Quorum sensing has been identified in many bacteria to offer cells unique capacity for cell density-dependent response. With this cell-cell communication mechanism, a population of bacterial cells is able to respond to environmental cues as a whole to exhibit coordinated and synchronized behavior. A wildtype quorum sensing system is activated at a specific cell density under a defined condition. In many applications, however, engineered quorum-sensing systems with altered responses are desired. We have engineered quorum sensing components LuxI, LuxR and RhlI for improved functions. We also have engineered a quorum sensing promoter for reduced basal expression levels. With these engineered components, we have constructed and enhanced various artificial genetic circuits, including genetic positive feedback loop, genetic AND gates and genetic oscillators. We also have demonstrated that these engineered quorum sensing systems can function as an efficient gene expression regulatory approach. Such an approach allows entirely autonomous and tunable activation of gene expression, a strategy superior to other inducible gene regulatory methods. Finally, I will discuss our effect to construct a synthetic symbiotic ecosystem, a method particularly useful for co-culture to implement complex metabolic engineering strategies.