Messing with bacterial quorum sensing

Abstract

Quorum sensing is widely recognized as an efficient mechanism to regulate expression of specific genes responsible for communal behavior in bacteria. Several bacterial phenotypes essential for the successful establishment of symbiotic, pathogenic, or commensal relationships with eukaryotic hosts, including motility, exopolysaccharide production, biofilm formation, and toxin production, are often regulated by quorum sensing. Interestingly, eukaryotes produce quorum-sensing-interfering (QSI) compounds that have a positive or negative influence on the bacterial signaling network. This eukaryotic interference could result in further fine-tuning of bacterial quorum sensing. Furthermore, recent work involving the synthesis of structural homologs to the various quorum-sensing signal molecules has resulted in the development of additional QSI compounds that could be used to control pathogenic bacteria. The creation of transgenic plants that express bacterial quorum-sensing genes is yet another strategy to interfere with bacterial behavior. Further investigation on the manipulation of quorum-sensing systems could provide us with powerful tools against harmful bacteria.

FIG. 1.

Schematic representation of bacterial quorum sensing. At low population densities, basal-level production of autoinducer molecules results in the rapid dilution of the autoinducer signals in the surrounding environment. At high population densities, an increase in bacterial number results in accumulation of autoinducers beyond a threshold concentration, leading to the activation of the response regulator proteins, which in turn initiate the quorum-sensing cascade.

FIG. 2.

Quorum-sensing cross talk between A. tumefaciens and its host plant. The transfer and integration of bacterial T-DNA into plant cells result in tumorogenesis, leading to crown gall disease in plants. The tumor cells directed by the bacterial DNA produce and release opines, which are metabolized by the A. tumefaciens present in the soil around the plant roots. The conjugal transfer of the Ti plasmid among the rapidly proliferating A. tumefaciens in soil is regulated by bacterial quorum sensing as well as by plant-produced opines.