Chemical Signal Links Bacterial Systems

Bacteria communicate and coordinate with each other using a networking system called quorum sensing. In the case of Pseudomonas aeruginosa, its quorum-sensing network actually consists of three systems, called las,pqs, and rhl, which work together to control the bacteria’s virulence genes. Earlier research findings have suggested that there might be more to the story, however. Las, which modulates the other two systems, shuts down in bacteria found in patient samples, even though the bacteria remain virulent. In addition, low-phosphate conditions have been shown to activate pqs and rhl independent of las. As a possible explanation, Lian-Hui Zhang at the Institute of Molecular & Cell Biology, in Singapore, and coworkers have found a new chemical signaling molecule, dubbed IQS, whose production is controlled separately by las and by the bacterium’s stress-response system (Nat. Chem. Biol., DOI: 10.1038/nchembio.1225). When engineered bacteria don’t produce IQS, the pqs and rhl systems don’t operate. But under phosphate-limited conditions, the researchers found, the bacterium’s stress-response system turns on IQS production, even without las. By using a combination of ultraviolet absorbance spectroscopy, mass spectrometry, and NMR spectroscopy, Zhang and coworkers identified IQS as 2-(2-hydroxyphenyl)-thiazole-4-carbaldehyde. The findings suggest that, in addition to quorum sensing, the stress-response system could be a target for antibacterial drugs.