the biofilm formation by regulating core targets in quorum sensing system. In GO process, it was found that the core targets were significantly enriched in multiple biological processes involving locomotion, chemotaxis and motility mediated by flagellum/cilium, which was related to KEGG pathways such as bacterial chemotaxis, oxidative phosphorylation, ribosome, biofilm formation, cyanoamino acid metabolism and quorum sensing. Finally, the binding of quinic acid with core targets rhlA, rhlR and rhlB were validated by molecular docking and RT-qPCR.

Conclusions

In summary, the study verified the in vitro and in vivo antibiofilm effects of LJF against P. aeruginosa and elucidated the active ingredients in LJF and its conceivable pharmacological mechanism, indicating that quinic acid could have the potential of an antibiofilm agent against P. aeruginosa and related infections.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00481-8.

5-Fluorouracil blocks quorum-sensing of biofilm-embedded methicillin-resistant Staphylococcus aureus in mice

Antibiotic-resistant pathogens often escape antimicrobial treatment by forming protective biofilms in response to quorum-sensing communication via diffusible autoinducers. Biofilm formation by the nosocomial pathogen methicillin-resistant Staphylococcus aureus (MRSA) is triggered by the quorum-sensor autoinducer-2 (AI-2), whose biosynthesis is mediated by methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTAN) and S-ribosylhomocysteine lyase (LuxS). Here, we present a high-throughput screening platform for small-molecular inhibitors of either enzyme. This platform employs a cell-based assay to report non-toxic, bioavailable and cell-penetrating inhibitors of AI-2 production, utilizing engineered human cells programmed to constitutively secrete AI-2 by tapping into the endogenous methylation cycle via ectopic expression of codon-optimized MTAN and LuxS. Screening of a library of over 5000 commercial compounds yielded 66 hits, including the FDA-licensed cytostatic anti-cancer drug 5-fluorouracil (5-FU). Secondary screening and validation studies showed that 5-FU is a potent quorum-quencher, inhibiting AI-2 production and release by MRSA, Staphylococcus epidermidis, Escherichia coli and Vibrio harveyi. 5-FU efficiently reduced adherence and blocked biofilm formation of MRSA in vitro at an order-of-magnitude-lower concentration than that clinically relevant for anti-cancer therapy. Furthermore, 5-FU reestablished antibiotic susceptibility and enabled daptomycin-mediated prevention and clearance of MRSA infection in a mouse model of human implant-associated infection.

Mechanisms Used by Probiotics to Confer Pathogen Resistance to Teleost Fish

Probiotics have been defined as live microorganisms that when administered in adequate amounts confer health benefits to the host. The use of probiotics in aquaculture is an attractive bio-friendly method to decrease the impact of infectious diseases, but is still not an extended practice. Although many studies have investigated the systemic and mucosal immunological effects of probiotics, not all of them have established whether they were actually capable of increasing resistance to different types of pathogens, being this the outmost desired goal. In this sense, in the current paper, we have summarized those experiments in which probiotics were shown to provide increased resistance against bacterial, viral or parasitic pathogens. Additionally, we have reviewed what is known for fish probiotics regarding the mechanisms through which they exert positive effects on pathogen resistance, including direct actions on the pathogen, as well as positive effects on the host.

Screening strategies for quorum sensing inhibitors in combating bacterial infections

Interference with quorum sensing (QS) represents an antivirulence strategy with a significant promise for the treatment of bacterial infections and a new approach to restoring antibiotic tolerance. Over the past two decades, a novel series of studies have reported that quorum quenching approaches and the discovery of quorum sensing inhibitors (QSIs) have a strong impact on the discovery of anti-infective drugs against various types of bacteria. The discovery of QSI was demonstrated to be an appropriate strategy to expand the anti-infective therapeutic approaches to complement classical antibiotics and antimicrobial agents. For the discovery of QSIs, diverse approaches exist and develop in-step with the scale of screening as well as specific QS systems. This review highlights the latest findings in strategies and methodologies for QSI screening, involving activity-based screening with bioassays, chemical methods to seek bacterial QS pathways for QSI discovery, virtual screening for QSI screening, and other potential tools for interpreting QS signaling, which are innovative routes for future efforts to discover additional QSIs to combat bacterial infections.

•

Interference with QSrepresents a promising antivirulence strategy for the treatment of bacterial infections. The discovery ofQSIs was demonstrated as an appropriate strategy to expand the anti-infective therapeutic arsenal to complement classical antibiotics and antimicrobial agents.

•

For the discovery of QSIs, diverse approaches exist and develop in-step with the scale of screening and targeted QS systems.

•

Few previous reviews have summarized the strategies and approaches of QSI screening, whereas this review highlights the recent findings in QSI screening strategies and methodologies.

Quorum Sensing Communication: Molecularly Connecting Cells, Their Neighbors, and Even Devices

Quorum sensing (QS) is a molecular signaling modality that mediates molecular-based cell–cell communication. Prevalent in nature, QS networks provide bacteria with a method to gather information from the environment and make decisions based on the intel. With its ability to autonomously facilitate both inter- and intraspecies gene regulation, this process can be rewired to enable autonomously actuated, but molecularly programmed, genetic control. On the one hand, novel QS-based genetic circuits endow cells with smart functions that can be used in many fields of engineering, and on the other, repurposed QS circuitry promotes communication and aids in the development of synthetic microbial consortia. Furthermore, engineered QS systems can probe and intervene in interkingdom signaling between bacteria and their hosts. Lastly, QS is demonstrated to establish conversation with abiotic materials, especially by taking advantage of biological and even electronically induced assembly processes; such QS-incorporated biohybrid devices offer innovative ways to program cell behavior and biological function.

Mechanisms and the role of probiotic Bacillus in mitigating fish pathogens in aquaculture

Diseases are natural components of the environment, and many have economic implications for aquaculture and fisheries. Aquaculture is a fast-growing industry with the aim to meet the high protein demand of the ever-increasing global population; however, the emergence of diseases is a major setback to the industry. Probiotics emerged as a better solution to curb the disease problem in aquaculture among many alternatives. Probiotic Bacillus has been proven to better combat a wide range of fish pathogens relative to other probiotics in aquaculture; therefore, understanding the various mechanisms used by Bacillus in combating diseases will help improve their mode of action hence yielding better results in their combat against pathogens in the aquaculture industry. Thus, an overview of the mechanisms (production of bacteriocins, suppression of virulence gene expression, competition for adhesion sites, production of lytic enzymes, production of antibiotics, immunostimulation, competition for nutrients and energy, and production of organic acids) used by Bacillus probiotics in mitigating fish pathogens ranging from Aeromonas, Vibrio, Streptococcus, Yersinia, Pseudomonas, Clostridium, Acinetobacter, Edwardsiella, Flavobacterium, white spot syndrome virus, and infectious hypodermal and hematopoietic necrosis virus proven to be mitigated by Bacillus have been provided.

The bitterness of genitourinary infections: Properties, ligands of genitourinary bitter taste receptors and mechanisms linking taste sensing to inflammatory processes in the genitourinary tract

BACKGROUND

Though, first identified in the gastrointestinal tract, bitter taste receptors are now believed to be ubiquitously expressed in several regions of the body, including the respiratory tract, where they play a critical role in sensing and clearance of excess metabolic substrates, toxins, debris, and pathogens. More recently, bitter taste receptor expression has been reported in cells, tissues and organs of the genitourinary (GU) system, suggesting that these receptors may play an integral role in mediating inflammatory responses to microbial aggression in the GU tract. However, the mechanisms, linking bitter taste receptor sensing with inflammatory responses are not exactly clear. Here, I review recent data on the properties and ligands of bitter taste receptors and suggest mechanisms of bitter taste receptor signaling in the GU tract, and the molecular pathways that link taste sensing to inflammatory responses in GU tract.

METHOD

Computer-aided search was conducted in Scopus, PubMed, Web of Science and Google Scholar for relevant peer-reviewed articles published between 1990 and 2018, investigating the functional implication of bitter taste receptors in GU infections, using the following keywords: extra-oral bitter taste receptors, bitter taste receptors, GU bitter taste receptors, kidney OR renal OR ureteral OR urethral OR bladder OR detrusor smooth muscle OR testes OR spermatozoa OR prostate OR vaginal OR cervix OR ovarian OR endometrial OR myometrial OR placenta OR cutaneous bitter taste receptors. To identify research gaps on etiopathogenesis of GU infections/inflammation, additional search was conducted using the following keywords: GU inflammatory signaling, GU microbes, GU bacteria, GU virus, GU protozoa, GU microbial metabolites, and GU infection. The retrieved articles were filtered and further screened for relevance according to the aim of the study. A narrative review was performed for selected literatures.

RESULTS

Bitter taste receptors of the GU tract may constitute essential components of the pathogenetic mechanisms of GU infections/inflammation that are activated by microbial components, known as quorum sensing signal molecules. Based on accumulating evidences, indicating that taste receptors may signal downstream to activate inflammatory cascades, in addition to the nitric oxide-induced microbicidal effects produced upon taste receptor activation, it is suggested that the anti-inflammatory activities of bitter taste receptor stimulation are mediated via pathways involving the nuclear factor κB by downstream signaling of the metabolic and stress sensors, adenosine monophosphate-activated protein kinase and nicotinamide adenine dinucleotide-dependent silent mating type information regulation 2 homolog 1 (sirtuin 1), resulting to the synthesis of anti-inflammatory cytokines/chemokines, and antimicrobial factors, which ultimately, under normal conditions, leads to the elimination of microbial aggression.

CONCLUSIONS

GU bitter taste receptors may represent critical players in GU tract infections/inflammation. Bitter taste receptors may serve as important therapeutic target for treatment of a number of infectious diseases that affect the GU tract.

Label-Free Biosensors for Laboratory-Based Diagnostics of Infections: Current Achievements and New Trends

Infections pose a serious global public health problem and are a major cause of premature mortality worldwide. One of the most challenging objectives faced by modern medicine is timely and accurate laboratory-based diagnostics of infectious diseases. Being a key factor of timely initiation and success of treatment, it may potentially provide reduction in incidence of a disease, as well as prevent outbreak and spread of dangerous epidemics. The traditional methods of laboratory-based diagnostics of infectious diseases are quite time- and labor-consuming, require expensive equipment and qualified personnel, which restricts their use in case of limited resources. Over the past six decades, diagnostic technologies based on lateral flow immunoassay (LFIA) have been and remain true alternatives to modern laboratory analyzers and have been successfully used to quickly detect molecular ligands in biosubstrates to diagnose many infectious diseases and septic conditions. These devices are considered as simplified formats of modern biosensors. Recent advances in the development of label-free biosensor technologies have made them promising diagnostic tools that combine rapid pathogen indication, simplicity, user-friendliness, operational efficiency, accuracy, and cost effectiveness, with a trend towards creation of portable platforms. These qualities exceed the generally accepted standards of microbiological and immunological diagnostics and open up a broad range of applications of these analytical systems in clinical practice immediately at the site of medical care (point-of-care concept, POC). A great variety of modern nanoarchitectonics of biosensors are based on the use of a broad range of analytical and constructive strategies and identification of various regulatory and functional molecular markers associated with infectious bacterial pathogens. Resolution of the existing biosensing issues will provide rapid development of diagnostic biotechnologies.

Phenolics with Bactericidal Activity Alter Motility and Biofilm Formation in Enterotoxigenic, Enteropathogenic, and Enterohemorrhagic Escherichia coli

Most Escherichia coli strains are innocuous to human beings; however, some strains can cause diarrhea and are grouped into pathotypes. Since current trends promote the use of natural-origin compounds to control bacteria, in this study, the effects of the phenolic compounds (PCs) tannic acid (TA), gallic acid (GA), methyl gallate (MG), and epigallocatechin gallate (EG) on the growth, swarming motility, biofilm formation, and expression of selected virulence genes of three E. coli pathotypes (enteropathogenic Escherichia coli [EPEC], enterohemorrhagic Escherichia coli [EHEC], and enterotoxigenic Escherichia coli [ETEC]) were evaluated. Minimum bactericidal concentrations (MBCs) were determined by using microtiter plates, and the effects of sublethal PC concentrations on swarming motility were evaluated on Luria-Bertani agar. Biofilm formation was assessed in microtiter plates via crystal violet staining, and the expression levels of genes involved in biofilm formation (flhC, fliA, fliC, and csgA) and swarming motility (csgD and cyaA) were evaluated via quantitative PCR. All PC were bactericidal with minimal bactericidal concentrations ranging from 0.07 to 2.1 mg/mL. At concentrations lower than the MBC, PCs decreased swarming motility (14.8-100%). GA reduced biofilm formation in all of the tested strains; however, TA, MG, and EG induced biofilm formation in some strains at specific concentrations. TA induced the overexpression of csgA, csgD, and cyaA, whereas the other PCs did not have any effects or reduced their expression levels. The PCs tested in this study showed potential to control E. coli strains belonging to the EHEC, ETEC, and EPEC pathotypes by affecting their growth, swarming motility, and virulence gene expression; however, proper concentrations must be used to avoid the induction of undesirable virulence factor genes.

Harnessing bacterial interactions to manage infections: a review on the opportunistic pathogen Pseudomonas aeruginosa as a case example

During infections, bacterial pathogens can engage in a variety of interactions with each other, ranging from the cooperative sharing of resources to deadly warfare. This is especially relevant in opportunistic infections, where different strains and species often co-infect the same patient and interact in the host. Here, we review the relevance of these social interactions during opportunistic infections using the human pathogen Pseudomonas aeruginosa as a case example. In particular, we discuss different types of pathogen-pathogen interactions, involving both cooperation and competition, and elaborate on how they impact virulence in multi-strain and multi-species infections. We then review evolutionary dynamics within pathogen populations during chronic infections. We particuarly discuss how local adaptation through niche separation, evolutionary successions and antagonistic co-evolution between pathogens can alter virulence and the damage inflicted on the host. Finally, we outline how studying bacterial social dynamics could be used to manage infections. We show that a deeper appreciation of bacterial evolution and ecology in the clinical context is important for understanding microbial infections and can inspire novel treatment strategies.

Impact of the structure-activity relationship of AHL analogues on quorum sensing in Gram-negative bacteria

With the emergence of microbial resistance pathogens, recent research aims at studying new mechanisms of action of antibiotics. This review discusses the mechanisms and types of quorum sensing (QS) inhibitors in Gram negative bacteria. It illustrates all published data available in literature pertaining to novel compounds that showed activity against different targets in the quorum sensing pathways in Gram negative bacteria. A systemic overview has been conducted by searching PubMed, Medline, and the Cochrane Library and data extraction of all quorum sensing inhibitors with their mechanisms of action have been collected. This review will focus on signaling autoinducer AI-1 in Gram negative bacteria. The biological activity of the antagonists is mainly reported as IC₅₀ (the concentration of an inhibitor where the response is reduced by half).

Focusing quorum sensing signalling by nano-magnetic assembly

Quorum sensing (QS) exists widely among bacteria, enabling a transition to multicellular behaviour after bacterial populations reach a particular density. The coordination of multicellularity enables biotechnological application, dissolution of biofilms, coordination of virulence, and so forth. Here, a method to elicit and subsequently disperse multicellular behaviour among QS-negative cells is developed using magnetic nanoparticle assembly. We fabricated magnetic nanoparticles (MNPs, ∼5 nm) that electrostatically collect wild-type (WT) Escherichia coli BL21 cells and brings them into proximity of bioengineered E. coli [CT104 (W3110 lsrFG^- luxS^- pCT6 + pET-DsRed)] reporter cells that exhibit a QS response after receiving autoinducer-2 (AI-2). By shortening the distance between WT and reporter cells (e.g., increasing local available AI-2 concentrations), the QS response signalling was amplified four-fold compared to that in native conditions without assembly. This study suggests potential applications in facilitating intercellular communication and modulating multicellular behaviours based on user-specified designs.

Quorum Sensing Inhibition by Marine Bacteria

Antibiotic resistance has been increasingly reported for a wide variety of bacteria of clinical significance. This widespread problem constitutes one of the greatest challenges of the twenty-first century. Faced with this issue, clinicians and researchers have been persuaded to design novel strategies in order to try to control pathogenic bacteria. Therefore, the discovery and elucidation of the mechanisms underlying bacterial pathogenesis and intercellular communication have opened new perspectives for the development of alternative approaches. Antipathogenic and/or antivirulence therapies based on the interruption of quorum sensing pathways are one of several such promising strategies aimed at disarming rather than at eradicating bacterial pathogens during the course of colonization and infection. This review describes mechanisms of bacterial communication involved in biofilm formation. An overview of the potential of marine bacteria and their bioactive components as QS inhibitors is further provided.

A scalable peptide-GPCR language for engineering multicellular communication

Engineering multicellularity is one of the next breakthroughs for Synthetic Biology. A key bottleneck to building multicellular systems is the lack of a scalable signaling language with a large number of interfaces that can be used simultaneously. Here, we present a modular, scalable, intercellular signaling language in yeast based on fungal mating peptide/G-protein-coupled receptor (GPCR) pairs harnessed from nature. First, through genome-mining, we assemble 32 functional peptide-GPCR signaling interfaces with a range of dose-response characteristics. Next, we demonstrate that these interfaces can be combined into two-cell communication links, which serve as assembly units for higher-order communication topologies. Finally, we show 56 functional, two-cell links, which we use to assemble three- to six-member communication topologies and a three-member interdependent community. Importantly, our peptide-GPCR language is scalable and tunable by genetic encoding, requires minimal component engineering, and should be massively scalable by further application of our genome mining pipeline or directed evolution.

Enzymatic Transition States and Drug Design

Transition state theory teaches that chemically stable mimics of enzymatic transition states will bind tightly to their cognate enzymes. Kinetic isotope effects combined with computational quantum chemistry provides enzymatic transition state information with sufficient fidelity to design transition state analogues. Examples are selected from various stages of drug development to demonstrate the application of transition state theory, inhibitor design, physicochemical characterization of transition state analogues, and their progress in drug development.

Recent progresses on synthesized LuxS inhibitors: A mini-review

Design and synthesis of LuxS enzyme inhibitors otherwise known as S-ribosylhomocysteine analogues, to target quorum sensing in bacteria, has been considerably developed within the last decade. This review presents which molecules have been synthesized to target LuxS enzyme in other words inhibitors of S-ribosylhomocysteinase. It reports their tested biological activity as LuxS inhibitors when available. A systematic overview has been conducted by searching PubMed, Medline, and The Cochrane Library and data extraction of all synthesized S-ribosylhomocysteine analogues has been collected. This mini-review shows limited data to date on this area and should continue to be studied.

Nanoparticles for Signaling in Biodiagnosis and Treatment of Infectious Diseases

Advances in nanoparticle-based systems constitute a promising research area with important implications for the treatment of bacterial infections, especially against multidrug resistant strains and bacterial biofilms. Nanosystems may be useful for the diagnosis and treatment of viral and fungal infections. Commercial diagnostic tests based on nanosystems are currently available. Different methodologies based on nanoparticles (NPs) have been developed to detect specific agents or to distinguish between Gram-positive and Gram-negative microorganisms. Also, biosensors based on nanoparticles have been applied in viral detection to improve available analytical techniques. Several point-of-care (POC) assays have been proposed that can offer results faster, easier and at lower cost than conventional techniques and can even be used in remote regions for viral diagnosis. Nanoparticles functionalized with specific molecules may modulate pharmacokinetic targeting recognition and increase anti-infective efficacy. Quorum sensing is a stimuli-response chemical communication process correlated with population density that bacteria use to regulate biofilm formation. Disabling it is an emerging approach for combating its pathogenicity. Natural or synthetic inhibitors may act as antibiofilm agents and be useful for treating multi-drug resistant bacteria. Nanostructured materials that interfere with signal molecules involved in biofilm growth have been developed for the control of infections associated with biofilm-associated infections.

Production, detection and application perspectives of quorum sensing autoinducer-2 in bacteria

Autoinducer-2 (AI-2) is a major signal molecule in bacterial quorum sensing (QS) besides N-acyl homoserine lactones (AHLs or AI-1). AI-2 mediated QS pathways have been proved to regulate gene expression and physiological behaviors of bacteria in either intraspecies or interspecies communication. Recent reviews have mainly summarized AI-2 structures, AI-2 mediated QS pathways and the role of AI-2 in gene regulation, etc. In this article, we present a comprehensive review of AI-2 production, detection and applications. Firstly, intracellular AI-2 synthetic routes were outlined and environmental influences on AI-2 production were focused. Furthermore, recent advances in AI-2 detection and quantification were elucidated from an overall perspective. An in-depth understanding of mechanisms and features of various detection methods may facilitate development of new technologies aimed at signal molecule detection. Finally, utilization of AI-2 mediated QS in health improvement, water treatment and drug production indicate promising and extensive application perspectives of QS strategies.

Quorum-Sensing Systems as Targets for Antivirulence Therapy

The development of novel therapies to control diseases caused by antibiotic-resistant pathogens is one of the major challenges we are currently facing. Many important plant, animal, and human pathogens regulate virulence by quorum sensing, bacterial cell-to-cell communication with small signal molecules. Consequently, a significant research effort is being undertaken to identify and use quorum-sensing-interfering agents in order to control diseases caused by these pathogens. In this review, an overview of our current knowledge of quorum-sensing systems of Gram-negative model pathogens is presented as well as the link with virulence of these pathogens, and recent advances and challenges in the development of quorum-sensing-interfering therapies are discussed.

Incorporating LsrK AI-2 quorum quenching capability in a functionalized biopolymer capsule

Antibacterial resistance is an issue of increasing severity as current antibiotics are losing their effectiveness and fewer antibiotics are being developed. New methods for combating bacterial virulence are required. Modulating molecular communication among bacteria can alter phenotype, including attachment to epithelia, biofilm formation, and even toxin production. Intercepting and modulating communication networks provide a means to attenuate virulence without directly interacting with the bacteria of interest. In this work, we target communication mediated by the quorum sensing (QS) bacterial autoinducer-2, AI-2. We have assembled a capsule of biological polymers alginate and chitosan, attached an AI-2 processing kinase, LsrK, and provided substrate, ATP, for enzymatic alteration of AI-2 in culture fluids. Correspondingly, AI-2 mediated QS activity is diminished. All components of this system are "biofabricated"-they are biologically derived and their assembly is accomplished using biological means. Initially, component quantities and kinetics were tested as assembled in microtiter plates. Subsequently, the identical components and assembly means were used to create the "artificial cell" capsules. The functionalized capsules, when introduced into populations of bacteria, alter the dynamics of the AI-2 bacterial communication, attenuating QS activated phenotypes. We envision the assembly of these and other capsules or similar materials, as means to alter QS activity in a biologically compatible manner and in many environments, including in humans.

Regulation of bacteria population behaviors by AI-2 "consumer cells" and "supplier cells"

Background

Autoinducer-2 (AI-2) is a universal signal molecule and enables an individual bacteria to communicate with each other and ultimately control behaviors of the population. Harnessing the character of AI-2, two kinds of AI-2 “controller cells” (“consumer cells” and “supplier cells”) were designed to “reprogram” the behaviors of entire population.

Results

For the consumer cells, genes associated with the uptake and processing of AI-2, which includes LsrACDB, LsrFG, LsrK, were overexpressed in varying combinations. Four consumer cell strains were constructed: Escherichia coli MG1655 pLsrACDB (NK-C1), MG1655 pLsrACDBK (NK-C2), MG1655 pLsrACDBFG (NK-C3) and MG1655 pLsrACDBFGK (NK-C4). The key enzymes responsible for production of AI-2, LuxS and Mtn, were also overexpressed, yielding strains MG1655 pLuxS (NK-SU1), and MG1655 pLuxS-Mtn (NK-SU2). All the consumer cells could decrease the environmental AI-2 concentration. NK-C2 and NK-C4 were most effective in AI-2 uptake and inhibited biofilm formation. While suppliers can increase the environmental AI-2 concentration and NK-SU2 was most effective in supplying AI-2 and facilitated biofilm formation. Further, reporter strain, MG1655 pLGFP was constructed. The expression of green fluorescent protein (GFP) in reporter cells was initiated and guided by AI-2. Mixture of consumer cells and reporter cells suggest that consumer cells can decrease the AI-2 concentration. And the supplier cells were co-cultured with reporter cells, indicating that supplier cells can provide more AI-2 compared to the control.

Conclusions

The consumer cells and supplier cells could be used to regulate environmental AI-2 concentration and the biofilm formation. They can also modulate the AI-2 concentration when they were co-cultured with reporter cells. It can be envisioned that this system will become useful tools in synthetic biology and researching new antimicrobials.

Electronic supplementary material

The online version of this article (10.1186/s12866-017-1107-2) contains supplementary material, which is available to authorized users.

Impact of phenolic compounds in the acyl homoserine lactone-mediated quorum sensing regulatory pathways

Quorum sensing (QS) is a cell density-dependent regulation of virulent bacterial gene expression by autoinducers that potentially pertains in the epidemic of bacterial virulence. This study was initially designed to evaluate the effect of 5 phenolic compounds in the modulation of QS and virulence factors of Chromobacterium violaceum and Pseudomonas aeruginosa, and to determine the mechanisms of their effects. Biosensor strains were used to assess antibacterial and anti-QS effect of these compounds. Only methyl gallate (MG) among these compounds demonstrated profound anti-QS effect in the preliminary study, and thus only MG was utilized further to evaluate the effects on the synthesis and activity of acyl homoserine lactone (AHL) in C. violaceum and on the modulation of biofilm, motility, proteolytic, elastase, pyocyanin, and rhamnolipid activity in P. aeruginosa. Finally, the effect of MG on the expression of QS-regulated genes of P. aeruginosa was verified. MG suppressed both the synthesis and activity of AHL in C. violaceum. It also restricted the biofilm formation and other QS-associated virulence factor of P. aeruginosa. MG concentration-dependently suppressed the expression of lasI/R, rhlI/R, and pqsA of P. aeruginosa and was non-toxic in in vitro study. This is the first report of the anti-QS mechanism of MG.

Autoinducer-2 analogs and electric fields - an antibiotic-free bacterial biofilm combination treatment

Bacterial biofilms are a common cause of chronic medical implant infections. Treatment and eradication of biofilms by conventional antibiotic therapy has major drawbacks including toxicity and side effects associated with high-dosage antibiotics. Additionally, administration of high doses of antibiotics may facilitate the emergence of antibiotic resistant bacteria. Thus, there is an urgent need for the development of treatments that are not based on conventional antibiotic therapies. Presented herein is a novel bacterial biofilm combination treatment independent of traditional antibiotics, by using low electric fields in combination with small molecule inhibitors of bacterial quorum sensing - autoinducer-2 analogs. We investigate the effect of this treatment on mature Escherichia coli biofilms by application of an alternating and offset electric potential in combination with the small molecule inhibitor for 24 h using both macro and micro-scale devices. Crystal violet staining of the macro-scale biofilms shows a 46 % decrease in biomass compared to the untreated control. We demonstrate enhanced treatment efficacy of the combination therapy using a high-throughput polydimethylsiloxane-based microfluidic biofilm analysis platform. This microfluidic flow cell is designed to reduce the growth variance of in vitro biofilms while providing an integrated control, and thus allows for a more reliable comparison and evaluation of new biofilm treatments on a single device. We utilize linear array charge-coupled devices to perform real-time tracking of biomass by monitoring changes in optical density. End-point confocal microscopy measurements of biofilms treated with the autoinducer analog and electric fields in the microfluidic device show a 78 % decrease in average biofilm thickness in comparison to the negative controls and demonstrate good correlation with real-time optical density measurements. Additionally, the combination treatment showed 76 % better treatment efficacy compared to conventional antibiotic therapy. Taken together these results suggest that the antibiotic-free combination treatment described here may provide an effective alternative to traditional antibiotic therapies against bacterial biofilm infections. Use of this combination treatment in the medical and environmental fields would alleviate side effects associated with high-dosage antibiotic therapies, and reduce the rise of antibiotic-resistant bacteria.

Relationship of Triamine-Biocide Tolerance of Salmonella enterica Serovar Senftenberg to Antimicrobial Susceptibility, Serum Resistance and Outer Membrane Proteins

A new emerging phenomenon is the association between the incorrect use of biocides in the process of disinfection in farms and the emergence of cross-resistance in Salmonella populations. Adaptation of the microorganisms to the sub-inhibitory concentrations of the disinfectants is not clear, but may result in an increase of sensitivity or resistance to antibiotics, depending on the biocide used and the challenged Salmonella serovar. Exposure of five Salmonella enterica subsp. enterica serovar Senftenberg (S. Senftenberg) strains to triamine-containing disinfectant did not result in variants with resistance to antibiotics, but has changed their susceptibility to normal human serum (NHS). Three biocide variants developed reduced sensitivity to NHS in comparison to the sensitive parental strains, while two isolates lost their resistance to serum. For S. Senftenberg, which exhibited the highest triamine tolerance (6 × MIC) and intrinsic sensitivity to 22.5% and 45% NHS, a downregulation of flagellin and enolase has been demonstrated, which might suggest a lower adhesion and virulence of the bacteria. This is the first report demonstrating the influence of biocide tolerance on NHS resistance. In conclusion, there was a potential in S. Senftenberg to adjust to the conditions, where the biocide containing triamine was present. However, the adaptation did not result in the increase of antibiotic resistance, but manifested in changes within outer membrane proteins’ patterns. The strategy of bacterial membrane proteins’ analysis provides an opportunity to adjust the ways of infection treatments, especially when it is connected to the life-threating bacteremia caused by Salmonella species.

Acinetobacter baumannii quorum-sensing signalling molecule induces the expression of drug-resistance genes

Quorum-sensing signalling molecules such as N-acyl homoserine lactones (AHLs) enable certain Gram-negative bacteria to respond to environmental changes through behaviours, such as biofilm formation and flagellar movement. The present study aimed to identify Acinetobacter baumannii AHLs and assess their influence on antibiotic resistance. A clinical isolate of A. baumannii strain S (AbS) was collected from the wound of a burn patient and high-performance liquid chromatography and tandem quadrupole or quadrupole time-of-flight high-resolution mass spectrometry was used to identify AbS AHLs. Antibiotic sensitivity was assessed in an AHL-deficient AbS mutant (AbS-M), and the expression of drug-resistance genes in the presence of meropenem in AbS, AbS-M and AbS-M treated with the AHL N-3-hydroxy-dodecanoyl-homoserine lactone (N-3-OH-C₁₂-HSL). AbS-M was more sensitive to meropenem and piperacillin than wild-type AbS, but resistance was restored by supplementation with N-3-OH-C₁₂-HSL. In addition, meropenem-treated AbS-M expressed lower levels of the drug-resistance genes oxacillinase 51, AmpC, AdeA and AdeB; treatment with N-3-OH-C₁₂-HSL also restored the expression of these genes. Overall, the results of the present study indicate that N-3-OH-C₁₂-HSL may be involved in regulating the expression of drug-resistance genes in A. baumannii. Therefore, this quorum-sensing signalling molecule may be an important target for treating multidrug-resistant A. baumannii infections.

Bacterial tweets and podcasts #signaling#eavesdropping#microbialfightclub

Once thought to live independently, bacteria are now known to be highly social organisms. Their behaviors ranges from cooperatively forming complex multispecies communities to fiercely competing for resources. Work over the past fifty years has shown that bacteria communicate through diverse mechanisms, such as exchanging diffusible molecules, exporting molecules in membrane vesicles, and interacting through direct cell-cell contact. These methods allow bacteria to sense and respond to other cells around them and coordinate group behavior. In this review, we share the discoveries and lessons learned in the field of bacterial communication with the aim of providing insights to parasitologists and other researchers working on related questions.

Electrochemical Measurement of the β-Galactosidase Reporter from Live Cells: A Comparison to the Miller Assay

In order to match our ability to conceive of and construct cells with enhanced function, we must concomitantly develop facile, real-time methods for elucidating performance. With these, new designs can be tested in silico and steps in construction incrementally validated. Electrochemical monitoring offers the above advantages largely because signal transduction stems from direct electron transfer, allowing for potentially quicker and more integrated measurements. One of the most common genetic reporters, β-galactosidase, can be measured both spectrophotometrically (Miller assay) and electrochemically. However, since the relationship between the two is not well understood, the electrochemical methods have not yet garnered the attention of biologists. With the aim of demonstrating the utility of an electrochemical measurement to the synthetic biology community, we created a genetic construct that interprets and reports (with β-galactosidase) on the concentration of the bacterial quorum sensing molecule autoinducer-2. In this work, we provide a correlation between electrochemical measurements and Miller Units. We show that the electrochemical assay works with both lysed and whole cells, allowing for the prediction of one from the other, and for continuous monitoring of cell response. We further present a conceptually simple and generalized mathematical model for cell-based β-galactosidase reporter systems that could aid in building and predicting a variety of synthetic biology constructs. This first-ever in-depth comparison and analysis aims to facilitate the use of electrochemical real-time monitoring in the field of synthetic biology as well as to facilitate the creation of constructs that can more easily communicate information to electronic systems.

Exploiting Quorum Sensing Interfering Strategies in Gram-Negative Bacteria for the Enhancement of Environmental Applications

Quorum sensing (QS) is a widespread intercellular form of communication to coordinate physiological processes and cooperative activities of bacteria at the population level, and it depends on the production, secretion, and detection of small diffusible autoinducers, such as acyl-homoserine lactones (AHLs), auto-inducing oligo-peptides (AIPs) and autoinducer 2. In this review, the function of QS autoinducers of gram-negative bacteria in different aspects of wastewater treatment systems is examined. Based on research primarily performed over the past 10 years, QS involvement in the formation of biofilm and aerobic granules and changes of the microbial community and degradation/transformation pathways is discussed. In particular, the QS pathway in the role of bacterial infections and disease prevention in aquaculture is addressed. Interference of QS autoinducer-regulated pathways is considered potential treatment for a variety of environmentally related problems. This review is expected to serve as a stepping stone for further study and development strategies based on the mediation of QS-regulated pathways to enhance applications in both wastewater treatment systems and aquaculture.

Novel reporter for identification of interference with acyl homoserine lactone and autoinducer-2 quorum sensing

Two reporter strains were established to identify novel biomolecules interfering with bacterial communication (quorum sensing [QS]). The basic design of these Escherichia coli-based systems comprises a gene encoding a lethal protein fused to promoters induced in the presence of QS signal molecules. Consequently, these E. coli strains are unable to grow in the presence of the respective QS signal molecules unless a nontoxic QS-interfering compound is present. The first reporter strain designed to detect autoinducer-2 (AI-2)-interfering activities (AI2-QQ.1) contained the E. coli ccdB lethal gene under the control of the E. coli lsrA promoter. The second reporter strain (AI1-QQ.1) contained the Vibrio fischeri luxI promoter fused to the ccdB gene to detect interference with acyl-homoserine lactones. Bacteria isolated from the surfaces of several marine eukarya were screened for quorum- quenching (QQ) activities using the established reporter systems AI1-QQ.1 and AI2-QQ.1. Out of 34 isolates, two interfered with acylated homoserine lactone (AHL) signaling, five interfered with AI-2 QS signaling, and 10 were demonstrated to interfere with both signal molecules. Open reading frames (ORFs) conferring QQ activity were identified for three selected isolates (Photobacterium sp., Pseudoalteromonas sp., and Vibrio parahaemolyticus). Evaluation of the respective heterologously expressed and purified QQ proteins confirmed their ability to interfere with the AHL and AI-2 signaling processes.

A small-molecule norspermidine and norspermidine-hosting polyelectrolyte coatings inhibit biofilm formation by multi-species wastewater culture

Norspermidine is a potent and non-bactericidal small-molecule inhibitor of biofilm growth. In this study, impacts of norspermidine on biofilm control and existing biofilm dispersal by a mixed culture from wastewater treatment systems were investigated. A surface-mediated releasing approach for prevention of bacterial biofilm formation was established via encapsulating norspermidine into polyelectrolyte multilayer coatings. Results showed that the presence of norspermidine (500-1000 μM) in medium remarkably prevented biofilm formation. Norspermidine was also effective in disassembling pre-formed biofilms. Norspermidine-containing multilayer coatings were successfully fabricated on glass slides via layer-by-layer deposition in polyethylenimine (PEI) and poly(acrylic acid) (PAA) solution. This coating exhibited a high anti-biofilm property against a mixed culture and three pure strains (Bacillus subtilis, Pseudomonas aeruginosa, and Escherichia coli). The loading amount and space distribution of norspermidine in the multilayer coating were key factors influencing its anti-biofilm efficacy. The polymer coating with norspermidine loaded in each bilayer (each-layer-type) exhibited better anti-biofilm efficacy than the bottom-type and the top-type coating, which showed a stable biofilm inhibition rate of about 60 % even after 5-day leaching in aqueous solution. Norspermidine could retard bacterial adhesion and destruct biofilm matrix by reducing exopolysaccharides and extracellular DNA (eDNA) associated with bacteria instead of growth inhibition. Norspermidine and the norspermidine-hosting coatings in this study offer a great potential for the control of biofilms in the settings of water purification and wastewater treatment systems, which shows the advantage of broad spectrum and less risk of evolved bacterial resistance compared to conventional microbicidal agents (e.g., antibiotics).

Functionalizing Soft Matter for Molecular Communication

The information age was enabled by advances in microfabrication and communication theory that allowed information to be processed by electrons and transmitted by electromagnetic radiation. Despite immense capabilities, microelectronics has limited abilities to access and participate in the molecular-based communication that characterizes our biological world. Here, we use biological materials and methods to create components and fabricate devices to perform simple molecular communication functions based on bacterial quorum sensing (QS). Components were created by protein engineering to generate a multidomain fusion protein capable of sending a molecular QS signal, and by synthetic biology to engineer E. coli to receive and report this QS signal. The device matrix was formed using stimuli-responsive hydrogel-forming biopolymers (alginate and gelatin). Assembly of the components within the device matrix was achieved by physically entrapping the cell-based components, and covalently conjugating the protein-based components using the enzyme microbial transglutaminase. We demonstrate simple devices that can send or receive a molecular QS signal to/from the surrounding medium, and a two-component device in which one component generates the signal (i.e., issues a command) that is acted upon by the second component. These studies illustrate the broad potential of biofabrication to generate molecular communication devices.

Geminal dihalogen isosteric replacement in hydrated AI-2 affords potent quorum sensing modulators

Geminal dibromo moiety can replace hydrated carbonyl groups in AI-2, a quorum sensing autoinducer, without diminution of activity. This group can form halogen bond with active site electron donor.