Evidence for a signaling system in Helicobacter pylori: detection of a luxS-encoded autoinducer - PubMed (original) (raw)
Evidence for a signaling system in Helicobacter pylori: detection of a luxS-encoded autoinducer
E A Joyce et al. J Bacteriol. 2000 Jul.
Abstract
Helicobacter pylori possesses a homolog of the luxS gene, initially identified by its role in autoinducer production for the quorum-sensing system 2 in Vibrio harveyi. The genomes of several other species of bacteria, notably Escherichia coli, Salmonella enterica serovar Typhimurium, and Vibrio cholerae, also include luxS homologs. All of these bacteria have been shown to produce active autoinducers capable of stimulating the expression of the luciferase operon in V. harveyi. In this report, we demonstrate that H. pylori also synthesizes a functional autoinducer (AI-2) that can specifically activate signaling system 2 in V. harveyi. Maximal activity is produced during early log phase, and the activity is diminished when cells enter stationary phase. We show that AI-2 is not involved in modulating any of the known or putative virulence factors in H. pylori and that a luxS null mutant has a two-dimensional protein profile identical to that of its isogenic parent strain. We discuss the implications of having an AI-2-like quorum-sensing system in H. pylori and suggest possible roles that it may play in H. pylori infection.
Figures
FIG. 1
Alignment of the V. harveyi and putative H. pylori LuxS proteins.
FIG. 2
H. pylori produces a _luxS_-dependent AI-2 activity. Cell-free supernatants were tested for the ability to induce luminescence expression in V. harveyi BB170. Ten percent cell-free supernatants or sterile media were mixed with the reporter strain in microtiter plates and incubated at 30°C on a rotary shaker. Aliquots were taken, and both cell density and light production were determined. Activity is reported as fold activation of luminescence of BB170 over the level of luminescence when sterile media were added. Assays were repeated at least two times. (A) Wild-type H. pylori and Typhimurium 14028 supernatants contain signaling substances that induce expression of luminescence in V. harveyi BB170, while the luxS deletion strain EJ103 does not. (B) H. pylori luxS expression in E. coli DH5α restores AI-2 activity. The error bars indicate standard deviations.
FIG. 3
Specific activity of H. pylori AI-2 is maximal in early log phase and decreases in late log phase. H. pylori Alston was grown for 31 h under microaerobic conditions in BBH. At 0, 5, 8, 10, 25, and 31 h, cell-free culture fluids were prepared. Cell density was measured by diluting and plating cell aliquots at each time point (line). AI-2 activity was assayed for the ability to stimulate expression of bioluminescence in the V. harveyi reporter strain BB170 (bars). Specific activity was determined by dividing the fold activation of luminescence values by the total number of bacterial cells present at each time point.
References
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