VanT, a central regulator of quorum sensing signalling in Vibrio anguillarum

.......................................................................................................................................................... 5 PAPERS IN THIS THESIS.................................................................................................................................. 6 ABBREVIATIONS ............................................................................................................................................... 7 INTRODUCTION................................................................................................................................................. 8 A. VIBRIONACEAE ............................................................................................................................................. 8 B. SURVIVAL OF VIBRIOS IN AQUATIC ENVIRONMENTS ..................................................................................... 9 C. VIBRIO ANGUILLARUM .................................................................................................................................. 10 D. VIBRIOSIS.................................................................................................................................................... 11 E. PORTAL OF ENTRY....................................................................................................................................... 12 F. VIRULENCE FACTORS .................................................................................................................................. 13 G. TREATMENT AND PROPHYLAXIS.................................................................................................................. 16 H. QUORUM SENSING: AN OVERVIEW .............................................................................................................. 17 I. QUORUM SENSING SIGNALLING IN GRAM-NEGATIVE BACTERIA.................................................................. 18 I.1 LuxI/LuxR-like quorum sensing system ........................................................................................... 18 I1.1 AHLs structure ......................................................................................................................................... 19 I1.2 AHLs synthesis and LuxI-type synthase................................................................................................... 20 I1.3 V. fischeri LuxR-type transcriptional regulator. ....................................................................................... 22 I1.4 Biodiversity of LuxI/LuxR quorum sensing systems............................................................................... 23 I.2 V. harveyi-type quorum sensing systems ......................................................................................... 24 I2.1 The V. harveyi quorum sensing signalling cascade .................................................................................. 24 I2.2 V. fischeri possesses both a V. harveyi-type and a LuxI/LuxR quorum sensing system. ......................... 27 I2.3 Biodiversity of V. harveyi-type quorum sensing systems......................................................................... 28 I2.4 AinS/LuxM family of AHLs synthase ...................................................................................................... 30 I2.5 Furanosyl borate diester (AI-2) and LuxS family ..................................................................................... 31 I2.6 CAI-1........................................................................................................................................................ 32 I2.7 The phosphotransferase LuxU .................................................................................................................. 33 I2.8 The sigm54-dependent regulator LuxO and small regulatory RNAs........................................................ 34 I2.9 The family of V. harveyi LuxR homologues are members of the TetR family......................................... 35 I2.10 Functions of V. harveyi LuxR homologues .............................................................................................. 36 J. QUORUM SENSING SIGNALLING IN GRAM-POSITIVE BACTERIA.................................................................... 38 J.1 Bacillus subtilis: cooperation or antagonism of the signals depends on the autoinducers concentration. .................................................................................................................................. 39 J.2 Staphylococcus aureus and the ultraspecificity of the signal .......................................................... 40 K. BACTERIAL CROSS-TALK............................................................................................................................. 41 L. BACTERIAL INTERFERENCE ......................................................................................................................... 42 M. INTERKINGDOM SIGNALLING....................................................................................................................... 44 N. QUORUM SENSING, AN INTEGRAL COMPONENT OF BACTERIAL GLOBAL REGULATORY NETWORKS. ............ 45 O. THE ALTERNATIVE SIGMA FACTOR RPOS .................................................................................................... 47 AIMS OF THIS THESIS.................................................................................................................................... 49 RESULTS AND DISCUSSION ......................................................................................................................... 50 P. VANT, A HOMOLOGUE OF VIBRIO HARVEYI LUXR, REGULATES SERINE, METALLOPROTEASE, PIGMENT, AND BIOFILM PRODUCTION IN VIBRIO ANGUILLARUM (PAPER I) ........................................................................... 50 P.1 AHL analysis in the vanT mutant..................................................................................................... 51 P.2 Regulation of the metalloprotease empA by VanT........................................................................... 52 P.3 Identification of additional genes regulated by VanT...................................................................... 52 P3.1 VanT regulates pigment production.......................................................................................................... 53 P3.2 VanT regulates exopolyssacharide (EPS) production............................................................................... 53 P3.3 VanT regulates serine biosynthesis:.......................................................................................................... 54 P.4 VanT is not essential for virulence .................................................................................................. 55 Q. A DISTINCTIVE DUAL-CHANNEL QUORUM SENSING SYSTEM OPERATES IN VIBRIO ANGUILLARUM (PAPER II) 55 Q.1 Quorum sensing regulates vanT expression .................................................................................... 56 Q.2 The two V. harveyi-like quorum sensing systems VanM/VanN and VanS/VanPQ are functionally redundant in V. anguillarum............................................................................................................ 57 Q.3 VanU is not required by VanN and VanQ to repress vanT.............................................................. 57 Q.4 VanT negatively autoregulates its own expression.......................................................................... 58 Q.5 Model of quorum sensing signalling in V. anguillarum................................................................... 60