Regulatory networks controlling transition between planktonic and biofilm lifestyle. The external frames illustrate the bacterial envelope with one or two membranes (OM: outer membrane, IM: inner membrane) according to Gram-positive (C) and Gram-negative bacteria (A, B, and D), respectively. A Control of biofilm formation in P. aeruginosa through the TCS GacS (HK)/GacA (RR) mediated by sRNA rsmY and rsmZ gene transcription and modulated by RetS and LadS, two additional HK in P. aeruginosa. B Control of EPS alginate in P. aeruginosa, which further impacts biofilm architecture by the system ECF sigma factor AlgU - anti-sigma MucA - AlgP (IM)-AlgW (periplasmic) complex: 1) activation of AlgW/AlgP, 2) cleavage of MucA, 3) release of AlgU, 4) activation of the alg UmucABCD operon. C Control of S. aureus biofilm formation through the Agr QS system: 1) AgrD autoinducer production, 2) AgrD autoinducer accumulation in the extracellular medium where it reaches a threshold, 3) activation of the TCS AgrCA by AgrD at the threshold concentration, 4) AgrA-dependent activation of the sRNA RNA III expression repressing expression of genes involved in biofilm formation together with amplification loop of agrABCD. D Control of P. aeruginosa biofilm formation through the intracellular second messenger c-di-GMP level controlled by the FimX protein having DGC and PDE domains, a RR domain, and a PAS domain. Note that in FimX protein only PDE activity is detectable (continuous arrow), whereas DGC activity is undetectable (dotted arrow).