The master regulator for adhesive curli fimbriae expression; necessary for transcription of the csgBAC/ymdA operon. Plays a positive role in biofilm formation. May have the capability to respond to starvation and/or high cell density by activating csgBA transcription. Low-level constitutive expression confers an adherent curli fimbriae-expressing phenotype, up-regulates 10 genes and down-regulates 14 others. In experiments done with low-level constitutively expressed protein. Regulation is very complex. Strongly induced at 28 degrees Celsius (at protein level), transcription regulation requires c-di-GMP, although the mechanism is currently unknown. c-di-GMP levels are stimulated by the diguanylate cyclase DgcM and repressed by the c-di-GMP phosphodiesterase PdeR (YciR) (PubMed:17010156). Transcription directly repressed by MqsA, and indirectly repressed by MqsA via MqsA's repression of rpoS (PubMed:24212724). No curli production.