QUORUM SENSING IN AEROMONAS-HYDROPHILA AND AEROMONAS-SALMONICIDA - IDENTIFICATION OF THE LUXRI HOMOLOGS AHYRI AND ASARI AND THEIR COGNATE N-ACYLHOMOSERINE LACTONE SIGNAL MOLECULES

Citation
S. Swift et al., QUORUM SENSING IN AEROMONAS-HYDROPHILA AND AEROMONAS-SALMONICIDA - IDENTIFICATION OF THE LUXRI HOMOLOGS AHYRI AND ASARI AND THEIR COGNATE N-ACYLHOMOSERINE LACTONE SIGNAL MOLECULES, Journal of bacteriology, 179(17), 1997, pp. 5271-5281
Citations number
66
Categorie Soggetti
Microbiology
Journal title
ISSN journal
00219193
Volume
179
Issue
17
Year of publication
1997
Pages
5271 - 5281
Database
ISI
SICI code
0021-9193(1997)179:17<5271:QSIAAA>2.0.ZU;2-P
Abstract
Spent culture supernatants from both Aeromonas hydrophila and Aeromona s salmonicida activate a range of biosensors responsive to N-acylhomos erine lactones (AHLs). The genes for a quorum sensing signal generator and a response regulator were cloned from each Aeromonas species and termed ahyRI and asaRI respectively. Protein sequence homology analysi s places the gene products within the growing family of LuxRI: homoIog s. ahyR and asaR are transcribed divergently from ahyI and asaI respec tively, and in both Aeromonas species, the genes downstream have been identified by DNA sequence and PCR analysis. Downstream of both ahyI a nd asaI is a gene with close homology to iciA, an inhibitor of chromos ome replication in Escherichia coli, a finding which implies that in A eromonas, cell division may be linked to quorum sensing. The major sig nal molecule synthesized via both AhyI and AsaI was purified from spen t culture supernatants and identified as N-(butanoyl)-L-homoserine lac tone (BHL) by thin-layer chromatography, high-pressure liquid chromato graphy analysis, and mass spectrometry. In addition, a second, minor A HL, N-hexanoyl-L-homoserine lactone, was identified. Transcriptional r eporter studies with ahyI::luxCDABE fusions indicate that AhyR and BHL are both required for ahyI transcription. For A. salmonicida, althoug h the addition of exogenous BHL gives only a small stimulation of the production of serine protease with comparison to the control culture, the incorporation of a longer-chain AHL, N-(3-oxodecanoyl)-L-homoserin e lactone, reduced the final level (by approximately 50%) and delayed the appearance (from an A(650) of 0.9 in the control to an A(650) of 1 .2 in the test) of protease in the culture supernatant. These data add A. hydrophila and A. salmonicida to the growing family of gram-negati ve bacteria now known to control gene expression through quorum sensin g.