Regine Hengge

Bio: Regine Hengge is an academic researcher from Humboldt University of Berlin. The author has contributed to research in topics: rpoS & Sigma factor. The author has an hindex of 40, co-authored 80 publications receiving 7716 citations. Previous affiliations of Regine Hengge include Free University of Berlin.

Principles of c-di-GMP signalling in bacteria.

Abstract: On the stage of bacterial signal transduction and regulation, bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) has long played the part of Sleeping Beauty. c-di-GMP was first described in 1987, but only recently was it recognized that the enzymes that 'make and break' it are not only ubiquitous in the bacterial world, but are found in many species in huge numbers. As a key player in the decision between the motile planktonic and sedentary biofilm-associated bacterial 'lifestyles', c-di-GMP binds to an unprecedented range of effector components and controls diverse targets, including transcription, the activities of enzymes and larger cellular structures. This Review focuses on emerging principles of c-di-GMP signalling using selected systems in different bacteria as examples.

Genome-Wide Analysis of the General Stress Response Network in Escherichia coli: σS-Dependent Genes, Promoters, and Sigma Factor Selectivity

Abstract: The σS (or RpoS) subunit of RNA polymerase is the master regulator of the general stress response in Escherichia coli. While nearly absent in rapidly growing cells, σS is strongly induced during entry into stationary phase and/or many other stress conditions and is essential for the expression of multiple stress resistances. Genome-wide expression profiling data presented here indicate that up to 10% of the E. coli genes are under direct or indirect control of σS and that σS should be considered a second vegetative sigma factor with a major impact not only on stress tolerance but on the entire cell physiology under nonoptimal growth conditions. This large data set allowed us to unequivocally identify a σS consensus promoter in silico. Moreover, our results suggest that σS-dependent genes represent a regulatory network with complex internal control (as exemplified by the acid resistance genes). This network also exhibits extensive regulatory overlaps with other global regulons (e.g., the cyclic AMP receptor protein regulon). In addition, the global regulatory protein Lrp was found to affect σS and/or σ70 selectivity of many promoters. These observations indicate that certain modules of the σS-dependent general stress response can be temporarily recruited by stress-specific regulons, which are controlled by other stress-responsive regulators that act together with σ70 RNA polymerase. Thus, not only the expression of genes within a regulatory network but also the architecture of the network itself can be subject to regulation.

Inverse regulatory coordination of motility and curli-mediated adhesion in Escherichia coli

Abstract: Depending on environmental conditions, bacteria can exhibit very different “lifestyles.” They can occur in a motile single-cellular or planktonic state or as sedentary cells that use adhesive fimbriae to cluster together and form biofilms on surfaces (O’Toole et al. 2000; Hall-Stoodley et al. 2004). With Escherichia coli grown in complex medium, these states can be observed successively, with cells transiently becoming highly motile during the post-exponential growth phase (Adler and Templeton 1967; Amsler et al. 1993; Zhao et al. 2007) followed by the induction of adhesive curli fimbriae during entry into stationary phase (Olsen et al. 1989). Motility and adhesion can also be expected to be mutually exclusive—being sticky seems counterproductive for swimming around, whereas adhesion and settling down might require reduced activity of the force-generating flagellar “propellers.” A convenient way to realize such an inverse coordination would be to endow the flagellar/motility control system with at least one component that plays an inhibitory role in the adhesion control system and vice versa. In E. coli, both motility and curli-mediated adhesion are under the control of regulatory feedforward cascades, each with a master regulator at the top, which acts as a massive environmental signal integrator. For flagellar expression and motility, this master regulator is the FlhDC complex (FlhD4C2, with the flhDC operon being defined as the flagellar class 1 operon) (Liu and Matsumura 1994; Wang et al. 2006). FlhDC activates the expression of class 2 operons, which encode the inner part of the flagellum (i.e., the hook basal body that also acts as a secretion system for the outer components) as well as the flagellar σ subunit of RNA polymerase (RNAP), FliA (σ28 or σF), and its anti-σ factor, FlgM. Upon secretion of FlgM, which occurs as soon as the basal body secretion system is functional, FliA is released to activate class 3 operons that encode the outer subunits of the flagellum, additional proteins required for flagellar function and chemotaxis, as well as a number of proteins of still unknown function (Chilcott and Hughes 2000; Karlinsey et al. 2000; Aldrigde et al. 2006). Adhesive curli fimbriae, on the other hand, are expressed during entry into stationary phase (in cells that grow below 30°C). Curli fimbriae are involved in both cell–cell aggregation and surface adhesion (Barnhart and Chapman 2006). The curli control cascade is a module within the general stress response, for which the σS (RpoS) σ subunit of RNAP acts as the master regulator (Hengge-Aronis 2000). In parallel, σS-containing RNAP (EσS) activates the expression of MlrA (a MerR-like regulator) and YdaM (a GGDEF protein, see below), which, together with EσS again, are essential to activate transcription of the csgD gene. The CsgD protein (also called AgfD in Salmonella) is an essential activator for the curli structural gene operon (csgBAC), and cooperates with the vegetative RNAP at the csgB promoter (Romling et al. 2000; Brown et al. 2001; Gerstel et al. 2003; Weber et al. 2006). Another key player in the control of motility and curli expression—i.e., in bacterial “lifestyle” switching—is the signaling molecule bis-(3′–5′)-cyclic-diguanosine monophosphate (c-di-GMP) (for recent reviews, see Romling et al. 2005; Jenal and Malone 2006; Ryan et al. 2006; Tamayo et al. 2007). Overproduction of certain diguanylate cyclases (DGC; characterized by GGDEF domains) interferes with motility and strongly activates the expression of curli fimbriae and the biofilm matrix component cellulose in enteric bacteria, whereas overproduction of certain c-di-GMP-degrading phosphodiesterases (PDE; carrying EAL domains) produces the opposite phenotype. In recent mutational and biochemical analyses, specific DGCs and PDEs have been assigned antagonistic roles in the regulation of curli expression (Kader et al. 2006; Weber et al. 2006; Simm et al. 2007). For E. coli , these are YdaM (the GGDEF protein already mentioned above) and YciR (a GGDEF + EAL protein), which control csgD transcription (Weber et al. 2006). Another EAL protein, YhjH, was shown to play a positive role in motility (Ko and Park 2000; Rychlik et al. 2002; Frye et al. 2006; Ryjenkov et al. 2006). However, the molecular details of c-di-GMP action in the control of curli expression and motility have not been characterized. The questions addressed by our study are the following: Do the FlhDC/motility and σS/curli control cascades really directly communicate to inversely coordinate their activities? And, if so, what are the factors involved, and are (some of) these factors c-di-GMP control systems; i.e., GGDEF/EAL proteins? With the present study, we identified several such factors acting at different hierarchical levels of the control network established, we provide evidence that throwing the motility-to-adhesion switch requires a precise down-regulation of motility at the transcriptional, proteolytic, and protein activity levels, and we present a framework model for the logic and the sequence of molecular events underlying this phenotypic “lifestyle” change in E. coli during entry into stationary phase.

Microanatomy at Cellular Resolution and Spatial Order of Physiological Differentiation in a Bacterial Biofilm

Abstract: Bacterial biofilms are highly structured multicellular communities whose formation involves flagella and an extracellular matrix of adhesins, amyloid fibers, and exopolysaccharides. Flagella are produced by still-dividing rod-shaped Escherichia coli cells during postexponential growth when nutrients become suboptimal. Upon entry into stationary phase, however, cells stop producing flagella, become ovoid, and generate amyloid curli fibers. These morphological changes, as well as accompanying global changes in gene expression and cellular physiology, depend on the induction of the stationary-phase sigma subunit of RNA polymerase, σ S (RpoS), the nucleotide second messengers cyclic AMP (cAMP), ppGpp, and cyclic-di-GMP, and a biofilm-controlling transcription factor, CsgD. Using flagella, curli fibers, a CsgD::GFP reporter, and cell morphology as “anatomical” hallmarks in fluorescence and scanning electron microscopy, different physiological zones in macrocolony biofilms of E. coli K-12 can be distinguished at cellular resolution. Small ovoid cells encased in a network of curli fibers form the outer biofilm layer. Inner regions are characterized by heterogeneous CsgD::GFP and curli expression. The bottom zone of the macrocolonies features elongated dividing cells and a tight mesh of entangled flagella, the formation of which requires flagellar motor function. Also, the cells in the outer-rim growth zone produce flagella, which wrap around and tether cells together. Adjacent to this growth zone, small chains and patches of shorter curli-surrounded cells appear side by side with flagellated curli-free cells before curli coverage finally becomes confluent, with essentially all cells in the surface layer being encased in “curli baskets.” IMPORTANCE Heterogeneity or cellular differentiation in biofilms is a commonly accepted concept, but direct evidence at the microscale has been difficult to obtain. Our study reveals the microanatomy and microphysiology of an Escherichia coli macrocolony biofilm at an unprecedented cellular resolution, with physiologically different zones and strata forming as a function of known global regulatory networks that respond to biofilm-intrinsic gradients of nutrient supply. In addition, this study identifies zones of heterogeneous and potentially bistable CsgD and curli expression, shows bacterial curli networks to strikingly resemble Alzheimer plaques, and suggests a new role of flagella as an architectural element in biofilms.

Biofilms: an emergent form of bacterial life.

Abstract: Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms - such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials - all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.

Cyclic GMP-AMP Synthase is a Cytosolic DNA Sensor that Activates the Type-I Interferon Pathway

Abstract: The presence of DNA in the cytoplasm of mammalian cells is a danger signal that triggers host immune responses such as the production of type I interferons. Cytosolic DNA induces interferons through the production of cyclic guanosine monophosphate–adenosine monophosphate (cyclic GMP-AMP, or cGAMP), which binds to and activates the adaptor protein STING. Through biochemical fractionation and quantitative mass spectrometry, we identified a cGAMP synthase (cGAS), which belongs to the nucleotidyltransferase family. Overexpression of cGAS activated the transcription factor IRF3 and induced interferon-β in a STING-dependent manner. Knockdown of cGAS inhibited IRF3 activation and interferon-β induction by DNA transfection or DNA virus infection. cGAS bound to DNA in the cytoplasm and catalyzed cGAMP synthesis. These results indicate that cGAS is a cytosolic DNA sensor that induces interferons by producing the second messenger cGAMP.

Resistance of Bacillus endospores to extreme terrestrial and extraterrestrial environments.

Abstract: Endospores of Bacillus spp., especially Bacillus subtilis, have served as experimental models for exploring the molecular mechanisms underlying the incredible longevity of spores and their resistance to environmental insults. In this review we summarize the molecular laboratory model of spore resistance mechanisms and attempt to use the model as a basis for exploration of the resistance of spores to environmental extremes both on Earth and during postulated interplanetary transfer through space as a result of natural impact processes.

Cyclic-GMP-AMP Is An Endogenous Second Messenger in Innate Immune Signaling by Cytosolic DNA

Abstract: Cytosolic DNA induces type I interferons and other cytokines that are important for antimicrobial defense but can also result in autoimmunity. This DNA signaling pathway requires the adaptor protein STING and the transcription factor IRF3, but the mechanism of DNA sensing is unclear. We found that mammalian cytosolic extracts synthesized cyclic guanosine monophosphate–adenosine monophosphate (cyclic GMP-AMP, or cGAMP) in vitro from adenosine triphosphate and guanosine triphosphate in the presence of DNA but not RNA. DNA transfection or DNA virus infection of mammalian cells also triggered cGAMP production. cGAMP bound to STING, leading to the activation of IRF3 and induction of interferon-β. Thus, cGAMP functions as an endogenous second messenger in metazoans and triggers interferon production in response to cytosolic DNA.