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Salehi-Najafabadi A, Tehrani Fateh S, Amoabediny G, Hamedi J. Insights into additional lactone-based signaling circuits in Streptomyces: existence of acyl-homoserine lactones and LuxI/LuxR homologs in six Streptomyces species. Front Microbiol 2024; 15:1342637. [PMID: 38389542 PMCID: PMC10883386 DOI: 10.3389/fmicb.2024.1342637] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Accepted: 01/18/2024] [Indexed: 02/24/2024] Open
Abstract
Acyl-homoserine lactones (AHLs), mediating pivotal physiological activities through quorum sensing (QS), have conventionally been considered limited to Gram-negative bacteria. However, few reports on the existence of AHLs in Gram-positive bacteria have questioned this conception. Streptomyces, as Gram-positive bacteria already utilizing a lactone-based QS molecule (i.e., gamma-butyrolactones), are yet to be explored for producing AHLs, considering their metabolic capacity and physiological distinction. In this regard, our study examined the potential production of AHLs within Streptomyces by deploying HPLC-MS/MS methods, which resulted in the discovery of multiple AHL productions by S. griseus, S. lavendulae FRI-5, S. clavuligerus, S. nodosus, S. lividans, and S. coelicolor A3(2). Each of these Streptomyces species possesses a combination of AHLs of different size ranges, possibly due to their distinct properties and regulatory roles. In light of additional lactone molecules, we further confirm that AHL- and GBL-synthases (i.e., LuxI and AfsA enzyme families, respectively) and their receptors (i.e., LuxR and ArpA) are evolutionarily distinct. To this end, we searched for the components of the AHL signaling circuit, i.e., AHL synthases and receptors, in the Streptomyces genus, and we have identified multiple potential LuxI and LuxR homologs in all 2,336 Streptomyces species included in this study. The 6 Streptomyces of interest in this study also had at least 4 LuxI homologs and 97 LuxR homologs. In conclusion, AHLs and associated gene regulatory systems could be more widespread within the prokaryotic realm than previously believed, potentially contributing to the control of secondary metabolites (e.g., antibiotics) and their complex life cycle, which leads to substantial industrial and clinical applications.
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Affiliation(s)
- Amir Salehi-Najafabadi
- Department of Microbial Biotechnology, School of Biology and Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, Tehran, Iran
- Research Center for New Technologies in Life Science Engineering, University of Tehran, Tehran, Iran
| | - Sepand Tehrani Fateh
- Research Center for New Technologies in Life Science Engineering, University of Tehran, Tehran, Iran
- School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Ghasem Amoabediny
- Research Center for New Technologies in Life Science Engineering, University of Tehran, Tehran, Iran
- Faculty of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran
| | - Javad Hamedi
- Department of Microbial Biotechnology, School of Biology and Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, Tehran, Iran
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Wang N, Gao J, Liu Y, Wang Q, Zhuang X, Zhuang G. Realizing the role of N-acyl-homoserine lactone-mediated quorum sensing in nitrification and denitrification: A review. CHEMOSPHERE 2021; 274:129970. [PMID: 33979914 DOI: 10.1016/j.chemosphere.2021.129970] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 02/04/2021] [Accepted: 02/08/2021] [Indexed: 06/12/2023]
Abstract
Nitrification and denitrification are crucial processes in the nitrogen cycle, a vital microbially driven biogeochemical cycle. N-acyl-homoserine lactone (AHL)-mediated quorum sensing (QS) is widespread in bacteria and plays a key role in their physiological status. Recently, there has been an increase in research into how the AHL-mediated QS system is involved in nitrification and denitrification. Consequentially, the AHL-mediated QS system has been considered a promising regulatory approach in nitrogen metabolism processes, with high potential for real-world applications. In this review, the universal presence of QS in nitrifiers and denitrifiers is summarized. Many microorganisms taking part in nitrification and denitrification harbor QS genes, and they may produce AHLs with different chain lengths. The phenotypes and processes affected by QS in real-world applications are also reviewed. In wastewater bioreactors, QS could affect nitrogen metabolism efficiency, granule aggregation, and biofilm formation. Furthermore, methods commonly used to identify the existence and functions of QS, including physiological tests, genetic manipulation and omics analyses are discussed.
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Affiliation(s)
- Na Wang
- CAS Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jie Gao
- CAS Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Ying Liu
- CAS Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China; School of Life Sciences, University of Science and Technology of China, Hefei, 230026, China
| | - Qiuying Wang
- CAS Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Xuliang Zhuang
- CAS Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Guoqiang Zhuang
- CAS Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, China.
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3
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Whole-Genome Sequencing of Pantoea sp. Strain RIT388, a Potential Oral Opportunistic Pathogen Isolated from a Chewing Stick ( Distemonanthus benthamianus). Microbiol Resour Announc 2020; 9:9/9/e01468-19. [PMID: 32107300 PMCID: PMC7046821 DOI: 10.1128/mra.01468-19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this study, we report the isolation, identification, characterization, and whole-genome sequence of the endophyte Pantoea sp. strain RIT388, isolated from Distemonanthus benthamianus, a plant known for its antifungal and antibacterial properties that is commonly used for chewing sticks.
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Froes TQ, Baldini RL, Vajda S, Castilho MS. Structure-based Druggability Assessment of Anti-virulence Targets from Pseudomonas aeruginosa. Curr Protein Pept Sci 2020; 20:1189-1203. [PMID: 31038064 DOI: 10.2174/1389203720666190417120758] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Revised: 02/12/2019] [Accepted: 02/28/2019] [Indexed: 11/22/2022]
Abstract
Antimicrobial Resistance (AMR) represents a serious threat to health and the global economy. However, interest in antibacterial drug development has decreased substantially in recent decades. Meanwhile, anti-virulence drug development has emerged as an attractive alternative to fight AMR. Although several macromolecular targets have been explored for this goal, their druggability is a vital piece of information that has been overlooked. This review explores this subject by showing how structure- based freely available in silico tools, such as PockDrug and FTMap, might be useful for designing novel inhibitors of the pyocyanin biosynthesis pathway and improving the potency/selectivity of compounds that target the Pseudomonas aeruginosa quorum sensing mechanism. The information provided by hotspot analysis, along with binding site features, reveals novel druggable targets (PhzA and PhzS) that remain largely unexplored. However, it also highlights that in silico druggability prediction tools have several limitations that might be overcome in the near future. Meanwhile, anti-virulence drug targets should be assessed by complementary methods, such as the combined use of FTMap/PockDrug, once the consensus druggability classification reduces the risk of wasting resources on undruggable proteins.
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Affiliation(s)
- Thamires Q Froes
- Programa de Pos-Graduacao em Biotecnologia da Universidade Estadual de Feira de Santana, Feira de Santana, BA, Brazil.,aculdade de Farmácia da Universidade Federal da Bahia, Bahia, Salvador, BA, Brazil
| | - Regina L Baldini
- Departamento de Bioquimica, Instituto de Quimica, Universidade de Sao Paulo. Sao Paulo, SP, Brazil
| | - Sandor Vajda
- College of Engineering, Boston University, Boston, MA, United States
| | - Marcelo S Castilho
- Programa de Pos-Graduacao em Biotecnologia da Universidade Estadual de Feira de Santana, Feira de Santana, BA, Brazil.,aculdade de Farmácia da Universidade Federal da Bahia, Bahia, Salvador, BA, Brazil.,College of Engineering, Boston University, Boston, MA, United States
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Communication within East Antarctic Soil Bacteria. Appl Environ Microbiol 2019; 86:AEM.01968-19. [PMID: 31628145 DOI: 10.1128/aem.01968-19] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 10/09/2019] [Indexed: 01/01/2023] Open
Abstract
Antarctica, being the coldest, driest, and windiest continent on Earth, represents the most extreme environment in which a living organism can survive. Under constant exposure to harsh environmental threats, terrestrial Antarctica remains home to a great diversity of microorganisms, indicating that the soil bacteria must have adapted a range of survival strategies that require cell-to-cell communication. Survival strategies include secondary metabolite production, biofilm formation, bioluminescence, symbiosis, conjugation, sporulation, and motility, all of which are often regulated by quorum sensing (QS), a type of bacterial communication. Until now, such mechanisms have not been explored in terrestrial Antarctica. In this study, LuxI/LuxR-based quorum sensing (QS) activity was delineated in soil bacterial isolates recovered from Adams Flat, in the Vestfold Hills region of East Antarctica. Interestingly, we identified the production of potential homoserine lactones (HSLs) with chain lengths ranging from medium to long in 19 bacterial species using three biosensors, namely, Agrobacterium tumefaciens NTL4, Chromobacterium violaceum CV026, and Escherichia coli MT102, in conjunction with thin-layer chromatography (TLC). The majority of detectable HSLs were from Gram-positive species not previously known to produce HSLs. This discovery further expands our understanding of the microbial community capable of this type of communication, as well as provides insights into physiological adaptations of microorganisms that allow them to survive in the harsh Antarctic environment.IMPORTANCE Quorum sensing, a type of bacterial communication, is widely known to regulate many processes, including those that confer a survival advantage. However, little is known about communication by bacteria residing within Antarctic soils. Employing a combination of bacterial biosensors, analytical techniques, and genome mining, we found a variety of Antarctic soil bacteria speaking a common language, via LuxI/LuxR-based quorum sensing, thus potentially supporting survival in a mixed microbial community. This study reports potential quorum sensing activity in Antarctic soils and has provided a platform for studying physiological adaptations of microorganisms that allow them to survive in the harsh Antarctic environment.
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Molecular basis for the substrate specificity of quorum signal synthases. Proc Natl Acad Sci U S A 2017; 114:9092-9097. [PMID: 28784791 DOI: 10.1073/pnas.1705400114] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
In several Proteobacteria, LuxI-type enzymes catalyze the biosynthesis of acyl-homoserine lactones (AHL) signals using S-adenosyl-l-methionine and either cellular acyl carrier protein (ACP)-coupled fatty acids or CoA-aryl/acyl moieties as progenitors. Little is known about the molecular mechanism of signal biosynthesis, the basis for substrate specificity, or the rationale for donor specificity for any LuxI member. Here, we present several cocrystal structures of BjaI, a CoA-dependent LuxI homolog that represent views of enzyme complexes that exist along the reaction coordinate of signal synthesis. Complementary biophysical, structure-function, and kinetic analysis define the features that facilitate the unusual acyl conjugation with S-adenosylmethionine (SAM). We also identify the determinant that establishes specificity for the acyl donor and identify residues that are critical for acyl/aryl specificity. These results highlight how a prevalent scaffold has evolved to catalyze quorum signal synthesis and provide a framework for the design of small-molecule antagonists of quorum signaling.
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In silico analyses of conservational, functional and phylogenetic distribution of the LuxI and LuxR homologs in Gram-positive bacteria. Sci Rep 2017; 7:6969. [PMID: 28765541 PMCID: PMC5539150 DOI: 10.1038/s41598-017-07241-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 06/26/2017] [Indexed: 11/08/2022] Open
Abstract
LuxI and LuxR are key factors that drive quorum sensing (QS) in bacteria through secretion and perception of the signaling molecules e.g. N-Acyl homoserine lactones (AHLs). The role of these proteins is well established in Gram-negative bacteria for intercellular communication but remain under-explored in Gram-positive bacteria where QS peptides are majorly responsible for cell-to-cell communication. Therefore, in the present study, we explored conservation, potential function, topological arrangements and evolutionarily aspects of these proteins in Gram-positive bacteria. Putative LuxI/LuxR containing proteins were retrieved using the domain-based strategy from InterPro v62.0 meta-database. Conservational analyses via multiple sequence alignment and domain showed that these are well conserved in Gram-positive bacteria and possess relatedness with Gram-negative bacteria. Further, Gene ontology and ligand-based functional annotation explain their active involvement in signal transduction mechanism via QS signaling molecules. Moreover, Phylogenetic analyses (LuxI, LuxR, LuxI + LuxR and 16s rRNA) revealed horizontal gene transfer events with significant statistical support among Gram-positive and Gram-negative bacteria. This in-silico study offers a detailed overview of potential LuxI/LuxR distribution in Gram-positive bacteria (mainly Firmicutes and Actinobacteria) and their functional role in QS. It would further help in understanding the extent of interspecies communications between Gram-positive and Gram-negative bacteria through QS signaling molecules.
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Discovery of new diketopiperazines inhibiting Burkholderia cenocepacia quorum sensing in vitro and in vivo. Sci Rep 2016; 6:32487. [PMID: 27580679 PMCID: PMC5007513 DOI: 10.1038/srep32487] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 08/08/2016] [Indexed: 02/08/2023] Open
Abstract
Burkholderia cenocepacia, an opportunistic respiratory pathogen particularly relevant for cystic fibrosis patients, is difficult to eradicate due to its high level of resistance to most clinically relevant antimicrobials. Consequently, the discovery of new antimicrobials as well as molecules capable of inhibiting its virulence is mandatory. In this regard quorum sensing (QS) represents a good target for anti-virulence therapies, as it has been linked to biofilm formation and is important for the production of several virulence factors, including proteases and siderophores. Here, we report the discovery of new diketopiperazine inhibitors of the B. cenocepacia acyl homoserine lactone synthase CepI, and report their anti-virulence properties. Out of ten different compounds assayed against recombinant CepI, four were effective inhibitors, with IC50 values in the micromolar range. The best compounds interfered with protease and siderophore production, as well as with biofilm formation, and showed good in vivo activity in a Caenorhabditis elegans infection model. These molecules were also tested in human cells and showed very low toxicity. Therefore, they could be considered for in vivo combined treatments with established or novel antimicrobials, to improve the current therapeutic strategies against B. cenocepacia.
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9
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Kimura N. Metagenomic approaches to understanding phylogenetic diversity in quorum sensing. Virulence 2014; 5:433-42. [PMID: 24429899 DOI: 10.4161/viru.27850] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Quorum sensing, a form of cell-cell communication among bacteria, allows bacteria to synchronize their behaviors at the population level in order to control behaviors such as luminescence, biofilm formation, signal turnover, pigment production, antibiotics production, swarming, and virulence. A better understanding of quorum-sensing systems will provide us with greater insight into the complex interaction mechanisms used widely in the Bacteria and even the Archaea domain in the environment. Metagenomics, the use of culture-independent sequencing to study the genomic material of microorganisms, has the potential to provide direct information about the quorum-sensing systems in uncultured bacteria. This article provides an overview of the current knowledge of quorum sensing focused on phylogenetic diversity, and presents examples of studies that have used metagenomic techniques. Future technologies potentially related to quorum-sensing systems are also discussed.
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Affiliation(s)
- Nobutada Kimura
- Bioproduction Research Institute; National Institute of Advanced Industrial Science and Technology (AIST); Tsukuba, Ibaraki Japan
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10
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Stacy DM, Welsh MA, Rather PN, Blackwell HE. Attenuation of quorum sensing in the pathogen Acinetobacter baumannii using non-native N-Acyl homoserine lactones. ACS Chem Biol 2012; 7:1719-28. [PMID: 22853441 DOI: 10.1021/cb300351x] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Many bacterial pathogens use quorum sensing (QS) to control virulence. As a result, the development of methods to intercept QS has attracted significant interest as a potential anti-infective therapy. Acinetobacter baumannii has emerged as a pan-drug-resistant pathogen and displays a remarkable ability to persist in hospital settings despite desiccation and antimicrobial treatment. Recent studies have shown that A. baumannii QS mutants have limited motility and fail to form mature biofilms; these phenotypes are linked to its ability to persist on biotic and abiotic surfaces and increase its pathogenicity. A. baumannii uses N-(3-hydroxydodecanoyl)-l-homoserine lactone (OH-dDHL) and its putative cognate receptor, AbaR, for QS. We sought to identify non-native ligands capable of blocking or promoting AbaR activity in A. baumannii for use as chemical probes to modulate QS phenotypes in this pathogen. We screened a focused library of synthetic, non-native N-acyl homoserine lactones (AHLs) to identify such compounds, and several highly potent antagonists and agonists were uncovered, with IC(50) and EC(50) values in the low micromolar range, respectively. The strongest AbaR antagonists largely contained aromatic acyl groups, whereas the AbaR agonists closely resembled OH-dDHL. Notably, the 10 most potent AbaR antagonists also strongly inhibited A. baumannii motility, and five antagonists reduced biofilm formation in A. baumannii by up to 40%. The discovery of these compounds is significant, as they represent, to our knowledge, the first non-native modulators of QS in A. baumannii to be reported and could find utility as new tools to study the role and timing of QS phenotypes in A. baumannii infections.
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Affiliation(s)
- Danielle M. Stacy
- Department of Chemistry, University of Madison−Wisconsin, 1101 University
Ave., Madison, Wisconsin 53706, United States
| | - Michael A. Welsh
- Department of Chemistry, University of Madison−Wisconsin, 1101 University
Ave., Madison, Wisconsin 53706, United States
| | - Philip N. Rather
- Department of Microbiology and
Immunology, Emory University School of Medicine, 3001 Rollins Research Center, Atlanta, Georgia 30322, United States
- Research Service, Veterans Affairs Medical Center, 1670 Clairmont Rd.,
Decatur, Georgia 30033, United States
| | - Helen E. Blackwell
- Department of Chemistry, University of Madison−Wisconsin, 1101 University
Ave., Madison, Wisconsin 53706, United States
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Li Z, Nair SK. Quorum sensing: how bacteria can coordinate activity and synchronize their response to external signals? Protein Sci 2012; 21:1403-17. [PMID: 22825856 DOI: 10.1002/pro.2132] [Citation(s) in RCA: 113] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Revised: 07/18/2012] [Accepted: 07/18/2012] [Indexed: 01/14/2023]
Abstract
Quorum sensing is used by a large variety of bacteria to regulate gene expression in a cell-density-dependent manner. Bacteria can synchronize population behavior using small molecules called autoinducers that are produced by cognate synthases and recognized by specific receptors. Quorum sensing plays critical roles in regulating diverse cellular functions in bacteria, including bioluminescence, virulence gene expression, biofilm formation, and antibiotic resistance. The best-studied autoinducers are acyl homoserine lactone (AHL) molecules, which are the primary quorum sensing signals used by Gram-negative bacteria. In this review we focus on the AHL-dependent quorum sensing system and highlight recent progress on structural and mechanistic studies of AHL synthases and the corresponding receptors. Crystal structures of LuxI-type AHL synthases provide insights into acyl-substrate specificity, but the current knowledge is still greatly limited. Structural studies of AHL receptors have facilitated a more thorough understanding of signal perception and established the molecular framework for the development of quorum sensing inhibitors.
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Affiliation(s)
- Zhi Li
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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Abstract
The bioluminescence emitted by the marine bacterium Vibrio fischeri is a particularly striking result of individual microbial cells co-ordinating a group behaviour. The genes responsible for light production are principally regulated by the LuxR-LuxI quorum-sensing system. In addition to LuxR-LuxI, numerous other genetic elements and environmental conditions control bioluminescence production. Efforts to mathematically model the LuxR-LuxI system are providing insight into the dynamics of this autoinduction behaviour. The Hawaiian squid Euprymna scolopes forms a natural symbiosis with V. fischeri, and utilizes the symbiont-derived bioluminescence for certain nocturnal behaviours, such as counterillumination. Recent work suggests that the tissue with which V. fischeri associates not only can detect bioluminescence but may also use this light to monitor the V. fischeri population.
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Affiliation(s)
- Tim Miyashiro
- Department of Medical Microbiology and Immunology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706-1521, USA.
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13
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Quorum sensing and expression of virulence in pectobacteria. SENSORS 2012; 12:3327-49. [PMID: 22737011 PMCID: PMC3376562 DOI: 10.3390/s120303327] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 02/21/2012] [Accepted: 03/02/2012] [Indexed: 01/23/2023]
Abstract
Quorum sensing (QS) is a population density-dependent regulatory mechanism in which gene expression is coupled to the accumulation of a chemical signaling molecule. QS systems are widespread among the plant soft-rotting bacteria. In Pectobacterium carotovorum, at least two QS systems exist being specified by the nature of chemical signals involved. QS in Pectobacterium carotovorum uses N-acylhomoserine lactone (AHL) based, as well as autoinducer-2 (AI-2) dependent signaling systems. This review will address the importance of the QS in production of virulence factors and interaction of QS with other regulatory systems in Pectobacterium carotovorum.
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Pasotti L, Quattrocelli M, Galli D, De Angelis MGC, Magni P. Multiplexing and demultiplexing logic functions for computing signal processing tasks in synthetic biology. Biotechnol J 2011; 6:784-95. [DOI: 10.1002/biot.201100080] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Revised: 05/02/2011] [Accepted: 05/27/2011] [Indexed: 11/09/2022]
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Affiliation(s)
- Mair E A Churchill
- Department of Pharmacology and Program in Structural Biology and Biophysics, The University of Colorado School of Medicine, Aurora, Colorado 80045, USA.
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16
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Abstract
This review describes the chemistry of the bacterial biofilms including the chemistry of their constituents and signalling compounds that mediate or inhibit the formation of biofilms. Systems are described with special emphasis, in which quorum sensing molecules (autoinducers) trigger the formation of biofilms. In the first instance, N-acyl-L-homoserine lactones (AHLs) are the focus of this review, whereas the inter-species signal known as furanosyl borate diester and peptide autoinducers used by Gram-positive bacteria are not discussed in detail. Since the first discovery of an AHL autoinducer from Vibrio fischeri a large and further increasing number of different AHL structures from Gram-negative bacteria have been identified. This review gives a summary of all known AHL autoinducers and producing bacterial species. A few systems are discussed, where biofilm formation is suppressed by enzymatic degradation of AHL molecules or interference of secondary metabolites from other species with the quorum sensing systems of communicating bacteria. Finally, the multi-channel quorum sensing system, the intracellular downstream processing of the signal, and the resulting response of whole populations including biofilm formation are discussed for the Vibrio genus that has been extensively investigated.
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Affiliation(s)
- Jeroen S Dickschat
- Institute of Organic Chemistry, Technical University of Braunschweig, Hagenring 30, Braunschweig, Germany.
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17
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Kambam PKR, Sayut DJ, Niu Y, Eriksen DT, Sun L. Directed evolution of LuxI for enhanced OHHL production. Biotechnol Bioeng 2008; 101:263-72. [DOI: 10.1002/bit.21901] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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18
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Chalupowicz L, Manulis-Sasson S, Itkin M, Sacher A, Sessa G, Barash I. Quorum-sensing system affects gall development incited by Pantoea agglomerans pv. gypsophilae. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2008; 21:1094-1105. [PMID: 18616406 DOI: 10.1094/mpmi-21-8-1094] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The quorum-sensing (QS) regulatory system of the gall-forming Pantoea agglomerans pv. gypsophilae was identified. Mass spectral analysis, together with signal-specific biosensors, demonstrated that P. agglomerans pv. gypsophilae produced N-butanoyl-l-homoserine lactone (C4-HSL) as a major and N-hexanoyl-l-homoserine lactone (C6-HSL) as a minor QS signal. Homologs of luxI and luxR regulatory genes, pagI and pagR, were characterized in strain P. agglomerans pv. gypsophilae Pag824-1 and shown to be convergently transcribed and separated by 14 bp. The deduced PagI (23.8 kDa) and PagR (26.9 kDa) show high similarity with SmaI (41% identity) and SmaR (43% identity), respectively, of Serratia sp. American Type Culture Collection 39006. PagR possesses characteristic autoinducer binding and a helix-turn-helix DNA-binding domain. Gall formation by P. agglomerans pv. gypsophilae depends on a plasmid-borne hrp/hrc gene cluster, type III effectors, and phytohormones. Disruption of pagI, pagR, or both genes simultaneously in Pag824-1 reduced gall size in gypsophila cuttings by 50 to 55% when plants were inoculated with 10(6) CFU/ml. Higher reductions in gall size (70 to 90%) were achieved by overexpression of pagI or addition of exogenous C4-HSL. Expression of the hrp/hrc regulatory gene hrpL and the type III effector pthG in the pagI mutant, as measured with quantitative reverse-transcriptase polymerase chain reaction, was reduced by 5.8 and 6.6, respectively, compared with the wild type, suggesting an effect of the QS system on the Hrp regulon.
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Affiliation(s)
- Laura Chalupowicz
- Department of Plant Pathology and Weed Research, ARO, The Volcani Center, Bet Dagan, Israel
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Wang YJ, Huang JJ, Leadbetter JR. Acyl-HSL signal decay: intrinsic to bacterial cell-cell communications. ADVANCES IN APPLIED MICROBIOLOGY 2007; 61:27-58. [PMID: 17448787 DOI: 10.1016/s0065-2164(06)61002-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Ya-Juan Wang
- Environmental Science and Engineering, California Institute of Technology, Pasadena, CA 91125, USA
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Penalver CGN, Cantet F, Morin D, Haras D, Vorholt JA. A plasmid-borne truncated luxI homolog controls quorum-sensing systems and extracellular carbohydrate production in Methylobacterium extorquens AM1. J Bacteriol 2006; 188:7321-4. [PMID: 17015673 PMCID: PMC1636247 DOI: 10.1128/jb.00649-06] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A cryptic plasmid of Methylobacterium extorquens AM1 was found to encode tslI, a truncated luxI homolog. tslI was shown to be expressed and to control transcription of the acyl-homoserine lactone (HSL) synthase gene msaI and thus, indirectly, acyl-HSL production. In addition, tslI was found to positively regulate extracellular polysaccharide production.
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Affiliation(s)
- Carlos G Nieto Penalver
- Institute of Microbiology, Swiss Federal Institute of Technology Zurich, ETH Hönggerberg, Zurich, Switzerland
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21
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Abstract
Homologs of quorum-sensing luxR and luxI regulatory genes, avsR and avsI, were identified in Agrobacterium vitis strain F2/5. Compared to other LuxI proteins from related species, the deduced AvsI shows the greatest identity to SinI (71%) from Sinorhizobium meliloti Rm1021. AvsR possesses characteristic autoinducer binding and helix-turn-helix DNA binding domains and shares a high level of identity with SinR (38%) from Rm1021. Site-directed mutagenesis of avsR and avsI was performed, and both genes are essential for hypersensitive-like response (HR) and necrosis. Two hypothetical proteins (ORF1 and ORF2) that are positioned downstream of avsR-avsI are also essential for the phenotypes. Profiles of N-acyl-homoserine lactones (AHLs) isolated from the wild type and mutants revealed that disruption of avsI, ORF1, or ORF2 abolished the production of long-chain AHLs. Disruption of avsR reduces long-chain AHLs. Expression of a cloned avsI gene in A. tumefaciens strain NT1 resulted in synthesis of long-chain AHLs. The necrosis and HR phenotypes of the avsI and avsR mutants were fully complemented with cloned avsI. The addition of synthetic AHLs (C(16:1) and 3-O-C(16:1)) complemented grape necrosis in the avsR, avsI, ORF1, and ORF2 mutants. It was determined by reverse transcriptase PCR that the expression level of avsI is regulated by avsR but not by aviR or avhR, two other luxR homologs which were previously shown to be associated with induction of a tobacco hypersensitive response and grape necrosis. We further verified that avsR regulates avsI by measuring the expression of an avsI::lacZ fusion construct.
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Affiliation(s)
- Guixia Hao
- Department of Plant Pathology, NYSAES, Cornell University, Geneva, NY 14456, USA
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22
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Perry LL, Bright NG, Carroll RJ, Scott MC, Allen MS, Applegate BM. Molecular characterization of autoinduction of bioluminescence in the Microtox indicator strain Vibrio fischeri ATCC 49387. Can J Microbiol 2006; 51:549-57. [PMID: 16175203 DOI: 10.1139/w05-019] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Repeated attempts to clone the luxI from Vibrio fischeri ATCC 49387 failed to produce a clone carrying a functional LuxI. Sequence data from the clones revealed the presence of a polymorphism when compared with previously published luxI sequences, prompting further characterization of bioluminescence regulation in V. fischeri ATCC 49387. Further investigation of V. fischeri ATCC 49387 revealed that its LuxI protein lacks detectable LuxI activity due to the presence of a glutamine residue at position 125 in the deduced amino acid sequence. Specific bioluminescence in V. fischeri ATCC 49387 increases with increasing cell density, indicative of a typical autoinduction response. However, conditioned medium from this strain does not induce bioluminescence in an ATCC 49387 luxR-plux-based acyl homoserine lactone reporter strain, but does induce bioluminescence in ATCC 49387. It has been previously shown that a V. fischeri MJ-1 luxI mutant exhibits autoinduction of bioluminescence through N-octanoyl-L-homoserine lactone, the product of the AinS autoinducer synthase. However, a bioreporter based on luxR-plux from V. fischeri ATCC 49387 responded poorly to conditioned medium from V. fischeri ATCC 49387 and also responded poorly to authentic N-octanoyl-DL-homoserine lactone. A similar MJ-1-based bioreporter showed significant induction under the same conditions. A putative ainS gene cloned from ATCC 49387, unlike luxI from ATCC 49387, expresses V. fischeri autoinducer synthase activity in Escherichia coli. This study suggests that a regulatory mechanism independent of LuxR and LuxI but possibly involving AinS is responsible for the control of autoinduction of bioluminescence in V. fischeri ATCC 49387.
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Affiliation(s)
- Lynda L Perry
- Department of Food Science, Purdue University, IN 47907-2009, USA
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23
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Brader G, Sjöblom S, Hyytiäinen H, Sims-Huopaniemi K, Palva ET. Altering Substrate Chain Length Specificity of an Acylhomoserine Lactone Synthase in Bacterial Communication. J Biol Chem 2005; 280:10403-9. [PMID: 15634689 DOI: 10.1074/jbc.m408603200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Quorum sensing mediated by specific signal compounds (autoinducers) allows bacteria to monitor their cell density and enables a synchronized regulation of target gene sets. The best studied group of autoinducers are the acylhomoserine lactones (AHSLs), which are central to the regulation of virulence in many plant and animal pathogens. Variation of the acyl side chain of the AHSLs underlies the observed species specificity of this communication system. Here we show that even different strains of the plant pathogen Erwinia carotovora employ different dialects of this language and demonstrate the molecular basis for the acyl chain length specificity of distinct AHSL synthases. Under physiological concentrations, only the cognate AHSL with the "right" acyl chain is recognized as a signal that will switch on virulence genes. Mutagenesis of the AHSL synthase gene expI(SCC1) identified the changes M127T and F69L as sufficient to effectively alter ExpI(SCC1) (an N-3-oxohexanoyl-l-homoserine lactone producer) substrate specificity to that of an N-3-oxooctanoyl-l-homoserine lactone producer. Our data identify critical residues that define the size of the substrate-binding pocket of the AHSL synthase and will help in understanding and manipulating this bacterial language.
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Affiliation(s)
- Günter Brader
- Viikki Biocenter, Faculty of Biosciences, Department of Biological and Environmental Sciences, Division of Genetics, P. O. Box 56, University of Helsinki, FIN-00014 Helsinki, Finland
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24
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Pappas KM, Weingart CL, Winans SC. Chemical communication in proteobacteria: biochemical and structural studies of signal synthases and receptors required for intercellular signalling. Mol Microbiol 2004; 53:755-69. [PMID: 15255890 DOI: 10.1111/j.1365-2958.2004.04212.x] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cell-cell communication via the production and detection of chemical signal molecules has been the focus of a great deal of research over the past decade. One class of chemical signals widely used by proteobacteria consists of N-acyl-homoserine lactones, which are synthesized by proteins related to LuxI of Vibrio fischeri and are detected by proteins related to the V. fischeri LuxR protein. A related marine bacterium, Vibrio harveyi, communicates using two chemical signals, one of which, autoinducer-2 (AI-2), is a furanone borate diester that is synthesized by the LuxS protein and detected by a periplasmic protein called LuxP. Evidence from a number of laboratories suggests that AI-2 may be used as a signal by diverse groups of bacteria, and might permit intergeneric signalling. These two families of signalling systems have been studied from the perspectives of physiology, ecology, biochemistry, and more recently, structural biology. Here, we review the biochemistry and structural biology of both acyl-homoserine-lactone-dependent and AI-2-dependent signalling systems.
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Affiliation(s)
- Katherine M Pappas
- Department of Genetics and Biotechnology, Faculty of Biology, University of Athens, Athens, Greece
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25
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Gould TA, Schweizer HP, Churchill MEA. Structure of the Pseudomonas aeruginosa acyl-homoserinelactone synthase LasI. Mol Microbiol 2004; 53:1135-46. [PMID: 15306017 DOI: 10.1111/j.1365-2958.2004.04211.x] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The LasI/LasR quorum-sensing system plays a pivotal role in virulence gene regulation of the opportunistic human pathogen, Pseudomonas aeruginosa. Here we report the crystal structure of the acyl-homoserine lactone (AHL) synthase LasI that produces 3-oxo-C12-AHL from the substrates 3-oxo-C12-acyl-carrier protein (acyl-ACP) and S-adenosyl-L-methionine. The LasI six-stranded beta sheet platform, buttressed by three alpha helices, forms a V-shaped substrate-binding cleft that leads to a tunnel passing through the enzyme that can accommodate the acyl-chain of acyl-ACP. This tunnel places no apparent restriction on acyl-chain length, in contrast to a restrictive hydrophobic pocket seen in the AHL-synthase EsaI. Interactions of essential conserved N-terminal residues, Arg23, Phe27 and Trp33, suggest that the N-terminus forms an enclosed substrate-binding pocket for S-adenosyl-L-methionine. Analysis of AHL-synthase surface residues identified a binding site for acyl-ACP, a role that was supported by in vivo reporter assay analysis of the mutated residues, including Arg154 and Lys150. This structure and the novel explanation of AHL-synthase acyl-chain-length selectivity promise to guide the design of Pseudomonas aeruginosa-specific quorum-sensing inhibitors as antibacterial agents.
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Affiliation(s)
- Ty A Gould
- Department of Pharmacology, Program in Biomolecular Structure, The University of Colorado Health Sciences Center, 4200 E. Ninth Ave, Denver, CO 80262, USA
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26
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Abstract
Members of the rhizobia are distinguished for their ability to establish a nitrogen-fixing symbiosis with leguminous plants. While many details of this relationship remain a mystery, much effort has gone into elucidating the mechanisms governing bacterium-host recognition and the events leading to symbiosis. Several signal molecules, including plant-produced flavonoids and bacterially produced nodulation factors and exopolysaccharides, are known to function in the molecular conversation between the host and the symbiont. Work by several laboratories has shown that an additional mode of regulation, quorum sensing, intercedes in the signal exchange process and perhaps plays a major role in preparing and coordinating the nitrogen-fixing rhizobia during the establishment of the symbiosis. Rhizobium leguminosarum, for example, carries a multitiered quorum-sensing system that represents one of the most complex regulatory networks identified for this form of gene regulation. This review focuses on the recent stream of information regarding quorum sensing in the nitrogen-fixing rhizobia. Seminal work on the quorum-sensing systems of R. leguminosarum bv. viciae, R. etli, Rhizobium sp. strain NGR234, Sinorhizobium meliloti, and Bradyrhizobium japonicum is presented and discussed. The latest work shows that quorum sensing can be linked to various symbiotic phenomena including nodulation efficiency, symbiosome development, exopolysaccharide production, and nitrogen fixation, all of which are important for the establishment of a successful symbiosis. Many questions remain to be answered, but the knowledge obtained so far provides a firm foundation for future studies on the role of quorum-sensing mediated gene regulation in host-bacterium interactions.
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Affiliation(s)
- Juan E González
- Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75083-0688, USA.
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27
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Abstract
Members of the rhizobia are distinguished for their ability to establish a nitrogen-fixing symbiosis with leguminous plants. While many details of this relationship remain a mystery, much effort has gone into elucidating the mechanisms governing bacterium-host recognition and the events leading to symbiosis. Several signal molecules, including plant-produced flavonoids and bacterially produced nodulation factors and exopolysaccharides, are known to function in the molecular conversation between the host and the symbiont. Work by several laboratories has shown that an additional mode of regulation, quorum sensing, intercedes in the signal exchange process and perhaps plays a major role in preparing and coordinating the nitrogen-fixing rhizobia during the establishment of the symbiosis. Rhizobium leguminosarum, for example, carries a multitiered quorum-sensing system that represents one of the most complex regulatory networks identified for this form of gene regulation. This review focuses on the recent stream of information regarding quorum sensing in the nitrogen-fixing rhizobia. Seminal work on the quorum-sensing systems of R. leguminosarum bv. viciae, R. etli, Rhizobium sp. strain NGR234, Sinorhizobium meliloti, and Bradyrhizobium japonicum is presented and discussed. The latest work shows that quorum sensing can be linked to various symbiotic phenomena including nodulation efficiency, symbiosome development, exopolysaccharide production, and nitrogen fixation, all of which are important for the establishment of a successful symbiosis. Many questions remain to be answered, but the knowledge obtained so far provides a firm foundation for future studies on the role of quorum-sensing mediated gene regulation in host-bacterium interactions.
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Affiliation(s)
- Juan E González
- Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75083-0688, USA.
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28
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Chakrabarti S, Sowdhamini R. Functional sites and evolutionary connections of acylhomoserine lactone synthases. Protein Eng Des Sel 2003; 16:271-8. [PMID: 12736370 DOI: 10.1093/proeng/gzg031] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Acylhomoserine lactone (AHL) synthases act as chemical communication signals or pheromones in Gram-negative bacteria and regulate diverse physiological events in a cell density-dependent manner. The recent crystal structure determination of EsaI, a key enzyme in this pathway, shows that the AHL synthase superfamily members adopt the fold of the N-acetyltransferase superfamily. We suggest, by the identification of intermediate sequences, that the two superfamilies are evolutionarily related. Evolutionary trace analyses of aligned sequences and docking studies have been used to discuss functionally important residues of EsaI homologues.
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Affiliation(s)
- Saikat Chakrabarti
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, UAS-GKVK Campus, Bangalore 560 065, India
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29
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Chin-A-Woeng TFC, Bloemberg GV, Lugtenberg BJJ. Phenazines and their role in biocontrol by Pseudomonas bacteria. THE NEW PHYTOLOGIST 2003; 157:503-523. [PMID: 33873412 DOI: 10.1046/j.1469-8137.2003.00686.x] [Citation(s) in RCA: 159] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Various rhizosphere bacteria are potential (micro)biological pesticides which are able to protect plants against diseases and improve plant yield. Knowledge of the molecular mechanisms that govern these beneficial plant-microbe interactions enables optimization, enhancement and identification of potential synergistic effects in plant protection. The production of antifungal metabolites, induction of systemic resistance, and the ability to compete efficiently with other resident rhizobacteria are considered to be important prerequisites for the optimal performance of biocontrol agents. Intriguing aspects in the molecular mechanisms of these processes have been discovered recently. Phenazines and phloroglucinols are major determinants of biological control of soilborne plant pathogens by various strains of fluorescent Pseudomonas spp. This review focuses on the current state of knowledge on biocontrol by phenazine-producing Pseudomonas strains and the action, biosynthesis, and regulation mechanisms of the production of microbial phenazines.
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Affiliation(s)
| | - Guido V Bloemberg
- Institute of Molecular Plant Sciences, Leiden University, The Netherlands
| | - Ben J J Lugtenberg
- Institute of Molecular Plant Sciences, Leiden University, The Netherlands
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30
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Fuqua C, Greenberg EP. Listening in on bacteria: acyl-homoserine lactone signalling. Nat Rev Mol Cell Biol 2002; 3:685-95. [PMID: 12209128 DOI: 10.1038/nrm907] [Citation(s) in RCA: 711] [Impact Index Per Article: 32.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Bacterial cell-to-cell signalling has emerged as a new area in microbiology. Individual bacterial cells communicate with each other and co-ordinate group activities. Although a lot of detail is known about the mechanisms of a few well-characterized bacterial communication systems, other systems have been discovered only recently. Bacterial intercellular communication has become a target for the development of new anti-virulence drugs.
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Affiliation(s)
- Clay Fuqua
- Department of Biology, Indiana University, Jordan Hall 142, 1001 East 3rd Street, Bloomington, Indiana 47405, USA
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31
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Watson WT, Minogue TD, Val DL, von Bodman SB, Churchill MEA. Structural basis and specificity of acyl-homoserine lactone signal production in bacterial quorum sensing. Mol Cell 2002; 9:685-94. [PMID: 11931774 DOI: 10.1016/s1097-2765(02)00480-x] [Citation(s) in RCA: 195] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Synthesis and detection of acyl-homoserine lactones (AHLs) enables many gram-negative bacteria to engage in quorum sensing, an intercellular signaling mechanism that activates differentiation to virulent and biofilm lifestyles. The AHL synthases catalyze acylation of S-adenosyl-L-methionine by acyl-acyl carrier protein and lactonization of the methionine moiety to give AHLs. The crystal structure of the AHL synthase, EsaI, determined at 1.8 A resolution, reveals a remarkable structural similarity to the N-acetyltransferases and defines a common phosphopantetheine binding fold as the catalytic core. Critical residues responsible for catalysis and acyl chain specificity have been identified from a modeled substrate complex and verified through functional analysis in vivo. A mechanism for the N-acylation of S-adenosyl-L-methionine by 3-oxo-hexanoyl-acyl carrier protein is proposed.
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Affiliation(s)
- William T Watson
- Department of Pharmacology, The University of Colorado Health Sciences Center, 4200 E. Ninth Avenue, Denver, CO 80262, USA
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32
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Affiliation(s)
- Stephen C Winans
- Department of Microbiology, Cornell University, Ithaca, New York 14853, USA
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33
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Fuqua C, Parsek MR, Greenberg EP. Regulation of gene expression by cell-to-cell communication: acyl-homoserine lactone quorum sensing. Annu Rev Genet 2002; 35:439-68. [PMID: 11700290 DOI: 10.1146/annurev.genet.35.102401.090913] [Citation(s) in RCA: 940] [Impact Index Per Article: 42.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Quorum sensing is an example of community behavior prevalent among diverse bacterial species. The term "quorum sensing" describes the ability of a microorganism to perceive and respond to microbial population density, usually relying on the production and subsequent response to diffusible signal molecules. A significant number of gram-negative bacteria produce acylated homoserine lactones (acyl-HSLs) as signal molecules that function in quorum sensing. Bacteria that produce acyl-HSLs can respond to the local concentration of the signaling molecules, and high population densities foster the accumulation of inducing levels of acyl-HSLs. Depending upon the bacterial species, the physiological processes regulated by quorum sensing are extremely diverse, ranging from bioluminescence to swarming motility. Acyl-HSL quorum sensing has become a paradigm for intercellular signaling mechanisms. A flurry of research over the past decade has led to significant understanding of many aspects of quorum sensing including the synthesis of acyl-HSLs, the receptors that recognize the acyl-HSL signal and transduce this information to the level of gene expression, and the interaction of these receptors with the transcriptional machinery. Recent studies have begun to integrate acyl-HSL quorum sensing into global regulatory networks and establish its role in developing and maintaining the structure of bacterial communities.
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Affiliation(s)
- C Fuqua
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
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34
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Swift S, Downie JA, Whitehead NA, Barnard AM, Salmond GP, Williams P. Quorum sensing as a population-density-dependent determinant of bacterial physiology. Adv Microb Physiol 2002; 45:199-270. [PMID: 11450110 DOI: 10.1016/s0065-2911(01)45005-3] [Citation(s) in RCA: 211] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The discovery that bacterial cells can communicate with each other has led to the realization that bacteria are capable of exhibiting much more complex patterns of co-operative behaviour than would be expected for simple unicellular microorganisms. Now generically termed 'quorum sensing', bacterial cell-to-cell communication enables a bacterial population to mount a unified response that is advantageous to its survival by improving access to complex nutrients or environmental niches, collective defence against other competitive microorganisms or eukaryotic host defence mechanisms and optimization of population survival by differentiation into morphological forms better adapted to combating environmental threats. The principle of quorum sensing encompasses the production and release of signal molecules by bacterial cells within a population. Such molecules are released into the environment and, as cell numbers increase, so does the extracellular level of signal molecule, until the bacteria sense that a threshold has been reached and gene activation, or in some cases depression or repression, occurs via the activity of sensor-regulator systems. In this review, we will describe the biochemistry and molecular biology of a number of well-characterized N-acylhomoserine lactone quorum sensing systems to illustrate how bacteria employ cell-to-cell signalling to adjust their physiology in accordance with the prevailing high-population-density environment.
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Affiliation(s)
- S Swift
- Institute of Infections and Immunity, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2RD UK
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35
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Whitehead NA, Barnard AM, Slater H, Simpson NJ, Salmond GP. Quorum-sensing in Gram-negative bacteria. FEMS Microbiol Rev 2001; 25:365-404. [PMID: 11524130 DOI: 10.1111/j.1574-6976.2001.tb00583.x] [Citation(s) in RCA: 919] [Impact Index Per Article: 40.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
It has become increasingly and widely recognised that bacteria do not exist as solitary cells, but are colonial organisms that exploit elaborate systems of intercellular communication to facilitate their adaptation to changing environmental conditions. The languages by which bacteria communicate take the form of chemical signals, excreted from the cells, which can elicit profound physiological changes. Many types of signalling molecules, which regulate diverse phenotypes across distant genera, have been described. The most common signalling molecules found in Gram-negative bacteria are N-acyl derivatives of homoserine lactone (acyl HSLs). Modulation of the physiological processes controlled by acyl HSLs (and, indeed, many of the non-acyl HSL-mediated systems) occurs in a cell density- and growth phase-dependent manner. Therefore, the term 'quorum-sensing' has been coined to describe this ability of bacteria to monitor cell density before expressing a phenotype. In this paper, we review the current state of research concerning acyl HSL-mediated quorum-sensing. We also describe two non-acyl HSL-based systems utilised by the phytopathogens Ralstonia solanacearum and Xanthomonas campestris.
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Affiliation(s)
- N A Whitehead
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Building O, Downing Site, CB2 1QW, Cambridge, UK
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36
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Chin-A-Woeng TF, van den Broek D, de Voer G, van der Drift KM, Tuinman S, Thomas-Oates JE, Lugtenberg BJ, Bloemberg GV. Phenazine-1-carboxamide production in the biocontrol strain Pseudomonas chlororaphis PCL1391 is regulated by multiple factors secreted into the growth medium. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2001; 14:969-979. [PMID: 11497469 DOI: 10.1094/mpmi.2001.14.8.969] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Pseudomonas chlororaphis PCL1391 controls tomato foot and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici. The production of phenazine-1-carboxamide (PCN) is crucial for this biocontrol activity. In vitro production of PCN is observed only at high-population densities, suggesting that production is under the regulation of quorum sensing. The main autoinducer molecule produced by PCL1391 was identified structurally as N-hexanoyl-L-homoserine lactone (C6-HSL). The two other autoinducers that were produced comigrate with N-butanoyl-L-homoserine lactone (C4-HSL) and N-octanoyl-L-homoserine lactone (C8-HSL). Two PCL1391 mutants lacking production of PCN were defective in the genes phzI and phzR, respectively, the nucleotide sequences of which were determined completely. Production of PCN by the phzI mutant could be complemented by the addition of exogenous synthetic C6-HSL, but not by C4-HSL, C8-HSL, or any other HSL tested. Expression analyses of Tn5luxAB reporter strains of phzI, phzR, and the phz biosynthetic operon clearly showed that phzI expression and PCN production is regulated by C6-HSL in a population density-dependent manner. The introduction of multiple copies of the regulatory genes phzI and phzR on various plasmids resulted in an increase of the production of HSLs, expression of the PCN biosynthetic operon, and consequently, PCN production, up to a sixfold increase in a copy-dependent manner. Surprisingly, our expression studies show that an additional, yet unidentified factor(s), which are neither PCN nor C4-HSL or C8-HSL, secreted into the growth medium of the overnight cultures, is involved in the positive regulation of phzI, and is able to induce PCN biosynthesis at low cell densities in a growing culture, resulting in an increase of PCN production.
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Affiliation(s)
- T F Chin-A-Woeng
- Leiden University, Institute of Molecular Plant Sciences, The Netherlands.
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37
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Abstract
The view of bacteria as unicellular organisms has strong roots in the tradition of culturing bacteria in liquid media. However, in nature microbial activity is mainly associated with surfaces where bacteria form highly structured and cooperative consortia which are commonly referred to as biofilms. The ability of bacteria to organize structurally and to distribute metabolic activities between the different members of the consortium demands a high degree of coordinated cell-cell interaction. Recent work has established that many bacteria employ sophisticated intercellular communication systems that rely on small signal molecules to control the expression of multiple target genes. In Gram-negative bacteria, the most intensively investigated signal molecules are N-acyl-L-homoserine lactones (AHLs), which are utilized by the bacteria to monitor their own population densities in a process known as 'quorum sensing'. These density-dependent regulatory systems rely on two proteins, an AHL synthase, usually a member of the LuxI family of proteins, and an AHL receptor protein belonging to the LuxR family of transcriptional regulators. At low population densities cells produce a basal level of AHL via the activity of an AHL synthase. As the cell density increases, AHL accumulates in the growth medium. On reaching a critical threshold concentration, the AHL molecule binds to its cognate receptor which in turn leads to the induction/repression of AHL-regulated genes. To date, AHL-dependent quorum sensing circuits have been identified in a wide range of gram-negative bacteria where they regulate various functions including bioluminescence, plasmid conjugal transfer, biofilm formation, motility, antibiotic biosynthesis, and the production of virulence factors in plant and animal pathogens. Moreover, AHL signal molecules appear to play important roles in the ecology of complex consortia as they allow bacterial populations to interact with each other as well as with their eukaryotic hosts.
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Affiliation(s)
- L Eberl
- Lehrstuhl für Mikrobiologie, Technische Universität München, Freising, Germany.
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38
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Hanzelka BL, Parsek MR, Val DL, Dunlap PV, Cronan JE, Greenberg EP. Acylhomoserine lactone synthase activity of the Vibrio fischeri AinS protein. J Bacteriol 1999; 181:5766-70. [PMID: 10482519 PMCID: PMC94098 DOI: 10.1128/jb.181.18.5766-5770.1999] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Acylhomoserine lactones, which serve as quorum-sensing signals in gram-negative bacteria, are produced by members of the LuxI family of synthases. LuxI is a Vibrio fischeri enzyme that catalyzes the synthesis of N-(3-oxohexanoyl)-L-homoserine lactone from an acyl-acyl carrier protein and S-adenosylmethionine. Another V. fischeri gene, ainS, directs the synthesis of N-octanoylhomoserine lactone. The AinS protein shows no significant sequence similarity with LuxI family members, but it does show sequence similarity with the Vibrio harveyi LuxM protein. The luxM gene is required for the synthesis of N-(3-hydroxybutyryl)-L-homoserine lactone. To gain insights about whether AinS and LuxM represent a second family of acylhomoserine lactone synthases, we have purified AinS as a maltose-binding protein (MBP) fusion protein. The purified MBP-AinS fusion protein catalyzed the synthesis of N-octanoylhomoserine lactone from S-adenosylmethionine and either octanoyl-acyl carrier protein or, to a lesser extent, octanoyl coenzyme A. With the exception that octanoyl coenzyme A served as an acyl substrate for the MBP-AinS fusion protein, the substrates for and reaction kinetics of the MBP-AinS fusion protein were similar to those of the several LuxI family members previously studied. We conclude that AinS is an acylhomoserine lactone synthase and that it represents a second family of such enzymes.
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Affiliation(s)
- B L Hanzelka
- Department of Microbiology, University of Iowa, Iowa City, Iowa 52242, USA
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Rodelas B, Lithgow JK, Wisniewski-Dye F, Hardman A, Wilkinson A, Economou A, Williams P, Downie JA. Analysis of quorum-sensing-dependent control of rhizosphere-expressed (rhi) genes in Rhizobium leguminosarum bv. viciae. J Bacteriol 1999; 181:3816-23. [PMID: 10368158 PMCID: PMC93861 DOI: 10.1128/jb.181.12.3816-3823.1999] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The rhi genes of Rhizobium leguminosarum biovar viciae are expressed in the rhizosphere and play a role in the interaction with legumes, such as the pea. Previously (K. M. Gray, J. P. Pearson, J. A. Downie, B. E. A. Boboye, and E. P. Greenberg, J. Bacteriol. 178:372-376, 1996) the rhiABC operon had been shown to be regulated by RhiR and to be induced by added N-(3-hydroxy-7-cis-tetradecenoyl)-L-homoserine lactone (3OH, C14:1-HSL). Mutagenesis of a cosmid carrying the rhiABC and rhiR gene region identified a gene (rhiI) that affects the level of rhiA expression. Mutation of rhiI slightly increased the number of nodules formed on the pea. The rhiI gene is (like rhiA) regulated by rhiR in a cell density-dependent manner. RhiI is similar to LuxI and other proteins involved in the synthesis of N-acyl-homoserine lactones (AHLs). Chemical analyses of spent culture supernatants demonstrated that RhiI produces N-(hexanoyl)-L-homoserine lactone (C6-HSL) and N-(octanoyl)-L-homoserine lactone (C8-HSL). Both of these AHLs induced rhiA-lacZ and rhiI-lacZ expression on plasmids introduced into an Agrobacterium strain that produces no AHLs, showing that rhiI is positively regulated by autoinduction. However, in this system no induction of rhiA or rhiI with 3OH,C14:1-HSL was observed. Analysis of the spent culture supernatant of the wild-type R. leguminosarum bv. viciae revealed that at least seven different AHLs are made. Mutation of rhiI decreased the amounts of C6-HSL and C8-HSL but did not block their formation, and in this background the rhiI mutation did not significantly affect the expression levels of the rhiI gene or rhiABC genes or the accumulation of RhiA protein. These observations suggest that there are additional loci involved in AHL production in R. leguminosarum bv. viciae and that they affect rhiI and rhiABC expression. We postulate that the previously observed induction of rhiA by 3OH,C14:1-HSL may be due to an indirect effect caused by induction of other AHL production loci.
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Affiliation(s)
- B Rodelas
- John Innes Centre, Colney, Norwich NR4 7UH, United Kingdom
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Parsek MR, Val DL, Hanzelka BL, Cronan JE, Greenberg EP. Acyl homoserine-lactone quorum-sensing signal generation. Proc Natl Acad Sci U S A 1999; 96:4360-5. [PMID: 10200267 PMCID: PMC16337 DOI: 10.1073/pnas.96.8.4360] [Citation(s) in RCA: 338] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Acyl homoserine lactones (acyl-HSLs) are important intercellular signaling molecules used by many bacteria to monitor their population density in quorum-sensing control of gene expression. These signals are synthesized by members of the LuxI family of proteins. To understand the mechanism of acyl-HSL synthesis we have purified the Pseudomonas aeruginosa RhlI protein and analyzed the kinetics of acyl-HSL synthesis by this enzyme. Purified RhlI catalyzes the synthesis of acyl-HSLs from acyl-acyl carrier proteins and S-adenosylmethionine. An analysis of the patterns of product inhibition indicated that RhlI catalyzes signal synthesis by a sequential, ordered reaction mechanism in which S-adenosylmethionine binds to RhlI as the initial step in the enzymatic mechanism. Because pathogenic bacteria such as P. aeruginosa use acyl-HSL signals to regulate virulence genes, an understanding of the mechanism of signal synthesis and identification of inhibitors of signal synthesis has implications for development of quorum sensing-targeted antivirulence molecules.
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Affiliation(s)
- M R Parsek
- Department of Microbiology, University of Iowa, Iowa City, IA 52242, USA
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Fuqua C, Greenberg EP. Self perception in bacteria: quorum sensing with acylated homoserine lactones. Curr Opin Microbiol 1998; 1:183-9. [PMID: 10066485 DOI: 10.1016/s1369-5274(98)80009-x] [Citation(s) in RCA: 229] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A variety of Gram-negative bacteria produce membrane permeant, acylated homoserine lactone (HL) pheromones that act as cell density cues. Synthesis and response to these factors requires proteins homologous to the Luxl acylhomoserine lactone synthase and the LuxR transcription factor from Vibrio fischeri. Recent genetic and biochemical studies have begun to provide a mechanistic understanding of acyl HL dependent gene regulation. Examination of the role of acyl HLs in diverse bacteria positions LuxR-Luxl type systems within an increasingly broad regulatory context and suggests that, in some bacteria, they comprise a global regulatory circuit.
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Affiliation(s)
- C Fuqua
- Department of Biology, Trinity University, San Antonio, TX 78212, USA.
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Jiang Y, Camara M, Chhabra SR, Hardie KR, Bycroft BW, Lazdunski A, Salmond GP, Stewart GS, Williams P. In vitro biosynthesis of the Pseudomonas aeruginosa quorum-sensing signal molecule N-butanoyl-L-homoserine lactone. Mol Microbiol 1998; 28:193-203. [PMID: 9593307 DOI: 10.1046/j.1365-2958.1998.00789.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In Pseudomonas aeruginosa, synthesis of the quorum-sensing signal molecules N-butanoyl-L-homoserine lactone (BHL) and N-hexanoyl-L-homoserine lactone (HHL) requires the Luxl homologue Rhll(Vsml). By using thin-layer chromatography in conjunction with high-performance liquid chromatography (HPLC) and mass spectrometry, we show that purified Rhll can catalyse the biosynthesis of BHL and HHL using either S-adenosylmethionine (SAM) or homoserine lactone (HSL) but not homoserine as the source of the homoserine lactone moiety. As we were unable to detect homoserine lactone in cytoplasmic extracts of Escherichia coli, we conclude that SAM is the natural substrate for Rhll-directed N-acylhomoserine lactone (AHL) biosynthesis. The N-acyl chain of BHL and HHL can be supplied by the appropriately charged coenzyme A derivative (either n-butanoyl-CoA or n-hexanoyl-CoA). The specificity of Rhll for charged CoA derivatives is demonstrated as Rhll was unable to generate AHLs detectable in our bioassays from acetyl-CoA, malonyl-CoA, n-octanoyl-CoA, n-decanoyl-CoA, DL-beta-hydroxybutanoyl-CoA or crotonoyl-CoA. Rhll was also unable to use N-acetyl-S-3-oxobutanoylcysteamine, a chemical mimic for 3-oxobutanoyl-CoA. Furthermore, the Rhll-catalysed synthesis of BHL and HHL was most efficiently driven when NADPH was included in the reaction mixture.
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Affiliation(s)
- Y Jiang
- Department of Pharmaceutical Sciences, University of Nottingham, UK
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Rosemeyer V, Michiels J, Verreth C, Vanderleyden J. luxI- and luxR-homologous genes of Rhizobium etli CNPAF512 contribute to synthesis of autoinducer molecules and nodulation of Phaseolus vulgaris. J Bacteriol 1998; 180:815-21. [PMID: 9473034 PMCID: PMC106959 DOI: 10.1128/jb.180.4.815-821.1998] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Autoinduction plays an important role in intercellular communication among symbiotic and pathogenic gram-negative bacteria. We report here that a nitrogen-fixing symbiont of Phaseolus vulgaris, Rhizobium etli CNPAF512, produces at least seven different autoinducer molecules. One of them exhibits a growth-inhibitory effect like that of the bacteriocin small [N-(3R-hydroxy-7-cis-tetradecanoyl)-L-homoserine lactone]. At least two of the other autoinducers are synthesized by a LuxI-homologous autoinducer synthase. The corresponding luxI homologous gene (raiI) and a luxR homolog (raiR) have been identified and characterized. Enhanced expression of raiI is dependent on cell density and on the presence of one or more autoinducer molecules synthesized by R. etli CNPAF512. A raiI mutant was shown to release only three different autoinducer molecules; a raiR mutant releases four different autoinducer molecules. Examination of different mutants for nodulation of beans showed that raiI is involved in the restriction of nodule number, whereas nitrogen-fixing activity in terms of acetylene reduction per nodule was not affected.
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Affiliation(s)
- V Rosemeyer
- F. A. Janssens Laboratory of Genetics, Heverlee, Belgium
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Abstract
Pseudomonas aeruginosa is a bacterium responsible for severe nosocomial infections, life-threatening infections in immunocompromised persons, and chronic infections in cystic fibrosis patients. The bacterium's virulence depends on a large number of cell-associated and extracellular factors. Cell-to-cell signaling systems control the expression and allow a coordinated, cell-density-dependent production of many extracellular virulence factors. We discuss the possible role of cell-to-cell signaling in the pathogenesis of P. aeruginosa infections and present a rationale for targeting cell-to-cell signaling systems in the development of new therapeutic approaches.
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Affiliation(s)
- C Van Delden
- University of Rochester, School of Medicine and Dentistry, New York, USA
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Pierson LS, Wood DW, Pierson EA. Homoserine lactone-mediated gene regulation in plant-associated bacteria. ANNUAL REVIEW OF PHYTOPATHOLOGY 1998; 36:207-225. [PMID: 15012498 DOI: 10.1146/annurev.phyto.36.1.207] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Many plant-associated bacteria produce and utilize diffusible N-acyl-homoserine lactones (AHLs) to regulate the expression of specific bacterial genes and operons. AHL-mediated regulation utilizes two genes that encode proteins similar to the LuxI/LuxR system originally studied in the marine symbiont Vibrio fischeri. The LuxI-type proteins are AHL synthases that assemble the diffusible AHL signal. The LuxR-type proteins are AHL-responsive transcriptional regulatory proteins. LuxR proteins control the transcription of specific bacterial genes in response to the levels of AHL signal. To date, AHL-mediated gene regulation has been identified in a broad range of gram-negative bacteria, most of which are host-associated. However, it seems unlikely that such a widely conserved regulatory mechanism would be limited only to host-microbe interactions. These signals probably play central roles in ecological interactions among organisms in microbial communities by affecting communication among bacterial populations as well as between bacterial populations and their eukaryotic hosts.
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Affiliation(s)
- L S Pierson
- Department of Plant Pathology, University of Arizona, Tucson, Arizona 85721, USA.
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Puskas A, Greenberg EP, Kaplan S, Schaefer AL. A quorum-sensing system in the free-living photosynthetic bacterium Rhodobacter sphaeroides. J Bacteriol 1997; 179:7530-7. [PMID: 9393720 PMCID: PMC179706 DOI: 10.1128/jb.179.23.7530-7537.1997] [Citation(s) in RCA: 170] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Rhodobacter sphaeroides is a free-living, photoheterotrophic bacterium known for its genomic and metabolic complexity. We have discovered that this purple photosynthetic organism possesses a quorum-sensing system. Quorum sensing occurs in a number of eukaryotic host-associated gram-negative bacteria. In these bacteria there are two genes required for quorum sensing, the luxR and luxI homologs, and there is an acylhomoserine lactone signal molecule synthesized by the product of the luxI homolog. In R. sphaeroides, synthesis of a novel homoserine lactone signal, 7,8-cis-N-(tetradecenoyl)homoserine lactone, is directed by a luxI homolog termed cerI. Two open reading frames immediately upstream of cerI are proposed to be components of the quorum-sensing system. The first of these is a luxR homolog termed cerR, and the second is a small open reading frame of 159 bp. Inactivation of cerI in R. sphaeroides results in mucoid colony formation on agar and formation of large aggregates of cells in liquid cultures. Clumping of CerI mutants in liquid culture is reversible upon addition of the acylhomoserine lactone signal and represents a phenotype unlike those controlled by quorum sensing in other bacteria.
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Affiliation(s)
- A Puskas
- Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, Houston 77224, USA
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