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Regulation of Vibrio vulnificus virulence by the LuxS quorum‐sensing system
Author(s) -
Kim Soo Young,
Lee Shee Eun,
Kim Young Ran,
Kim Choon Mee,
Ryu Phil Youl,
Choy Hyon E.,
Chung Sun Sik,
Rhee Joon Haeng
Publication year - 2003
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2003.03536.x
Subject(s) - vibrio vulnificus , vibrio harveyi , biology , quorum sensing , microbiology and biotechnology , autoinducer , complementation , mutant , wild type , virulence , vibrio , bacteria , biochemistry , gene , genetics
Summary Vibrio vulnificus is a halophilic estuarine bacterium that causes fatal septicaemia and necrotizing wound infections. We tested whether V. vulnificus produces signalling molecules (autoinducer 1 and/or 2) stimulating Vibrio harveyi quorum‐sensing system 1 and/or 2. Although there was no evidence for signalling system 1, we found that V. vulnificus produced a signalling activity in the culture supernatant that induced luminescence expression in V. harveyi through signalling system 2. Maximal autoinducer 2 (AI‐2) activity was observed during mid‐exponential to early stationary phase and disappeared in the late stationary phase when V. vulnificus was grown in heart infusion broth containing 2.5% NaCl. V. vulnificus showed increased signalling activity when it was cultured in the presence of glucose (0.5%) and at low pH (pH 6.0). From a cosmid library of V. vulnificus type strain ATCC 29307, we have identified the AI‐2 synthase gene ( luxS Vv ) showing 80% identity with that of V. harveyi ( luxS Vh ) at the amino acid level. To investigate the pathogenic role of luxS Vv , a deletion mutant of the clinical isolate V. vulnificus MO6‐24/O was constructed. The luxS Vv mutant showed a significant delay in protease production and an increase in haemolysin production. The decreased protease and increased haemolysin activities were restored to the isogenic wild‐type level by complementation with the wild‐type luxS Vv allele. The change in phenotypes was also complemented by logarithmic phase spent media produced by the wild‐type bacteria. Transcriptional activities of the haemolysin gene ( vvhA ) and protease gene ( vvpE ) were also observed in the mutant using chromosomal P vvhA :: lacZ and P vvpE :: lacZ transcriptional reporter constructs: transcription of vvhA was increased and of vvpE decreased by the mutation. The mutation resulted in an attenuation of lethality to mice. Intraperitoneal LD 50 of the luxS Vv mutant increased by 10‐ and 750‐fold in ferric ammonium citrate‐non‐overloaded and ferric ammonium citrate‐overloaded mice respectively. The time required for the death of mice was also significantly delayed in the luxS Vv mutant. Cytotoxic activity of the organism against HeLa cells, measured by lactate dehydrogenase (LDH) release assay, was also decreased significantly by the mutation. Taken together, the V. vulnificus LuxS quorum‐sensing system seems to play an important role in co‐ordinating the expression of virulence factors.