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VanT, a central regulator of quorum sensing signalling in Vibrio anguillarum
Umeå University, Faculty of Medicine, Molecular Biology.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Many bacteria produce signal molecules that serve in a cell-to-cell communication system termed quorum sensing. This signalling system allows a bacterial population to co-ordinately regulate functions according to their cell number in a defined environment. As bacterial growth progresses towards the stationary phase, signalling molecules accumulate in the growth medium and, above a certain threshold level, regulate the expression of genes involved in diverse functions. Most of the functions monitored by quorum sensing are most beneficial when they are performed as a population than by single cells, such as virulence factor production, biofilm formation, conjugation and bioluminescence.

Vibrio anguillarum is a bacterial pathogen that causes terminal hemorrhagic septicaemia in marine fish. V. anguillarum possesses multiple quorum sensing circuits similar to the LuxI/LuxR and the V. harveyi-type systems. In this study, a characterisation of the quorum sensing-regulated transcriptional activator VanT was made. VanT belongs to the V. harveyi LuxR family of transcriptional regulators, which play a central role in quorum sensing signalling in Vibrio species. VanT was shown to regulate serine, metalloprotease, pigment, exopolysaccharide (EPS) and biofilm production. VanT repressed an EPS locus that plays a critical role in bacterial colonization of the fish integument and virulence.

The V. harveyi-like quorum sensing systems were shown to limit rather than induce vanT expression throughout growth in V. anguillarum. In contrast to homologous proteins in other Vibrio spp., the quorum sensing phosphorelay protein VanU and the response regulator VanO had antagonistic roles in the regulation of vanT expression. Unlike other members of the luxR family, vanT was expressed at low cell density and no significant induction due to quorum sensing regulation was seen.

Interestingly, VanT expression was induced by the alternative sigma factor RpoS as the cells entered stationary phase. RpoS was shown to regulate VanT expression post-transcriptionally by promoting vanT mRNA stability. VanT and RpoS were important for bacterial survival under stress conditions, indicating that VanT is likely an essential factor of V. anguillarum stress response.

Place, publisher, year, edition, pages
Umeå: Molekylärbiologi (Teknisk-naturvetenskaplig fakultet) , 2006. , 96 p.
Series
Doctoral thesis / Umeå University, Department of Molecular Biology
Keyword [en]
Vibriosis, Vibrio anguillarum, quorum sensing, two-component phosphorelay systems
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-702ISBN: 91-7264-022-7 (print)OAI: oai:DiVA.org:umu-702DiVA: diva2:144265
Public defence
2006-03-10, major groove, 6L, Inst. för Molekylärbiologi, Umeå Universitet, 09:00 (English)
Opponent
Supervisors
Available from: 2006-02-15 Created: 2006-02-15 Last updated: 2009-10-01Bibliographically approved
List of papers
1. VanT, a Homologue of Vibrio harveyi LuxR, Regulates Serine, Metalloprotease, Pigment, and Biofilm Production in Vibrio anguillarum
Open this publication in new window or tab >>VanT, a Homologue of Vibrio harveyi LuxR, Regulates Serine, Metalloprotease, Pigment, and Biofilm Production in Vibrio anguillarum
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2002 (English)In: Journal of Bacteriology, ISSN 0021-9193, E-ISSN 1098-5530, Vol. 184, no 6, 1617-1629 p.Article in journal (Refereed) Published
Abstract
Identifiers
urn:nbn:se:umu:diva-4950 (URN)10.1128/JB.184.6.1617-1629.2002 (DOI)11872713 (PubMedID)
Available from: 2006-02-15 Created: 2006-02-15 Last updated: 2017-12-14Bibliographically approved
2. A distinctive dual-channel quorum-sensing system operates in Vibrio anguillarum.
Open this publication in new window or tab >>A distinctive dual-channel quorum-sensing system operates in Vibrio anguillarum.
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2004 (English)In: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 52, no 6, 1677-1689 p.Article in journal (Refereed) Published
Abstract [en]

Many bacterial cells communicate using diffusible signal molecules to monitor cell population density via a process termed quorum sensing. In marine Vibrio species, the Vibrio harveyi-type LuxR protein is a key player in a quorum-sensing phosphorelay cascade, which controls the expression of virulence, symbiotic and survival genes. Previously, we characterized Vibrio anguillarum homologues of LuxR (VanT) and LuxMN (VanMN) and, in this study, we have identified homologues of LuxPQ (VanPQ) and LuxOU (VanOU). In contrast to other Vibrio species, vanT was expressed at low cell density and showed no significant induction as the cell number increased. In addition, although the loss of VanO increased vanT expression, the loss of VanU, unexpectedly, decreased it. Both VanN and VanQ were required for repression of vanT even in a vanU mutant, suggesting an alternative route for VanNQ signal transduction other than via VanU. VanT negatively regulated its own expression by binding and repressing the vanT promoter and by binding and activating the vanOU promoter. The signal relay results in a cellular response as expression of the metalloprotease, empA, was altered similar to that of vanT in all the mutants. Consequently, the V. anguillarum quorum-sensing phosphorelay systems work differently from those of V. harveyi and may be used to limit rather than induce vanT expression.

Keyword
Bacterial Proteins/genetics/*metabolism, DNA; Bacterial/chemistry/isolation & purification, Gene Expression Regulation; Bacterial, Genes; Bacterial, Genes; Reporter, Metalloproteases/biosynthesis, Molecular Sequence Data, Mutation, Phosphoproteins/genetics, Phosphotransferases/genetics, RNA; Bacterial/analysis, RNA; Messenger/analysis, Repressor Proteins/genetics, Sequence Analysis; DNA, Sequence Homology, Signal Transduction, Trans-Activators/genetics, Transcription Factors/genetics, Vibrio/*genetics/growth & development/*physiology, Virulence/genetics, beta-Galactosidase/metabolism
Identifiers
urn:nbn:se:umu:diva-17994 (URN)10.1111/j.1365-2958.2004.04083.x (DOI)15186417 (PubMedID)
Available from: 2007-11-26 Created: 2007-11-26 Last updated: 2017-12-14Bibliographically approved
3. Post-transcriptional regulation of the Vibrio anguillarum quorum-sensing regulator vanT by RpoS
Open this publication in new window or tab >>Post-transcriptional regulation of the Vibrio anguillarum quorum-sensing regulator vanT by RpoS
(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4952 (URN)
Available from: 2006-02-15 Created: 2006-02-15 Last updated: 2010-01-13Bibliographically approved
4. Vibrio anguillarum colonization of rainbow trout integument requires a DNA locus involved in exopolysaccharide transport and biosynthesis.
Open this publication in new window or tab >>Vibrio anguillarum colonization of rainbow trout integument requires a DNA locus involved in exopolysaccharide transport and biosynthesis.
2007 (English)In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 9, no 2, 370-382 p.Article in journal (Refereed) Published
Abstract [en]

Vibrio anguillarum, part of the normal flora of the aquatic milieu, causes a fatal haemorrhagic septicaemia in marine fish. In this study, a rainbow trout model was used to characterize the colonization of fish skin by V. anguillarum. Within 5 h after infection, the bacterium penetrated the skin mucosal layer, attached to the scales within 12 h, and formed a biofilm by 24-48 h. Two divergently transcribed putative operons, orf1-wbfD-wbfC-wbfB and wza-wzb-wzc, were shown to play a role in skin colonization and virulence. The first operon encodes proteins of unknown function. The wza-wzb-wzc genes encode a secretin, tyrosine kinase and tyrosine phosphatase, respectively, which are similar to proteins in polysaccharide transport complexes. Compared with the wild type, polar mutations in wza, orf1 and wbfD caused a decrease in exopolysaccharide biosynthesis but not lipopolysaccharide biosynthesis. The wza and orf1 mutants did not attach to fish scales; whereas, the wbfD mutant had a wild-type phenotype. Moreover, the wza and orf1 mutants had decreased exoprotease activity, in particular the extracellular metalloprotease EmpA, as well as mucinase activity suggesting that these mutations also affect exoenzyme secretion. Thus, the exopolysaccharide transport system in V. anguillarum is required for attachment to fish skin, possibly preventing mechanical removal of bacteria via natural sloughing of mucus.

Keyword
Animals, Bacterial Adhesion/genetics/physiology, Bacterial Proteins/genetics/physiology, Biofilms/growth & development, Biological Transport/genetics, Genes; Bacterial, Mutation, Oncorhynchus mykiss/*microbiology, Operon, Polysaccharides; Bacterial/biosynthesis/*metabolism, Skin/anatomy & histology/microbiology, Vibrio/*genetics/metabolism/pathogenicity, Virulence/genetics
Identifiers
urn:nbn:se:umu:diva-18024 (URN)10.1111/j.1462-2920.2006.01147.x (DOI)17222135 (PubMedID)
Available from: 2007-11-26 Created: 2007-11-26 Last updated: 2017-12-14Bibliographically approved

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