DAO 65:43-52 (2005)  -  doi:10.3354/dao065043

Quorum sensing signal molecules (acylated homoserine lactones) in Gram-negative fish pathogenic bacteria*

Jesper B. Bruhn1,**, Inger Dalsgaard2, Kristian F. Nielsen3, Christiane Buchholtz1, Jens L. Larsen4, Lone Gram1

1Danish Institute for Fisheries Research, Department of Seafood Research, Søltoft Plads c/o Technical University of Denmark bldg. 221, 2800 Kgs. Lyngby, Denmark
2Danish Institute for Fisheries Research, Fish Disease Laboratory, Stigbøjlen 4, 1870 Frederiksberg, Denmark
3Centre for Microbial Biotechnology, Technical University of Denmark bldg. 221, 2800 Kgs. Lyngby, Denmark
4Department of Veterinary Pathobiology, Stigbøjlen 4, Royal Veterinary and Agricultural University, 1870 Frederiksberg C,Denmark
*Part of this paper was presented as a poster at the 2nd ASM Conference on Cell-Cell Communication in Bacteria, Banff, Alberta, Canada
**Email: jbb@dfu.min.dk

ABSTRACT: The aim of the present study was to investigate the production of quorum sensing signals (specifically acylated homoserine lactones, AHLs) among a selection of strains of Gram-negative fish bacterial pathogens. These signals are involved in the regulation of virulence factors in some human and plant-pathogenic bacteria. A total of 59 strains, representing 9 different fish pathogenic species, were tested against 2 AHL monitor bacteria (Agrobacterium tumefaciens NT1 [pZLR4] and Chromobacterium violaceum CV026) in a well diffusion assay and by thin-layer chromatography (TLC). Representative samples were further characterized by high performance liquid chromatography-high resolution mass spectrometry (HPLC-HR-MS). AHLs were produced by all strains of Aeromonas salmonicida, Aeromonas hydrophila, Yersinia ruckeri, Vibrio salmonicida, and Vibrio vulnificus. Some strains of atypical Aeromonas salmonicida and Vibrio splendidus were also positive. Aeromonas species produced N-butanoyl homoserine lactone (BHL) and N-hexanoyl homoserine lactone (HHL) and 1 additional product, whereas N-3-oxo-hexanoyl homoserine lactone (OHHL) and HHL were detected in Vibrio salmonicida. N-3-oxo-octanoyl homoserine lactone (OOHL) and N-3-octanoyl homoserine lactone (OHL) were detected in Y. ruckeri. AHLs were not detected from strains of Photobacterium damselae, Flavobacterium psychrophilum or Moritella viscosa. AHLs were extracted from fish infected with Y. ruckeri but not from fish infected with A. salmonicida. In conclusion, the production of quorum sensing signals, AHLs, is common among the strains that we examined. If the AHL molecules regulate the expression of the virulence phenotype in these bacteria, as shown to occur in some bacterial pathogens, novel disease control measures may be developed by blocking AHL-mediated communication and suppressing virulence.

KEY WORDS: Quorum sensing · Signal molecules · Acylated homoserine lactones ·AHL · Fish pathogenic bacteria

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