Cyclic‐di‐GMP‐mediated signalling within the σ^S network of Escherichia coli

Abstract

SummaryBis-(3Ј-5Ј)-cyclic-di-guanosine monophosphate (c-di-GMP) is a bacterial signalling molecule produced by diguanylate cyclases (DGC, carrying GGDEF domains) and degraded by specific phosphodiesterases (PDE, carrying EAL domains). Neither its full physiological impact nor its effector mechanisms are currently understood. Also, the existence of multiple GGDEF/EAL genes in the genomes of most species raises questions about output specificity and robustness of c-di-GMP signalling. Using microarray and gene fusion analyses, we demonstrate that at least five of the 29 GGDEF/EAL genes in Escherichia coli are not only stationary phase-induced under the control of the general stress response master regulator s S (RpoS), but also exhibit differential control by additional environmental and temporal signals. Two of the corresponding proteins, YdaM (GGDEF only) and YciR (GGDEF + EAL), which in vitro show DGC and PDE activity, respectively, play an antagonistic role in the expression of the biofilm-associated curli fimbriae. This control occurs at the level of transcription of the curli and cellulose regulator CsgD. Moreover, we show that H-NS positively affects curli expression by inversely controlling the expression of ydaM and yciR. Furthermore, we demonstrate a temporally fine-tuned GGDEF cascade in which YdaM controls the expression of another GGDEF protein, YaiC. By genome-wide microarray analysis, evidence is provided that YdaM and YciR strongly and nearly exclusively control CsgD-regulated genes. We conclude that specific GGDEF/EAL proteins have very distinct expression patterns, and when present in physiological amounts, can act in a highly precise, non-global and perhaps microcompartmented manner on a few or even a single specific target(s).

The diguanylate cyclase YddV controls production of the exopolysaccharide poly-N-acetylglucosamine (PNAG) through regulation of the PNAG biosynthetic pgaABCD operon

“…Overexpression of YdaM did not affect the CR phenotype in MG1655 and in its DpgaA mutant derivative, but it conferred a weak red phenotype upon the curli-deficient mutant and the DcsgA/DbcsA double mutant impaired in both curli and cellulose production. Since YdaM controls the production of both curli and cellulose via expression of the csgD gene (Weber et al, 2006), this observation suggests that either YdaM or CsgD triggers the production of yet additional cell surfaceassociated structures able to bind CR. In contrast to AdrA and YdaM, YcdT expression led to no detectable changes in CR phenotype in any of the strains tested (Fig.…”

“…Regulation of EPS production by DGCs can take place at different levels: cellulose production is stimulated by AdrA through allosteric activation of the cellulose synthase protein machinery (Zogaj et al, 2001;Simm et al, 2004); the YdeH protein affects PNAG production through stabilization of the PgaD protein (Boehm et al, 2009); and finally, the YdaM protein activates curli and cellulose production via upregulation of csgDEFG transcription (Weber et al, 2006). We tested the possibility that the YddV protein regulates PNAG production by affecting transcription of the pgaABCD operon, encoding the proteins involved in PNAG biosynthesis.…”

“…In order to study the specific effects of YddV on the production of extracellular structures, we cloned the yddV gene into the pGEM-T Easy plasmid, which allows constitutive expression of cloned genes in the absence of IPTG induction. We compared yddV with three different DGC-encoding genes: adrA, encoding an activator of cellulose production (Zogaj et al, 2001); ycdT, located in the pgaABCD locus and co-regulated with the PNAGbiosynthetic genes (Jonas et al, 2008); and ydaM, required for expression of curli-encoding genes (Weber et al, 2006). Plasmid-driven expression of each of the four genes resulted in a significant increase in intracellular c-di-GMP concentrations, consistent with production of active proteins; however, while overproduction of the AdrA and the YdaM proteins resulted in a more than 150-fold increase in intracellular c-di-GMP, in agreement with previous observations , YcdT and YddV only enhanced c-di-GMP concentration by about 10-fold (Fig.…”

“…In addition, c-di-GMP biosynthesis affects important cellular processes, such as morphological differentiation and cell replication in Caulobacter crescentus (Paul et al, 2004), cell motility (Méndez-Ortiz et al, 2006;Jonas et al, 2008) and virulence factor production (Kulasakara et al, 2006;Hammer & Bassler, 2009). In Enterobacteria, c-di-GMP seems to be involved in regulation of adhesion factors, such as curli and cellulose, important for adaptation and survival outside the warm-blooded host (Simm et al, 2004;Kader et al, 2006;Weber et al, 2006;Solano et al, 2009), as also suggested by the observation that expression of the several diguanylate cyclase (DGC)-encoding genes is turned on at a growth temperature of 30 u C or lower (Weber et al, 2006;Sommerfeldt et al, 2009). Intracellular levels of c-di-GMP are regulated by two classes of isoenzymes: DGCs (c-di-GMP biosynthetic enzymes), also termed GGDEF proteins from the conserved Gly-Gly-AspGlu-Phe motif in their catalytic domains, and c-di-GMP phosphodiesterases (PDEs), which degrade c-di-GMP (Cotter & Stibitz, 2007).…”

“…A second messenger, bis-(39,59)-cyclic diguanylic acid, better known as cyclic-di-GMP (c-di-GMP), plays a pivotal role in biofilm formation and maintenance by stimulating production of EPS and adhesion factors (Ross et al, 1991;Simm et al, 2004;Kader et al, 2006;Weber et al, 2006). In addition, c-di-GMP biosynthesis affects important cellular processes, such as morphological differentiation and cell replication in Caulobacter crescentus (Paul et al, 2004), cell motility (Méndez-Ortiz et al, 2006; Jonas et al, 2008) and virulence factor production (Kulasakara et al, 2006;Hammer & Bassler, 2009).…”