Bacterial inter-species communication mediated by the autoinducer-2 signal

Dissertation presented to obtain the Ph.D degree in Biology by Universidade Nova de Lisboa, Instituto de Tecnologia Química e Biológica, Instituto Gulbenkian de Ciência.During the last few decades, scientists have come to appreciate the immense complexity in bacterial signaling interactions that sustain microbial communities. Quorum-sensing (QS) is a cell-cell communication process whereby single cell bacteria regulate gene expression synchronously in a population in response to self-produced extracellular signal molecules, called autoinducers. Autoinducer-2 (AI-2), the synthase of which, LuxS, is present in both Gram-negative and Gram-positive bacteria, was proposed to represent a non-species-specific signal that mediates inter-species communication. In enteric bacteria, extracellular AI-2 levels peak in late exponential phase and rapidly decline as bacteria continue to grow. This depletion occurs because AI-2 activates the expression of an operon, lsr (for LuxS Regulated), encoding the Lsr transporter and enzymes that degrade the signal. As the Lsr system imports self and non-self AI-2, lsr-containing bacteria can interfere with AI-2 signaling of other species and shut off group behaviors regulated by this molecule: this system represents the first example of interference with a bacterial inter-species QS signal.(...)Fundação para a Ciência e Tecnologia financial support with the grant SFRH / BD / 28543 / 2006