Regulation of Lux Genes in Vibrio Fischeri: Control of Symbiosis-Related Gene Expression System in a Marine Bacterium PDF Download
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Author: Everett P. Greenberg
Publisher:
ISBN:
Category :
Languages : en
Pages : 5
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Book Description
The lux genes of Vibrio fischeri encode the ability of this marine bacterium to produce light. V. fischeri occurs at high density in specialized light-emitting organs of certain marine fish, where the light produced is used by the fish. V. fischeri is also found in seawater, where it exists as a member of the bacterioplankton. In the planktonic habitat light-production is not useful and in fact V. fischeri possesses a genetic control mechanism which enables light production when the bacteria exist in the symbiotic state but does not allow synthesis of the light-emitting system when V. fischeri is in the planktonic habitat. This regulatory phenomenon is termed auto induction, and the aim of this research is to fully elucidate the mechanism of auto induction. Specific objectives of this research effort include a structure/function analysis of the sensory receptor; the LuxR protein, purification of the LuxR protein and development of a defined in vitro assay for studying lux gene transcription. Keywords: Maine bacteria; Symbiosis genes; Gene regulation; Auto induction; Luminescence; Chemical communication. (KT).
Author: Everett P. Greenberg
Publisher:
ISBN:
Category :
Languages : en
Pages : 5
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Book Description
The lux genes of Vibrio fischeri encode the ability of this marine bacterium to produce light. V. fischeri occurs at high density in specialized light-emitting organs of certain marine fish, where the light produced is used by the fish. V. fischeri is also found in seawater, where it exists as a member of the bacterioplankton. In the planktonic habitat light-production is not useful and in fact V. fischeri possesses a genetic control mechanism which enables light production when the bacteria exist in the symbiotic state but does not allow synthesis of the light-emitting system when V. fischeri is in the planktonic habitat. This regulatory phenomenon is termed auto induction, and the aim of this research is to fully elucidate the mechanism of auto induction. Specific objectives of this research effort include a structure/function analysis of the sensory receptor; the LuxR protein, purification of the LuxR protein and development of a defined in vitro assay for studying lux gene transcription. Keywords: Maine bacteria; Symbiosis genes; Gene regulation; Auto induction; Luminescence; Chemical communication. (KT).
Author:
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ISBN:
Category :
Languages : en
Pages : 637
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Author: Paul V. Dunlap
Publisher:
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Category :
Languages : en
Pages : 8
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The goals of our research are to investigate the molecular mechanisms controlling luminescence gene expression of the symbiotic, light-organ bacterium Vibrio fischeri; and to identify and investigate the regulation of other symbiosis functions in this marine bacterium. During the past year, we have: 1) completed studies in Escherichia coli cya and crp mutants on expression of the luxR gene that demonstrate cAMP and CRP activate transcription of luxR and that the LuxR protein, possibly working in concert with auto-inducer, represses transcription from the luxR promoter (transcription negative auto-regulation); 2) isolated mutants of V. fischeri apparently deficient in adenylate cyclase and CRP, and demonstrated the requirement for cAMP and CRP in autoinduction of luminescence and in iron regulation of luminescence; 3) initiated studies in E. coli of the role of autoinducer in luxR negative autoregulation; and, 4) initiated work toward development of a gene transfer system for V. fischeri. Keywords: Bioluminescence; Symbiosis; Marine bacteria; Gene regulation. (KT).
Author: Gerald S. Shadel
Publisher:
ISBN:
Category : Vibrio fischeri
Languages : en
Pages : 346
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Author: Jessica Eason
Publisher:
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Category :
Languages : en
Pages : 0
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Animals can establish symbioses, or long-term physical associations, with certain bacteria, called symbionts, that can express specific traits that impact host physiology, behavior, and development. In many cases, these traits have positive effects on the host, e.g., boosting immunity to combat pathogens or other diseases, and increasing nutrient uptake. Hosts often acquire bacterial symbionts from environmental reservoirs, for which bacterial symbionts use strategies that promote survival of individual or populations of cells when experiencing different environmental conditions, and thus responding to different environmental cues. Determining underlying molecular mechanisms that facilitate bacterial adaptation in changing environments that result in symbiosis with a specific host(s) will increase understanding of how host-microbe symbioses are initiated and maintained. Bacteria can respond to bacterially produced molecules that enable bacterial cells to infer cell number in order to coordinate behaviors that facilitate host association and maintenance. This bacterial communication mechanism is called quorum sensing. Quorum-regulated sRNAs (Qrrs) are small regulatory sRNAs that post-transcriptionally regulate target mRNAs. Quorum sensing networks regulate expression of these sRNAs to fine-tune expression of bacterial traits including protease secretion, chemotaxis, motility, bioluminescence production and biofilm formation that can aid either individual or populations of bacterial cells in persistence within host environments. The studies described in this thesis use the mutualistic symbiotic relationship between the beneficial marine bacterium Vibrio fischeri and its host the Hawaiian Bobtail squid Euprymna scolopes as a model to investigate patterns of qrr expression within internal host compartments. V. fischeri has an established quorum sensing model for genetic regulation of bacterial traits that lead to colonization of a specialized squid compartment called the light organ. V. fischeri encodes a single qrr gene (qrr1) that is expressed when cell number is low. Post-transcriptional regulation by Qrr1 promotes motility and colonization of the squid host, while repressing bioluminescence production, an energetically costly trait only beneficial for large populations of V. fischeri inside of the light organ. Previous studies have investigated genetic regulation of qrr1 in culture, at the population level. To address whether qrrs are expressed within internal host compartments, experiments were performed using a fluorescent qrr1 promoter reporter to determine patterns of qrr1 expression in culture and in vivo. Experiments were performed where juvenile squid were exposed to V. fischeri expressing an established fluorescent qrr1 promoter reporter. Confocal images of the internal compartments of the light organ where V. fischeri are housed revealed heterogeneous qrr1 expression throughout V. fischeri populations. Similar experiments were performed using mutant V. fischeri lacking or over expressing genes encoding proteins that mediate qrr1 expression under different environmental conditions. Results suggest that the observed heterogeneous expression of qrr1 depends on two bacterial enhancing binding proteins, LuxO and SypG. The resulting model predicts that LuxO and SypG regulate qrr1 expression in a ubiquitously expressed subpopulation of V. fischeri cells inside the squid light organ. Culture-based experiments were performed using the same wild type and mutant V. fischeri expressing the same fluorescent qrr1 promoter reporter that were used in in vivo experiments to address how qrr1 expression is regulated in large populations of V. fischeri without the hurdle of colonization defects caused by genetic mutations within V. fischeri cells. Findings from this study also suggest that V. fischeri may heterogeneously express qrr1 as a bet-hedge strategy for maintenance and host colonization upon reentrance into the water column reservoir.
Author: Everett Greenberg
Publisher:
ISBN:
Category :
Languages : en
Pages : 4
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The general objective of the proposed research is to fully elucidate the mechanism of quorum sensing and response in bacteria by continuing investigations of the most well-developed model for this phenomenon, autoinduction of lux genes in Vibrio fischeri. This research should continue to reveal general rules governing regulation of bacterial genes used specifically in symbiotic associations with marine animals. This research program also has recently provided and should continue to provide insights into how bacteria interact with eukaryotic hosts in a more universal way. Little is known about synthesis of the autoinducer, the sensory signal, other than that it is catalyzed by the luxI gene product. Thus, an analysis of the structure and function of LuxI was initiated. This analysis involved the construction of point and deletion mutations in luxI and studies of the activity of the mutant proteins encoded by these defective genes. This analysis also involved studies of autoinducer synthesis in luxI-containing E. coli amino acid biosynthesis mutants, and studies of the biochemistry of purified enzymes.
Author: Claudia Lupp
Publisher:
ISBN:
Category : Bioluminescence
Languages : en
Pages : 372
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Book Description
Quorum sensing is a cell density-dependent bacterial gene regulatory mechanism used for the expression of colonization-related genes. The symbiotic relationship between the luminescent bacterium Vibrio fischeri and the Hawaiian bobtail squid Euprymna scolopes serves as a model system to study the molecular processes underlying bacterial colonization. This system is especially well-suited for the investigation of the impact of quorum sensing on colonization because (i) it is an easily accessible, natural, two-species colonization model, and (ii) quorum sensing regulates luminescence expression in V. fischeri, which allows the non-invasive detection of quorum-sensing activity both in culture and in symbiosis. While the impact of one of V. fischeri's quorum-sensing systems, lux, on luminescence expression and symbiotic competence has been extensively studied, little was known about other putative systems. The results of this study demonstrate that the V. fischeri ain system is essential for both maximal luminescence expression and symbiotic competence. The ain system predominantly induces luminescence expression at intermediate cell densities, which occur in culture, while the lux system is responsible for luminescence expression at the high cell densities found in symbiosis, suggesting the sequential induction of luminescence gene expression by these two systems. Furthermore, the ain quorum sensing system is important for the processes underlying colonization initiation, while the impact of the lux system is apparent only in later stages of the symbiosis, indicating distinct functions of these two systems during the colonization process. A global transcriptome. analysis of quorum-sensing mutants revealed that ain quorum sensing represses motility gene expression, providing a likely explanation for the initiation defect. Although it has been known that many bacterial species possess multiple quorum-sensing systems, this is the first study demonstrating that two quorum-sensing systems are employed to specifically regulate functions important at distinct cell densities occurring during the colonization process
Author: Sean Michael Callahan
Publisher:
ISBN:
Category :
Languages : en
Pages : 340
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Book Description
In the marine bacterium Vibrio fischeri two intercellular homoserine-Iactone signal molecules (luxI-dependent 30C6-HSL and the ainS-dependent C8-HSL) and the transcriptional activator LuxR regulate the luminescence system in a cell-density dependent manner by a process termed quorum sensing. In this study, five additional proteins whose production is regulated by quorum sensing are described, and the genes encoding four of the five proteins, denoted as QsrP, RibB, QsrV, and AcfA, are analyzed. Each protein is positively regulated by 30C6-HSL and LuxR and negatively regulated at low population density by C8-HSL. Probable LuxR/autoinducer binding sites are found in the promoter region of each. QsrP and RibB are encoded monocistronically, whereas AcfA and QsrV appear to be encoded by a two-gene operon. On the basis of sequence similarity to proteins of known function from other organisms, RibB is believed to be an enzyme that catalyzes the transformation of ribulose 5-phosphate to 3,4-dihydroxy-2- butanone 4-phosphate, a precursor for the xylene ring of riboflavin; AcfA is believed to be a pilus subunit; and the functions of QsrP and QsrV are unknown at this time. A qsrP mutant was reduced in its ability to colonize its symbiotic partner, Euprymna scolopes when placed in competition with the parent strain. On the other hand, a mutant strain of V. fischeri containing an insertion in acfA, which is believed to be polar with respect to qsrV, displayed enhanced colonization competence in a competition assay. A ribB mutant grew well on media not supplemented with additional riboflavin and displayed normal induction of luminescence. Both phenotypes suggest that the lack of a functional ribB gene is complemented by another gene of similar function in the mutant. Oriented divergently from acfA are open reading frames that code for two putative proteins that are similar in sequence to members of the LysR family of transcriptional regulators. Organization of the two divergent sets of genes and the shared promoter region suggests that transcription of acfA and qsrV may be regulated by one or both of these divergently transcribed proteins. This work defines a quorum-sensing regulon in V. fischeri. A model describing its regulation is presented.
Author: Michaela Jo Eickhoff
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Bacteria have the remarkable ability to rapidly and accurately detect and adapt to fluctuations in the environment. Often, transcriptional and post-transcriptional regulatory mechanisms function in concert to tune gene expression patterns that enhance survival and conserve resources under varying conditions. Among the changes bacteria monitor and respond to is the cell density and species composition of the vicinal community. Bacteria accomplish this using quorum sensing (QS), a cell-cell communication process that alters global gene expression patterns to foster the synchronous execution of collective behaviors. QS involves the production, release, accumulation, and group-wide detection of signaling molecules called autoinducers (AIs). The marine bacterium V. harveyi produces and responds to three AIs, which act in parallel. At low cell-density, AI concentrations are low, and a phosphorelay cascade leads to the activation of five small regulatory RNAs called Qrr1-5 that post-transcriptionally regulate target genes, leading to a downstream QS regulon of over 600 genes. Because Qrr1-5 largely function redundantly, the advantages of encoding five qrr genes are not well-understood. This work explores the transcriptional and post-transcriptional regulatory mechanisms controlling the QS regulon and how the V. harveyi QS response is altered in the presence of competing bacterial species. First, a new QS regulator called LuxT is discovered to repress the transcription of one Qrr small RNA, Qrr1. As a repressor of qrr1, LuxT indirectly regulates Qrr1 target mRNAs, demonstrating how Qrr1 can control gene expression independently of Qrr2-5. Second, LuxT is also identified as a global regulator that functions in parallel to QS to control over 400 genes. Finally, a co-culture model between V. harveyi and its competitor Vibrio fischeri is established to study QS interactions in competitive multi-species environments.
Author: K.E. Cooksey
Publisher: Springer Science & Business Media
ISBN: 9401149283
Category : Science
Languages : en
Pages : 562
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Book Description
Marine biological science is now studied at the molecular level and although research scientists depend on information gained using molecular techniques, there is no book explaining the philosophy of this approach. Molecular Approaches to the Study of the Ocean introduces the reasons why molecular technology is such a powerful tool in the study of the oceans, describing the types of techniques that can be used, why they are useful and gives examples of their application. Molecular biological techniques allow phylogenetic relationships to be explored in a manner that no macroscopic method can; although the book deals with organisms near the base of the marine food web, the ideas can be used in studies of macroorganisms as well as those in freshwater environments.
