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