FIG. 7.

Model depicting the regulation of dns by quorum sensing (based on reference 34). At low cell density (left), few autoinducer molecules are present in the environment. This is sensed by the quorum-sensing systems (CqsS and LuxPQ; not shown), and phosphate is transferred via LuxU to LuxO. LuxO∼P is active in conjunction with RpoN (σ⁵⁴) and inhibits the synthesis of the HapR regulator by inducing the expression of small regulatory RNAs (sRNAs) (posttranscriptional control). Under these conditions, the gene for the extracellular nuclease Dns is expressed. At high cell density (right), the phosphorylation cascade is reversed and LuxO is dephosphorylated. As a consequence, HapR accumulates, shutting down dns expression. HapR-mediated induction of comEA expression also occurs, provided that chitin is present (23).