FIGURE 1: Proposed model of the SiaA/B/C/D signaling network involved in regulation of biofilm and aggregate formation. Under normal conditions (such as in rich media), the protein kinase SiaB dominates and maintains most SiaC molecules phosphorylated, which precludes the promotion of the DGC activity of SiaD. Under stress conditions (such as SDS exposure), SiaA phosphatase is activated and most SiaC remains dephosphorylated; in this situation, the dephosphorylated SiaC interacts with SiaD to stimulate the DGC activity of SiaD and subsequently produces sufficient c-di-GMP, which leads to the formation of aggregates and biofilms.