PMC:2726282 / 15693-18246 JSONTXT

{"project":"2_test","denotations":[{"id":"18599074-11018124-62517934","span":{"begin":295,"end":297},"obj":"11018124"},{"id":"18599074-12142477-62517934","span":{"begin":295,"end":297},"obj":"12142477"},{"id":"18599074-12730325-62517934","span":{"begin":295,"end":297},"obj":"12730325"},{"id":"18599074-16311037-62517935","span":{"begin":431,"end":432},"obj":"16311037"},{"id":"18599074-12142477-62517936","span":{"begin":1292,"end":1294},"obj":"12142477"},{"id":"18599074-10691740-62517936","span":{"begin":1292,"end":1294},"obj":"10691740"},{"id":"18599074-11807075-62517937","span":{"begin":1617,"end":1619},"obj":"11807075"},{"id":"18599074-14731270-62517938","span":{"begin":1923,"end":1925},"obj":"14731270"},{"id":"18599074-11398398-62517938","span":{"begin":1923,"end":1925},"obj":"11398398"},{"id":"18599074-11717281-62517938","span":{"begin":1923,"end":1925},"obj":"11717281"},{"id":"18599074-9287021-62517939","span":{"begin":2551,"end":2553},"obj":"9287021"},{"id":"18599074-16879983-62517939","span":{"begin":2551,"end":2553},"obj":"16879983"},{"id":"18599074-16963779-62517939","span":{"begin":2551,"end":2553},"obj":"16963779"}],"text":"Both biofilm and motility are regulated by multiple, long regulatory cascades (Fig. 2a). This organisation is congruent with the observation that these developmental processes are regulated by multiple environmental conditions, ranging from nutritional deprivation to environmental stresses.6,7,43 In E. coli, several global TFs sit at the top in these regulatory cascades, namely, CRP, IHF and FNR, all sensing endogenous signals.2 Additional regulatory inputs are provided by more specialised TFs such as ArcA (aerobic respiration regulatory protein), EvgA (environmentally responsive activator) and TorR (trimethylamine N-oxide reductase regulator) involved in exogenous sensing. Remarkably, downstream players are enriched in two-component system partners: RcsAB (capsule biosynthesis regulator), OmpR (outer membrane protein regulator), CpxR (regulator of cell envelope proteins folding and degradation) and QseB (quorum sensing regulator) (see the next section). Consequently, the first developmental steps likely occur in most of the cellular population in response to nutritional (CRP) or respiration (FNR-ArcA) stresses, yet depending on nucleoid structure status (sensed through IHF), while the final steps critically depend on exogenous conditions, as observed in other bacteria.7,44 For instance, in Pseudomonas aeruginosa, the initial steps for biofilm development (motility and reversible attachment to solid surfaces) are independent of quorum sensing, whereas the final steps (irreversible attachment and biofilm maturation) are strongly dependent on quorum-sensing regulation, an exogenous condition.45 Both processes (motility and biofilm) must be tightly interconnected, since motility is important for the concerted movement of groups of bacteria over solid surfaces, followed by cell membrane modification, excretion of polysaccharides, causing them to be less motile and smaller in mature biofilms.46–48 Interestingly, in E. coli, the activation of nucleoid-associated proteins such as histone-like protein (HNS) occurs relatively early along both biofilm and chemotaxis developmental pathways. The expression of these nucleoid-associated proteins is known to be growth-phase dependent (HNS is mostly expressed in the exponential phase, whereas IHF and factor for inversion stimulation (FIS) are expressed in arrested growing cells and during the early exponential phase, respectively), pointing to an influence of nucleoid structure and specific bacterial growth phases on the first steps of these developmental processes.42,49,50"}