FIG 4 .

Cellular levels of c-di-GMP and a novel model of local c-di-GMP signaling. (A) Cellular c-di-GMP concentrations were determined for strains AR3110 and W3110 and for strain W3110 carrying mutations that affect biofilm matrix production (as shown in this panel) at different stages of the growth cycle (growing at 28°C in LB medium and sampled at the indicated OD₅₇₈ levels and overnight). (B) Cellular c-di-GMP concentrations were determined for derivatives of the W3110 pdeH mutant also carrying secondary mutations that eliminate the 12 DGCs of E. coli K-12 (grown as described for panel B, with samples taken at an OD₅₇₈ of 3). One picomole/mg cellular protein corresponds to approximately 60 molecules per cell or a cellular concentration of 60 nM (see also Fig. 2 legend). (C) The “fountain model” of local c-di-GMP signaling. In wild-type cells, the strongly expressed PdeH acts as a drain to maintain a low level of the cellular pool of c-di-GMP, with localized production by certain DGCs (the “fountains”) allowing activation of directly associated effector/target systems. In the absence of PdeH as a drain, local signaling is lost since the activities of the producing DGCs combine to drive up the level of the global cellular c-di-GMP pool.