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Smits THM, Jaenicke S, Rezzonico F, Kamber T, Goesmann A, Frey JE, Duffy B. Complete genome sequence of the fire blight pathogen Erwinia pyrifoliae DSM 12163T and comparative genomic insights into plant pathogenicity. BMC Genomics 2010; 11:2. [PMID: 20047678 PMCID: PMC2827408 DOI: 10.1186/1471-2164-11-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Accepted: 01/04/2010] [Indexed: 11/10/2022] Open
Abstract
Background Erwinia pyrifoliae is a newly described necrotrophic pathogen, which causes fire blight on Asian (Nashi) pear and is geographically restricted to Eastern Asia. Relatively little is known about its genetics compared to the closely related main fire blight pathogen E. amylovora. Results The genome of the type strain of E. pyrifoliae strain DSM 12163T, was sequenced using both 454 and Solexa pyrosequencing and annotated. The genome contains a circular chromosome of 4.026 Mb and four small plasmids. Based on their respective role in virulence in E. amylovora or related organisms, we identified several putative virulence factors, including type III and type VI secretion systems and their effectors, flagellar genes, sorbitol metabolism, iron uptake determinants, and quorum-sensing components. A deletion in the rpoS gene covering the most conserved region of the protein was identified which may contribute to the difference in virulence/host-range compared to E. amylovora. Comparative genomics with the pome fruit epiphyte Erwinia tasmaniensis Et1/99 showed that both species are overall highly similar, although specific differences were identified, for example the presence of some phage gene-containing regions and a high number of putative genomic islands containing transposases in the E. pyrifoliae DSM 12163T genome. Conclusions The E. pyrifoliae genome is an important addition to the published genome of E. tasmaniensis and the unfinished genome of E. amylovora providing a foundation for re-sequencing additional strains that may shed light on the evolution of the host-range and virulence/pathogenicity of this important group of plant-associated bacteria.
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Affiliation(s)
- Theo H M Smits
- Swiss National Competence Center for Fire Blight, Division of Plant Protection, Agroscope Changins-Wädenswil ACW, Wädenswil, Switzerland
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152
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Sperandio V. SdiA sensing of acyl-homoserine lactones by enterohemorrhagic E. coli (EHEC) serotype O157:H7 in the bovine rumen. Gut Microbes 2010; 1:432-5. [PMID: 21468228 PMCID: PMC3056111 DOI: 10.4161/gmic.1.6.14177] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2010] [Revised: 10/19/2010] [Accepted: 11/10/2010] [Indexed: 02/03/2023] Open
Abstract
Chemical communication mediates signaling between cells. Bacteria also engage in chemical signaling, termed quorum sensing (QS), to coordinate population-wide behavior. The bacterial pathogen enterohemorrhagic E. coli (EHEC), responsible for outbreaks of bloody diarrhea worldwide, exploits QS to promote expression of virulence factors in humans. Although EHEC is a human pathogen, it is a member of the gastrointestinal (GI) flora in cattle, the main reservoir for this bacterium. EHEC cattle colonization requires SdiA, a QS transcription factor that uses acyl-homoserine lactones (AHLs), for proper folding and function. EHEC harbors SdiA, but does not produce AHLs, consequently having to sense AHLs produced by other bacterial species. We recently showed that SdiA is necessary for efficient EHEC passage through the bovine GI tract, and show that AHLs are prominent within cattle rumen, but absent from the other sections of the GI tract. EHEC utilizes the locus of enterocyte effacement (LEE) to colonize the recto-anal junction of cattle, and the glutamate decarboxylase (gad) system to colonize cows. Transcription of the LEE genes is decreased by rumen AHLs through SdiA, while transcription of the gad acid resistant system is increased. It would be expensive for EHEC to express the LEE genes in the rumen where they are not necessary. However, in preparation for the acidic distal stomachs the EHEC gad is activated in the rumen. Hence AHL signaling through SdiA aids EHEC in gauging these environments, and modulates gene expression towards adaptation to a commensal life-style in cattle.1 Inasmuch as EHEC is largely prevalent in cattle herds, interference with SdiA-mediated QS inhibition of cattle colonization could be an attractive approach to diminish contamination of food products due to cattle shedding of this pathogen.
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153
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Atkinson S, Williams P. Quorum sensing and social networking in the microbial world. J R Soc Interface 2009; 6:959-78. [PMID: 19674996 PMCID: PMC2827448 DOI: 10.1098/rsif.2009.0203] [Citation(s) in RCA: 247] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Accepted: 07/10/2009] [Indexed: 12/15/2022] Open
Abstract
For many years, bacterial cells were considered primarily as selfish individuals, but, in recent years, it has become evident that, far from operating in isolation, they coordinate collective behaviour in response to environmental challenges using sophisticated intercellular communication networks. Cell-to-cell communication between bacteria is mediated by small diffusible signal molecules that trigger changes in gene expression in response to fluctuations in population density. This process, generally referred to as quorum sensing (QS), controls diverse phenotypes in numerous Gram-positive and Gram-negative bacteria. Recent advances have revealed that bacteria are not limited to communication within their own species but are capable of 'listening in' and 'broadcasting to' unrelated species to intercept messages and coerce cohabitants into behavioural modifications, either for the good of the population or for the benefit of one species over another. It is also evident that QS is not limited to the bacterial kingdom. The study of two-way intercellular signalling networks between bacteria and both uni- and multicellular eukaryotes as well as between eukaryotes is just beginning to unveil a rich diversity of communication pathways.
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Affiliation(s)
- Steve Atkinson
- Centre for Biomolecular Sciences, School of Molecular Medical Sciences, University of Nottingham, Nottingham NG7 2RD, UK.
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154
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Acyl-homoserine lactones can induce virus production in lysogenic bacteria: an alternative paradigm for prophage induction. Appl Environ Microbiol 2009; 75:7142-52. [PMID: 19783745 DOI: 10.1128/aem.00950-09] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Prophage typically are induced to a lytic cycle under stressful environmental conditions or when the host's survival is threatened. However, stress-independent, spontaneous induction also occurs in nature and may be cell density dependent, but the in vivo signal(s) that can trigger induction is unknown. In the present study, we report that acyl-homoserine lactones (AHL), the essential signaling molecules of quorum sensing in many gram-negative bacteria, can trigger phage production in soil and groundwater bacteria. This phenomenon also was operative in a lambda lysogen of Escherichia coli. In model coculture systems, we monitored the real-time AHL production from Pseudomonas aeruginosa PAO1 using an AHL bioluminescent sensor and demonstrated that lambda-prophage induction in E. coli was correlated with AHL production. As a working model in E. coli, we show that the induction responses of lambda with AHL remained unaffected when recA was deleted, suggesting that this mechanism does not involve an SOS response. In the same lambda lysogen we also demonstrated that sdiA, the AHL receptor, and rcsA, a positive transcriptional regulator of exopolysaccharide synthesis, are involved in the AHL-mediated induction process. These findings relate viral reproduction to chemical signals associated with high host cell abundance, suggesting an alternative paradigm for prophage induction.
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155
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Cell-to-Cell Signaling in Escherichia coli and Salmonella. EcoSal Plus 2009; 3. [PMID: 26443762 DOI: 10.1128/ecosalplus.5.5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Bacteria must be able to respond rapidly to changes in the environment in order to survive. One means of coordinating gene expression relies on tightly regulated and complex signaling systems. One of the first signaling systems that was described in detail is quorum sensing (QS). During QS, a bacterial cell produces and secretes a signaling molecule called an autoinducer (AI). As the density of the bacterial population increases, so does the concentration of secreted AI molecules, thereby allowing a bacterial species to coordinate gene expression based on population density. Subsequent studies have demonstrated that bacteria are also able to detect signal molecules produced by other species of bacteria as well as hormones produced by their mammalian hosts. These types of signaling interactions have been termed cell-to-cell signaling because the interaction does not rely on a threshold concentration of bacterial cells. This review discusses the three main types of cell-to-cell signaling mechanisms used by E. coli and Salmonella, including the LuxR process, in which E. coli and Salmonella detect signals produced by other species of bacteria; the LuxS/AI-2 system, in which E. coli and Salmonella participate in intra- and interspecies signaling; and the AI-3/ epinephrine/norepinephrine system, in which E. coli and Salmonella recognize self-produced AI, signal produced by other microbes, and/or the human stress hormones epinephrine or norepinephrine.
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156
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Abstract
Bacteria have been long considered primitive organisms, with a lifestyle focused on the survival and propagation of single cells. However, in the past few decades it became obvious that bacteria can display sophisticated group behaviors. For instance, bacteria can communicate amongst themselves and with their hosts, by producing, sensing, and responding to chemical signals. By doing so, they can sense their surroundings and adapt as to increase their chances of survival and propagation. Here, we review the discovery of bacterial intercellular communication, some of the signaling molecules identified to date, the role of intercellular signaling in symbiotic and pathogenic relationships between bacteria and their hosts and its implications for the development of new therapeutic strategies against human disease.
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Affiliation(s)
- L Caetano M Antunes
- Michael Smith Laboratories, University of British Columbia, Vancouver, BC, Canada.
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157
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158
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Subramoni S, Venturi V. LuxR-family 'solos': bachelor sensors/regulators of signalling molecules. MICROBIOLOGY-SGM 2009; 155:1377-1385. [PMID: 19383698 DOI: 10.1099/mic.0.026849-0] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
N-Acylhomoserine lactone (AHL) quorum-sensing (QS) signalling is the best-understood chemical language in proteobacteria. In the last 15 years a large amount of research in several bacterial species has revealed in detail the genetic, molecular and biochemical mechanisms underlying AHL signalling. These studies have revealed the role played by protein pairs of the AHL synthase belonging to the LuxI family and cognate LuxR-family AHL sensor-regulator. Proteobacteria however commonly possess a QS LuxR-family protein for which there is no obvious cognate LuxI synthase; these proteins are found in bacteria which possess a complete AHL QS system(s) as well as in bacteria that do not. Scientists are beginning to address the roles played by these proteins and it is emerging that they could allow bacteria to respond to endogenous and exogenous signals produced by their neighbours. AHL QS research thus far has mainly focused on a cell-density response involving laboratory monoculture studies. Recent findings on the role played by the unpaired LuxR-family proteins highlight the need to address bacterial behaviour and response to signals in mixed communities. Here we review recent progress with respect to these LuxR proteins, which we propose to call LuxR 'solos' since they act on their own without the need for a cognate signal generator. Initial investigations have revealed that LuxR solos have diverse roles in bacterial interspecies and interkingdom communication.
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Affiliation(s)
- Sujatha Subramoni
- International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
| | - Vittorio Venturi
- International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
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159
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Abstract
Bacteria can modulate their behavior by releasing and responding to the accumulation of signal molecules. This population co-ordination, referred to as quorum sensing, is prevalent in Gram-negative and Gram-positive bacteria. The essential constituents of quorum-sensing systems include a signal producer, or synthase, and a cognate transcriptional regulator that responds to the accumulated signal molecules. With the availability of bacterial genome sequences and an increased elucidation of quorum-sensing circuits, genes that code for additional transcriptional regulators, usually in excess of the synthase, have been identified. These additional regulators are referred to as 'orphan' regulators, because they are not directly associated with a synthase. Here, we review orphan regulators characterized in various Gram-negative bacteria and their role in expanding the bacterial regulatory network.
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Affiliation(s)
- Arati V Patankar
- Department of Molecular Biology and Immunology, Center at Fort Worth, University of North Texas Health Science, Fort Worth, TX 75080, USA
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160
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Venturi V, Subramoni S. Future research trends in the major chemical language of bacteria. HFSP JOURNAL 2009; 3:105-16. [PMID: 19794815 DOI: 10.2976/1.3065673] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Accepted: 12/16/2008] [Indexed: 01/22/2023]
Abstract
Microbiology was revolutionized in the 1990's by the discovery that many different bacterial species coordinate their behavior when they form a group. In fact, bacteria are now considered multicellular organisms capable of communicating and changing behavior in relation to their cell-density; since 1994 this has been called quorum sensing. This group behavior ensures survival and propagation of the community in many natural environments. Bacterial intercellular communication is mediated by different chemical signals that are synthesized by bacteria which are then either secreted or diffused in the external environment. Bacteria are then able to detect the type and concentration of the signal resulting in regulation of gene expression and, consequently, a synchronized response by the community. The predominant signalling molecules produced by Gram-negative bacteria are N-acyl derivatives of homoserine lactone (AHLs) which have been shown to be produced by over seventy bacterial species. In this essay we discuss the importance of quorum sensing via AHLs and highlight current and future trends in this important field of research.
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Affiliation(s)
- Vittorio Venturi
- Bacteriology Group, International Centre for Genetic Engineering and Biotechnology, 34012 Trieste, Italy
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161
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Lee J, Maeda T, Hong SH, Wood TK. Reconfiguring the quorum-sensing regulator SdiA of Escherichia coli to control biofilm formation via indole and N-acylhomoserine lactones. Appl Environ Microbiol 2009; 75:1703-16. [PMID: 19168658 PMCID: PMC2655446 DOI: 10.1128/aem.02081-08] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Accepted: 01/10/2009] [Indexed: 11/20/2022] Open
Abstract
SdiA is a homolog of quorum-sensing regulators that detects N-acylhomoserine lactone (AHL) signals from other bacteria. Escherichia coli uses SdiA to reduce its biofilm formation in the presence of both AHLs and its own signal indole. Here we reconfigured SdiA (240 amino acids) to control biofilm formation using protein engineering. Four SdiA variants were obtained with altered biofilm formation, including truncation variants SdiA1E11 (F7L, F59L, Y70C, M94K, and K153X) and SdiA14C3 (W9R, P49T, N87T, frameshift at N96, and L123X), which reduced biofilm formation by 5- to 20-fold compared to wild-type SdiA in the presence of endogenous indole. Whole-transcriptome profiling revealed that wild-type SdiA reduced biofilm formation by repressing genes related to indole synthesis and curli synthesis compared to when no SdiA was expressed, while variant SdiA1E11 induced genes related to indole synthesis in comparison to wild-type SdiA. These results suggested altered indole metabolism, and corroborating the DNA microarray results in regard to indole synthesis, variant SdiA1E11 produced ninefold more indole, which led to reduced swimming motility and cell density. Also, wild-type SdiA decreased curli production and tnaA transcription, while SdiA1E11 increased tnaA transcription (tnaA encodes tryptophanase, which forms indole) compared to wild-type SdiA. Hence, wild-type SdiA decreased biofilm formation by reducing curli production and motility, and SdiA1E11 reduced biofilm formation via indole. Furthermore, an AHL-sensitive variant (SdiA2D10, having four mutations at E31G, Y42F, R116H, and L165Q) increased biofilm formation sevenfold in the presence of N-octanoyl-DL-homoserine lactone and N-(3-oxododecatanoyl)-L-homoserine lactone. Therefore, SdiA can be evolved to increase or decrease biofilm formation, and biofilm formation may be controlled by altering sensors rather than signals.
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Affiliation(s)
- Jintae Lee
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA
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162
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Abstract
Pathogenic bacteria produce virulence factors only when they sense they are in a location in which the energy required for pathogenesis is warranted. One environmental factor monitored by pathogens is population density, either of its own population or of the population of a host's endogenous flora. To date, four systems have been described which allow pathogens to regulate virulence genes in a population-dependent manner. These systems are found in both Gram-positive and Gram-negative cells and utilize various mechanisms to control gene regulation at a transcriptional level, but they all have one feature in common: they detect autoinducers released by cells belonging to either the pathogen's population or that of the host's flora. This article explores the role of these four signalling systems in bacterial communities and how pathogens use these systems to control genes required during host invasion and infection.
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Affiliation(s)
- Christopher T. Parker
- University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9048, USA
| | - Vanessa Sperandio
- University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9048, USA
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163
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Zhou X, Meng X, Sun B. An EAL domain protein and cyclic AMP contribute to the interaction between the two quorum sensing systems in Escherichia coli. Cell Res 2009; 18:937-48. [PMID: 18560382 DOI: 10.1038/cr.2008.67] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Quorum sensing (QS) is a bacterial cell-cell communication process by which bacteria communicate using extracellular signals called autoinducers. Two QS systems have been identified in Escherichia coli K-12, including an intact QS system 2 that is stimulated by the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex and a partial QS system 1 that consists of SdiA (suppressor of cell division inhibitor) responding to signals generated by other microbial species. The relationship between QS system 1 and system 2 in E. coli, however, remains obscure. Here, we show that an EAL domain protein, encoded by ydiV, and cAMP are involved in the interaction between the two QS systems in E. coli. Expression of sdiA and ydiV is inhibited by glucose. SdiA binds to the ydiV promoter region in a dose-dependent, but nonspecific, manner; extracellular autoinducer 1 from other species stimulates ydiV expression in an sdiA-dependent manner. Furthermore, we discovered that the double sdiA-ydiV mutation, but not the single mutation, causes a 2-fold decrease in intracellular cAMP concentration that leads to the inhibition of QS system 2. These results indicate that signaling pathways that respond to important environmental cues, such as autoinducers and glucose, are linked together for their control in E. coli.
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Affiliation(s)
- Xianxuan Zhou
- Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China
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164
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Boyen F, Eeckhaut V, Van Immerseel F, Pasmans F, Ducatelle R, Haesebrouck F. Quorum sensing in veterinary pathogens: mechanisms, clinical importance and future perspectives. Vet Microbiol 2009; 135:187-95. [PMID: 19185433 DOI: 10.1016/j.vetmic.2008.12.025] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2008] [Revised: 12/23/2008] [Accepted: 12/24/2008] [Indexed: 11/27/2022]
Abstract
Under certain circumstances the individuals of a bacterial population may find advantages in acting together and making "collective decisions". This phenomenon is better known as quorum sensing. When the concentration of signal molecules produced by the surrounding bacteria exceeds a certain threshold, the bacterial population acts as a single organism, collectively expressing virulence genes, biofilm forming genes, etc. Several mechanisms of quorum sensing are discussed, each with its distinct signal molecules and respective receptors. Some of these mechanisms are restricted to sensing intraspecies signalling, but interspecies and even interkingdom signalling have also been described. Several veterinary pathogens such as Staphylococcus aureus, Staphylococcus pseudintermedius, Pseudomonas aeruginosa and Salmonella Typhimurium use quorum sensing as a means to optimize virulence gene expression and host colonization. Therefore, targeting of the QS mechanisms may provide a novel strategy for combating bacterial infections, also in veterinary medicine.
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Affiliation(s)
- F Boyen
- Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
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165
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166
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Abstract
Biofilms transform independent cells into specialized cell communities. Here are presented some insights into biofilm formation ascertained with the best-characterized strain, Escherichia coli. Investigations of biofilm formation and inhibition with this strain using whole-transcriptome profiling coupled to phenotypic assays, in vivo DNA binding studies and isogenic mutants have led to discoveries related to the role of stress, to the role of intra- and interspecies cell signalling, to the impact of the environment on cell signalling, to biofilm inhibition by manipulating cell signalling, to the role of toxin/antitoxin genes in biofilm formation, and to the role of small RNAs on biofilm formation and dispersal. Hence, E. coli is an excellent resource for determining paradigms in biofilm formation and biofilm inhibition.
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Affiliation(s)
- Thomas K Wood
- Artie McFerrin Department of Chemical Engineering, Texas A & M University, College Station, TX 77843-3122, USA.
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167
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Edrington TS, Farrow RL, Sperandio V, Hughes DT, Lawrence TE, Callaway TR, Anderson RC, Nisbet DJ. Acyl-homoserine-lactone autoinducer in the gastrointestinal [corrected] tract of feedlot cattle and correlation to season, E. coli O157:H7 prevalence, and diet. Curr Microbiol 2008; 58:227-32. [PMID: 18982388 DOI: 10.1007/s00284-008-9312-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2008] [Revised: 10/09/2008] [Accepted: 10/10/2008] [Indexed: 01/27/2023]
Abstract
Acyl-homoserine-lactone autoinducer (AHL) produced by nonenterohemorrhagic Escherichia coli species in cattle appears to be required for enterohemorrhagic E. coli (EHEC) colonization of the gastrointestinal tract (GIT). The current research aimed to examine the effect of season, diet, EHEC shedding, and location within the GIT on AHL prevalence in the ruminant. Luminal content samples were collected from the rumen and rectum of feedlot cattle at slaughter in the spring, summer, fall, and winter for culture of E. coli O157:H7 and AHL determination. During the spring collection, samples were additionally collected from the cecum and small intestine, but these samples all were AHL negative and therefore not examined again. To assess the influence of diet on AHL prevalence, 14 lambs were fed either 100% forage or 80% concentrate diets and experimentally inoculated with EHEC. At 8 days after infection, all the lambs were killed, and necropsies were taken, with luminal contents collected from the GIT. The collections from the feedlot cattle had AHL in 100% of the rumen content samples from the spring, summer, and fall, but not in any of the winter samples. No other GIT samples from feedlot cattle were AHL positive, and all the samples from the sheep study were AHL negative. The cattle seemed to show a weak correlation between ruminal AHL and EHEC prevalence. This research found AHL only in the rumen and not in the lower GIT of feedlot cattle. However, it is unclear whether this is because the pH of the lower gut destroys the AHL or because a lack of certain bacteria in the lower gut producing AHL.
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Affiliation(s)
- T S Edrington
- Food and Feed Safety Research Unit, Agricultural Research Service, United States Department of Agriculture, College Station, TX 77845, USA.
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168
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Borlee BR, Geske GD, Robinson CJ, Blackwell HE, Handelsman J. Quorum-sensing signals in the microbial community of the cabbage white butterfly larval midgut. THE ISME JOURNAL 2008; 2:1101-11. [PMID: 18650927 PMCID: PMC3904650 DOI: 10.1038/ismej.2008.70] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The overall goal of this study was to examine the role of quorum-sensing (QS) signals in a multispecies microbial community. Toward this aim, we studied QS signals produced by an indigenous member and an invading pathogen of the microbial community of the cabbage white butterfly (CWB) larval midgut (Pieris rapae). As an initial step, we characterized the QS system in Pantoea CWB304, which was isolated from the larval midgut. A luxI homolog, designated panI, is necessary for the production of N-acyl-L-homoserine lactones (AHLs) by Pantoea CWB304. To determine whether AHL signals are exchanged in the alkaline environment of the midgut, we constructed AHL-sensing bioluminescent reporter strains in Pantoea CWB304 and a panI mutant of this strain. In the gut of the CWB larvae, the reporter in an AHL-deficient Pantoea CWB304 detected AHLs when coinoculated with the wild type. To study the role of AHL signals produced by a community invader, we examined pathogenesis of Pseudomonas aeruginosa PAO1 in CWB larvae. Mortality induced by P. aeruginosa PAO1 was significantly reduced when signaling was interrupted by either a potent chemical inhibitor of QS or mutations in the lasI and rhlI AHL synthases of P. aeruginosa PAO1. These results show that AHLs are exchanged among bacteria in the alkaline gut of CWB larvae and contribute to disease caused by P. aeruginosa PAO1.
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Affiliation(s)
- Bradley R Borlee
- Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI 53706, USA
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169
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Lee J, Attila C, Cirillo SLG, Cirillo JD, Wood TK. Indole and 7-hydroxyindole diminish Pseudomonas aeruginosa virulence. Microb Biotechnol 2008; 2:75-90. [PMID: 21261883 PMCID: PMC3815423 DOI: 10.1111/j.1751-7915.2008.00061.x] [Citation(s) in RCA: 187] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Indole is an extracellular biofilm signal for Escherichia coli, and many bacterial oxygenases readily convert indole to various oxidized compounds including 7‐hydroxyindole (7HI). Here we investigate the impact of indole and 7HI on Pseudomonas aeruginosa PAO1 virulence and quorum sensing (QS)‐regulated phenotypes; this strain does not synthesize these compounds but degrades them rapidly. Indole and 7HI both altered extensively gene expression in a manner opposite that of acylhomoserine lactones; the most repressed genes encode the mexGHI‐opmD multidrug efflux pump and genes involved in the synthesis of QS‐regulated virulence factors including pyocyanin (phz operon), 2‐heptyl‐3‐hydroxy‐4(1H)‐quinolone (PQS) signal (pqs operon), pyochelin (pch operon) and pyoverdine (pvd operon). Corroborating these microarray results, indole and 7HI decreased production of pyocyanin, rhamnolipid, PQS and pyoverdine and enhanced antibiotic resistance. In addition, indole affected the utilization of carbon, nitrogen and phosphorus, and 7HI abolished swarming motility. Furthermore, 7HI reduced pulmonary colonization of P. aeruginosa in guinea pigs and increased clearance in lungs. Hence, indole‐related compounds have potential as a novel antivirulence approach for the recalcitrant pathogen P. aeruginosa.
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Affiliation(s)
- Jintae Lee
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA
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170
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Jayaraman A, Wood TK. Bacterial quorum sensing: signals, circuits, and implications for biofilms and disease. Annu Rev Biomed Eng 2008; 10:145-67. [PMID: 18647113 DOI: 10.1146/annurev.bioeng.10.061807.160536] [Citation(s) in RCA: 200] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Communication between bacteria, belonging to the same species or to different species, is mediated through different chemical signals that are synthesized and secreted by bacteria. These signals can either be cell-density related (autoinducers) or be produced by bacteria at different stages of growth, and they allow bacteria to monitor their environment and alter gene expression to derive a competitive advantage. The properties of these signals and the response elicited by them are important in ensuring bacterial survival and propagation in natural environments (e.g., human oral cavity) where hundreds of bacterial species coexist. First, the interaction between a signal and its receptor is very specific, which underlies intraspecies communication and quorum sensing. Second, when multiple signals are synthesized by the same bacterium, the signaling circuits utilized by the different signals are coordinately regulated with distinct overall circuit architecture so as to maximize the overall response. Third, the recognition of a universal communication signal synthesized by different bacterial species (interspecies communication), as well that of signals produced by eukaryotic cells (interkingdom communication), is also integral to the formation of multispecies biofilm communities that are important in infection and disease. The focus of this review is on the principles underlying signal-mediated bacterial communication, with specific emphasis on the potential for using them in two applications-development of synthetic biology modules and circuits, and the control of biofilm formation and infection.
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Affiliation(s)
- Arul Jayaraman
- Departments of Chemical Engineering and Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA.
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171
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Pumbwe L, Skilbeck CA, Wexler HM. Presence of quorum-sensing systems associated with multidrug resistance and biofilm formation in Bacteroides fragilis. MICROBIAL ECOLOGY 2008; 56:412-9. [PMID: 18188535 DOI: 10.1007/s00248-007-9358-3] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2007] [Revised: 11/20/2007] [Accepted: 12/06/2007] [Indexed: 05/18/2023]
Abstract
Bacteroides fragilis constitutes 1-2% of the natural microbiota of the human digestive tract and is the predominant anaerobic opportunistic pathogen in gastrointestinal infections. Most bacteria use quorum sensing (QS) to monitor cell density in relation to other cells and their environment. In Gram-negative bacteria, the LuxRI system is common. The luxR gene encodes a transcriptional activator inducible by type I acyl-homoserine lactone autoinducers (e.g., N-[3-oxohexanoyl] homoserine lactone and hexanoyl homoserine lactone [C6-HSL]). This study investigated the presence of QS system(s) in B. fragilis. The genome of American-type culture collection strain no. ATCC25285 was searched for QS genes. The strain was grown to late exponential phase in the presence or absence of synthetic C6-HSL and C8-HSL or natural homoserine lactones from cell-free supernatants from spent growth cultures of other bacteria. Growth, susceptibility to antimicrobial agents, efflux pump gene (bmeB) expression, and biofilm formation were measured. Nine luxR and no luxI orthologues were found. C6-HSL and supernatants from Yersinia enterocolitica, Vibrio cholerae, and Pseudomonas aeruginosa caused a significant (1) reduction in cellular density and (2) increases in expression of four putative luxR genes, bmeB3, bmeB6, bmeB7, and bmeB10, resistance to various antibiotics, which was reduced by carbonyl cyanide-m-chlorophenyl hydrazone (CCCP, an uncoupler that dissipates the transmembrane proton gradient, which is also the driving force of resistance nodulation division efflux pumps) and (3) increase in biofilm formation. Susceptibility of ATCC25285 to C6-HSL was also reduced by CCCP. These data suggest that (1) B. fragilis contains putative luxR orthologues, which could respond to exogenous homoserine lactones and modulate biofilm formation, bmeB efflux pump expression, and susceptibility to antibiotics, and (2) BmeB efflux pumps could transport homoserine lactones.
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MESH Headings
- Acyl-Butyrolactones/metabolism
- Bacteroides fragilis/genetics
- Bacteroides fragilis/growth & development
- Bacteroides fragilis/physiology
- Biofilms/growth & development
- Carbonyl Cyanide m-Chlorophenyl Hydrazone/pharmacology
- DNA, Bacterial/chemistry
- DNA, Bacterial/genetics
- Drug Resistance, Multiple, Bacterial/physiology
- Gene Expression Regulation, Bacterial
- Kinetics
- Microbial Sensitivity Tests
- Quorum Sensing/drug effects
- Quorum Sensing/physiology
- RNA, Bacterial/chemistry
- RNA, Bacterial/genetics
- RNA, Ribosomal, 16S/chemistry
- RNA, Ribosomal, 16S/genetics
- Repressor Proteins/genetics
- Repressor Proteins/physiology
- Reverse Transcriptase Polymerase Chain Reaction
- Trans-Activators/genetics
- Trans-Activators/physiology
- Uncoupling Agents/pharmacology
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Affiliation(s)
- Lilian Pumbwe
- Greater Los Angeles Veterans Administration Healthcare Systems, Wadsworth Anaerobe Laboratory, Bldg. 304, Room E3-224, 691/151J, Los Angeles, CA 90073, USA.
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172
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Ryan RP, Dow JM. Diffusible signals and interspecies communication in bacteria. MICROBIOLOGY-SGM 2008; 154:1845-1858. [PMID: 18599814 DOI: 10.1099/mic.0.2008/017871-0] [Citation(s) in RCA: 178] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Many bacteria use cell-cell communication mediated by diffusible signal molecules to monitor their population density or confinement to niches and to modulate their behaviour in response to these aspects of their environment. Work on signalling systems within individual species has formed a platform for studies of interspecies interactions that can occur within polymicrobial communities in nature. In addition to signalling between organisms that synthesize the same or related signal molecules, it is becoming evident that bacteria can sense signal molecules that they do not synthesize, thereby eavesdropping on signalling by other organisms in their immediate environment. Furthermore, molecules such as antibiotics that are considered not to be signals for the producing species can have effects on gene expression in other bacteria that indicate a signalling function. Interspecies signalling can lead to alteration in factors contributing to the virulence or persistence of bacterial pathogens as well as influencing the development of beneficial microbial communities. Here we review our current understanding of interspecies signalling in bacteria and the signals involved, what is known of the underlying signal transduction mechanisms and their influences on bacterial behaviour.
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Affiliation(s)
- Robert P Ryan
- BIOMERIT Research Centre, Department of Microbiology, BioSciences Institute, National University of Ireland, Cork, Ireland
| | - J Maxwell Dow
- BIOMERIT Research Centre, Department of Microbiology, BioSciences Institute, National University of Ireland, Cork, Ireland
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173
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Brominated furanones inhibit biofilm formation by Salmonella enterica serovar Typhimurium. Appl Environ Microbiol 2008; 74:6639-48. [PMID: 18791004 DOI: 10.1128/aem.01262-08] [Citation(s) in RCA: 150] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica serovar Typhimurium is a main cause of bacterial food-borne diseases. As Salmonella can form biofilms in which it is better protected against antimicrobial agents on a wide diversity of surfaces, it is of interest to explore ways to inhibit biofilm formation. Brominated furanones, originally extracted from the marine alga Delisea pulchra, are known to interfere with biofilm formation in several pathogens. In this study, we have synthesized a small focused library of brominated furanones and tested their activity against S. enterica serovar Typhimurium biofilm formation. We show that several furanones inhibit Salmonella biofilm formation at non-growth-inhibiting concentrations. The most interesting compounds are (Z)-4-bromo-5-(bromomethylene)-3-alkyl-2(5H)-furanones with chain lengths of two to six carbon atoms. A microarray study was performed to analyze the gene expression profiles of Salmonella in the presence of (Z)-4-bromo-5-(bromomethylene)-3-ethyl-2(5H)-furanone. The induced genes include genes that are involved in metabolism, stress response, and drug sensitivity. Most of the repressed genes are involved in metabolism, the type III secretion system, and flagellar biosynthesis. Follow-up experiments confirmed that this furanone interferes with the synthesis of flagella by Salmonella. No evidence was found that furanones act on the currently known quorum-sensing systems in Salmonella. Interestingly, pretreatment with furanones rendered Salmonella biofilms more susceptible to antibiotic treatment. Conclusively, this work demonstrates that particular brominated furanones have potential in the prevention of biofilm formation by Salmonella serovar Typhimurium.
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174
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Smith C, Song H, You L. Signal discrimination by differential regulation of protein stability in quorum sensing. J Mol Biol 2008; 382:1290-7. [PMID: 18721812 DOI: 10.1016/j.jmb.2008.08.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 07/30/2008] [Accepted: 08/02/2008] [Indexed: 11/29/2022]
Abstract
Quorum sensing (QS) is a communication mechanism exploited by a large variety of bacteria to coordinate gene expression at the population level. In Gram-negative bacteria, QS occurs via synthesis and detection of small chemical signals, most of which belong to the acyl-homoserine lactone class. In such a system, binding of an acyl-homoserine lactone signal to its cognate transcriptional regulator (R-protein) often induces stabilization and subsequent dimerization of the R-protein, which results in the regulation of downstream gene expression. Existence of diverse QS systems within and among species of bacteria indicates that each bacterium needs to distinguish among a myriad of structurally similar chemical signals. We show, using a mathematical model, that fast degradation of an R-protein monomer can facilitate discrimination of signals that differentially stabilize it. Furthermore, our results suggest an inverse correlation between the stability of an R-protein and the achievable limits of fidelity in signal discrimination. In particular, an unstable R-protein tends to be more specific to its cognate signal, whereas a stable R-protein tends to be more promiscuous. These predictions are consistent with experimental data on well-studied natural and engineered R-proteins and thus have implications for understanding the functional design of QS systems.
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Affiliation(s)
- Cameron Smith
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA
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175
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Smith JN, Dyszel JL, Soares JA, Ellermeier CD, Altier C, Lawhon SD, Adams LG, Konjufca V, Curtiss R, Slauch JM, Ahmer BMM. SdiA, an N-acylhomoserine lactone receptor, becomes active during the transit of Salmonella enterica through the gastrointestinal tract of turtles. PLoS One 2008; 3:e2826. [PMID: 18665275 PMCID: PMC2475663 DOI: 10.1371/journal.pone.0002826] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2008] [Accepted: 07/07/2008] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND LuxR-type transcription factors are typically used by bacteria to determine the population density of their own species by detecting N-acylhomoserine lactones (AHLs). However, while Escherichia and Salmonella encode a LuxR-type AHL receptor, SdiA, they cannot synthesize AHLs. In vitro, it is known that SdiA can detect AHLs produced by other bacterial species. METHODOLOGY/PRINCIPAL FINDINGS In this report, we tested the hypothesis that SdiA detects the AHL-production of other bacterial species within the animal host. SdiA did not detect AHLs during the transit of Salmonella through the gastrointestinal tract of a guinea pig, a rabbit, a cow, 5 mice, 6 pigs, or 12 chickens. However, SdiA was activated during the transit of Salmonella through turtles. All turtles examined were colonized by the AHL-producing species Aeromonas hydrophila. CONCLUSIONS/SIGNIFICANCE We conclude that the normal gastrointestinal microbiota of most animal species do not produce AHLs of the correct type, in an appropriate location, or in sufficient quantities to activate SdiA. However, the results obtained with turtles represent the first demonstration of SdiA activity in animals.
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Affiliation(s)
- Jenee N. Smith
- Department of Microbiology, The Ohio State University, Columbus, Ohio, United States of America
| | - Jessica L. Dyszel
- Department of Microbiology, The Ohio State University, Columbus, Ohio, United States of America
| | - Jitesh A. Soares
- Department of Microbiology, The Ohio State University, Columbus, Ohio, United States of America
| | - Craig D. Ellermeier
- Department of Microbiology and College of Medicine, University of Illinois, Urbana, Illinois, United States of America
| | - Craig Altier
- Department of Population Health and Pathobiology, North Carolina State University, Raleigh, North Carolina, United States of America
| | - Sara D. Lawhon
- Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, Texas, United States of America
| | - L. Garry Adams
- Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, Texas, United States of America
| | - Vjollca Konjufca
- Department of Biology, Washington University, St. Louis, Missouri, United States of America
| | - Roy Curtiss
- Department of Biology, Washington University, St. Louis, Missouri, United States of America
| | - James M. Slauch
- Department of Microbiology and College of Medicine, University of Illinois, Urbana, Illinois, United States of America
| | - Brian M. M. Ahmer
- Department of Microbiology, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail:
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176
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Indole cell signaling occurs primarily at low temperatures in Escherichia coli. ISME JOURNAL 2008; 2:1007-23. [PMID: 18528414 DOI: 10.1038/ismej.2008.54] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We have shown that the quorum-sensing signals acylhomoserine lactones, autoinducer-2 (AI-2) and indole influence the biofilm formation of Escherichia coli. Here, we investigate how the environment, that is, temperature, affects indole and AI-2 signaling in E. coli. We show in biofilms that indole addition leads to more extensive differential gene expression at 30 degrees C (186 genes) than at 37 degrees C (59 genes), that indole reduces biofilm formation (without affecting growth) more significantly at 25 and 30 degrees C than at 37 degrees C and that the effect is associated with the quorum-sensing protein SdiA. The addition of indole at 30 degrees C compared to 37 degrees C most significantly repressed genes involved in uridine monophosphate (UMP) biosynthesis (carAB, pyrLBI, pyrC, pyrD, pyrF and upp) and uracil transport (uraA). These uracil-related genes are also repressed at 30 degrees C by SdiA, which confirms SdiA is involved in indole signaling. Also, compared to 37 degrees C, indole more significantly decreased flagella-related qseB, flhD and fliA promoter activity, enhanced antibiotic resistance and inhibited cell division at 30 degrees C. In contrast to indole and SdiA, the addition of (S)-4,5-dihydroxy-2,3-pentanedione (the AI-2 precursor) leads to more extensive differential gene expression at 37 degrees C (63 genes) than at 30 degrees C (11 genes), and, rather than repressing UMP synthesis genes, AI-2 induces them at 37 degrees C (but not at 30 degrees C). Also, the addition of AI-2 induces the transcription of virulence genes in enterohemorrhagic E. coli O157:H7 at 37 degrees C but not at 30 degrees C. Hence, cell signals cause diverse responses at different temperatures, and indole- and AI-2-based signaling are intertwined.
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177
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Yoon Y, Sofos JN. Autoinducer-2 activity of gram-negative foodborne pathogenic bacteria and its influence on biofilm formation. J Food Sci 2008; 73:M140-7. [PMID: 18387117 DOI: 10.1111/j.1750-3841.2008.00697.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This study evaluated whether autoinducer-2 (AI-2) activity would be associated with biofilm formation by Salmonella and Escherichia coli O157:H7 strains on food contact surfaces. In study I, a Salmonella Typhimurium DT104 strain and an E. coli O157:H7 strain, both AI-2 positive, were individually inoculated into 50 mL of Luria-Bertani (LB) or LB + 0.5% glucose (LBG) broth, without or with stainless steel or polypropylene (Salmonella) coupons. At 0, 14 (Salmonella), 24, 48, and 72 h of storage (25 degrees C), cells in suspension and detached cells from the coupons, obtained by vortexing, were enumerated on tryptic soy agar. In study II, a Salmonella Thompson AI-2-positive strain and an AI-2-negative strain, and an E. coli O157:H7 AI-2-positive strain and an AI-2-negative strain were inoculated into LB broth with stainless steel coupons. Cells were enumerated as in study I. In both studies, AI-2 activity was determined in cell-free supernatants. Cell numbers of S. Typhimurium DT104 on biofilms were higher (P < 0.05) in LB than those in LBG, while the E. coli O157:H7 strain showed no difference (P>or= 0.05) in biofilm cell counts between LB and LBG after storage for 72 h. Both S. Typhimurium DT104 and E. coli O157:H7 strains produced higher (P < 0.05) AI-2 activity in LBG than LB cell suspensions. Cell counts of AI-2-positive and-negative S. Thompson and E. coli O157:H7 strains were not different (P>or= 0.05) within suspensions or coupons (study II). The results indicated that, under the conditions of this study, AI-2 activity of the pathogen strains tested may not have a major influence on biofilm formation on food contact surfaces, which was similar between AI-2-positive and -negative strains.
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Affiliation(s)
- Y Yoon
- Center for Meat Safety and Quality, Department of Animal Sciences, 1171 Campus Delivery, Colorado State University, Fort Collins, CO 80523, USA
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178
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Ryan RP, Fouhy Y, Garcia BF, Watt SA, Niehaus K, Yang L, Tolker-Nielsen T, Dow JM. Interspecies signalling via the Stenotrophomonas maltophilia diffusible signal factor influences biofilm formation and polymyxin tolerance in Pseudomonas aeruginosa. Mol Microbiol 2008; 68:75-86. [DOI: 10.1111/j.1365-2958.2008.06132.x] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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179
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Comparative analysis of the Photorhabdus luminescens and the Yersinia enterocolitica genomes: uncovering candidate genes involved in insect pathogenicity. BMC Genomics 2008; 9:40. [PMID: 18221513 PMCID: PMC2266911 DOI: 10.1186/1471-2164-9-40] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Accepted: 01/25/2008] [Indexed: 11/24/2022] Open
Abstract
Background Photorhabdus luminescens and Yersinia enterocolitica are both enteric bacteria which are associated with insects. P. luminescens lives in symbiosis with soil nematodes and is highly pathogenic towards insects but not to humans. In contrast, Y. enterocolitica is widely found in the environment and mainly known to cause gastroenteritis in men, but has only recently been shown to be also toxic for insects. It is expected that both pathogens share an overlap of genetic determinants that play a role within the insect host. Results A selective genome comparison was applied. Proteins belonging to the class of two-component regulatory systems, quorum sensing, universal stress proteins, and c-di-GMP signalling have been analysed. The interorganismic synopsis of selected regulatory systems uncovered common and distinct signalling mechanisms of both pathogens used for perception of signals within the insect host. Particularly, a new class of LuxR-like regulators was identified, which might be involved in detecting insect-specific molecules. In addition, the genetic overlap unravelled a two-component system that is unique for the genera Photorhabdus and Yersinia and is therefore suggested to play a major role in the pathogen-insect relationship. Our analysis also highlights factors of both pathogens that are expressed at low temperatures as encountered in insects in contrast to higher (body) temperature, providing evidence that temperature is a yet under-investigated environmental signal for bacterial adaptation to various hosts. Common degradative metabolic pathways are described that might be used to explore nutrients within the insect gut or hemolymph, thus enabling the proliferation of P. luminescens and Y. enterocolitica in their invertebrate hosts. A strikingly higher number of genes encoding insecticidal toxins and other virulence factors in P. luminescens compared to Y. enterocolitica correlates with the higher virulence of P. luminescens towards insects, and suggests a putative broader insect host spectrum of this pathogen. Conclusion A set of factors shared by the two pathogens was identified including those that are involved in the host infection process, in persistence within the insect, or in host exploitation. Some of them might have been selected during the association with insects and then adapted to pathogenesis in mammalian hosts.
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181
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Yao Y, Dickerson TJ, Hixon MS, Dyson HJ. NMR detection of adventitious xylose binding to the quorum-sensing protein SdiA of Escherichia coli. Bioorg Med Chem Lett 2007; 17:6202-5. [PMID: 17889538 PMCID: PMC2249169 DOI: 10.1016/j.bmcl.2007.09.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Revised: 09/04/2007] [Accepted: 09/05/2007] [Indexed: 11/22/2022]
Abstract
During the solution structure determination of the Escherichia coli quorum-sensing protein SdiA in the presence of N-octanoyl-l-homoserine lactone (HSL), NMR signals were detected in (13)C-filter-(13)C-filter spectra for the bound HSL molecule. An additional set of coupled signals, independent of those of HSL, were also detected, indicating the presence of another unlabeled molecule, also bound to the labeled SdiA. Analysis of the NMR spectrum of this ligand and of the mass spectrum of the dissociated components indicates that the ligand is most likely xylose. Further analysis of xylose-bound SdiA defines a site close to the C terminus, remote from the HSL binding site. These observations provide an example of the sensitivity of high-resolution NMR experiments and their ability to detect, identify, and map the adventitious binding of a small organic molecule to a protein.
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Affiliation(s)
- Yong Yao
- Departments of Molecular Biology and Chemistry, The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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182
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Haghjoo E, Galán JE. Identification of a transcriptional regulator that controls intracellular gene expression in Salmonella Typhi. Mol Microbiol 2007; 64:1549-61. [PMID: 17555437 DOI: 10.1111/j.1365-2958.2007.05754.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Salmonella enterica serovar Typhi (S. Typhi), the aetiological agent of typhoid fever, is an exclusively human pathogen. Little is known about specific factors that may confer to this bacterium its unique pathogenic features. One of these determinants is CdtB, a homologue of the active subunit of the cytolethal distending toxin, which causes DNA damage leading to cell cycle arrest and distension of intoxicated cells. A unique property of S. Typhi CdtB is that it is only synthesized when this bacterium is within an intracellular compartment. Through a genetic screen, we have identified a transcriptional regulatory protein that controls the intracellular expression of cdtB. This regulator, which we have named IgeR, is a member of the DeoR family of transcriptional regulatory proteins and is highly conserved in all S. enterica serovars. IgeR directly binds the cdtB promoter and represses its expression in the extracellular environment. Microarray analysis identified additional IgeR-regulated genes that are involved in virulence. Constitutive expression of igeR resulted in the reduction of intracellular expression of cdtB by S. Typhi and in significant impairment of the virulence of Salmonella enterica serovar Typhimurium (S. Typhimurium) in mice. We propose that IgeR may co-ordinate gene expression during Salmonella's transition from an extracellular to an intracellular environment.
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Affiliation(s)
- Erik Haghjoo
- Section of Microbial Pathogenesis, Yale University School of Medicine, Boyer Center for Molecular Medicine, New Haven, CT 06536, USA
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183
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Williams P, Winzer K, Chan WC, Cámara M. Look who's talking: communication and quorum sensing in the bacterial world. Philos Trans R Soc Lond B Biol Sci 2007; 362:1119-34. [PMID: 17360280 PMCID: PMC2435577 DOI: 10.1098/rstb.2007.2039] [Citation(s) in RCA: 494] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
For many years bacteria were considered primarily as autonomous unicellular organisms with little capacity for collective behaviour. However, we now appreciate that bacterial cells are in fact, highly communicative. The generic term 'quorum sensing' has been adopted to describe the bacterial cell-to-cell communication mechanisms which co-ordinate gene expression usually, but not always, when the population has reached a high cell density. Quorum sensing depends on the synthesis of small molecules (often referred to as pheromones or autoinducers) that diffuse in and out of bacterial cells. As the bacterial population density increases, so does the synthesis of quorum sensing signal molecules, and consequently, their concentration in the external environment rises. Once a critical threshold concentration has been reached, a target sensor kinase or response regulator is activated (or repressed) so facilitating the expression of quorum sensing-dependent genes. Quorum sensing enables a bacterial population to mount a co-operative response that improves access to nutrients or specific environmental niches, promotes collective defence against other competitor prokaryotes or eukaryotic defence mechanisms and facilitates survival through differentiation into morphological forms better able to combat environmental threats. Quorum sensing also crosses the prokaryotic-eukaryotic boundary since quorum sensing-dependent signalling can be exploited or inactivated by both plants and mammals.
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Affiliation(s)
- Paul Williams
- Institute of Infection, Immunity and Inflammation, Centre for Biomolecular Sciences, School of Molecular Medical Sciences, University of Nottingham, Nottingham NG7 2RD, UK.
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184
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Coulthurst SJ, Clare S, Evans TJ, Foulds IJ, Roberts KJ, Welch M, Dougan G, Salmond GPC. Quorum sensing has an unexpected role in virulence in the model pathogen Citrobacter rodentium. EMBO Rep 2007; 8:698-703. [PMID: 17557113 PMCID: PMC1905894 DOI: 10.1038/sj.embor.7400984] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 03/30/2007] [Accepted: 04/23/2007] [Indexed: 11/09/2022] Open
Abstract
The bacterial mouse pathogen Citrobacter rodentium causes attaching and effacing (AE) lesions in the same manner as pathogenic Escherichia coli, and is an important model for this mode of pathogenesis. Quorum sensing (QS) involves chemical signalling by bacteria to regulate gene expression in response to cell density. E. coli has never been reported to have N-acylhomoserine lactone (AHL) QS, but it does utilize luxS-dependent signalling. We found production of AHL QS signalling molecules by an AE pathogen, C. rodentium. AHL QS is directed by the croIR locus and a croI mutant is affected in its surface attachment, although not in Type III secretion. AHL QS has an important role in virulence in the mouse as, unexpectedly, the QS mutant is hypervirulent; by contrast, we detected no impact of luxS inactivation. Further study of QS in Citrobacter should provide new insights into AE pathogenesis. As the croIR locus might have been horizontally acquired, AHL QS might exist in some strains of pathogenic E. coli.
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Affiliation(s)
- Sarah J Coulthurst
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Simon Clare
- Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, UK
| | - Terry J Evans
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Ian J Foulds
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Kevin J Roberts
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Martin Welch
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Gordon Dougan
- Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, UK
| | - George P C Salmond
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
- Tel: +44 1223 333650; Fax: +44 1223 766108; E-mail:
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185
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Indole is an inter-species biofilm signal mediated by SdiA. BMC Microbiol 2007; 7:42. [PMID: 17511876 PMCID: PMC1899176 DOI: 10.1186/1471-2180-7-42] [Citation(s) in RCA: 331] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2006] [Accepted: 05/18/2007] [Indexed: 01/07/2023] Open
Abstract
Background As a stationary phase signal, indole is secreted in large quantities into rich medium by Escherichia coli and has been shown to control several genes (e.g., astD, tnaB, gabT), multi-drug exporters, and the pathogenicity island of E. coli; however, its impact on biofilm formation has not been well-studied. Results Through a series of global transcriptome analyses, confocal microscopy, isogenic mutants, and dual-species biofilms, we show here that indole is a non-toxic signal that controls E. coli biofilms by repressing motility, inducing the sensor of the quorum sensing signal autoinducer-1 (SdiA), and influencing acid resistance (e.g., hdeABD, gadABCEX). Isogenic mutants showed these associated proteins are directly related to biofilm formation (e.g., the sdiA mutation increased biofilm formation 50-fold), and SdiA-mediated transcription was shown to be influenced by indole. The reduction in motility due to indole addition results in the biofilm architecture changing from scattered towers to flat colonies. Additionally, there are 12-fold more E. coli cells in dual-species biofilms grown in the presence of Pseudomonas cells engineered to express toluene o-monooxygenase (TOM, which converts indole to an insoluble indigoid) than in biofilms with pseudomonads that do not express TOM due to a 22-fold reduction in extracellular indole. Also, indole stimulates biofilm formation in pseudomonads. Further evidence that the indole effects are mediated by SdiA and homoserine lactone quorum sensing is that the addition of N-butyryl-, N-hexanoyl-, and N-octanoyl-L-homoserine lactones repress E. coli biofilm formation in the wild-type strain but not with the sdiA mutant. Conclusion Indole is an interspecies signal that decreases E. coli biofilms through SdiA and increases those of pseudomonads. Indole may be manipulated to control biofilm formation by oxygenases of bacteria that do not synthesize it in a dual-species biofilm. Furthermore, E. coli changes its biofilm in response to signals it cannot synthesize (homoserine lactones), and pseudomonads respond to signals they do not synthesize (indole).
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Lee J, Bansal T, Jayaraman A, Bentley WE, Wood TK. Enterohemorrhagic Escherichia coli biofilms are inhibited by 7-hydroxyindole and stimulated by isatin. Appl Environ Microbiol 2007; 73:4100-9. [PMID: 17483266 PMCID: PMC1932762 DOI: 10.1128/aem.00360-07] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Since indole is present at up to 500 microM in the stationary phase and is an interspecies biofilm signal (J. Lee, A. Jayaraman, and T. K. Wood, BMC Microbiol. 7:42, 2007), we investigated hydroxyindoles as biofilm signals and found them also to be nontoxic interspecies biofilm signals for enterohemorrhagic Escherichia coli O157:H7 (EHEC), E. coli K-12, and Pseudomonas aeruginosa. The genetic basis of EHEC biofilm formation was also explored, and notably, virulence genes in biofilm cells were repressed compared to those in planktonic cells. In Luria-Bertani medium (LB) on polystyrene with quiescent conditions, 7-hydroxyindole decreased EHEC biofilm formation 27-fold and decreased K-12 biofilm formation 8-fold without affecting the growth of planktonic cells. 5-Hydroxyindole also decreased biofilm formation 11-fold for EHEC and 6-fold for K-12. In contrast, isatin (indole-2,3-dione) increased biofilm formation fourfold for EHEC, while it had no effect for K-12. When continuous-flow chambers were used, confocal microscopy revealed that EHEC biofilm formation was reduced 6-fold by indole and 10-fold by 7-hydroxyindole in LB. Whole-transcriptome analysis revealed that isatin represses indole synthesis by repressing tnaABC 7- to 37-fold in EHEC, and extracellular indole levels were found to be 20-fold lower. Furthermore, isatin repressed the AI-2 transporters lsrABCDFGKR, while significantly inducing the flagellar genes flgABCDEFGHIJK and fliAEFGILMNOPQ (which led to a 50% increase in motility). 7-Hydroxyindole induces the biofilm inhibitor/stress regulator ycfR and represses cysADIJPU/fliC (which led to a 50% reduction in motility) and purBCDEFHKLMNRT. Isogenic mutants showed that 7-hydroxyindole inhibits E. coli biofilm through cysteine metabolism. 7-Hydroxyindole (500 microM) also stimulates P. aeruginosa PAO1 biofilm formation twofold; therefore, hydroxyindoles are interspecies bacterial signals, and 7-hydroxyindole is a potent EHEC biofilm inhibitor.
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Affiliation(s)
- Jintae Lee
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA
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187
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Abstract
AIM: TQuorum sensing (QS) is an important mechanism of cell-to-cell communication that involves density-dependent recognition of signaling molecules, resulting in modulation of gene expression. This phenomenon allows bacteria to act as a collective unit, i.e., a multicellular entity performing specific functions. Three major QS systems were used by bacteria. Various QS systems have been described in numerous enteric pathogens, and in many cases, the role of QS in the pathogenesis of the diseases caused by these organisms is not so clear-cut. Inhibition of QS signaling might represent a new target for antimicrobial therapy. The course and condition of disease in enteric pathogens may vary among different individuals due to variable levels of signaling molecules in the intestines of different individuals, which, in some degree, may lead to various levels of QS activity and transcription of QS-regulated genes in their intestines.
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Abstract
PURPOSE OF REVIEW This review presents advances in our understanding of how pathogenic, enteric bacteria use quorum sensing to regulate several traits that allow them to establish and maintain infection in their host, including motility, biofilm formation, and virulence-specific genes. RECENT FINDINGS Quorum sensing in enteric bacteria has been elusive for a long time. Recent data indicate that enteric bacteria use several quorum-sensing mechanisms including the LuxR-I quorum-sensing system, the LuxS/AI-2 system, and the AI-3/epinephrine/norepinephrine system to assess their environment and to recognize the host environment. These systems allow bacteria to communicate across species boundaries, and the AI-3/epinephrine/norepinephrine system is involved in interkingdom signaling. SUMMARY Recent developments in our understanding of the molecular and biochemical mechanisms involved in quorum sensing as well as the chemical signal(s) to which bacteria respond and their corresponding physiological responses will improve our understanding of bacterial pathogenesis and microbial flora-host interactions, and potentially lead to novel strategies for combating infection.
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Affiliation(s)
- Melissa M Kendall
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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189
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Janssens JCA, Metzger K, Daniels R, Ptacek D, Verhoeven T, Habel LW, Vanderleyden J, De Vos DE, De Keersmaecker SCJ. Synthesis of N-acyl homoserine lactone analogues reveals strong activators of SdiA, the Salmonella enterica serovar Typhimurium LuxR homologue. Appl Environ Microbiol 2006; 73:535-44. [PMID: 17085703 PMCID: PMC1796990 DOI: 10.1128/aem.01451-06] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
N-Acyl homoserine lactones (AHLs) are molecules that are synthesized and detected by many gram-negative bacteria to monitor the population density, a phenomenon known as quorum sensing. Salmonella enterica serovar Typhimurium is an exceptional species since it does not synthesize its own AHLs, while it does encode a LuxR homologue, SdiA, which enables this bacterium to detect AHLs that are produced by other species. To obtain more information about the specificity of the ligand binding by SdiA, we synthesized and screened a limited library of AHL analogues. We identified two classes of analogues that are strong activators of SdiA: the N-(3-oxo-acyl)-homocysteine thiolactones (3O-AHTLs) and the N-(3-oxo-acyl)-trans-2-aminocyclohexanols. To our knowledge, this is the first report of compounds (the 3O-AHTLs) that are able to activate a LuxR homologue at concentrations that are lower than the concentrations of the most active AHLs. SdiA responds with greatest sensitivity to AHTLs that have a keto modification at the third carbon atom and an acyl chain that is seven or eight carbon atoms long. The N-(3-oxo-acyl)-trans-2-aminocyclohexanols were found to be less sensitive to deactivation by lactonase and alkaline pH than the 3O-AHTLs and the AHLs are. We also examined the activity of our library with LuxR of Vibrio fischeri and identified three new inhibitors of LuxR. Finally, we performed preliminary binding experiments which suggested that SdiA binds its activators reversibly. These results increase our understanding of the specificity of the SdiA-ligand interaction, which could have uses in the development of anti-quorum-sensing-based antimicrobials.
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Affiliation(s)
- Joost C A Janssens
- Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium
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190
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Barnard AM, Salmond GP. Quorum Sensing: The Complexities of Chemical Communication between Bacteria. ACTA ACUST UNITED AC 2006. [DOI: 10.1159/000089986] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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191
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Giaouris ED, Nychas GJE. The adherence of Salmonella Enteritidis PT4 to stainless steel: the importance of the air-liquid interface and nutrient availability. Food Microbiol 2006; 23:747-52. [PMID: 16943077 DOI: 10.1016/j.fm.2006.02.006] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2005] [Accepted: 02/01/2006] [Indexed: 11/22/2022]
Abstract
Biofilm formation on stainless steel by Salmonella enterica serovar Enteritidis PT4 during growth in three different nutritious conditions was studied. The ability of micro-organisms to generate biofilms on the stainless steel surfaces was studied for a total period of 18 days at 20 degrees C, under three different experimental treatments: (i) growth medium (tryptone soy broth) was not refreshed (no further nutrients were provided) during the incubation period, (ii) growth medium was renewed every 2 days and (iii) growth medium was renewed every 2 days and at the same time the planktonic cells from the old medium were transferred to the new fresh medium. It was found that biofilms developed better and a higher number of adherent cells (ca. 10(7) cfu/cm(2)) were recovered when the organism was grown in periodically renewed nutrient medium than when the growth medium was not refreshed. Regardless of the availability of nutrients, biofilm development was better (range 2-3 logs greater) when coupons were not totally covered by the growth medium and part of the surface was exposed to the air-liquid interface, than when coupons were submerged in the medium. The results suggest that existence of air-liquid interface and adequate nutrient conditions provide the best environment for Salmonella Enteritidis PT4 biofilm formation on stainless steel. The possible role of stationary phase planktonic cells in biofilm development by sessile/attached microbial cells is also discussed.
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Affiliation(s)
- Efstathios D Giaouris
- Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Technology, Agricultural University of Athens, Greece
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192
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Abstract
In the conventional view of prokaryotic existence, bacteria live unicellularly, with responses to external stimuli limited to the detection of chemical and physical signals of environmental origin. This view of bacteriology is now recognized to be overly simplistic, because bacteria communicate with each other through small 'hormone-like' organic compounds referred to as autoinducers. These bacterial cell-to-cell signaling systems were initially described as mechanisms through which bacteria regulate gene expression via cell density and, therefore, they have been collectively termed quorum sensing. The functions controlled by quorum sensing are varied and reflect the needs of a particular species of bacteria to inhabit a given niche. Three major quorum-sensing circuits have been described: one used primarily by Gram-negative bacteria, one used primarily by Gram-positive bacteria, and one that has been proposed to be universal.
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Affiliation(s)
- Nicola C Reading
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9048, USA
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193
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Kim W, Surette MG. Coordinated regulation of two independent cell-cell signaling systems and swarmer differentiation in Salmonella enterica serovar Typhimurium. J Bacteriol 2006; 188:431-40. [PMID: 16385032 PMCID: PMC1347318 DOI: 10.1128/jb.188.2.431-440.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Almost all members of the genus Salmonella differentiate and migrate on semisolid surfaces in a coordinated population behavior known as swarming. Important virulence determinants are coupled to swarmer differentiation in several other pathogenic organisms, collectively suggesting that conditions that trigger swarming in the laboratory may fortuitously promote the cells to enter a robust physiological state relevant to the host environment. Here, we present evidence that expression of two independent cell-cell signaling systems are also coupled to swarmer differentiation in S. enterica serovar Typhimurium. Expression of both pfs and sdiA genes was up-regulated in the actively migrating swarmers compared to their vegetative counterparts propagated in broth or spread plated on the surface of swim, swarm, and solid media. Accordingly, swarmers produced elevated levels of a universally recognized signaling molecule, autoinducer-2, and exhibited increased sensitivity to N-acyl homoserine lactones (AHLs), signaling molecules that Salmonella does not produce. Expression of the rck operon was concomitantly up-regulated in the swarmers in an SdiA-dependent manner only in the presence of exogenous AHLs. In addition to the previously reported adaptive antibiotic resistance phenotype and global shift in metabolism, this work presents another component of the physiological changes that are specifically associated with swarmer differentiation in serovar Typhimurium and not simply due to growth on a surface.
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Affiliation(s)
- Wook Kim
- Department of Microbiology and Infectious Diseases, University of Calgary, 3330 Hospital Dr. NW, Calgary, Alberta, Canada T2N 4N1
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194
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Abstract
Quorum sensing in Escherichia coli and Salmonella has been an elusive topic for a long time. However, in the past 8 years, several research groups have demonstrated that these bacteria use several quorum-sensing systems, such as: the luxS/AI-2, AI-3/epinephrine/norepinephrine, indole, and the LuxR homolog SdiA to achieve intercellular signaling. The majority of these signaling systems are involved in interspecies communication, and the AI-3/epinephrine/norepinephrine signaling system is also involved in interkingdom communication. Both E. coli and Salmonella reside in the human intestine, which is the largest and most complex environment in the mammalian host. The observation that these bacteria evolved quorum-sensing systems primarily involved in interspecies communication may constitute an adaptation to this environment. The gastrointestinal tract harbors a high density and diversity of bacterial cells, with the majority of the flora residing in the colon (10(11)-10(12) bacterial cells/ml). Given the enormous number and diversity of bacteria inhabiting the gastrointestinal environment, it should not be surprising that the members of this community communicate amongst themselves and with the host itself to coordinate a variety of adaptive processes.
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Affiliation(s)
- Matthew Walters
- Department of Microbiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9048, USA
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195
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Yao Y, Martinez-Yamout MA, Dickerson TJ, Brogan AP, Wright PE, Dyson HJ. Structure of the Escherichia coli Quorum Sensing Protein SdiA: Activation of the Folding Switch by Acyl Homoserine Lactones. J Mol Biol 2006; 355:262-73. [PMID: 16307757 DOI: 10.1016/j.jmb.2005.10.041] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Revised: 10/12/2005] [Accepted: 10/14/2005] [Indexed: 10/25/2022]
Abstract
The three-dimensional structure of a complex between the N-terminal domain of the quorum sensing protein SdiA of Escherichia coli and a candidate autoinducer N-octanoyl-L-homoserine lactone (C8-HSL) has been calculated in solution from NMR data. The SdiA-HSL system shows the "folding switch" behavior that has been seen for quorum-sensing factors produced by other bacterial species. In the presence of C8-HSL, a significant proportion of the SdiA protein is produced in a folded, soluble form in an E.coli expression system, whereas in the absence of acyl homoserine lactones, the protein is expressed into insoluble inclusion bodies. In the three-dimensional structure, the autoinducer molecule is sequestered in a deep pocket in the hydrophobic core, forming an integral part of the core packing of the folded SdiA. The NMR spectra of the complex show that the bound C8-HSL is conformationally heterogeneous, either due to motion within the pocket or to heterogeneity of the bound structure. The C8-HSL conformation is defined by NOEs to the protein only at the terminal methyl group of the octanoyl chain. Unlike other well-studied bacterial quorum sensing systems such as LuxR of Vibrio fischeri and TraR of Agrobacterium tumefaciens, there is no endogenous autoinducer for SdiA in E.coli: the E.coli genome does not contain a gene analogous to the LuxI and TraI autoinducer synthetases. We show that two other homoserine lactone derivatives are also capable of acting as a folding-switch autoinducers for SdiA. The observed structural heterogeneity of the bound C8-HSL in the complex, together with the variety of autoinducer-type molecules that can apparently act as folding switches in this system, are consistent with the postulated biological function of the SdiA protein as a detector of the presence of other species of bacteria.
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Affiliation(s)
- Yong Yao
- Department of Molecular Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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Sha J, Pillai L, Fadl AA, Galindo CL, Erova TE, Chopra AK. The type III secretion system and cytotoxic enterotoxin alter the virulence of Aeromonas hydrophila. Infect Immun 2005; 73:6446-57. [PMID: 16177316 PMCID: PMC1230953 DOI: 10.1128/iai.73.10.6446-6457.2005] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Many gram-negative bacteria use a type III secretion system (TTSS) to deliver effector proteins into host cells. Here we report the characterization of a TTSS chromosomal operon from the diarrheal isolate SSU of Aeromonas hydrophila. We deleted the gene encoding Aeromonas outer membrane protein B (AopB), which is predicted to be involved in the formation of the TTSS translocon, from wild-type (WT) A. hydrophila as well as from a previously characterized cytotoxic enterotoxin gene (act)-minus strain of A. hydrophila, thus generating aopB and act/aopB isogenic mutants. The act gene encodes a type II-secreted cytotoxic enterotoxin (Act) that has hemolytic, cytotoxic, and enterotoxic activities and induces lethality in a mouse model. These isogenic mutants (aopB, act, and act/aopB) were highly attenuated in their ability to induce cytotoxicity in RAW 264.7 murine macrophages and HT-29 human colonic epithelial cells. The act/aopB mutant demonstrated the greatest reduction in cytotoxicity to cultured cells after 4 h of infection, as measured by the release of lactate dehydrogenase enzyme, and was avirulent in mice, with a 90% survival rate compared to that of animals infected with Act and AopB mutants, which caused 50 to 60% of the animals to die at a dose of three 50% lethal doses. In contrast, WT A. hydrophila killed 100% of the mice within 48 h. The effects of these mutations on cytotoxicity could be complemented with the native genes. Our studies further revealed that the production of lactones, which are involved in quorum sensing (QS), was decreased in the act (32%) and aopB (64%) mutants and was minimal (only 8%) in the act/aopB mutant, compared to that of WT A. hydrophila SSU. The effects of act and aopB gene deletions on lactone production could also be complemented with the native genes, indicating specific effects of Act and the TTSS on lactone production. Although recent studies with other bacteria have indicated TTSS regulation by QS, this is the first report describing a correlation between the TTSS and Act of A. hydrophila and the production of lactones.
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Affiliation(s)
- Jian Sha
- Department of Microbiology and Immunology, The University of Texas Medical School Branch, Galveston, 77555-1070, USA
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197
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Abstract
Many gram-negative bacteria synthesize N-acylhomoserine lactones (AHLs) and then use transcription factors of the LuxR family to sense and respond to AHL accumulation in the environment; this phenomenon is termed quorum sensing. Bacteria produce a variety of AHLs, and numerous bacterial reporter strains, or biosensors, that can detect subsets of these molecules have been constructed. Many of these are based on Escherichia coli because this species does not produce AHLs. However, both Escherichia and Salmonella spp. contain a LuxR homolog named SdiA that can detect exogenous AHL synthesized by other microbial species. In this study we have determined that sdiA of E. coli and Salmonella spp. can activate an RhlR-based biosensor plasmid in response to AHLs other than what the biosensor was designed to detect. SdiA does not activate LuxR-, LasR-, or AhyR-based biosensor plasmids, although the presence of sdiA in E. coli does interfere with the function of the AhyR-based biosensor. Because sdiA interferes with the function of two of the four reporters, we have constructed a set of E. coli biosensor strains that lack sdiA. The set includes control reporters that allow the luxR dependence of responses to be determined.
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Affiliation(s)
- Amber Lindsay
- Department of Microbiology, Ohio State University, Columbus, 43210-1292, USA
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198
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De Keersmaecker SCJ, Marchal K, Verhoeven TLA, Engelen K, Vanderleyden J, Detweiler CS. Microarray analysis and motif detection reveal new targets of the Salmonella enterica serovar Typhimurium HilA regulatory protein, including hilA itself. J Bacteriol 2005; 187:4381-91. [PMID: 15968047 PMCID: PMC1151768 DOI: 10.1128/jb.187.13.4381-4391.2005] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
DNA regulatory motifs reflect the direct transcriptional interactions between regulators and their target genes and contain important information regarding transcriptional networks. In silico motif detection strategies search for DNA patterns that are present more frequently in a set of related sequences than in a set of unrelated sequences. Related sequences could be genes that are coexpressed and are therefore expected to share similar conserved regulatory motifs. We identified coexpressed genes by carrying out microarray-based transcript profiling of Salmonella enterica serovar Typhimurium in response to the spent culture supernatant of the probiotic strain Lactobacillus rhamnosus GG. Probiotics are live microorganisms which, when administered in adequate amounts, confer a health benefit on the host. They are known to antagonize intestinal pathogens in vivo, including salmonellae. S. enterica serovar Typhimurium causes human gastroenteritis. Infection is initiated by entry of salmonellae into intestinal epithelial cells. The expression of invasion genes is tightly regulated by environmental conditions, as well as by many bacterial factors including the key regulator HilA. One mechanism by which probiotics may antagonize intestinal pathogens is by influencing invasion gene expression. Our microarray experiment yielded a cluster of coexpressed Salmonella genes that are predicted to be down-regulated by spent culture supernatant. This cluster was enriched for genes known to be HilA dependent. In silico motif detection revealed a motif that overlaps the previously described HilA box in the promoter region of three of these genes, spi4_H, sicA, and hilA. Site-directed mutagenesis, beta-galactosidase reporter assays, and gel mobility shift experiments indicated that sicA expression requires HilA and that hilA is negatively autoregulated.
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199
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Balestrino D, Haagensen JAJ, Rich C, Forestier C. Characterization of type 2 quorum sensing in Klebsiella pneumoniae and relationship with biofilm formation. J Bacteriol 2005; 187:2870-80. [PMID: 15805533 PMCID: PMC1070389 DOI: 10.1128/jb.187.8.2870-2880.2005] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Quorum sensing is a process by which bacteria communicate by using secreted chemical signaling molecules called autoinducers. Many bacterial species modulate the expression of a wide variety of physiological functions in response to changes in population density by this mechanism. In this study, the opportunistic pathogen Klebsiella pneumoniae was observed to secrete type 2 signaling molecules. A homologue of luxS, the gene required for AI-2 synthesis in Vibrio harveyi, was isolated from the K. pneumoniae genome. A V. harveyi bioassay showed the luxS functionality in K. pneumoniae and its ability to complement the luxS-negative phenotype of Escherichia coli DH5alpha. Autoinducer activity was detected in the supernatant, and maximum expression of specific messengers detected by quantitative reverse transcription-PCR analysis occurred during the late exponential phase. The highest levels of AI-2 were observed in minimal medium supplemented with glycerol. To determine the potential role of luxS in colonization processes, a K. pneumoniae luxS isogenic mutant was constructed and tested for its capacity to form biofilms in vitro on an abiotic surface and to colonize the intestinal tract in a murine model. No difference was observed in the level of intestinal colonization between the wild-type strain and the luxS mutant. Microscopic analysis of biofilm structures revealed that the luxS mutant was able to form a mature biofilm but with reduced capacities in the development of microcolonies, mostly in the early steps of biofilm formation. These data suggest that a LuxS-dependent signal plays a role in the early stages of biofilm formation by K. pneumoniae.
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Affiliation(s)
- Damien Balestrino
- Laboratoire de Bactériologie, Faculté de Pharmacie, Université d'Auvergne, 28 Place Henri Dunant, 63000 Clermont-Ferrand, France
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200
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Rychlik I, Barrow PA. Salmonella stress management and its relevance to behaviour during intestinal colonisation and infection. FEMS Microbiol Rev 2005; 29:1021-40. [PMID: 16023758 DOI: 10.1016/j.femsre.2005.03.005] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2004] [Revised: 03/04/2005] [Accepted: 03/30/2005] [Indexed: 01/13/2023] Open
Abstract
The enteric pathogen Salmonella enterica is exposed to a number of stressful environments during its life cycle within and outside its various hosts. During intestinal colonisation Salmonella is successively exposed to acid pH in the stomach, to the detergent-like activity of bile, to decreasing oxygen supply, to the presence of multiple metabolites produced by the normal gut microflora and finally it is exposed to cationic antimicrobial peptides present on the surface of epithelial cells. There are four major regulators controlling relevant stress responses in Salmonella, namely RpoS, PhoPQ, Fur and OmpR/EnvZ. Except for Fur, inactivation of genes encoding the other stress regulators results in attenuated virulence and such mutants can therefore be considered as vaccine candidates. In contrast, a decrease in oxygen supply monitored by Fnr and ArcAB, or oxidative stress controlled by OxyR and SoxRS is not regarded as a stress associated with host colonisation since inactivation of either of these systems does not result in reductions in colonisation. The role of quorum-sensing through luxS and sdiA is also considered as a regulator of virulence and colonisation.
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Affiliation(s)
- Ivan Rychlik
- Veterinary Research Institute, Hudcova 70, 621 32 Brno, Czech Republic.
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